HAM Radio 3/hamradioversion3.0examsandprograms1992.iso/tcp/nos18b/nosman8b.txt

Text File | 1992-01-08 | 152KB | 3,678 lines

        Network Operating System
        User Reference Manual


          Phil Karn, KA9Q
            and
        Gerard van der Grinten, PA0GRI






























      This manual reflects version 911229 of NOS 1.8b
      as released to the public by PA0GRI
















1.  The NOS.EXE Program

The MS-DOS executable file NOS.EXE (Further called Nos) provides Internet
(TCP/IP), NET/ROM and AX.25 facilities. Because it has an internal multi-
tasking operating system, Nos can act simultaneously as a client, a server
and a packet switch for all three sets of protocols. That is, while a local
user accesses remote services, the system can also provide those same ser-
vices to remote users while also switching IP, NET/ROM and AX.25 packets and
frames between other client and server nodes.

The keyboard and display is used by the local operator to control both host
and gateway level functions, for which a number of commands are provided.

1.1. Startup

nos [-b] [-s <#sockets>] [-d </directory>] [-v] [<startup file>]

When Nos is executed without arguments, it attempts to open the file
autoexec.nos in the root directory of the current drive. If it exists, it is
read and executed as though its contents were typed on the console as com-
mands. This feature is useful for attaching communication interfaces, confi-
guring network addresses, and starting the various services.

Four command-line options are accepted:

1.1.1. -b

The -b option specifies the use of BIOS for console output; the default is to
write directly to the video display buffer. Use this option if you are run-
ning under a windowing package and have trouble with output "bleeding
through" on top of other windows.

1.1.2. -s <noofsockets>

The -s option specifies the size of the socket array to be allocated within
Nos. This limits the number of network connections that may exist simultane-
ously; the default is 40.

1.1.3. -d </directory>

The -d option allows the user to specify a "root" directory for the confi-
guration and spool files; it defaults to the root directory of the system.

1.1.4. -v

The -v option allows the user to view command execution during the startup of
Nos. It lets the commands read from autoexec.nos echo before they are exe-
cuted. This is a nice help if Nos stops (hangs) during initialization.

After all command line options, the name of a alternate startup file may be
specified. This file is then opened and read instead of autoexec.nos.

1.2. DOS environement variables.

The following DOS environement variables can be used to specify things to
NOS.

1.2.1. TZ

The TZ variable should be set to the local timezone. Default is UTC. This is
used on the timestamp in smtp.

1.2.2. MAILER

The MAILER specifies what program should be started when the mail command is
entered. Default is BM.EXE.

1.2.3. COMSPEC

The COMSPEC specifies what command shell will be used to shell out of Nos.
This is normaly set by MS-DOS startup to COMMAND.COM. Default is also
COMMAND.COM.

1.2.4. TMP

The TMP variable is used to create a spot where temporary files are created.
Without TMP being set the temp files are created in the root directory. A
sample is "set TMP=C:\tmp\".

1.2.5. USER

The USER variable is used by ftp and Rlogin to set the username for the rlo-
gin daemon on the remote system. The default when not setting USER is guest.
Guess you don't like it, but that's life. With ftp the user is suggested in
the user name prompt. If a cr only is given the suggested name is used, oth-
erwise the given name.

2. Console modes

The console may be in one of two modes: command mode and converse mode.  In
command mode, the prompt net> is displayed and any of the commands described
in the Commands chapter may be entered. In converse mode, keyboard input is
processed according to the current session.

Sessions come in many types: Telnet, Ttylink, Rlogin, FTP, AX25, Finger, Com-
mand, NETROM, Ping, More, Dial, Dir, PPP PAP, Hopcheck and Tip.

In a Telnet, Ttylink, AX25, NETROM, Rlogin, or Tip session, keyboard input is
sent to the remote system and any output from the remote system is displayed
on the console. In an FTP session, keyboard input is first examined to see
if it is a known local command; if so it is executed locally. If not, it is
"passed through" to the remote FTP server.  (See the FTP Subcommands
chapter).  In a Ping session the user may test the path to a remote site, in
a More session, the user may examine a local file. A Hopcheck session is used
to trace the path taken by packets to reach a specified destination. A Finger
session is used to peek at a remote system for its users (and what they are
doing on some extended responses from UNIX systems). PPP PAP is used as a
link setup like slip between two systems.

The keyboard also has cooked and raw states.  In cooked state, input is
line-at-a-time; the user may use the line editing characters ^U, ^R, ^B, ^W
and backspace to erase the line, redisplay the line, redisplay the remainder
of the previous line, erase last word and erase the last character,
respectively. Hitting either return or line feed passes the complete line up
to the application. In raw mode, each character is immediately passed to the
application as it is typed. The keyboard is always in cooked state in com-
mand mode.  It is also cooked in converse mode on an AX25, FTP or NET/ROM
session. In a Telnet or Ttylink session it depends on whether the remote end
has issued (and the local end has accepted) the Telnet WILL ECHO option.
(See the echo command).

On the IBM-PC, the user may escape back to command mode by hitting the F10
key or the escape key.  On other systems, the user must enter the escape
character, which is by default control-] (hex 1d, ASCII GS). (Note that this
is distinct from the ASCII character of the same name). The escape character
can be changed (see the escape command). The F10 key can be redefined with
the fkey command so the user is now warned to leave one escape possibility
open for himself. Setting both F10 and escape to unreachable codes renders a
system unescapable and the user hung in a session.

In the IBM PC version, each session (including the command "session") has its
own screen.  When a new session is created, the command display is saved in
memory and the screen is cleared. When the command escape key (usually F10
or ^]) is hit, the current session screen is saved and the command screen is
restored. When a session is resumed, its screen is restored exactly as it
appeared when it was last current.

3. Commands

This section describes the commands recognized in command mode, or within a
startup file such as autoexec.nos. These are given in the following nota-
tion:

 command
 command literalparameter
 command subcommand <parameter>
 command [<optionalparameter>]
 command a | b


Many commands take subcommands or parameters, which may be optional or
required. In general, if a required subcommand or parameter is omitted, an
error message will summarize the available subcommands or required parame-
ters.  (Giving a '?' in place of the subcommand will also generate the mes-
sage. This is useful when the command word alone is a valid command.) If a
command takes an optional value parameter, issuing the command without the
parameter generally displays the current value of the variable. (Exceptions
to this rule are noted in the individual command descriptions.)

Two or more parameters separated by vertical bar(s) denote a choice between
the specified values. Optional parameters are shown enclosed in [brackets],
and a parameter enclosed in <angle brackets> should be replaced with an
actual value or string. For example, the notation <hostid> denotes an actual
host or gateway, which may be specified in one of two ways: as a numeric IP
address in dotted decimal notation (eg. 44.0.0.1.), or as a symbolic name
listed in the file domain.txt,

All commands and many subcommands may be abbreviated. You only need type
enough of a command's name to distinguish it from others that begin with the
same series of letters. Parameters, however, must be typed in full.

Certain FTP subcommands (eg. put, get, dir, etc) are recognized only in con-
verse mode with the appropriate FTP session; they are not recognized in com-
mand mode. (See the FTP Subcommands chapter.)

3.1. <CR>

Entering a carriage return (empty line) while in command mode puts you in
converse mode with the current session. If there is no current session, Nos
remains in command mode and reissues the net> prompt.

3.2. !

An alias for the shell command.

3.3. #

Commands starting with the hash mark (#) are ignored. This is mainly useful
for comments in the autoexec.nos file.

3.4. abort [<session #>]

Abort a FTP get, put or dir operation in progress. If issued without an argu-
ment, the current session is aborted. (This command works only on FTP ses-
sions.) When receiving a file, abort simply resets the data connection; the
next incoming data packet will generate a TCP RST (reset) response to clear
the remote server. When sending a file, abort sends a premature end-of-file.
Note that in both cases abort will leave a partial copy of the file on the
destination machine, which must be removed manually if it is unwanted.

3.5. arp

Display the Address Resolution Protocol table that maps IP addresses to their
subnet (link) addresses on subnetworks capable of broadcasting. For each IP
address entry the subnet type (eg. Ethernet, AX.25), subnet address and time
to expiration is shown. If the link address is currently unknown, the number
of IP datagrams awaiting resolution is also shown.

3.5.1. arp add <hostid> ether | ax25 | netrom | arcnet <etheraddr> |
<ax25addr>

Add a permanent entry to the table. It will not time out as will an
automatically-created entry, but must be removed with the arp drop command.

3.5.2. arp drop <hostid> ether | ax25 | netrom | arcnet

Delete a permanent entry from the arp table.

3.5.3. arp flush

Drop all automatically-created entries in the ARP table; permanent entries
are not affected.

3.5.4. arp publish <hostid> ether | ax25 | netrom | arcnet <etheraddr> |
<ax25addr>

This command is similar to the arp add command, but the system will also
respond to any ARP request it sees on the network that seeks the specified
address. (Use this feature with great care.)

3.6. asystat

Display statistics on attached asynchronous communications interfaces (8250
or 16550A), if any. The display for each port consists of three lines. The
first line gives the port label and the configuration flags; these indicate
whether the port is a 16550A chip, the trigger character if any, whether CTS
flow control is enabled, whether RLSD (carrier detect) line control is
enabled, and the speed in bits per second. (Receiving the trigger character
causes the driver to signal upper layer software that data is ready; it is
automatically set to the appropriate frame end character for SLIP, PPP and
NRS lines.)

The second line of the status display shows receiver (RX) event counts: the
total number of receive interrupts, received characters, receiver overruns
(lost characters) and the receiver high water mark. The high water mark is
the maximum number of characters ever read from the device during a single
interrupt. This is useful for monitoring system interrupt latency margins as
it shows how close the port hardware has come to overflowing due to the ina-
bility of the CPU to respond to a receiver interrupt in time. 8250 chips have
no FIFO, so the high water mark cannot go higher than 2 before overruns
occur. The 16550A chip, however, has a 16-byte receive FIFO which the
software programs to interrupt the CPU when the FIFO is one-quarter full.
The high water mark should typically be 4 or 5 when a 16550A is used; higher
values indicate that the CPU has at least once been slow to respond to a
receiver interrupt.

When the 16550A is used, a count of FIFO timeouts is also displayed on the RX
status line. These are generated automatically by the 16550A when three char-
acter intervals go by with more than 0 but less than 4 characters in the
FIFO. Since the characters that make up a SLIP or NRS frame are normally sent
at full line speed, this count will usually be a lower bound on the number of
frames received on the port, as only the last fragment of a frame generally
results in a timeout (and then only when the frame is not a multiple of 4
bytes long.)

Finally, the software fifo overruns and high water mark are displayed. These
indicate whether the <bufsize> parameter on the attach command needs to be
adjusted (see the Attach Commands chapter).

The third line shows transmit (TX) statistics, including a total count of
transmit interrupts, transmitted characters, the length of the transmit queue
in bytes, the number of status interrupts, and the number of THRE timeouts.
The status interrupt count will be zero unless CTS flow control or RLSD line
control has been enabled. The THRE timeout is a stopgap measure to catch
lost transmit interrupts, which seem to happen when there is a lot of
activity (ideally, this will be zero).

3.7. attach <hw type> ...

Configure and attach a hardware interface to the system. The details are
highly interface dependent and dependent on configuration flags in the file
config.h when the software is build. It can be that not all drivers listed
below will be included in your copy of Nos. Detailed instructions for each
driver are in the Attach Commands chapter. Drivers are available for the
following hardware types:

3.7.1. attach 3c500

Don't use this one anymore. Use the packet driver instead. This driver is
obsolete and not supported anymore.

3.7.2. attach asy

Standard PC asynchronous interface (com port) using the National 8250 or
16450 or 16550A chip or compatible equivalent.

3.7.3. attach axip

A "wormhole" ax25 digipeater device.

3.7.4. attach arcnet

A ARCnet driver via the PACKET driver.

3.7.5. attach drsi

N6TTO driver for the DRSI PCPA 8530 card.

3.7.6. attach eagle

WA3CVG/NG6Q driver for the Eagle Computer card (Zilog 8530).

3.7.7. attach hapn

KE3Z driver for the Hamilton Amateur Packet Network adapter board (Intel
8273).

3.7.8. attach hs

Special "high speed" 8530 driver for the WA4DSY 56kb/s modem.

3.7.9. attach kiss

This enables a multiplexed tnc type to be used for second channel. It is used
to connect a second port to an already attached asy interface. It will copy
most of the params of it's parent port.

3.7.10. attach netrom

This is a psuedo interface to enable NET/ROM operations.

3.7.11. attach packet

Driver for use with separate software "packet drivers" meeting the FTP
Software, Inc, Software Packet Driver specification.

3.7.12. attach pc100

Driver for the PACCOMM PC-100 (Zilog 8530) card.

3.7.13. attach pi

Dma driven 8530 scc board from VE3IFB.

3.7.14. attach scc

PE1CHL driver for generic 8530 cards.

3.7.15. attach slfp

Serial Line Faming Protocol packet driver.

An easy way to obtain a summary of the parameters required for a given device
is to issue a partial attach command (eg. attach packet.) This produces a
usage message giving the complete command format.

3.8. attended [off | on]

Displays or sets the global "I am present" flag in Nos. This flag is used in
the welcome header by incoming ttylink connections.

3.9. ax25 <subcommand>

These commands are for Ax25 interfaces.

3.9.1. ax25 bc <interface>

The bc command enables broadcasts via interface interface.

3.9.2. ax25 bcinterval [<seconds>]

The bcinterval displays or sets the time in seconds between bc broadcasts.
On display both the interval and the countdown values are shown.

3.9.3. ax25 blimit [<limit>]

Display or set the AX25 retransmission backoff limit. Normally each succes-
sive AX25 retransmission is delayed by twice the value of the previous inter-
val; this is called binary exponential backoff. When the backoff reaches the
blimit setting it is held at that value, which defaults to 30. To prevent
the possibility of "congestive collapse" on a loaded channel, blimit should
be set at least as high as the number of stations sharing the channel. Note
that this is applicable only on actual AX25 connections; UI frames will never
be retransmitted by the AX25 layer.

3.9.4. ax25 bctext ["broadcast text"]

The bctext command displays or sets the text to be send for broadcast mes-
sages send out every bcinterval seconds.

3.9.5. ax25 digipeat [on | off]

Display or set the digipeater enable flag. If the axip interface is used this
flag MUST be on , otherwise the digipeat function will not work at all.

3.9.6. ax25 filter <0 | 1 | 2 | 3>

The filter commands enables or disables the logging in the heard lists of
source and destination ax25addresses. This is a bitwise or function where
the 01 value is for source stations and the 02 value for destination sta-
tions. When the bit is off , logging is enabled, when on disabeled.

3.9.7. ax25 flush

Clear the AX.25 "heard" list (see ax25 heard).

3.9.8. ax25 heard [<interface>]

Display the AX.25 "heard" list. For each interface that is configured to use
AX.25, a list of all ax25addresses heard through that interface is shown,
along with a count of the number of packets heard from each station and the
interval, in hr:min:sec format, since each station was last heard. The local
station always appears first in the listing; the packet count actually
reflects the number of packets transmitted. This entry is always present even
if no packets have been sent. If interface is given, only the heard list for
that interface is displayed.  Note that logging of heard stations is con-
trolled with the ax25 filter command.

3.9.9. ax25 hearddest [<interface>]

Displays the destination list, i.e. the addressed to stations. Next to the
time the last transmission to that station the time that station replied (if
heard) is displayed. This gives a good reference to see if a station is
reachable and responding.

3.9.10. ax25 irtt [<milliseconds>]

Display or set the initial value of smoothed round trip time to be used when
a new AX25 connection is created. The value is in milliseconds. The actual
round trip time will be learned by measurement once the connection has been
established.

3.9.11. ax25 kick <axcb>

Force a retransmission on the specified AX.25 control block.  The control
block address can be found with the ax25 status command.

3.9.12. ax25 maxframe [<count>]

Establish the maximum number of frames that will be allowed to remain unack-
nowledged at one time on new AX.25 connections. This number cannot be greater
than 7. Without count it will display the current setting. Note that the
maximum outstaning frame count only works with virtual connections. UI frames
are not affected.

