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NET User Reference Manual (NOS Version) Phil Karn, KA9Q 1. The NET.EXE Program The MS-DOS executable file net.exe provides Internet (TCP/IP), NET/ROM and AX.25 facilities. Because it has an internal multi- tasking operating system, net.exe can act simultaneously as a client, a server and a packet switch for all three sets of proto- cols. That is, while a local user accesses remote services, the system can also provide those same services 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 com- mands are provided. 1.1. Installation Net.exe uses the following directory structure: /spool /spool/help /spool/mail /spool/mqueue /spool/rqueue /spool/news By default, the /spool directory is placed in the root directory of the current drive. However, a subdirectory may be specified with the -d command-line option described below. If a subdirec- tory is given, the alias, autoexec.net, dialer, domain.txt and ftpusers configuration files must also be located there. The "/spool" directory and its sub-directories are used by the bbs, SMTP and NNTP services. The areas, forward.bbs, history, mail.log, rewrite and signatur configuration files are located here. The alias, forward.bbs and rewrite files are described in the document "maildoc", which should be found at the same location as this file. 1.2. net [-b] [-s <sockets>] [-d <directory>] [<startup file>] 1.2.1. -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 running under a windowing package and have trouble with output "bleeding through" on top of other windows. May 28, 1991 - 2 - 1.2.2. -s The -s option specifies the size of the socket array to be allo- cated within net.exe. This limits the number of network connec- tions that may exist simultaneously. The default is 40. 1.2.3. -d The -d option allows the user to specify a directory for the con- figuration and spool files; it defaults to the root directory of the system. 1.2.4. Startup file After all command-line options, the name of a startup file may be specified. If no startup file is specified, net.exe attempts to open a file named autoexec.net in the configuration directory of the current drive. If the file exists, it is read and executed as though its contents were typed on the console as commands. (See the Commands chapter.) This feature is useful for attaching communication interfaces, configuring network addresses, and starting the various services. 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, including Telnet, FTP, AX25, NETROM, Ping, More, Hopcheck and Tip. In a Telnet, AX25, NETROM, or Tip session, keyboard input is sent to the remote system and any out- put from the remote system is displayed on the console. In a 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 Subcom- mands chapter). In a Ping session the user may test the path to a remote site, and 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 Tip session provides a "dumb terminal" service that bypasses all network protocols. The keyboard also has cooked and raw states. In cooked state, input is line-at-a-time; the user may use the line editing char- acters ^U, ^R and backspace to erase the line, redisplay the line and erase the last character, respectively. Hitting either return or line feed passes the complete line up to the applica- tion. In raw state, each character is immediately passed to the application as it is typed. The keyboard is always in cooked state in command mode. It is also cooked in converse mode on an AX25, FTP or NET/ROM session. In a Telnet 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 hit- ting the F10 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 May 28, 1991 - 3 - same name). The escape character can be changed (see the escape command). 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) 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 chapter describes the commands recognized in command mode, or within a startup file such as autoexec.net. These are given in the following notation: command command literal_parameter command subcommand <parameter> command [<optional_parameter>] 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 avail- able subcommands or required parameters. (Giving a '?' in place of the subcommand will also generate the message. 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 vari- able. (Exceptions to this rule are noted in the individual com- mand 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 sym- bolic 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 converse mode with the appropriate FTP session; they are not recognized in command mode. (See the FTP Subcommands chap- ter.) Note that certain commands may have been configured out of a given copy of net.exe to save disk and memory. If a command has been configured out, it will not appear in the list produced by the "?" command, nor will it be recognized by the command inter- preter. 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 May 28, 1991 - 4 - no current session, net.exe remains in command mode. 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.net file. 3.4. abort [<session #>] Abort a FTP get, put or dir operation in progress. If issued without an argument, the current session is aborted. (This com- mand works only on FTP sessions.) 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 manu- ally 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 data- grams awaiting resolution is also shown. 3.5.1. arp add <hostid> ethernet | ax25 <ethernet address> | <ax25_address> 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 publish <hostid> ethernet | ax25 <ethernet address> | <ax25_address> This command is similar to the arp add command, but system will also respond to any ARP request it sees on the network that seeks the specified address. Use this feature with great care. 3.5.3. arp drop <hostid> ax25 | ethernet Remove the specified entry from the ARP table. 