3.9.13. ax25 mycall [<ax25addr>]

Display or set the default local AX.25 address. The standard format is used,
(eg. KA9Q-0 or WB6RQN-5). This command must be given before any attach com-
mands using AX.25 mode are given.

3.9.14. ax25 paclen [<size>]

Limit the size of I-fields on new AX.25 connections.  If IP datagrams or
fragments larger than this are transmitted, they will be transparently frag-
mented at the AX.25 level, sent as a series of I frames, and reassembled back
into a complete IP datagram or fragment at the other end of the link. To have
any effect on IP datagrams, this parameter should be less than or equal to
the MTU of the associated interface.

3.9.15. ax25 pthresh [<size>]

Display or set the poll threshold to be used for new AX.25 Version 2 connec-
tions.  The poll threshold controls retransmission behavior as follows. If
the oldest unacknowledged I-frame size is less than the poll threshold, it
will be sent with the poll (P) bit set if a timeout occurs. If the oldest
unacked I-frame size is equal to or greater than the threshold, then a RR or
RNR frame, as appropriate, with the poll bit set will be sent if a timeout
occurs.

The idea behind the poll threshold is that the extra time needed to send a
"small" I-frame instead of a supervisory frame when polling after a timeout
is small, and since there's a good chance the I-frame will have to be sent
anyway (i.e., if it were lost previously) then you might as well send it as
the poll. But if the I-frame is large, send a supervisory (RR/RNR) poll
instead to determine first if retransmitting the oldest unacknowledged I-
frame is necessary; the timeout might have been caused by a lost acknowledge-
ment.  This is obviously a tradeoff, so experiment with the poll threshold
setting. The default is 128 bytes, one half the default value of paclen.

3.9.16. ax25 reset <axcb>

Delete the AX.25 connection control block at the specified address.

3.9.17. ax25 retry [<count>]

Limit the number of successive unsuccessful retransmission attempts on new
AX.25 connections. If this limit is exceeded, link re-establishment is
attempted. If this fails retry times, then the connection is abandoned and
all queued data is deleted.

3.9.18. ax25 route

Display the AX.25 routing table that specifies the digipeaters to be used in
reaching a given station.

3.9.18.1. ax25 route add <target> [digis ... ]

Add an entry to the AX.25 routing table. An automatic ax25 route add is exe-
cuted if digipeaters are specified in an AX25 connect command, or if a con-
nection is received from a remote station via digipeaters. Such automatic
routing table entries won't override locally created entries, however.

3.9.18.2. ax25 route drop <target>

Drop an entry for target from the AX.25 routing table.

3.9.18.3. ax25 route mode <target> [vc | datagram | interface]

Sets the mode to vc | datagram | interface for target. Interface is the
default for that interface. Vc is a virtual circuit (ax25 connected mode) and
datagram is unconnected mode, (AX25 UI frames).

3.9.19. ax25 status [<axcb>]

Without an argument, display a one-line summary of each AX.25 control block.
If the address of a particular control block is specified, the contents of
that control block are dumped in more detail. Note that the send queue units
are frames, while the receive queue units are bytes.

3.9.20. ax25 t3 [<milliseconds>]

Display or set the AX.25 idle "keep alive" timer. Value is in milliseconds.

3.9.21. ax25 t4 [<seconds>]

Display or set the AX.25 Link "redundancy" timer. Value is in seconds.  When
no exchange has been had during this time the link is reset and closed.

3.9.22. ax25 timertype [l | e | o]

Sets or displays the type of timer used for retransmission and recovery:
linear, exponential or original.

3.9.23. ax25 version [1 | 2]

Display or set the version of the AX.25 protocol to attempt to use on new
connections. The default is 1 (the version that does not use the poll/final
bits).

3.9.24. ax25 window [<size>]

Set the number of bytes that can be pending on an AX.25 receive queue beyond
which I frames will be answered with RNR (Receiver Not Ready) responses.
This presently applies only to suspended interactive AX.25 sessions, since
incoming I-frames containing network (IP, NET/ROM) packets are always pro-
cessed immediately and are not placed on the receive queue. However, when an
AX.25 connection carries both interactive and network packet traffic, an RNR
generated because of backlogged interactive traffic will also stop network
packet traffic from being sent.

3.10. bbs

Enter the local bbs port (same as a telnet session to your own station).
 Current commands are:
 help  ? <command>
 area  a [<area>]
 bye  b
 chat  c
 download d <filename>
 escape e [<escape char.]
 finger f [<user>]
 gateway  d <interface> <ax25addr> [[<ax25addr>] . ]
 help  h [<command>]
 info  i
 heard j
 kill  k <msg number>
 list  l [<msg number>]
 netrom n Users | Nodes | Connect
 read  r [<msg number>]
 send  s[f] <usename[@hostid] [<fromaddr>] [$bulid]
 send repl sr [<mgs number>]
 telnet t <hostid>
 upload u <filename>
 verbose  v <n>
 what  w [<directory>]
 zap  z <filename>
 sysop @

3.11. bootp <subcommand>

This is a bootp server / client, included into Nos. It is picked up from the
University of Michigan in Ann Arbor. It is included into the sources of Nos
but is not used nor tested by me. (PA0GRI) Its usability is fague but the
discussions on tcp-group drove me to include this for possible use of reus-
able addresses.

3.11.1. bootp start

Starts the bootp server.

3.11.2. bootp stop

Stops the bootp server.

3.11.3. bootp dns [<ipaddr>]

Display or set the list of domain name servers for bootp.

3.11.4. bootp dyip [<iface> | <iface> <ipaddr1> <ipaddr2> | <iface> off]

Display or set the interface address range. The range is between ipaddr1 and
ipaddr2, both in dot notation.

3.11.5. bootp host [<hostaddr> <hardware type> <hardware addr> <ip addr>
[boot file]]

Display or activate a bootp process. Hardware type is netrom, ether, macap-
pletalk or ax25. Hardware addr is the interface name. Ip addr must be in dot
notation.

3.11.6. bootp rmhost <ipaddr>

Delete ipaddr from the host table.

3.11.7. bootp homedir [<directory> | default]

Display or set the directory where the bootp files reside. The default direc-
tory is bpfiles.

3.11.8. bootp defaultfile [<bootfile> | default]

Display or set the file name of the bootp file. The default is boot.

3.11.9. bootp logfile [<filename> | default] [on | off]

Starts or stops the logging of bootp requests to filename or the default file
name bootplog.

3.11.10. bootp logscreen [on | off]

Enables or disables the logging of bootp to the screen.

3.12. bootpd

This starts the server daemon for bootp.

3.13. cd [<dirname>]

Change the current working directory, and display the new setting.  Without
an argument, cd simply displays the current directory without change. The
pwd command is an alias for cd.

3.14. close [<session>]

Close the specified session; without an argument, close the current session.
On an AX.25 session, this command initiates a disconnect. On a FTP or Telnet
session, this command sends a FIN (i.e., initiates a close) on the session's
TCP connection.  This is an alternative to asking the remote server to ini-
tiate a close (QUIT to FTP, or the logout command appropriate for the remote
system in the case of Telnet). When either FTP or Telnet sees the incoming
half of a TCP connection close, it automatically responds by closing the out-
going half of the connection. Close is more graceful than the reset command,
in that it is less likely to leave the remote TCP in a "half-open" state.

3.15. comm <interface> <text-string>

The comm command sends text-string via interface. This can be used to send
straight text to an tnc still in TAPR command mode during Nos startup. Note
that to preserve spaces tabs etc. to include the string between double quote
characters. Aka: comm ax1 "start kiss"

3.16. connect <iface> <ax25addr> [<digipeater> ... ]

Initiate a "vanilla" AX.25 session to the specified ax25addr using the
specified interface. Data sent on this session goes out in conventional AX.25
packets with no upper layer protocol.  The de-facto presentation standard
format is used, in that each packet holds one line of text, terminated by a
carriage return. A single AX.25 connection may be used for terminal-to-
terminal, IP and NET/ROM traffic. The three types of data being automati-
cally separated by their AX.25 Level 3 Protocol IDs.

Up to 7 optional digipeaters may be given; note that the word via is NOT
needed. If digipeaters are specified, they are automatically added to the
AX25 routing table as though the ax25 route add command had been given before
issuing the connect command.

3.17. delete <filename>

The filename is removed from the file system.

3.18. detach <iface>

Detach a previously attached interface from the system. All IP routing table
entries referring to this interface are deleted, and forwarding references by
any other interface to this interface are removed.

3.19. dialer <iface> [<file> [<seconds> [<pings> [<hostid>]

Setup an autodialer session for the interface.  Whenever the interface is
idle for the interval in <seconds>, the autodialer will ping the <hostid>.
If there is no answer after <pings> attempts, the autodialer will execute the
special commands contained in the <dialer-file>.

If the interval in <seconds> is zero, a previous dialer command process will
be removed. If the number of <pings> is zero, the <dialer-file> will be exe-
cuted without pinging the <hostid>.

The file may have any valid name, and must be located in the configuration
root directory (see the Installion section). The commands in the file are
described in the Dialer Subcommands chapter.
 Commands in file are:

3.19.1. control <up | down>


3.19.2. send <string> [<milliseconds>]

Sends string to the interface. If milliseconds is given, inter character tim-
ing is milliseconds milliseconds.

3.19.3. speed <bps>

Displays or sets the current interface speed to bps baud.

3.19.4. status <up | down>

3.19.5. wait <milliseconds> [<string> [speed]]

Wait the amount of milliseconds. If string is given, incoming characters from
the interface are compared with string. If an compare is found and speed is
the string speed, the next numbers read from the interface is the new bau-
drate used. This works like HAYES response CONNECT 9600. The wait command
could habe been "wait 10 CONNECT speed". This waits 10 seconds for the
CONNECT response from the modem.

3.20. dir [<dirname>]

List the contents of the specified directory on the console. If no argument
is given, the current directory is listed. Note that this command works by
first listing the directory into a temporary file, and then creating a more
session to display it. After this completes, the temporary file is deleted.

3.21. disconnect [<session>]

An alias for the close command (for the benefit of AX.25 users).

3.22. domain <subcommand>

The domain commands control and show the working of the name to internet
address mapping software. NOS currently only has a client with a simple file
reading local server. A real server is needed to service the community for
their growing needs.

3.22.1. domain addserver <hostid>

Add a domain name server to the list of name servers. Note that, when this
command is given in the autoexec.nos file the ip address command should given
be before this command is used. (If not, Nos will not kow how to resolve the
address, and an answer will never be recognized, or worse: just plain hangs
the system.)

3.22.2. domain cache <subcommand>

Following commands work on the domain cache. These are resource records (see
RFC 1033/1034) held in memory.

3.22.2.1. domain cache clean [<yes | no>]

Displays or sets the discard of expired resource records. Expired records
have their timeout value decremented to zero. Normaly resource records get a
default timeout value of 1800 seconds. After this time they are considered
"old" and if referenced again the domain name resolver should be enquired
again. When clean is off (the default), expired records will be retained; if
no replacement can be obtained from another domain name server, these records
will continue to be used.

When clean is on, expired records will be removed from the file whenever any
new record is added to the file.

3.22.2.2. domain cache list

This command shows the current content of the in memory cache for resource
records.

3.22.2.3. domain cache size [<size>]

Display or set the nominal maximum size of the local memory cache.  The
default is 20.

(Note: The cache may be temporarily larger when waiting for new records to be
written to the domain.txt file.)

3.22.2.4. domain cache wait [<seconds>]

Display or set the interval in seconds to wait for additional activity before
updating the domain.txt file. The default is 300 seconds (5 minutes).

3.22.3. domain dropserver <hostid>

Remove a domain name server from the list of name servers.  You are warned
when you delete the last name server.

3.22.4. domain listservers

List the currently configured domain name servers, along with statistics on
how many queries and replies have been exchanged with each one, response
times, etc.

3.22.5. domain maxwait [<timeout>]

This sets a timeout value (1 to 255 seconds) to a query or domain name
server.  This is not set for a already defined server but will be used for a
newly defined name server. Also the value is used for domain nslookups. Note
that name servers can have (PC based) trouble finding records in an large
database. The default is set to 30 seconds.

3.22.6. domain retry [<retries>]

The retry value (number) limits the number of queries send out to remote
domain  name  resolvers  before giving up and telling you that host
xyzzy.ampr.org does not exist. The total time lost with a query is retries *
timeout * number of domain servers defined.

3.22.7. domain suffix [<domain suffix> | none]

Display or specify the default domain name suffix to be appended to a host
name when it contains no periods. For example, if the suffix is set to
ampr.org. and the user enters telnet ka9q, the domain resolver will attempt
to find ka9q.ampr.org.. If the host name being sought contains one or more
periods, however, the default suffix is NOT applied if the last part of the
name is less than 5 characters and contains only letters; e.g.,
 telnet foo.bar would NOT be turned into foo.bar.ampr.org..
 telnet foo.ka9q will be turned into foo.ka9q.ampr.org.. Note that a trail-
ing dot (.) is required for the suffix. If the suffix is the string none
(without trailing period) the current suffix is cleared and forgotten.

3.22.8. domain trace [on | off]

Display or set the flag controlling the tracing of domain server requests and
responses. Trace messages will be seen only if a domain name being sought is
not found in the local cache file, domain.txt.

3.22.9. domain translate [off | on]

Display or set the flag that controls the translation of ip adress in dot
notation into symbolic names. The translation process makes heavely use of
reverse domain name lookups. Do not set this flag unless you have a good and
fast connection to a domain name server or have a fast domain.txt handler and
domain.txt contains all IN-ADDR.ARPA. records you ever wanted.

3.22.10. domain verbose [off | on]

Display or set the flag controlling the return of a full name (true) or only
the first name (dot delimiter) (false). This is for IP address to name trans-
lation only.

3.23. drsistat

Shows the statistics for all configured drsi boards.

3.24. dump <hex-address | .> [decimal-range]

The dump command shows memory in hex and ascii. Hex-address is a 32 bit value
for a PC split into page address and page offset. A splitting colon is not
used nor accepted. If decimal-range is not given , 128 bytes are displayed.
dump . displayes memory starting at the end of a previous dump command.

3.25. echo [accept | refuse]

Display or set the flag controlling client Telnet's response to a remote WILL
ECHO offer.

The Telnet presentation protocol specifies that in the absence of a nego-
tiated agreement to the contrary, neither end echoes data received from the
other. In this mode, a Telnet client session echoes keyboard input locally
and nothing is actually sent until a carriage return is typed. Local line
editing is also performed: backspace deletes the last character typed, while
control-U deletes the entire line.

When communicating from keyboard to keyboard the standard local echo mode is
used, so the setting of this parameter has no effect. However, many timeshar-
ing systems (eg. UNIX) prefer to do their own echoing of typed input.  (This
makes screen editors work right, among other things). Such systems send a
Telnet WILL ECHO offer immediately upon receiving an incoming Telnet connec-
tion request. If echo accept is in effect, a client Telnet session will
automatically return a DO ECHO response. In this mode, local echoing and
editing is turned off and each key stroke is sent immediately (subject to the
Nagle tinygram algorithm in TCP). While this mode is just fine across an
Ethernet, it is clearly inefficient and painful across slow paths like packet
radio channels. Specifying echo refuse causes an incoming WILL ECHO offer to
be answered with a DONT ECHO; the client Telnet session remains in the local
echo mode. Sessions already in the remote echo mode are unaffected. (Note:
Berkeley Unix has a bug in that it will still echo input even after the
client has refused the WILL ECHO offer. To get around this problem, enter the
stty -echo command to the shell once you have logged in.)

3.26. eol [unix | standard]

Display or set Telnet's end-of-line behavior when in remote echo mode.  In
standard mode, each key is sent as-is. In unix mode, carriage returns are
translated to line feeds. This command is not necessary with all UNIX sys-
tems; use it only when you find that a particular system responds to line
feeds but not carriage returns. Only SunOS release 3.2 seems to exhibit this
behavior; later releases are fixed.

3.27. escape [<char>]

Display or set the current command-mode escape character in hex. On the PC,
the escape character is default ^]. The alternate escape key is F10 unless
F10 is redefined with fkey.

3.28. etherstat

Display 3-Com Ethernet controller statistics (if configured).

3.29. exit

Exit the nos program and return to MS-DOS.

3.30. finger <user@hostid> | <@hostid>

Issue a network finger request for user user at host hostid. This creates a
client session which may be interrupted, resumed, reset, etc, just like a
Telnet client session. If only @hostid is given, all users on that host are
identified.

3.31. fkey [<number> [<string>]]

Fkey displays or sets values for the programmable keys on the PC keyboard.
fkey alone gives a display of all remapable keys and their number. fkey
number displays the current value for that key. fkey number string assigns
string to that key. Control characters can be created by prefixing then with
an ^ character. A cr is ^M. To insert an ^ in the string 2 ^'s next to each
other are needed. Following is the map of keys and their number. F1 is func-
tion key 1. Sf1 is Shift function key 1. Cf1 is Control function key 1. Af1
is Alt function key 1. Etc. The right most row is the numeric keypad.

 key number  key number  key number  key number key  number
 f1  59  sf1  84  cf1  94  af1 104 pgup  73
 f2  60  sf2  85  cf2  95  af2 105 pgdn  81
 f3  61  sf3  86  cf3  96  af3 106 home  71
 f4  62  sf4  87  cf4  97  af4 107 end 79
 f5  63  sf5  88  cf5  98  af5 108 arup  72
 f6  64  sf6  89  cf6  99  af6 109 ardn  80
 f7  65  sf7  90  cf7 100  af7 110 ar l  75
 f8  66  sf8  91  cf8 101  af8 111 ar r  77
 f9  67  sf9  92  cf9 102  af9 112 ins 82
 f10 68  sf10 93  cf10 103  af10 113 del 83
The mapping is taken to look like a vt100 / ansi keyboard.  Currently
assigned value strings for following keys:
 number string key
 59 " 33OP"  /* F1 */
 60 " 33OQ"  /* F2 */
 61 " 33OR"  /* F3 */
 62 " 33OS"  /* F4 */
 71 " 10" /* home*/
 72 " 33[A"  /* up arrow*/
 73 " 25" /* pgup */
 75 " 33[D"  /* left arrow */
 77 " 33[C"  /* right arrow */
 79 " 05" /* end */
 80 " 33[B"  /* down arrow */
 81 " 12" /* pgdn */
 82 " 01" /* ins */
 83 " 177" /* del */

3.32. ftp <hostid>

Open an FTP control channel to the specified remote host and enter converse
mode on the new session.  Responses from the remote server are displayed
directly on the screen. See theFTP Subcommands chapter for descriptions of
the commands available in a FTP session.

3.33. ftype [ascii | binary | image | logical <size>]

This command displays or sets the default start file mode (ascii or binary)
for ftp transfers. If ftype binary or image is given the next ftp session
started will be in binary type. No binary command is needed once the session
is started. In case of logical, the "word" size is set to size.

3.34. help

Display a brief summary of top-level commands.

3.35. hop <subcommands>

These commands are used to test the connectivity of the network.

3.35.1. hop check <hostid>

Initiate a hopcheck session to the specified host. This uses a series of UDP
"probe" packets with increasing IP TTL fields to determine the sequence of
gateways in the path to the specified destination. This function is patterned
after the UNIX traceroute facility.

ICMP message tracing should be turned off before this command is executed
(see the icmp trace command).

3.35.2. hop maxttl [<hops>]

Display or set the maximum TTL value to be used in hop check sessions.  This
effectively bounds the radius of the search.

3.35.3. hop maxwait [<seconds>]

Display or set the maximum interval, in seconds, that a hopcheck session will
wait for responses at each stage of the trace. The default is 5 seconds.

3.35.4. hop queries [<count>]

Display or set the number of UDP probes that will be sent at each stage of
the trace. The default is 3.

3.35.5. hop trace [on | off]

Display or set the flag that controls the display of additional information
during a hop check session.

3.36. hostname [<name>]

Display or set the local host's name. By convention this should be the same
as the host's primary domain name. This string is used only in the greeting
messages of the various network servers; note that it does NOT set the
system's IP address.

If <name> is the same as an <iface> (see the Attach commands chapter), this
command will search for a CNAME domain resource record which corresponds to
the IP address of the <iface>.

3.37. hs

Display statistics about the HS high speed HDLC driver (if configured and
active).

3.38. icmp <subcommand>

These commands are used for the Internet Control Message Protocol service.

3.38.1. icmp echo [on | off]

Display or set the flag controlling the asynchronous display of ICMP Echo
Reply packets. This flag must be on for one-shot pings to work (see the ping
command.)

3.38.2. icmp status

Display statistics about the Internet Control Message Protocol (ICMP),
including the number of ICMP messages of each type sent or received.

3.38.3. icmp trace [on | off]

Display or set the flag controlling the display of ICMP error messages. These
informational messages are generated by Internet routers in response to rout-
ing, protocol or congestion problems. This option should be turned off before
using the hop check facility because it relies on ICMP Time Exceeded mes-
sages, and the asynchronous display of these messages will be mingled with
hop check command output.

3.39. ifconfig

Display a list of interfaces, with a short status for each.

3.39.1. ifconfig [<iface> [[[ <subcommand> <param>] <subcommand> <param>]
. ]

When only iface is given, a extended interface status is displayed. Multiple
subcommand / parameter can be put on one line.

3.39.2. ifconfig <iface> broadcast <addr>

Set the broadcast address of interface iface to addr. Addr can eighter be an
ax25addr or an etheraddr, depending on the interface type, with 1's in the
host part of the address. This is related to the netmask sub-command.  See
also the arp command.

3.39.3. ifconfig <iface> encapsulation <slip | ax25 | ether | encap | ppp>

Sets the encapsulation for interface iface to slip / ax25 / ether / encap /
ppp.

3.39.4. ifconfig <iface> forward <iface-2>

When a forward is defined, all output for interface iface is redirected to
the interface directed by iface-2. To remove the forward, set <iface-2> to
<iface>.

3.39.5. ifconfig <iface> ipaddress <addr>

Set the IP address to addr for this interface. This might be nessesary when a
system acts as a gateway. Like an system with IP address 44.137.1.8 has an
Internet access via its ethernet. The Internet IP address could  be
129.179.122.10. An ifconfig ec0 ipaddress 129.179.122.10 sets the correct
address for that interface. Now routing to that system will work. (Note that
the 44.x.x.x address is NOT connected to the Internet.) See also the host-
name and ip address commands.

3.39.6. ifconfig <iface> linkaddress <hardware-dependant>

Set the hardware dependant address for this interface. For AX.25 this can be
the callsign, for ethernet a new ethernet address.

3.39.7. ifconfig <iface> mtu <param>

Set the maximum transfer unit to param octeds (bytes). See the Setting ...
MTU, MSS and Window chapter for more information.

3.39.8. ifconfig <iface> netmask <address>

Set the sub-net mask for this interface. The <address> takes the form of an
IP address with 1's in the network and subnet parts of the address, and 0's
in the host part of the address. Sample: ifconfig ec0 netmask 0xfff00
for a class C network (24 bits). This is related to the broadcast sub-
command. See also the route command.

3.39.9. ifconfig <iface> rxbuf <size>

Set the receive buffer size.

3.40. info

Info gives information about the version of Nos currently running and its
buildin configuration. The configuration info is build with defines in
config.h in the source distribution. That way it gives automatically correct
configuration information.

3.41. ip <subcommand>

These commands are used for the Internet Protocol service.

3.41.1.  ip access <permit|deny|delete> <dest  addr>[/<bits>]  <ifname>
[lowport [higport]]

Set or display access control for IP routing functions. This command imple-
ments router access functions to NosFp. Permit enables dest-addr packets to
be routed via ifname. Deny disables those. If lowport is not given, all ports
are assumed. If only lowport is given, that port is only checked for permis-
sion If lowport and highport are given, that is the range of ports
permitted/denied.  Dest-addr can be the word all for all addresses possible.
Lowport can be the word none for all ports. The ip access delete must match
a previous defined permit or deny to be able to delete that definition. Some
samples:
 ip access permit 44/8 ax0
 ip access deny all ax0 1 1023
 ip access permit all ax0 If no access list is created, all interfaces might
carry all types. If an access control is defined for an interface there must
be an permit defined for that interface to allow trafic. Thus an partial
denyal without an permit is an complete denyal.

3.41.2. ip address [<hostid>]

Display or set the default local IP address. This command must be given
before an attach command if it is to be used as the default IP address for
the interface.

3.41.3. ip rtimer [<seconds>]

Display or set the IP reassembly timeout. The default is 30 seconds.  Value
is in seconds.

3.41.4. ip status

Display Internet Protocol (IP) statistics, such as total packet counts and
error counters of various types.

3.41.5. ip ttl [<hops>]

Display or set the default time-to-live value placed in each outgoing IP
datagram. This limits the number of switch hops the datagram will be allowed
to take. The idea is to bound the lifetime of the packet should it become
caught in a routing loop, so make the value slightly larger than the number
of hops across the network you expect to transit packets. The default is set
at compilation time to the official recommended value for the Internet.

3.42. isat [on | off]

Display or set the AT flag. Normaly this flag is set when an interface is
attached with an interrupt of 8 or higher. This is to signal that the second
interrupt controllerc in a AT also needs an return of interrupt signal.  If
an AT type clock is in use, this command will allow measurement of time in
milliseconds, rather than clock ticks (55 milliseconds per clock tick). Dur-
ing I/O initialisation this flag is set if the monitor prom has the standard
byte 0xfc at address f000:fffe.

3.43. kick [<session>]

Kick all sockets associated with a session; if no argument is given, kick the
current session.  Performs the same function as the ax25 kick and tcp kick
commands, but is easier to type.

3.44. log [stop | <filename>]

Display the current log filename or set the filename for logging server ses-
sions. If stop is given as the argument, logging is terminated (the servers
themselves are unaffected). If a file name is given as an argument, server
session log entries will be appended to it.

3.45. mail

This command will start a shell escape command. The mailer used is defined
with the DOS environment variable MAILER, wich defaults to BM.EXE.

3.46. mbox [<subcommand>]

Display the status of the mailbox server system (if configured).

3.46.1. mbox attend [yes | no]

Displays or sets the attended flag on. This is used to announce in the mail-
box if the station mannager is willing to attend his station (chat).

3.46.2. mbox kick

To kick the mailbox back in activity after retry timeouts.

3.46.3. mbox maxmsg

To display or set the maximum number of messages per area when an notesfile
is shown to a user. This reserves lots of memory for every mailbox session.

3.46.4. mbox motd

Display ot set the mailbox welcoming Message Of The Day.

3.46.5. mbox status

An alias for just entering mbox on the prompt line.

3.46.6. mbox timer [<seconds>]

Display the current interval and time remainig or set the mailbox forwarding
timer.

3.46.7. mbox tiptimeout

Displays or sets the timeout value for tip connection timeout. After timeout
seconds of no activity the connection is closed.

3.46.8. mbox trace [yes | no]

Displays or sets mailbox forward trace code flag. The trace is very minimal
but every one working on mailbox/forward code now has a common flag Mtrace.

3.47. memory <subcommand>

These commands are used for memory allocation.

3.47.1. memory efficient [yes | no]

Displays or sets the search algorithm for buffer memory. When set the search
is always started from the beginning of the free list. This is slower but
keeps memory fragmentation to a minimum. When clear search is started on the
end, accounting for more memory fragmentation but keeping speed. Roumers
state that you should include this command as the first line in autoexec.nos.
The current releases default sets efficient to yes.

3.47.2. memory freelist

Display the storage allocator free list. Each entry consists of a starting
address, in hex, and a size, in decimal bytes.

3.47.3. memory ibufsize [<size>]

Display or set the size of the buffers in the interrupt buffer pool.  The
size should be set to the largest type of buffer plus a header size of 22.
For example: If your ax25 is the omly interface and a packet length of 256 is
defined, the ibufsize should be 256 + 10 * 6 + 22. The 10 * 6 is the ax25
header (source , destination and 8 digipeaters).

3.47.4. memory nibufs [<number>]

Display or set the number of interrupt buffer pool buffers. If the number of
buffers is set, the statistics in the memory status display are reset for
number of interrupt buffer fails. The minimum available value is set to the
requested number of buffers. A roule of thumb for the number of buffers is
to watch the statistics and keep a minimum of 2 free buffers. Increase or
decrease as required.

3.47.5. memory sizes

Display a histogram of storage allocator request sizes. Each histogram bin is
a binary order of magnitude (i.e., a factor of 2).

3.47.6. memory status

Display a summary of storage allocator statistics. The first line shows the
base address of the heap, its total size, the amount of heap memory available
in bytes and as a percentage of the total heap size, and the amount of memory
left over (i.e., not placed on the heap at startup) and therefore available
for shell subcommands.

The second line shows the total number of calls to allocate and free blocks
of memory, the difference of these two values (i.e., the number of allocated
blocks outstanding), the number of allocation requests that were denied due
to lack of memory, and the number of calls to free() that attempted to free
garbage (eg. by freeing the same block twice or freeing a garbled pointer).

The third line shows the garbage collection status. Garbage collection is a
separate process running every second. If memory is "low" garbage collection
routines are called in "Red alert" mode, else in "Yellow alert".

The fourth line shows the number of calls to malloc and free that occurred
with interrupts off. In normal situations these values should be zero. The
fourth line shows statistics for the special pool of fixed-size buffers used
to satisfy requests for memory at interrupt time. The variables shown are the
number of buffers currently in the pool, their size, and the number of
requests that failed due to exhaustion of the pool.

The fifth line shows the current setting of the interrupt buffer pool, its
minimal value and the number of no buffers available. These statistics are
reset when a memory nibufs <number> command is given.

3.47.7. memory thresh [<size>]

Displays or sets the memory threshold size in bytes. If memory gets below
this value , no more new sessions are started or accepted.

3.48. mkdir <dirname>

Create a sub-directory in the current working directory.

3.49. mode <iface> [vc | datagram]

Control the default transmission mode on the specified AX.25 interface.  In
datagram mode, IP packets are encapsulated in AX.25 UI frames and transmitted
without any other link level mechanisms, such as connections or acknowledge-
ments.

In vc (virtual circuit) mode, IP packets are encapsulated in AX.25 I frames
and are acknowledged at the link level according to the AX.25 protocol. Link
level connections are opened if necessary.

In both modes, ARP is used to map IP to AX.25 addresses. The defaults can be
overridden with the type-of-service (TOS) bits in the IP header. Turning on
the "reliability" bit causes I frames to be used, while turning on the "low
delay" bit uses UI frames. (The effect of turning on both bits is undefined
and subject to change).

In both modes, IP-level fragmentation is done if the datagram is larger than
the interface MTU. In virtual circuit mode, however, the resulting datagram
(or fragments) is further fragmented at the AX.25 layer if it (or they) are
still larger than the AX.25 paclen parameter. In AX.25 fragmentation,
datagrams are broken into several I frames and reassembled at the receiving
end before being passed to IP. This is preferable to IP fragmentation when-
ever possible because of decreased overhead (the IP header isn't repeated in
each fragment) and increased robustness (a lost fragment is immediately
retransmitted by the link layer).

3.50. more <file> [<file> ...]

Display the specified file(s) a screen at a time. To proceed to the next
screen, press the space bar; to cancel the display, hit the 'q' key. A CR
advances a line. The more command creates a session that you can suspend and
resume just like any other session.

3.51. motd [<"message of the day">]

Display the current message or sets the welcome message to the defined
string.

3.52. multitask [on | off]

Displays or sets the multi task flag. If set Nos continues to service its
interrupts and handling of normal operation when put in the background by
executing a shell escape. Some programs do not like to miss valuable time
taken away this way and weard results can happen. Clearing the flag stops all
activiity fron Nos when put in the background.

3.53. netrom <subcommand>


3.53.1. netrom acktime [<milliseconds>]

Displays or sets the ack delay timer, similary to ax25 t2.

3.53.2. netrom bcnodes <iface>

Initiates an immediate broadcast of nodelist on iface.

3.53.3. netrom connect <node>

Start a connection to node.

3.53.4. netrom choketime [<milliseconds>]

Display or set the time breaking a send choke. Choke is the term netrom uses
for flow control conditions.

3.53.5. netrom derate [on | off]

Display or set automatic derating of netrom routes on link failure.

3.53.6. netrom interface <iface> <alias> <quality>

Define a netrom interface iface having a alias of alias. The quality can be
between 1 and 255. For compatibility with other implementations set this to
192 normaly. A check is made that the interface is of type CLAX25, meaning
NETROM capable media.

3.53.7. netrom irtt [<milliseconds>]

Display or set the initial round trip time.

3.53.8. netrom kick <&nrcb>

Give the control block a kick to get activity going again.

3.53.9. netrom load [<filename>]

When fully implemented reloads a saved netrom node list to continue from
where you left when you saved the list. All entry's read are time decremented
as if normal time just went on. If it took some time (obsotimer * x) your
list could be empty as they all timed out.

3.53.10. netrom minquality [<value>]

Display or set the minimum quality for recognizing a node entry.  Entry's
below this value are not considered valuable for usage.

3.53.11. netrom nodefilter <subcommand>

Node filtering.

3.53.11.1. netrom nodefilter add <neighbor> <iface>

Allow neighbor to give us node updates.

3.53.11.2. netrom nodefilter drop <neighbor> <iface>

Disallow neighbor to give us node updates.

3.53.11.3. netrom nodefilter mode [none | accept | reject]

Display or set the initial filter schema. None accepts all.  Accept,accepts
only from nodes defined in netrom nodefilter add lists. Reject,no accepts
from nodes defined in netrom nodefilter add lists.

3.53.12. netrom nodetimer [<seconds>]

Display or set the interval our node list is transmitted.

3.53.13. netrom obsotimer [<seconds>]

Display or set the time a node quality gets decremented.

3.53.14. netrom promiscious [off | on]

Enables nodes with a higher quality than defined with minquality. If on, all
nodes are received, independent od nodefilter.

3.53.15. netrom qlimit [<bytes>]

Display or set the maximum queue limit for chat. Similar to ax25 window.

3.53.16. netrom reset <&nrcb>

Remove the control block. You can find the control block with socket.

3.53.17. netrom retries [<value>]

Display or set the maximum number of retries on connect, disconnect or data.

3.53.18. netrom route <subcommand>

Netrom routing commands.

3.53.18.1. netrom route add <alias> <destination> <iface> <quality> <neigh-
bor>

Add a netrom route.

3.53.18.2. netrom route drop <destination> <neighbor> <iface>

Delete a netrom route.

3.53.18.3. netrom route info <destination>

Display the route it would take to get to destination.

3.53.19. netrom status

Displays all netrom connections.

3.53.20. netrom save [<filename>]

When fully implemented, saves the current netrom node list in memory to
/netrom.sav or filename, if given.

3.53.21. netrom timertype [exponential | linear]

Displays or sets the type of backoff.

3.53.22. netrom ttl [<hops>]

Display or set the maximum number of hops a frame might hop before discarded,
if it did not reach its destination before.

3.53.23. netrom user [<username>]

Display or set our netrom user name.

3.53.24. netrom verbose [off | on]

Display or set the verbose flag. If set all nodes known to us are transmitted
each time the nodetimer expires. If off, only your stations node ident is
send out.

3.53.25. netrom window [<frames>]

Display or set the size of the sliding window. This is the largest send and
receive window we might negotiate.

3.54. nntp <subcommand>

Network news transfer protocol has the following subcommands:

3.54.1. nntp addserver <nntpserver> <seconds> [<range>] [<groups>]

Add a nntp news server to quiry every seconds interval for new articles
specified by the nntp groups command. Range can be a limit in time to query
like nntp addserver someserver 600 22:00-23:00, to only query the server
between 10 and 11pm. Multiple nntp add can be used co concatenate groups (up
to 512 bytes) The interval seconds can be set to 0, so that normaly the nntp
client does not query the server regulary but an nntp kick nntpserver can be
used to start a session.

3.54.2. nntp directory <directory>

Show or set default directory for spooling news. This is not the control
directory but the (alternate) place to spool articles to.

3.54.3. nntp dropserver <nntpserver>


3.54.4. nntp groups <group> [<group> ...]

Set or display currently set newsgroups.

3.54.5. nntp kick <nntpserver>

Kick the client to get in touch with the named server.

3.54.6. nntp listservers

Lists the curently defined servers.

3.55. nntp quiet [yes | no]

Shows or sets the flag controlling the display of newly received nntp news
messages. The smpt quiet fag controls the beep following the message. If
both are off, nothing is shown, keeping the display from getting hung on
-more- when running unattended.

3.56. nntp trace <level>

Sets or shows the current trace level for the nntp client. 0 No tracing 1
(default) displays serious errors. 2 displays as 1 and transient errors. 3
displays as 2 and session progress. 4 displays as 3 and actual received
articles. 5 displays errors.

3.57. nrstat

Displays the netrom interface statistics.

3.58. param <iface> [<param> ...]

Invoke a device-specific control routine. On a KISS TNC interface, this
sends control packets to the TNC. Data bytes are treated as decimal. For
example, param ax0 1 255 will set the keyup timer (type field = 1) on the
KISS TNC configured as ax0 to 2.55 seconds (255 x .01 sec). On a SLIP inter-
face, the param command allows the baud rate to be read (without arguments)
or set. The implementation of this command for the various interface drivers
is incomplete and subject to change.

3.59. ping <hostid> [<length> [<milliseconds> [<incflag>]]]

Ping (send ICMP Echo Request packets to) the specified host. By default the
data field contains only a small timestamp to aid in determining round trip
time; if the optional length argument is given, the appropriate number of
data bytes (consisting of hex 55) are added to the ping packets.

If milliseconds is specified, pings will be repeated indefinitely at the
specified number of milliseconds; otherwise a single, "one shot" ping is
done. Responses to one-shot pings appear asynchronously on the command
screen, while repeated pings create a session that may be suspended and
resumed. Pinging continues until the session is manually reset.

The incflag option causes a repeated ping to increment the target IP address
for each ping; it is an experimental feature for searching blocks of IP
addresses for active hosts.

3.60. pop <subcommand>

The pop client provides an automatic interface to the pop server that is
totaly transparen to the user; all that the user needs to do is to set a few
key parameters and the client will take it from there, appart from registring
with the server station manager for setting up the user data. (see pop user-
data command. To read more about pop, read rfc937. The following paragraph
describe the pop subcommands.

3.60.1. pop mailbox [<name>]

Show the defined name or sets the name to name for POP mail queries to the
mailhost. The server keeps the mail in the mailbox name located in
/spool/mail/name.txt. This is a mandatory parameter.

3.60.2. pop mailhost [<ipaddr>]

Show the currently defined host address for a pop server or sets the IP
address to the system named ipaddr for POP connections. This is a mandatory
parameter.

3.60.3. pop kick

Start a POP connection now. (one shot connection)

3.60.4. pop timer [<seconds>]

Show the current setting and time remaining untill next server enquiry or
when seconds is given, defines the interval that a pop connection is started
every <seconds> to retrieve mail from the server system. When the timer is
not set the client is only started with a pop kick command.

3.60.5. pop userdata <name> <password>

Sets up the userdata used for validation on the POP server system. Note that
<name> and <password> are case sensitive. When only pop userdata is entered
to show the values only the <name> is shown. (ultimate in security, if you
realy want to see the password look in the "ether"). Remember: the name and
password should also be defined at the server site in the popusers file.

3.61. ppp <subcommands>

These commands are used for Point to Point Protocol interfaces.
This implementation of PPP is designed to be as complete as possible.
Because of this, the number of options can be rather daunting. However, a
typical PPP configuration might include the following commands:

 attach asy 0x3f8 4 ppp pp0 4096 1500 9600
 dial pp0 30 <hostid> 3 dialer.pp0
 #
 ppp pp0 lcp local accm 0
 ppp pp0 lcp local compress address on
 ppp pp0 lcp local compress protocol on
 ppp pp0 lcp local magic on
 ppp pp0 lcp open active
 #
 ppp pp0 ipcp local compress tcp 16 1
 ppp pp0 ipcp open active
 #
 route add default pp0


3.61.1. ppp <iface>

Display the status of the PPP interface.

3.61.2. ppp <iface> lcp ...

These commands are used for the LCP [Link Control Protocol] configuration.

3.61.2.1. ppp <iface> lcp close

Shutdown the PPP interface.

3.61.2.2. ppp <iface> lcp local ...

These commands control the configuration of the local side of the link.  If
an option is specified, the parameters will be used as the initial values in
configuration requests. If not specified, that option will not be requested.

For each of these options, the allow parameter will permit the remote to
include that option in its response, even when the option is not included in
the request. By default, all options are allowed.

3.61.2.2.1. ppp <iface> lcp local accm [ <bitmap> | allow [on | off] ]

Display or set the Async Control Character Map. The default is 0xff.

3.61.2.2.2. ppp <iface> lcp local authenticate [ pap | none | allow [on |
off] ]

Display or set the authentication protocol. The default is none.

3.61.2.2.3. ppp <iface> lcp local compress address/control [ on | off |
allow [on | off] ]

Display or set the option to compress the address and control fields of the
PPP HLDC-like header.  This is generally desirable for slow asynchronous
links, and undesirable for fast or synchronous links. The default is off.

3.61.2.2.4. ppp <iface> lcp local compress protocol [ on | off | allow [on |
off] ]

Display or set the option to compress the protocol field of the PPP HLDC-like
header.  This is generally desirable for slow asynchronous links, and
undesirable for fast or synchronous links. The default is off.

3.61.2.2.5. ppp <iface> lcp local magic [ on | off | <value> | allow [on |
off] ]

Display or set the initial Magic Number. The default is off (zero).

3.61.2.2.6. ppp <iface> lcp local mru [ <size> | allow [on | off] ]

Display or set the Maximum Receive Unit. The default is 1500.

3.61.2.2.7. ppp <iface> lcp local default

Reset the options to their default values.

3.61.2.3. ppp <iface> lcp open active | passive

Wait for the physical layer to come up. If active, initiate configuration
negotiation. If passive, wait for configuration negotiation from the remote.

3.61.2.4. ppp <iface> lcp remote ...

These commands control the configuration of the remote side of the link. The
options are identical to those of the local side. If an option is specified,
the parameters will be used in responses to the remote's configuration
requests. If not specified, that option will be accepted if it is allowed.

For each of these options, the allow parameter will permit the remote to
specify that option in its request. By default, all options are allowed.

3.61.2.5. ppp <iface> lcp timeout [<seconds>]

Display or set the interval to wait between configuration or termination
attempts. The default is 3 seconds.

3.61.2.6. ppp <iface> lcp try ...

These commands are used for the various counters.

3.61.2.6.1. ppp <iface> lcp try configure [<count>]

Display or set the number of configuration requests sent. The default is 10.

3.61.2.6.2. ppp <iface> lcp try failure [<count>]

Display or set the number of bad configuration requests allowed from the
remote. The default is 5.

3.61.2.6.3. ppp <iface> lcp try terminate [<count>]

Display or set the number of termination requests sent before shutdown.  The
default is 2.

3.61.3. ppp <iface> ipcp ...

These commands are used for the IPCP [Internet Protocol Control Protocol]
configuration.

The close, open, timeout and try sub-commands are identical to the LCP
(described above).

3.61.3.1. ppp <iface> ipcp local ...

These commands control the configuration of the local side of the link.  If
an option is specified, the parameters will be used as the initial values in
configuration requests. If not specified, that option will not be requested.

For each of these options, the allow parameter will permit the remote to
include that option in its response, even when the option is not included in
the request. By default, all options are allowed.

3.61.3.1.1. ppp <iface> ipcp local address [ <hostid> | allow [on | off] ]

Display or set the local address for negotiation purposes. If an address of
0 is specified, the other side of the link will supply the address. By
default, no addresses are negotiated.

3.61.3.1.2. ppp <iface> ipcp local compress [ tcp <slots> [<flag>] | none |
allow [on | off] ]

Display or set the compression protocol. The default is none.

The tcp <slots> specifies the number of "conversation" slots, which must be 1
to 255.  (This may be limited at compilation time to a smaller number.) A
good choice is in the range 4 to 16.

The tcp <flag> is 0 (don't compress the slot number) or 1 (OK to compress the
slot number). KA9Q can handle compressed slot numbers, so the default is 1.

3.61.3.2. ppp <iface> ipcp remote ...

These commands control the configuration of the remote side of the link. The
options are identical to those of the local side. If an option is specified,
the parameters will be used in responses to the remote's configuration
requests. If not specified, that option will be accepted if it is allowed.

For each of these options, the allow parameter will permit the remote to
specify that option in its request. By default, all options are allowed.

3.61.4. ppp <iface> pap ...

These commands are used for the PAP [Password Authentication Protocol] confi-
guration.

The timeout and try sub-commands are identical to the LCP (described above).
However, the terminate counter is unused.

3.61.4.1. ppp <iface> pap user [ <username> [<password>] ]

Display or set the username (the password may be set, but not displayed).
When the username is specified, but no password is supplied, the ftpusers
file is searched for the password. When a username/password is unknown or
rejected, a session will appear at the console to prompt for a new
username/password.

3.61.5. ppp <iface> trace [<flags>]

Display or set the flags that control the logging of information during PPP
link configuration.

The flag value is 0 for none, 1 for basic, and 2 for general. Values greater
than 2 are usually not compiled, and are described in the appropriate source
files where they are defined.

3.62. ps

Display all current processes in the system. The fields are as follows:

PID - Process ID (the address of the process descriptor).

SP - The current value of the process stack pointer.

stksize - The size of the stack allocated to the process.

maxstk - The apparent peak stack utilization of this process. This is done in
a somewhat heuristic fashion, so the numbers should be treated as approxi-
mate. If this number reaches or exceeds the stksize figure, the system is
almost certain to crash; the nos.exe program should be recompiled to give the
process a larger allocation when it is started.

event - The event this task is waiting for, if it is not runnable.

fl - Process status flags. There are three: I (Interrupts enabled), W (Wait-
ing for event) and S (suspended). The I flag is set whenever a task has exe-
cuted a pwait() call (wait for event) without first disabling hardware inter-
rupts. Only tasks that wait for hardware interrupt events will turn off this
flag; this is done to avoid critical sections and missed interrupts. The W
flag indicates that the process is waiting for an event; the event column
will be non-blank. Note that although there may be several runnable processes
at any time (shown in the ps listing as those without the W flag and with
blank event fields) only one process is actually running at any one instant
(The Refrigerator Light Effect says that the ps command is always the one
running when this display is generated.)

3.63. pwd [<dirname>]

An alias for the cd command.

3.64. rarp <subcommand>

This uses the reverse address resolution protocol.

3.64.1. rarp query <iface> <callsign>

This starts a reverse resolution request via iface to find the IP address for
callsign. It counts down for 10 seconds before giving up listening for an
answer.

3.65. record [off | <filename>]

Append to filename all data received on the current session.  Data sent on
the current session is also written into the file except for Telnet sessions
in remote echo mode. The command record off stops recording and closes the
file.

3.66. remote [-p <port>] [-k <key>] [-a <kickaddr>] <hostid> exit | reset |
kick

Send a UDP packet to the specified host commanding it to exit the Nos pro-
gram, reset the processor, or force a retransmission on TCP connections. For
this command to be accepted, the remote system must be running the remote
server and the port number specified in the remote command must match the
port number given when the server was started on the remote system.  If the
port numbers do not match, or if the remote server is not running on the tar-
get system, the command packet is ignored. Even if the command is accepted
there is no acknowledgement.

The kick command forces a retransmission timeout on all TCP connections that
the remote node may have with the local node. If the -a option is used, con-
nections to the specified host are kicked instead. No key is required for the
kick subcommand.

The exit and reset subcommands are mainly useful for restarting the nos pro-
gram on a remote unattended system after the configuration file has been
updated. The remote system should invoke the Nos program automatically upon
booting, preferably in an infinite loop. For example, under MS-DOS the boot
disk should contain the following in autoexec.bat:

 :loop
 nos
 goto :loop



3.66.1. remote -s <key>

The exit and reset subcommands of remote require a password. The password is
set on a given system with the -s option, and it is specified in a command to
a remote system with the -k option. If no password is set with the -s option,
then the exit and reset subcommands are disabled.

Note that remote is an experimental feature in NOS; it is not yet supported
by any other TCP/IP implementation.

3.67. rename <oldfilename> <newfilename>

Rename oldfilename to newfilename.

3.68. reset [<session>]

Reset the specified session; if no argument is given, reset the current ses-
sion.  This command should be used with caution since it does not reliably
inform the remote end that the connection no longer exists. (In TCP a reset
(RST) message will be automatically generated should the remote TCP send any-
thing after a local reset has been done. In AX.25 the DM message performs a
similar role.  Both are used to get rid of a lingering half-open connection
after a remote system has crashed.)

3.69. rip <subcommand>

These commands are used for the RIP service.

3.69.1. rip accept <gateway>

Remove the specified gateway from the RIP filter table, allowing future
broadcasts from that gateway to be accepted.

3.69.2. rip add <hostid> <seconds> [<flags>]

Add an entry to the RIP broadcast table. The IP routing table will be sent to
hostid every interval of seconds. If flags is specified as 1, then "split
horizon" processing will be performed for this destination. That is, any IP
routing table entries pointing to the interface that will be used to send
this update will be removed from the update. If split horizon processing is
not specified, then all routing table entries except those marked "private"
will be sent in each update. (Private entries are never sent in RIP pack-
ets).

Triggered updates are always done. That is, any change in the routing table
that causes a previously reachable destination to become unreachable will
trigger an update that advertises the destination with metric 15, defined to
mean "infinity".

Note that for RIP packets to be sent properly to a broadcast address, there
must exist correct IP routing and ARP table entries that will first steer the
broadcast to the correct interface and then place the correct link-level
broadcast address in the link-level destination field. If a standard IP
broadcast address convention is used (eg. 128.96.0.0 or 128.96.255.255) then
chances are you already have the necessary IP routing table entry, but
unusual subnet or cluster-addressed networks may require special attention.
However, an arp add command will be required to translate this address to the
appropriate link level broadcast address. For example,

arp add 128.96.0.0 ethernet ff:ff:ff:ff:ff:ff

for an Ethernet network (ip address is a sample only!!!), and

arp add 44.255.255.255 ax25 qst-0

for an AX25 packet radio channel. (If multiple AX25 interfaces, make a unique
address for each interface.)

3.69.3. rip drop <dest>

Remove an entry from the RIP broadcast table.

3.69.4. rip merge [on | off]

This flag controls an experimental feature for consolidating redundant
entries in the IP routing table. When rip merging is enabled, the table is
scanned after processing each RIP update. An entry is considered redundant if
the target(s) it covers would be routed identically by a less "specific"
entry already in the table. That is, the target address(es) specified by the
entry in question must also match the target addresses of the less specific
entry and the two entries must have the same interface and gateway fields.
For example, if the routing table contains


Dest  Len Interface Gateway  Metric P Timer Use
1.2.3.4  32 ethernet0 128.96.1.2  1  0 0  0
1.2.3   24 ethernet0 128.96.1.2  1  0 0  0


then the first entry would be deleted as redundant since packets sent to
1.2.3.4 will still be routed correctly by the second entry. Note that the
relative metrics of the entries are ignored.

3.69.5. rip refuse <gateway>

Refuse to accept RIP updates from the specified gateway by adding the gateway
to the RIP filter table. It may be later removed with the rip accept command.

3.69.6. rip request <gateway>

Send a RIP Request packet to the specified gateway, causing it to reply with
a RIP Response packet containing its routing table.

3.69.7. rip status

Display RIP status, including a count of the number of packets sent and
received, the number of requests and responses, the number of unknown RIP
packet types, and the number of refused RIP updates from hosts in the filter
table. A list of the addresses and intervals to which periodic RIP updates
are being sent is also shown, along with the contents of the filter table.

3.69.8. rip trace [0 | 1 | 2]

This variable controls the tracing of incoming and outgoing RIP packets.
Setting it to 0 disables all RIP tracing. A value of 1 causes changes in the
routing table to be displayed, while packets that cause no changes cause no
output. Setting the variable to 2 produces maximum output, including tracing
of RIP packets that cause no change in the routing table.

3.69.9. rip ttl <seconds>

Displays or sets the time to live timer to seconds. Normal timeout value is
240 seconds. This is not the ttl in a rip broadcast (16 = infinite). Set
this timer before starting rip. Change this timer only in cooperation with
your surrounding nodes. Default is 240 seconds.

3.70. rlogin host

Sets up an rlogin session via port 511 to an *NIX compatible station. Defaut
terminal is an ansi (as defined with the fkeys) compatible terminal. Default
user name is guest. (Redefine with set USER= environement variable).

3.71. rmdir <dirname>

Remove a sub-directory from the current working directory.

3.72. route

With no arguments, route displays the IP routing table.

3.72.1. route add <desthostid>[/bits] | default <iface> [<gatewayhostid> |
direct [<metric>]]

This command adds an entry to the routing table. It requires at least two
more arguments, the hostid of the target destination and the name of the
interface to which its packets should be sent. If the destination is not
local, the gateway's hostid should also be specified. (If the interface is a
point-to-point link, then gatewayhostid may be omitted even if the target is
non-local because this field is only used to determine the gateway's link
level address, if any.  If the destination  is  directly  reachable,
gatewayhostid is also unnecessary since the destination address is used to
determine the interface link address). If rspf is used and the system is a
switch / router to multiple routes the keyword direct can be used i.s.o a
gatewayhostid to set the metric higher as the default 1. This way routes
advertized by other rspf stations can be cheaper and get selected. If direct
is given but metric not, an new algoritm is used to set the metric dependent
on the number of subnet mask bits.

The optional /bits suffix to the destination host id specifies how many
leading bits in the host id are to be considered significant in the routing
comparisons. If not specified, 32 bits (i.e., full significance) is assumed.
With this option, a single routing table entry may refer to many hosts all
sharing a common bit string prefix in their IP addresses. For example, ARPA
Class A, B and C networks would use suffixes of /8, /16 and /24 respectively;
the command

route add 44/8 sl0 44.64.0.2


causes any IP addresses beginning with "44" in the first 8 bits to be routed
to 44.64.0.2; the remaining 24 bits are "don't-cares".

When an IP address to be routed matches more than one entry in the routing
table, the entry with largest bits parameter (i.e., the "best" match) is
used. This allows individual hosts or blocks of hosts to be exceptions to a
more general rule for a larger block of hosts.

The special destination default is used to route datagrams to addresses not
matched by any other entries in the routing table; it is equivalent to speci-
fying a /bits suffix of /0 to any destination hostid.  Care must be taken
with default entries since two nodes with default entries pointing at each
other will route packets to unknown addresses back and forth in a loop until
their  time-to-live (TTL) fields expire.  (Routing loops for specific
addresses can also be created, but this is less likely to occur acciden-
tally).

There are two build in interfaces: loopback and encap.  Loopback is for
internal purposes only. The encap is an IP encapsulator interface. This is
used to encapsulate a complete IP datagram into a IP datagram so that it gets
"piggy-backed". It is often used to carry ampr.org datagrams (net44) over the
Internet. Note that the Internet is fully connected and that ampr.org is (at
least) very loose.  This way two sites can interchange net44 datagrams to
each other. Some extra notes: A Internet gateway has 2 IP addresses: one on
ampr.org and one on the Internet. You should make sure that the interface
connected to the Internet has the ifconfig ipaddr set correctly. Note: This
previously only worked as gateway for other stations. There was some guessing
done in picking an IP address when encap is used localy. The guessing takes
the worst guess. (always wrong with a 2.7 Murphy factor) The code now uses
the local IP address as source when the route starts at the local station. If
this is not what you want, you can overrule this by setting the IP address of
the psuedo encap interface to what you want it to be.

Some extra notes on encap: I have 3 systems on an ethernet with network
129.179.122.128/25. In the office I have another net linked to the Internet.
The addresses there are in the 129.179.122.0/25 range. Now i have a radio
link with 44.137.0.2 and 44.137.1.2 on respective sites. On the 44.137.0.2
system i have route add 44.0.0.0/8 encap 44.137.1.1 99. On a next system on
my local ethernet i have 44.137.0.1 / 129.179.122.129. To get from that sys-
tem to say 44.62.0.1 i have to add an encap to my local gateway with route
add  44.0.0.0/8  encap  129.179.122.130. A  route  add  default ec0
129.179.122.130 gives me access to the Internet. Otherwise it will lookup
the address for the interface to be used to reach 129.179.122.130 and will
use 129.179.122.129. Now 44.62.0.1 will NEVER know where it came from. So
adding the encap on the second system solves the problem.

Here are some examples of the route command:

# Route datagrams to IP address 44.0.0.3 to SLIP line #0.
# No gateway is needed because SLIP is point-to point.
route add 44.0.0.3 sl0

# Route all default traffic to the gateway on the local Ethernet
# with IP address 44.0.0.1
route add default ec0 44.0.0.1

# The local Ethernet has an ARPA Class-C address assignment;
# route all IP addresses beginning with 192.4.8 to it
route add 192.4.8/24 ec0

# The station with IP address 44.0.0.10 is on the local AX.25 channel
route add 44.0.0.10 ax0

# An encapsulation link to 192.4.8.12 where the subnet 44.64.0.0 is
accessible. The internet does not know where we are but we just use them
with what they know:
route add 44.64.0.0/16 encap 192.4.8.12 4



3.72.2. route addprivate <dest hostid>[/bits] | default <iface> [<gateway
hostid> [<metric>]]

This command is identical to route add except that it also marks the new
entry as private; it will never be included in outgoing RIP updates.

3.72.3. route drop <dest hostid>

route drop deletes an entry from the table. If a packet arrives for the
deleted address and a default route is in effect, it will be used.

3.73. rspf <subcmd>

RSPF is the Radio Shortest Path First protocol. Each station listens for RRH
(Router to Router Hello) messages. When such a RRH message is received, Nos
will figure out if the link is bi-directional by pinging the other station.
The protocol is described in the RSPF 2.1 specification.

3.73.1. rspf interface <interface> <quality> <horizon>

<interface> is the required interface rspf should use. quality is from 1 to
127 horizon is between 1 to 255 End nodes should have the quality set to 1.
Immediate nodes normaly set the quality to 8. The normaly used value for hor-
izon is 32.

3.73.2. rspf mode [vc | datagram | none]

Without arguments, displays the preferred mode for RSPF. Modes are VC (Vir-
tual Cirquit) and Datagram. none resets the preferred mode.

3.73.3. rspf rrhtimer [seconds]

Without arguments, displays the rrh timer value.

3.73.4. rspf suspecttimer [seconds]

Without arguments, displays the suspect timer value.

3.73.5. rspf timer [seconds]

Without arguments, displays the update timer value.

To activate RSPF, do the following. Set the broadcast address for the desti-
nation interface, example ax0.
 ifconfig ax0 broadcast 44.255.255.255

This automatically creates a routing entry for 44.255.255.255 in the routing
table. If intend to use RSPF on more than one interface, those interfaces
must each have different broadcast adresses. Else the routing entries will be
overwriten by the next definition.

Configure ax0 as an RSPF interface with horizon 32 and a quality of 1 (hops).
This is typical for an end node. replace the 1 with an 8 for immediate nodes.
 rspf interface ax0 1 32
 Set the interval between RRH messages.
 rspf rrhtimer 900
 Define how long it takes until an idle link is suspected to be bad.
 rspf suspecttimer 2000
 Set the interval between routing updates.
 rspf timer 900

3.74. sccstat

Display the defined PE1CHL scc driver statistics.

3.75. session [[<session>] [flowmode [on | off]]]

Without arguments, displays the list of current sessions, including session
number, remote TCP or AX.25 address and the address of the TCP or AX.25 con-
trol block. An asterisk (*) is shown next to the current that session.
Entering a session number as an argument to the session command will put you
in converse mode with that session. If the Telnet session; entering a blank
line at this point puts you in converse mode with server is enabled, the user
is notified of an incoming request and a session number is automatically
assigned. The user may then select the session normally to converse with the
remote user as though the session had been locally initiated.  Adding the
flowmode displays or enables / disables setting of *more* handling for that
session. This is handy for example by long directory listings comming from an
ftp session. Escaping to command mode before issuing the dir command and
entering "session # flowmode on" gives a page at a time to look at. At any
time you can escape out again and switch flowmode off.

3.76. shell

Suspends Nos and executes a sub-shell ("command processor" under MS-DOS).
When the sub-shell exits, Nos resumes (under MS-DOS, enter the exit command).
Note: see the COMSPEC environement variable.  Background activity (FTP
servers, etc) is also suspended while the subshell executes. Note that this
will fail unless there is sufficient unused memory for the sub-shell and
whatever command the user tries to run.

3.77. smtp <subcommand>

These commands are used for the Simple Message Transport Protocol service
(that is, mail).

3.77.1. smtp batch [yes | no]

If set smtp will batch the commands into one frame. When off only one command
is send and a response is waited for. Some old and flaky smtp servers cannot
handle more than one command at a time. Nos can handle multiple. If you are
not hindered by an old smpt server, setting batch reduces bandwith.

3.77.2. smtp gateway [<hostid>]

Displays or sets the host to be used as a "smart" mail relay. Any mail sent
to a host not in the host table will instead be sent to the gateway for for-
warding.

3.77.3. smtp kick

Run through the outgoing mail queue and attempt to deliver any pending mail.
This command allows the user to "kick" the mail system manually. Normally,
this command is periodically invoked by a timer whenever Nos is running.

3.77.4. smtp kill [<jobid>]

Kill the job and delete the message.

3.77.5. smtp list

List the current jobs. A "L" means locked and in progress. It is wise to add
in autoexec.bat a "del /spool/mqueue/*.lck" command

3.77.6. smtp maxclients [<count>]

Displays or sets the maximum number of simultaneous outgoing SMTP sessions
that will be allowed. The default is 10; reduce it if network congestion is a
problem.

3.77.7. smtp mode [queue | route]

Sets the smtp delivery mode. If queue, all messages are left in /spool/rqueue
for external forwarding and handling. If route, messages are handled, if for
local, appended to a mailbox or if remote, they are forwarded.

3.77.8. smtp mxlookup [yes | no]

Displays or sets a flag enabling or disabling MX record lookups. This can be
enabled if a domain server is available in the near distance (reachable). It
should be disabled (default) if no domain server is in reach to satisfy the
MX query. Note that MX record handling is very limited in NOS. If an answer
from a domain name server comes in it is taken to be the destination.

3.77.9. smtp quiet [yes | no]

Enables or disables the message that new mail arrived at this system.

3.77.10. smtp timer [<seconds>]

Displays or sets the interval, between scans of the outbound mail queue. For
example, smtp timer 600 will cause the system to check for outgoing mail
every 10 minutes and attempt to deliver anything it finds, subject of course
to the smtp maxclients limit. Setting a value of zero disables queue scanning
altogether, note that this is the default! This value is recommended for
stand alone IP gateways that never handle mail, since it saves wear and tear
on the floppy disk drive.

3.77.11. smtp trace [<value>]

Displays or sets the trace flag in the SMTP client, allowing you to watch
SMTP's conversations as it delivers mail. Zero (the default) disables trac-
ing.

3.78. socket [[<socket #>] [flowmode [yes | no]]]

Without an argument, displays all active sockets, giving their index and
type, the address of the associated protocol control block and the and owner
process ID and name. If the index to an active socket is supplied, the status
display for the appropriate protocol is called. For example, if the socket
refers to a TCP connection, the display will be that given by the tcp status
command with the protocol control block address. Flow mode can be set or
cleared on a session if so wanted. This comes in handy when a large directory
is displayed by ftp. Escaping from the session just before entering dir and
setting flowmode and returning to that session, gives a screen full at a time
with -more- processing.

3.79. source <filename>

Read subsequent commands from filename until EOF. Then resume reading com-
mands from the previous stream. This can be used to keep routing statements
in a separate file, wich can be read at some point in autoexec.nos.

3.80. start ax25 | discard | echo | finger | ftp | netrom | remote | pop |
rip | smtp | telnet | tip | ttylink

Start the specified Internet server, allowing remote connection requests.

3.81. status

Displays load information on Nos. When started, how long running, open files
etc.

3.82. stop ax25 | discard | echo | finger | ftp | netrom | remote | pop |
rip | smtp | telnet | tip | ttylink

Stop the specified Internet server, rejecting any further remote connect
requests. Existing connections are allowed to complete normally.

3.83. tail <filename>

This does a more on the last couple of lines of file filename.

3.84. tcp <subcommand>

These commands are used for the Transmission Control Protocol service.

3.84.1. tcp irtt [<milliseconds>]

Display or set the initial round trip time estimate, in milliseconds, to be
used for new TCP connections until they can measure and adapt to the actual
value. The default is 5000 milliseconds (5 seconds). Increasing this when
operating over slow channels will avoid the flurry of retransmissions that
would otherwise occur as the smoothed estimate settles down at the correct
value. Note that this command should be given before servers are started in
order for it to have effect on incoming connections.

TCP also keeps a cache of measured round trip times and mean deviations
(MDEV) for current and recent destinations. Whenever a new TCP connection is
opened, the system first looks in this cache. If the destination is found,
the cached IRTT and MDEV values are used. If not, the default IRTT value men-
tioned above is used, along with a MDEV of 0.  This feature is fully
automatic, and it can improve performance greatly when a series of connec-
tions are opened and closed to a given destination (eg. a series of FTP file
transfers or directory listings).

3.84.2. tcp kick <tcbaddr>

If there is unacknowledged data on the send queue of the specified TCB, this
command forces an immediate retransmission.

3.84.3. tcp mss [<size>]

Display or set the TCP Maximum Segment Size in bytes that will be sent on all
outgoing TCP connect request (SYN segments). This tells the remote end the
size of the largest segment (packet) it may send. Changing MSS affects only
future connections; existing connections are unaffected.

3.84.4. tcp reset <tcbaddr>

Deletes the TCP control block at the specified address.

3.84.5. tcp rtt <tcbaddr> <milliseconds>

Replaces the automatically computed round trip time in the specified TCB with
the rtt in milliseconds. This command is useful to speed up recovery from a
series of lost packets since it provides a manual bypass around the normal
backoff retransmission timing mechanisms.

3.84.6. tcp status [<tcbaddr>]

Without arguments, displays several TCP-level statistics, plus a summary of
all existing TCP connections, including TCB address, send and receive queue
sizes, local and remote sockets, and connection state. If tcbaddr is speci-
fied, a more detailed dump of the specified TCB is generated, including send
and receive sequence numbers and timer information.

3.84.7. tcp syndata [yes | no]

Display or set the tcp syn + data pigybacking flag. Some tcp systems cannot
handle syn + data together.

3.84.8. tcp timertype [linear | exponential]

Displays the current setting or sets the timer type backoff algoritm.

3.84.9. tcp trace [yes | no]

Display or set the tcp trace flag on or off.

3.84.10. tcp window [<size>]

Displays or sets the default receive window size in bytes to be used by TCP
when creating new connections. Existing connections are unaffected.

3.85. telnet <hostid> [<port>]

Creates a Telnet session to the specified host and enters converse mode.  If
<port> is given that number is used. Default port is 23.

3.86. test

Start an internal test for an overflow problem that might appear in the clock
function of some AT computers.

3.87. thirh-party [yes | no]

This is a restriction setter for some countries where stations are not
allowed to handle thirth party mail traffic.

3.88. ttylink <hostid> [<port>]

Creates a Telnet session to the specified host and enters converse mode.  If
<port> is given that number is used. Default port is 87. This uses a split
screen interface for easy conversation.

3.89. tip <iface>

Creates a tip session that connects to the specified interface in "dumb ter-
minal" mode.  The interface must have already been attached with the attach
command. Any packet traffic (IP datagrams, etc) routed to the interface
while this session exists will be discarded. To close a tip session, use the
reset command. It will then revert to normal slip, nrs or kiss mode opera-
tion.

This feature is primarily useful for manually establishing SLIP connections.
At present, only the built-in "com" ports can be used with this command.

3.90. trace [<iface> [off | <btio> [<tracefile>]]]

Controls packet tracing by the interface drivers. Specific bits enable trac-
ing of the various interfaces and the amount of information produced. Trac-
ing is controlled on a per-interface basis; without arguments, trace gives a
list of all defined interfaces and their tracing status. Output can be lim-
ited to a single interface by specifying it, and the control flags can be
change by specifying them as well. The flags are given as a hexadecimal
number which is interpreted as follows:

 O - Enable tracing of output packets if 1, disable if 0
 I - Enable tracing of input packets if 1, disable if 0
 T - Controls type of tracing:
 0 - Protocol headers are decoded, but data is not displayed
 1 - Protocol headers are decoded, and data (but not the
  headers themselves) are displayed as ASCII characters,
  64 characters/line. Unprintable characters are displayed
  as periods.
 2 - Protocol headers are decoded, and the entire packet
  (headers AND data) is also displayed in hexadecimal
  and ASCII, 16 characters per line.
 B - Broadcast filter flag. If set, only packets specifically addressed
 to this node will be traced; broadcast packets will not be displayed.

If tracefile is not specified, tracing will be to the console.

3.91. udp status

3.92. verbose [0 | 1 | 2 | 3]

Set or display the level of message output in file transfers.  Verbose 0
gives the least output, and verbose 3 the most, as follows:

0 - Display error messages only.
1 - Display error messages plus a one-line summary after each transfer
 giving the name of the file, its size, and the transfer time and rate.
2 - Display error and summary messages plus the progress messages generated
 by the remote FTP server. (This setting is the default.)
3 - Display all messages. In addition, a "hash mark" (#) is displayed for
 every 1,000 bytes sent or received.

If a command is sent to the remote server because it is not recognized
locally, the response is always displayed, regardless of the setting of ver-
bose. This is necessary for commands like pwd (display working directory),
which would otherwise produce no message at all if verbose were set to 0 or
1.

Displays the status of all UDP receive queues.

3.93. upload [<filename>]

Opens filename and sends it on the current session as though it were typed on
the terminal.

3.94. watch

Displays the current software stopwatch values, with min and max readings for
each. This facility allows a programmer to measure the execution time of
critical sections of code with microsecond resolution. This command is sup-
ported only on the IBM PC, and the meaning of each stopwatch value depends on
where the calls have been inserted for test purposes; the distribution copy
of nos usually has no stopwatch calls.

3.95. watchdog [on | off]

Enables or disables the watchdog timer. If internal operations cease for 300
second and watchdog is enabled, a system reset is performed. See the remote
command for setting up autoexec.bat.

3.96. ?

Same as the help command.

4. Attach Commands

This chapter details the attach commands for the various hardware interface
drivers. Not all of these drivers may be configured into every Nos binary; a
list of the available types may be obtained by entering the command attach ?.

Some parameters are accepted by several drivers. They are:

4.0.1. <bufsize>

For asynchronous devices (eg. COM ports operating in SLIP or NRS mode) this
parameter specifies the size of the receiver's ring buffer. It should be
large enough to hold incoming data at full line speed for the longest time
that the system may be busy in MS-DOS or the BIOS doing a slow I/O operation
(eg. to a floppy disk). A kilobyte is usually more than sufficient.

For synchronous devices (eg. the scc, hs, pc100, hapn and drsi interfaces
operating in HDLC mode), the bufsize parameter specifies the largest packet
that may be received on the interface. This should be set by mutual agree-
ment among stations sharing the channel. For standard AX.25 with a maximum
I-frame data size of 256 bytes, a value of 325 should provide an adequate
safety margin. On higher speed channels (eg. 56kb/s) larger values (eg. 2K
bytes) will provide much better performance and allow full-sized Ethernet
packets to be carried without fragmentation.

4.0.2. <ioaddr>

The base address of the interface's control registers, in hex.

4.0.3. <vector>

The interface's hardware interrupt (IRQ) vector, in hex.

4.0.4. <iface>

The name (an arbitrary character string) to be assigned to this interface. It
is used to refer to the interface in ifconfig and route commands and in trace
output.

4.0.5. <mtu>

The Maximum Transmission Unit size, in bytes.  Datagrams larger than this
limit will be fragmented at the IP layer into smaller pieces. For AX.25 UI
frames, this limits the size of the information field. For AX.25 I frames,
however, the ax25 paclen parameter is also relevant. If the datagram or
fragment is still larger than paclen, it is also fragmented at the AX.25
level (as opposed to the IP level) before transmission. (See the ax25 paclen
command for further information).

4.0.6. <speed>

The speed in bits per second (eg. 2400).

4.1. attach 3c500 <ioaddr> <vector> arpa <iface> <qlen> <mtu> [<ipaddr>]

Attach a 3Com 3C501 Ethernet interface.  qlen is the maximum allowable
transmit queue length.  If the ipaddr parameter is not given, the value
associated with a prior ip address command will be used.

The use of this driver is not recommended; use the packet driver interface
with the loadable 3C501 packet driver instead.

4.2. attach asy <ioaddr> <vector> ax25 | nrs | ppp | slip <iface> <bufsize>
<mtu> <speed> [<v>]

Attach a standard PC "com port" (asynchronous serial port), using the
National 8250 or 16550A chip. Standard values on the IBM PC and clones for
ioaddr and vector are 0x3f8 and 4 for COM1, and 0x2f8 and 3 for COM2. If the
port uses a 16550A chip, it will be detected automatically and the FIFOs
enabled.

4.2.1. ax25

Similar to slip, except that an AX.25 header and a KISS TNC control header
are added to the front of the datagram before SLIP encoding. Either UI (con-
nectionless) or I (connection-oriented) AX.25 frames can be used; see the
mode command for details.

4.2.2. nrs

Use the NET/ROM asynchronous framing technique for communication with a local
NET/ROM TNC.

4.2.3. ppp

Point-to-Point-Protocol. Encapsulates datagrams in an HDLC-like frame. This
is a new Internet standard for point-to-point communication, compatible with
CCITT standards.

4.2.4. slip

Serial Line Internet Protocol. Encapsulates IP datagrams directly in SLIP
frames without a link header. This is for operation on point-to-point lines
and is compatible with 4.2BSD UNIX SLIP.

4.2.5. <crv>

The optional flags are a string of the characters "v": v enables Van Jacob-
son TCP/IP Header Compression, and is valid only for SLIP.

4.3. attach axip <iface> <mtu> <ipaddr> <callsign>

This creates a RFC1226 compatible AX.25 frame encapsulator for transmission
of AX.25 frames over the Internet. Iface will be the name of the interface,
ipaddr the address of the remote system and callsign the AX.25 callsign this
station is listening on for frames to digipeat. Note that each attached axip
interface should have a different callsign to listen to and this should also
be different from other callsign's used on this station.

4.4. attach drsi <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <chaspeed>
<chbspeed>

N6TTO driver for the Digital Radio Systems PCPA 8530 card. Since there are
two channels on the board, two interfaces are attached. They will be named
iface with 'a' and 'b' appended. bufsize is the receiver buffer size in
bytes; it must be larger than the largest frame to be received. chaspeed
and chbspeed are the speeds, in bits/sec, for the A and B channels, respec-
tively.

4.5. attach eagle <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <speed>

WA3CVG/NG6Q driver for the Eagle Computer card (Zilog 8530).

4.6. attach hapn <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> csma | full

KE3Z driver for the Hamilton Amateur Packet Network adapter (Intel 8273).
The csma | full parameter specifies whether the port should operate in car-
rier sense multiple access (CSMA) mode or in full duplex.

4.7. attach hs <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <keyupdelay>
<p>

Attach a DRSI PCPA or Eagle Computer interface card using a special "high
speed" 8530 driver.  This driver uses busy-wait loops to send and receive
each byte instead of interrupts, making it usable with high speed modems
(such as the WA4DSY 56kb/s modem) on slow systems. This does have the side
effect of "freezing" the system whenever the modem transmitter or receiver is
active.  This driver can operate only in CSMA mode, and it is recommended
that no other interfaces requiring small interrupt latencies be attached to
the same machine.

The keyupdelay parameter specifies the transmitter keyup delay in byte time
intervals. The p value specifies the transmitter persistence value in the
range 1-255; the corresponding slot time is fixed at one hardware clock tick,
about 55 ms on the PC.

As with the other 8530 drivers, this driver actually attaches two interfaces,
one for each 8530 channel.

4.8. attach packet <intvec> <iface> <txqlen> <mtu>

Driver for use with separate software "packet drivers" meeting the FTP
Software, Inc, Software Packet Driver specification. The driver must have
already been installed before the attach command is given. Packet drivers in
the Ethernet, ARCNET, SLIP, SLFP, and KISS/AX25 classes are supported.

intvec is the software interrupt vector used for communication to the packet
driver, and txqlen is the maximum number of packets that will be allowed on
the transmit queue.

4.9. attach pc100 <ioaddr> <vector> ax25 <iface> <bufsize> <speed>

Driver for the PACCOMM PC-100 (Zilog 8530) card.  Only AX.25 operation is
supported.

4.10. attach scc <devices> init <addr> <spacing> <Aoff> <Boff> <Dataoff>
<intack> <vec> [p | r]<clock> [<hdwe>] [<param>]

PE1CHL driver to initialize a generic SCC (8530) interface board prior to
actually attaching it. The parameters are as follows:

4.10.1. <devices>

The number of SCC chips to support.

4.10.2. <addr>

The base address of the first SCC chip (hex).

4.10.3. <spacing>

The spacing between the SCC chip base addresses.

4.10.4. <Aoff>

The offset from a chip's base address to its channel A control register.

4.10.5. <Boff>

The offset from a chip's base address to its channel B control register.

4.10.6. <Dataoff>

The offset from each channel's control register to its data register.

4.10.7. <intack>

The address of the INTACK/Read Vector port. If none, specify 0 to read from
RR3A/RR2B.

4.10.8. <vec>

The CPU interrupt vector for all connected SCCs.

4.10.9. <clock>

The clock frequency (PCLK/RTxC) of all SCCs in hertz. Prefix with 'p' for
PCLK, 'r' for RTxC clock (for baudrate gen).

4.10.10. <hdwe>

Optional hardware type. The following values are currently supported:  1 -
Eagle card, 2 - PACCOMM PC-100, 4 - PRIMUS-PC card (DG9BL), 8 - DRSI PCPA
card.

4.10.11. <param>

Optional extra parameter. At present, this is used only with the PC-100 and
PRIMUS-PC cards to set the modem mode. The value 0x22 is used with the PC-100
and 0x2 is used with the PRIMUS-PC card.

The attach scc ... init command must be given before the interfaces are actu-
ally attached with the following command.

4.11. attach scc <chan> slip | kiss | nrs | ax25 <iface> <mtu> <speed> <buf-
size> [<call>]

Attach an initialized SCC port to the system. The parameters are as follows:

4.11.1. <chan>

The SCC channel number to attach, 0 or 1 for the first chip's A or B port, 2
or 3 for the second chip's A or B port, etc.

4.11.2. slip | kiss | nrs | ax25

The operating mode of the interface. slip, kiss and nrs all operate the port
hardware in asynchronous mode; slip is Internet-standard serial line IP mode,
kiss generates SLIP frames containing KISS TNC commands and AX.25 packets and
nrs uses NET/ROM local serial link framing conventions to carry NET/ROM pack-
ets. Selecting ax25 mode puts the interface into synchronous HDLC mode that
is suitable for direct connection to a half duplex radio modem.

4.11.3. <speed>

The interface speed in bits per second (eg. 1200). Prefix with 'd' when an
external divider is available to generate the TX clock. When the clock source
is PCLK, this can be a /32 divider between TRxC and RTxC. When the clock is
at RTxC, the TX rate must be supplied at TRxC. This is needed only for full
duplex synchronous operation. When this arg is given as 'ext', the transmit
and receive clocks are external, and the internal baud rate generator (BRG)
and digital phase locked loop (DPLL) are not used.

4.12. Attach Examples

Here are some examples of the attach command:

# Attach a 3Com Ethernet controller using the standard 3Com address and
# vector (i.e., as it comes out of the box) to use ARPA-standard encapsulation.
# The receive queue is limited to 5 packets, and outgoing packets larger
# than 1500 bytes will be fragmented
attach 3c500 0x300 3 arpa ec0 5 1500

# Attach the PC asynch card normally known as "com1" (the first controller)
# to operate in point-to-point slip mode at 9600 baud, calling it "sl0".
# A 1024 byte receiver ring buffer is allocated. Outgoing packets larger
# than 256 bytes are fragmented.
attach asy 0x3f8 4 slip sl0 1024 256 9600

# Attach the secondary PC asynch card ("com2") to operate in AX.25 mode
# with an MTU of 576 bytes at 9600 baud with a KISS TNC, calling it "ax0".
# By default, IP datagrams are sent in UI frames
attach asy 0x2f8 3 ax25 ax0 1024 576 9600

# Attach a axip wormhole
attach axip ai0 256 129.179.122.10 pa0gri-11
# on the other side of the wormhole
attach axip ai0 256 129.179.122.130 pa0gri-12
# Now assume 129.179.122.10 has a AX.25 interface with callsign pa0gri-10
# and 129.179.122.130 a interface with callsign pa0gri-8
# Now a AX.25 frame like:
# pe1chl->pa0gri-11->pa0gri-8->pe1dna [ data]
# Received by pa0gri-11, set the has-been-digipeated change the interface
# callsign with the one it realy came in from and ecapsulates it
# in a IP frame type 93 and ships it to 129.179.122.130
# pe1chl->pa0gri-10*->pa0gri-8->pe1dna [ data]
# Arived at 129.179.122.130 the next digi is searched for and found.
# The frame is changed into:
# pe1chl->pa0gri-10*->pa0gri-12*->pe1dna [ data]
# so that on the way back the frame will find the "right" interface.

# Attach the packet driver loaded at interrupt 0x7e
# The packet driver is for an Ethernet interface
attach packet 0x7e ethernet 8 1500


5. FTP Subcommands

During converse mode with an FTP server, everything typed on the console is
first examined to see if it is a locally-known command. If not, the line is
passed intact to the remote server on the control channel. If it is one of
the following commands, however, it is executed locally. (Note that this gen-
erally involves other commands being sent to the remote server on the control
channel.)

5.1. dir [<file> | <directory> [<local file>]]

Without arguments, dir requests that a full directory listing of the remote
server's current directory be sent to the terminal. If one argument is
given, this is passed along in the LIST command; this can be a specific file
or subdirectory that is meaningful to the remote file system. If two argu-
ments are given, the second is taken as the local file into which the direc-
tory listing should be put (instead of being sent to the console). The PORT
command is used before the LIST command is sent.

5.2. get <remote file> [<local file>]

Asks the remote server to send the file specified in the first argument. The
second argument, if given, will be the name of the file on the local machine;
otherwise it will have the same name as on the remote machine. The PORT and
RETR commands are sent on the control channel.

5.3. hash

A synonym for the verbose 3 command.

5.4. ls [<file> | <directory> [<local file>]]

ls is identical to the dir command except that the "NLST" command is sent to
the server instead of the "LIST" command. This results in an abbreviated
directory listing, i.e., one showing only the file names themselves without
any other information.

5.5. mget <file> [<file> ...]

Fetch a collection of files from the server. File names may include wild card
characters; they will be interpreted and expanded into a list of files by the
remote system using the NLST command. The files will have the same name on
the local system that they had on the server.

5.6. mkdir <remote directory>

Creates a directory on the remote machine.

5.7. mput <file> [<file> ...]

Send a collection of files to the server. File names may include wild card
characters; they will be expanded locally into a list of files to be sent.
The files will have the same name on the server as on the local system.

5.8. put <local file> [<remote file>]

Asks the remote server to accept data, creating the file named in the first
argument. The second argument, if given, will be the name of the file on the
remote machine; otherwise it will have the same name as on the local machine.
The PORT and STOR commands are sent on the control channel.

5.9. rmdir <remote directory>

Deletes a directory on the remote machine.

5.10. type [a | i | l <bytesize>]

Tells both the local client and remote server the type of file that is to be
transferred.  The default, (wich can be changed with the ftype command) is
'a', which means ASCII (i.e., a text file).  Type 'i' means image, i.e.,
binary.  In ASCII mode, files are sent as varying length lines of text in
ASCII separated by cr/lf sequences; in IMAGE mode, files are sent exactly as
they appear in the file system. ASCII mode should be used whenever transfer-
ring text between dissimilar systems (e.g., UNIX and MS-DOS) because of their
different end-of-line and/or end-of-file conventions. When exchanging text
files between machines of the same type, either mode will work but IMAGE mode
is usually faster. Naturally, when exchanging raw binary files (executables,
compressed archives, etc) IMAGE mode must be used. Type 'l' (logical byte
size) is used when exchanging binary files with remote servers having oddball
word sizes (e.g., DECSYSTEM-10s and 20s). Locally it works exactly like
IMAGE, except that it notifies the remote system how large the byte size is.
bytesize is typically 8. The type command sets the local transfer mode and
generates the TYPE command on the control channel.

5.11. verbose [0 | 1 | 2 | 3]

Set or display the level of message output in file transfers.  Verbose 0
gives the least output, and verbose 3 the most, as follows:

0 - Display error messages only.
1 - Display error messages plus a one-line summary after each transfer
 giving the name of the file, its size, and the transfer time and rate.
2 - Display error and summary messages plus the progress messages generated
 by the remote FTP server. (This setting is the default.)
3 - Display all messages. In addition, a "hash mark" (#) is displayed for
 every 1,000 bytes sent or received.

If a command is sent to the remote server because it is not recognized
locally, the response is always displayed, regardless of the setting of ver-
bose. This is necessary for commands like pwd (display working directory),
which would otherwise produce no message at all if verbose were set to 0 or
1.

6. Dialer Subcommands

Each dialer command may (should) have a different dialer file.  The file
resides in the configuration directory, as specified in the Installation sec-
tion (see chapter 1). A typical dialer file might be:

 # Set the speed, and toggle DTR to ensure modem is in command mode.
 control down
 wait 3000
 speed 2400
 control up
 wait 3000
 # Dial, and wait for connection
 send "atdt555-12127"
 wait 45000 "CONNECT " speed
 wait 2000
 # PAD specific initialization
 send "7"
 wait 15000 "Terminal ="
 send "ppp7"
 wait 10 "70


6.0.1. control down | up

Control asy interface. The down option drops DTR and RTS.  The up option
asserts DTR and RTS.

6.0.2. send "string"

This dialer command will write the specified string to the interface.  The
string quote marks are required, and the string may not contain embedded con-
trol characters. However, the standard C string escape sequences are recog-
nized (\0 should not be used).

6.0.3. speed [ 9600 | 4800 | 2400 | 1200 | 300 ]

This dialer command will set the speed of the interface to one of the avail-
able speeds.  If the speed is missing, the speed will be displayed in the
dialer session window.

6.0.4. wait <milliseconds> [ "test string" ] [ speed ]

If only the time is specified, the dialer pauses for the desired number of
milliseconds.

Otherwise, the dialer reads until the test string is detected on the inter-
face.  If the string is not detected within the desired time, the autodialer
will reset. The string quote marks are required, and the string may not con-
tain embedded control characters.  However, the standard C string escape
sequences are recognized (\0 should not be used).

Finally, if the speed parameter is specified, the dialer will continue to
read characters until a non-digit is detected. The string read is converted
to an integer, and used to set the interface speed.  If the trailing non-
digit is not detected within the desired time, or the integer value is not a
valid speed, the autodialer will reset.

7. Installation

Nos uses the following file and directory structure:

 ~/alias
 ~/autoexec.nos
 ~/dialer
 ~/domain.txt
 ~/ftpusers
 ~/net.rc
 ~/netron.sav
 ~/popusers
 ~/finger/
 ~/spool/areas
 ~/spool/mail.log
 ~/spool/net.log
 ~/spool/forward.bbs
 ~/spool/history
 ~/spool/rewrite
 ~/spool/help/
 ~/spool/mail/
 ~/spool/mqueue/
 ~/spool/news/
 ~/spool/rqueue/
 ~/spool/signatur/


The ~ in front of all files is a directory offset definable with the -d
option on the Nos command line. Any name may be chosen and is default empty.
(eg. just /) If for example -d /net is given, the structure shifts to
/net/...  The alias, autoexec.nos, dialer, domain.txt net.rc, popusers and
ftpusers configuration files are located here. The netrom.sav file will be
created there.

The "/spool" directory and its sub-directories are used by the bbs, SMTP and
NNTP services. The areas, forward.bbs, history, mail.log and rewrite confi-
guration files are located here. The /spool/news directory can have many
subdirectories and each subdirectory can have subdirectories. Newsgroups are
split into heirarchical directory structures. A news article in newsgroup
rec.amateur.radio.packet   will   end  up  in
/spool/news/rec/amateur/radio/packet.txt.

7.1. The /ftpusers File

Since MS-DOS is a single-user operating system (some might say it is a glori-
fied bootstrap loader), it provides no access control; all files can be read,
written or deleted by the local user. It is usually undesirable to give such
open access to a system to remote network users. Net therefore provides its
own access control mechanisms.

The file ftpusers controls remote FTP and mailbox access. The FTP default is
no access; if this file does not exist, the FTP server will be unusable. A
remote user must first "log in" to the system with the USER and PASS com-
mands, giving a valid name and password listed in ftpusers, before he or she
can transfer files.

Each entry in ftpusers consists of a single line of the form

username password /path permissions

There must be exactly four fields, and there must be exactly one space
between each field.  Comments may be added after the last field. Comment
lines begin with '#' in column one.

username is the user's login name.

password is the required password. Note that this is in plain text; there-
fore it is not a good idea to give general read permission to the root direc-
tory. A password of '*' (a single asterisk) means that any password is
acceptable.

/path is the allowable prefix on accessible files. Before any file or direc-
tory operation, the current directory and the user- specified file name are
joined to form an absolute path name in "canonical" form (i.e., a full path
name starting at the root, with "./" and "../" references, as well as redun-
dant /'s, recognized and removed). The result MUST begin with the allowable
path prefix; if not, the operation is denied. This field must always begin
with a "/", i.e., at the root directory. Multiple directories can be speci-
fied by separating them with a ";" caracter and no whitespace around them.

permissions is a decimal number granting permission for read, create and
write operations. If the low order bit (0x1) is set, the user is allowed to
read a file subject to the path name prefix restriction.  If the next bit
(0x2) is set, the user is allowed to create a new file if it does not
overwrite an existing file. If the third bit (0x4) is set, the user is
allowed to write a file even if it overwrites an existing file, and in addi-
tion he may delete files. Again, all operations are allowed subject to the
path name prefix restrictions. Permissions may be combined by adding bits,
for example, 0x3 (= 0x2 + 0x1) means that the user is given read and create
permission, but not overwrite/delete permission.

Additional permission bits used by the mailbox and PPP are:

 1  Read files
 2  Create new files
 4  Overwrite and delete existing files
 8  AX.25 gateway operation allowed
 16 Telnet gateway operation allowed
 32 NET/ROM gateway operation allowed
 64 Remote sysop access allowed (DANGEROUS)
 128 This user is banned from BBS access (illegal user)
 256 Priv bit for PPP connection
 512 Priv bit for peerID/pass lookup


A username of anonymous has special meaning in the validation meganism.  If
anonymous is included as a valid user in ftpusers then any unknown user (not
in ftpusers) will be mapped into anonymous and get its permission bits and
file path. If anonymous is not included in ftpusers unknown users are not
permitted nor validated.

For example, suppose ftpusers on machine pc.ka9q.ampr.org contains the line

friendly test /testdir 7


A session using this account would look like this:

net> ftp pc.ka9q.ampr.org
Resolving pc.ka9q.ampr.org... Trying 128.96.160.1...
FTP session 1 connected to pc.ka9q.ampr.org
220 pc.ka9q.ampr.org FTP version 900418 ready at Mon May 7 16:27:18 1990
Enter user name: friendly
331 Enter PASS command
Password: test [not echoed]
230 Logged in
ftp>


The user now has read, write, overwrite and delete privileges for any file
under /testdir; he may not access any other files.

Here are some more sample entries in ftpusers:

karn foobar / 7  # User "karn" with password "foobar" may read,
   # write, overwrite and delete any file on the
   # system.

guest bletch /g/bogus;/public 3
   # User "guest" with password "bletch" may read
   # any file under /g/bogus and its subdirectories,
   # and /public and its subdirectories,
   # and may create a new file as long as it does
   # not overwrite an existing file. He may NOT
   # delete any files.

anonymous * /public 1  # User "anonymous" (any password) may read files
   # under /public and its subdirectories; he may
   # not create, overwrite or delete any files.


This last entry is the standard convention for keeping a repository of public
files; in particular, the username "anonymous" is an established ARPA conven-
tion.

7.2. The /popusers File

Here are the username / password combinations defined for the POP users.  It
has a simple convention:

user:password:

for every POP user such a line has to be added. The user and password fields
sould match the pop userdata statement of the remote user. Both user and
password have to be delimited with a colon character.

7.3. The /net.rc File

The net.rc file is a fast login file for known ftp stations. Each line starts
with the name of the ftp station. Following are a user and password statemend
to be send to the server for validation. The name, user and password are
separated with a space. Not a tab nore more than 1 space character. Follow-
ing is a sample net.rc file.

ucsd.edu anonymous [e-mail]
ka9q.ampr.org guest pa0gri

7.4. The /domain.txt File

Nos translates domain names (eg. "pc.ka9q.ampr.org") to IP addresses (eg.
128.96.160.3) through the use of an Internet Domain Name resolver and a local
"cache" file, domain.txt. Whenever the user specifies a domain name, the
local cache is searched for the desired entry. If it is present, it is used;
if not, and if domain name server(s) have been configured, a query is sent
over the network to the current server. If the server responds, the answer
is added to the domain.txt file for future use.  If the server does not
respond, any additional servers on the list are tried in a round-robin
fashion until one responds, or the retry limit is reached (see the domain
retry command).  If domain.txt does not contain the desired entry and there
are no configured domain name servers, then the request immediately fails.

If a domain name server is available, and if all references to host-ids in
your /autoexec.nos file are in IP address format, then it is possible to
start with a completely empty domain.txt file and have Nos build it for you.
However, you may wish to add your own entries to domain.txt, either because
you prefer to use symbolic domain names in your /autoexec.nos file or you
don't have access to a domain server and you need to create entries for all
of the hosts you may wish to access.

Each entry takes one line, and the fields are separated by tabs.  For exam-
ple:

pc.ka9q.ampr.org.  IN  A  128.96.160.3

IN is the class of the record. It means Internet, and it will be found in
all entries.  A is the type of the record, and it means that this is an
address record. Domain name pc.ka9q.ampr.org therefore has Internet address
128.96.160.3.

Another possible entry is the CNAME (Canonical Name) record. For example:

ka9q.ampr.org.  IN  CNAME  pc.ka9q.ampr.org.

This says that domain name "ka9q.ampr.org" is actually an alias for the sys-
tem with (primary, or canonical) domain name "pc.ka9q.ampr.org." When a
domain name having a CNAME record is given to Nos, the system automatically
follows the reference to the canonical name and returns the IP address asso-
ciated with that entry.

Entries added automatically by Nos will have an additional field between the
domain name and the class (IN) field. For example:

pc.ka9q.ampr.org.  3600 IN  A  128.96.160.3

This is the time-to-live value, in seconds, associated with the record
received from the server. Clients (such as Nos) caching these records are
supposed to delete them after the time-to-live interval has expired, allowing
for the possibility that the information in the record may become out of
date.

This implementation of Nos will decrement the TTL to zero, but will not
delete the record unless the "clean" flag is on (see the domain cache clean
command). When a remote server is not available, the old entry will be used.

When the TTL value is missing (as in the examples above), the record will
never expire, and must be managed by hand. Since domain.txt is a plain text
file, it may be easily edited by the user to add, change or delete records.
Additional types of records, include NS (name server) and SOA (start of
authority) may appear in domain.txt from remote server responses. These are
not currently used by Nos but are retained for future development (such as
the incorporation of a domain name server into Nos itself).

7.5. The /alias file.

SMTP server ALIAS file. This is for resolving a given target address into a
single or multiple entry mail list.
 Format:
 maillistname call1@host1 [call2@host2]...# comments

 pa0gri [e-mail]
 kelvin [e-mail]
 #
 bob [e-mail]
 ian [e-mail]
 jim [e-mail]
 john  [e-mail]
 ted [e-mail]
 ron [e-mail]
 tim [e-mail]
 gareth [e-mail]
 bolton [e-mail]
 julian [e-mail]
 #
 world [e-mail] [e-mail] [e-mail]
  [e-mail] [e-mail] [e-mail]
  [e-mail] [e-mail] [e-mail]
  [e-mail] [e-mail] [e-mail]
 #
 locals [e-mail] [e-mail] [e-mail]
  [e-mail] [e-mail] [e-mail]
  [e-mail] [e-mail] [e-mail]

Note that it is reaonable, and sometimes desiable, to have alias records in
the form:

  area area dest1 dest2

As the /alias file is scanned only once, this does not result in an infinite
recursion.

7.6. The /spool/areas file.

This file is a header file shown to a mailbox user when he requests the a
display. It should show all public mailboxes to read. Here is a sample:
 ---- Public -- Mail -- Areas ----
        |
 General -- Any old chit-chat that is clean.  |
 TcpIp  -- General Tcp/Ip messages. NOS etc.  |
 Bugs  -- Where to report bugs in Ka9q-NOS  |
 Updates -- Info - NOS version UPDATES by G1EMM.  |
        |
 ---------------

7.7. The /spool/forward.bbs file.

The mailbox reads a forwarding file, spool/forward.bbs. Here is a sample
file.
 wb0ttw 0006
 ax25 ax0 wb0ttw
 wb0ttw
 w0tn
 mspbul
 all
 ---
 wb0gdb
 netrom #msparh
 ..c msparh
 all The first word on the first line in a forwarding record is the name
of the BBS to forward to. This should be the same type of name which is shown
by the mbox status command. The second word is optional. It specifies a range
of hours when forwarding may take place. 0006 means that there will only be
forwarding to this station between midnight and 6am.

The second line specifies how to establish the connection. It should start
with the protocol (ax25, connect, tcp, telnet or netrom) and be followed by
all the parameters which are nessesary when Nos has to establish a connec-
tion.

Directly after the second line, there may be lines that start with a dot.
What follows after the dot will be send to the remote BBS as soon as the con-
nection is established.

Then follows the names of a number of message areas, publib or private.
Finally, there should be a couple of '-' signs to separate one forwarding
record from another.

7.8. The /spool/rewrite file.

Read the rewrite file for lines where the first word is a regular expression
and the second word are rewriting rules. An optional third field, containing
just the letter "r", when present, instructs Nos to restart the rewrite file,
using the new destination address. The special character '$' followed by a
digit denotes the string that matched a '*' character. The '*' characters are
numbered from 1 to 9. Example: the line "*@*.* $2@$1.ampr.org" would rewrite
the address "[e-mail]" to "[e-mail]".
 #
 *@g1emm.ampr.org $1
 *@g1emm.ampr $1
 *@g1emm $1
 #
 *!*!*!*!*!*!* $7%$6@$5@$4@$3@$2@$1
 *!*!*!*!*!* $6%$5@$4@$3@$2@$1
 *!*!*!*!* $5%$4@$3@$2@$1
 *!*!*!* $4%$3@$2@$1
 *!*!* $3%$2@$1
 *!* $2@$1
 !* $1 r
 #
 # The End

8. Setting Bufsize, Paclen, Maxframe, MTU, MSS and Window

Many Nos users are confused by these parameters and do not know how to set
them properly. This chapter will first review these parameters and then dis-
cuss how to choose values for them. Special emphasis is given to avoiding
interoperability problems that may appear when communicating with non-Nos
implementations of AX.25.

8.1. Hardware Parameters


8.1.1. Bufsize

This parameter is required by most of Nos's built-in HDLC drivers (eg. those
for the DRSI PCPA and the Paccomm PC-100). It specifies the size of the
buffer to be allocated for each receiver port. HDLC frames larger than this
value cannot be received.

There is no default bufsize; it must be specified in the attach command for
the interface.

8.2. AX25 Parameters

8.2.1. Paclen

Paclen limits the size of the data field in an AX.25 I-frame. This value does
not include the AX.25 protocol header (source, destination and digipeater
addresses).

Since unconnected-mode (datagram) AX.25 uses UI frames, this parameter has no
effect in unconnected mode.

The default value of paclen is 256 bytes.

8.2.2. Maxframe

This parameter controls the number of I-frames that Nos may send on an AX.25
connection before it must stop and wait for an acknowledgement. Since the
AX.25/LAPB sequence number field is 3 bits wide, this number cannot be larger
than 7.

Since unconnected-mode (datagram) AX.25 uses UI frames that do not have
sequence numbers, this parameter does not apply to unconnected mode.

The default value of maxframe in Nos is 1 frame.

8.3. IP and TCP Parameters

8.3.1. MTU

The MTU (Maximum Transmission Unit) is an interface parameter that limits the
size of the largest IP datagram that it may handle. IP datagrams routed to
an interface that are larger than its MTU are each split into two or more
fragments. Each fragment has its own IP header and is handled by the network
as if it were a distinct IP datagram, but when it arrives at the destination
it is held by the IP layer until all of the other fragments belonging to the
original datagram have arrived. Then they are reassembled back into the com-
plete, original IP datagram. The minimum acceptable interface MTU is 28
bytes: 20 bytes for the IP (fragment) header, plus 8 bytes of data.

There is no default MTU in Nos; it must be explicitly specified for each
interface as part of the attach command.

8.3.2. MSS

MSS (Maximum Segment Size) is a TCP-level parameter that limits the amount of
data that the remote TCP will send in a single TCP packet. MSS values are
exchanged in the SYN (connection request) packets that open a TCP connection.
In the Nos implementation of TCP, the MSS actually used by TCP is further
reduced in order to avoid fragmentation at the local IP interface. That is,
the local TCP asks IP for the MTU of the interface that will be used to reach
the destination. It then subtracts 40 from the MTU value to allow for the
overhead of the TCP and IP headers. If the result is less than the MSS
received from the remote TCP, it is used instead.

The default value of MSS is 512 bytes.

8.3.3. Window

This is a TCP-level parameter that controls how much data the local TCP will
allow the remote TCP to send before it must stop and wait for an acknowledge-
ment. The actual window value used by TCP when deciding how much more data to
send is referred to as the effective window. This is the smaller of two
values: the window advertised by the remote TCP minus the unacknowledged data
in flight, and the congestion window, an automatically computed time-varying
estimate of how much data the network can handle.

The default value of Window is 2048 bytes.

8.4. Discussion


8.4.1. IP Fragmentation vs AX.25 Segmentation

IP-level fragmentation often makes it possible to interconnect two dissimilar
networks, but it is best avoided whenever possible. One reason is that when
a single IP fragment is lost, all other fragments belonging to the same
datagram  are effectively also lost and the entire datagram must be
retransmitted by the source. Even without loss, fragments require the allo-
cation of temporary buffer memory at the destination, and it is never easy to
decide how long to wait for missing fragments before giving up and discarding
those that have already arrived. A reassembly timer controls this process.
In Nos it is (re)initialized with the ip rtimer parameter (default 30
seconds) whenever progress is made in reassembling a datagram (i.e., a new
fragment is received). It is not necessary that all of the fragments belong-
ing to a datagram arrive within a single timeout interval, only that the
interval between fragments be less than the timeout.

Most subnetworks that carry IP have MTUs of 576 bytes or more, so intercon-
necting them with subnetworks having smaller values can result in consider-
able fragmentation. For this reason, IP implementors working with links or
subnets having unusually small packet size limits are encouraged to use tran-
sparent fragmentation, that is, to devise schemes to break up large IP
datagrams into a sequence of link or subnet frames that are immediately
reassembled on the other end of the link or subnet into the original, whole
IP datagram without the use of IP-level fragmentation. Such a scheme is pro-
vided in AX.25 Version 2.1. It can break a large IP or NET/ROM datagram into
a series of paclen-sized AX.25 segments (not to be confused with TCP seg-
ments), one per AX.25 I-frame, for transmission and reassemble them into a
single datagram at the other end of the link before handing it up to the IP
or NET/ROM module.  Unfortunately, the segmentation procedure is a new
feature in AX.25 and is not yet widely implemented; in fact, Nos is so far
the only known implementation. This creates some interoperability problems
between Nos and non-Nos nodes, in particular, standard NET/ROM nodes being
used to carry IP datagrams. This problem is discussed further in the section
on setting the MTU.

8.4.2. Setting paclen and bufsize

The more data you put into an AX.25 I frame, the smaller the AX.25 headers
are in relation to the total frame size. In other words, by increasing
paclen, you lower the AX.25 protocol overhead. Also, large data packets
reduce the overhead of keying up a transmitter, and this can be an important
factor with higher speed modems. On the other hand, large frames make bigger
targets for noise and interference. Each link has an optimum value of paclen
that is best discovered by experiment.

Another thing to remember when setting paclen is that the AX.25 version 2.0
specification limits it to 256 bytes. Although Nos can handle much larger
values, some other AX.25 implementations (including digipeaters) cannot and
this may cause interoperability problems. Even Nos may have trouble with cer-
tain KISS TNCs because of fixed-size buffers. The original KISS TNC code for
the TNC-2 by K3MC can handle frames limited in size only by the RAM in the
TNC, but some other KISS TNCs cannot.

Nos's built-in HDLC drivers (SCC, PC-100, DRSI, etc) allocate receive buffers
according to the maximum expected frame size, so it is important that these
devices be configured with the correct bufsize. To do this, you must know the
size of the largest possible frame that can be received. The paclen parameter
controls only the size of the data field in an I-frame and not the total size
of the frame as it appears on the air. The AX.25 spec allows up to 8 digi-
peaters, so the largest possible frame is (paclen + 72) bytes. So you should
make bufsize at least this large.

Another important consideration is that the more recent versions of NOS
improve interrupt response by maintaining a special pool of buffers for use
by the receive routines. These buffers are currently fixed in size to 2048
bytes and this can be changed only by editing config.h and recompiling NOS.
This limits bufsize; in fact, attempting to set a larger value may cause the
driver not to work at all. This situation can be detected by running the
memory status command and looking for a non-zero count of Ibuffail events,
although these events can also occur occasionally during normal operation.

One of the drawbacks of AX.25 that there is no way for one station to tell
another how large a packet it is willing to accept. This requires the sta-
tions sharing a channel to agree beforehand on a maximum packet size. TCP is
different, as we shall see.

8.4.3. Setting Maxframe

For best performance on a half-duplex radio channel, maxframe should always
be set to 1. The reasons are explained in the paper Link Level Protocols
Revisited by Brian Lloyd and Phil Karn, which appeared in the proceedings of
the ARRL 5th Computer Networking Conference in 1986.

8.4.4. Setting MTU

TCP/IP header overhead considerations similar to those of the AX.25 layer
when setting paclen apply when choosing an MTU. However, certain subnetwork
types supported by Nos have well-established MTUs, and these should always be
used unless you know what you're doing: 1500 bytes for Ethernet, and 508
bytes for ARCNET. The MTU for PPP is automatically negotiated, and defaults
to 1500.  Other subnet types, including SLIP and AX.25, are not as well
standardized.

SLIP has no official MTU, but the most common implementation (for BSD UNIX)
uses an MTU of 1006 bytes. Although Nos has no hard wired limit on the size
of a received SLIP frame, this is not true for other systems. Interoperabil-
ity problems may therefore result if larger MTUs are used in Nos.

Choosing an MTU for an AX.25 interface is more complex. When the interface
operates in datagram (UI-frame) mode, the paclen parameter does not apply.
The MTU effectively becomes the paclen of the link.  However, as mentioned
earlier, large packets sent on AX.25 connections are automatically segmented
into I-frames no larger than paclen bytes. Unfortunately, as also mentioned
earlier, Nos is so far the only known implementation of the new AX.25 segmen-
tation procedure. This is fine as long as all of the NET/ROM nodes along a
path are running Nos, but since the main reason Nos supports NET/ROM is to
allow use of existing NET/ROM networks, this is unlikely.

So it is usually important to avoid AX.25 segmentation when running IP over
NET/ROM.  The way to do this is to make sure that packets larger than paclen
are never handed to AX.25. A NET/ROM transport header is 5 bytes long and a
NET/ROM network header takes 15 bytes, so 20 bytes must be added to the size
of an IP datagram when figuring the size of the AX.25 I-frame data field. If
paclen is 256, this leaves 236 bytes for the IP datagram. This is the default
MTU of the netrom pseudo-interface, so as long as paclen is at least 256
bytes, AX.25 segmentation can't happen. But if smaller values of paclen are
used, the netrom MTU must also be reduced with the ifconfig command.

On the other hand, if you're running IP directly on top of AX.25, chances are
all of the nodes are running Nos and support AX.25 segmentation. In this
case there is no reason not to use a larger MTU and let AX.25 segmentation do
its thing. If you choose an MTU on the order of 1000-1500 bytes, you can
largely avoid IP-level fragmentation and reduce TCP/IP-level header overhead
on file transfers to a very low level. And you are still free to pick what-
ever paclen value is appropriate for the link.

8.4.5. Setting MSS


The setting of this TCP-level parameter is somewhat less critical than the IP
and AX.25 level parameters already discussed, mainly because it is automati-
cally lowered according to the MTU of the local interface when a connection
is created. Although this is, strictly speaking, a protocol layering viola-
tion (TCP is not supposed to have any knowledge of the workings of lower
layers) this technique does work well in practice. However, it can be
fooled; for example, if a routing change occurs after the connection has been
opened and the new local interface has a smaller MTU than the previous one,
IP fragmentation may occur in the local system.

The only drawback to setting a large MSS is that it might cause avoidable
fragmentation at some other point within the network path if it includes a
"bottleneck" subnet with an MTU smaller than that of the local interface.
(Unfortunately, there is presently no way to know when this is the case.
There is ongoing work within the Internet Engineering Task Force on a "MTU
Discovery" procedure to determine the largest datagram that may be sent over
a given path without fragmentation, but it is not yet complete.) Also, since
the MSS you specify is sent to the remote system, and not all other TCPs do
the MSS-lowering procedure yet, this might cause the remote system to gen-
erate IP fragments unnecessarily.

On the other hand, a too-small MSS can result in a considerable performance
loss, especially when operating over fast LANs and networks that can handle
larger packets. So the best value for MSS is probably 40 less than the larg-
est MTU on your system, with the 40-byte margin allowing for the TCP and IP
headers. For example, if you have a SLIP interface with a 1006 byte MTU and
an Ethernet interface with a 1500 byte MTU, set MSS to 1460 bytes. This
allows you to receive maximum-sized Ethernet packets, assuming the path to
your system does not have any bottleneck subnets with smaller MTUs.

8.4.6. Setting Window

A sliding window protocol like TCP cannot transfer more than one window's
worth of data per round trip time interval. So this TCP-level parameter con-
trols the ability of the remote TCP to keep a long "pipe" full. That is, when
operating over a path with many hops, offering a large TCP window will help
keep all those hops busy when you're receiving data. On the other hand,
offering too large a window can congest the network if it cannot buffer all
that data. Fortunately, new algorithms for dynamic controlling the effective
TCP flow control window have been developed over the past few years and are
now widely deployed. Nos includes them, and you can watch them in action
with the tcp status <tcb> or socket <sockno> commands. Look at the cwind
(congestion window) value.

In most cases it is safe to set the TCP window to a small integer multiple of
the MSS, (eg. 4times), or larger if necessary to fully utilize a high
bandwidth*delay product path. One thing to keep in mind, however, is that
advertising a certain TCP window value declares that the system has that much
buffer space available for incoming data. Nos does not actually preallocate
this space; it keeps it in a common pool and may well "overbook" it, exploit-
ing the fact that many TCP connections are idle for long periods and gambling
that most applications will read incoming data from an active connection as
soon as it arrives, thereby quickly freeing the buffer memory.  However, it
is possible to run Nos out of memory if excessive TCP window sizes are adver-
tised and either the applications go to sleep indefinitely (eg. suspended
Telnet sessions) or a lot of out-of-sequence data arrives. It is wise to
keep an eye on the amount of available memory and to decrease the TCP window
size (or limit the number of simultaneous connections) if it gets too low.

Depending on the channel access method and link level protocol, the use of a
window setting that exceeds the MSS may cause an increase in channel colli-
sions. In particular, collisions between data packets and returning ack-
nowledgements during a bulk file transfer may become common. Although this
is, strictly speaking, not TCP's fault, it is possible to work around the
problem at the TCP level by decreasing the window so that the protocol
operates in stop-and-wait mode. This is done by making the window value
equal to the MSS.

8.5. Summary

In most cases, the default values provided by Nos for each of these parame-
ters will work correctly and give reasonable performance. Only in special
circumstances such as operation over a very poor link or experimentation with
high speed modems should it be necessary to change them.