3.5.4. arp flush Drop all automatically-created entries in the ARP table. Perma- nent entries are not affected. 3.6. asystat Display statistics on attached asynchronous communications inter- faces (8250 or 16550A), if any. The display for each port con- sists 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, May 28, 1991 - 5 - and the speed in bits per second. (Receiving the trigger charac- ter causes the driver to signal upper layer software that data is ready; it is automatically set to the appropriate frame end char- acter 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 charac- ters, receiver overruns (lost characters) and the receiver high water mark. The high water mark is the maximum number of charac- ters 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 inability 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 inter- rupt 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 dis- played on the RX status line. These are generated automatically by the 16550A when three character 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 dis- played. 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. Detailed instructions for each driver are in the Attach Commands chapter. 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. ax25 ... These commands are used to control the AX.25 amateur radio link level protocol. May 28, 1991 - 6 - 3.8.1. ax25 blimit [<count>] Display or set the AX25 retransmission backoff limit. Normally each successive AX25 retransmission is delayed by twice the value of the previous interval; this is called binary exponential back- off. 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. 3.8.2. ax25 dest Display the AX25 destination monitoring database. Each callsign seen in the destination field of an AX25 frame is displayed (most recent first), along with the time since it was last referenced. The time since the same callsign was last seen in the source field of an AX25 frame on the same interface is also shown. If the callsign has never been seen in the source field of a frame, then this field is left blank. (This indicates that the destina- tion is either a multicast address or a "hidden station".) 3.8.3. ax25 digipeat [on | off] Display or set the digipeater enable flag. 3.8.4. ax25 flush Clear the AX.25 "heard" list (see ax25 heard). 3.8.5. ax25 heard Display the AX.25 "heard" list. For each interface that is con- figured to use AX.25, a list of all callsigns 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 list is sorted in most- recently-heard order. The local station is included in the list- ing; the packet count reflects the number of packets transmitted. This count will be correct whether or not the modem monitors its own transmissions. 3.8.6. 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 mea- surement once the connection has been established. 3.8.7. ax25 kick <axcb> Force a retransmission on the specified AX.25 control block. 3.8.8. ax25 maxframe [<count>] Establish the maximum number of frames that will be allowed to remain unacknowledged at one time on new AX.25 connections. This number cannot be greater than 7. May 28, 1991 - 7 - 3.8.9. ax25 mycall [<call>] Display or set the local AX.25 address. The standard format is used (eg. KA9Q-0 or WB6RQN-5). This command must be given before any attach commands using AX.25 mode are given. 3.8.10. ax25 paclen [<size>] Limit the size of I-fields on new AX.25 connections. If IP data- grams or fragments larger than this are transmitted, they will be transparently fragmented 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. 3.8.11. ax25 pthresh [<size>] Display or set the poll threshold to be used for new AX.25 Ver- sion 2 connections. 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 acknowledgement. This is obviously a tradeoff, so experiment with the poll threshold setting. The default is 128 bytes, one half the default value of paclen. 3.8.12. ax25 reset <axcb> Delete the AX.25 connection control block at the specified address. 3.8.13. 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. A value of 0 means "infinity"; the retry limit is disabled. retry 3.8.14. ax25 route Display the AX.25 routing table that specifies the digipeaters to be used in reaching a given station. 3.8.14.1. ax25 route add <target> [digis ... ] Add an entry to the AX.25 routing table. An automatic ax25 route add is executed if digipeaters are specified in an AX25 connect May 28, 1991 - 8 - command, or if a connection is received from a remote station via digipeaters. Such automatic routing table entries won't override locally created entries, however. 3.8.14.2. ax25 route drop <target> Drop an entry from the AX.25 routing table. 3.8.15. 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. 3.8.16. ax25 t3 [<milliseconds>] Display or set the AX.25 idle "keep alive" timer. Value is in milliseconds. 3.8.17. 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). 3.8.18. 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 processed 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. 3.9. BOOTP The bootp client and server are added to KA9Q to provide auto- matic configuration capabilities. With this suite of extensions, a KA9Q host can automatically configure its IP address, subnet mask, broadcast address, host name, the default gateway, the name servers, and default boot file. This simplifies host configura- tion. The bootp server supports dynamic IP address assignment. If a bootp request is made by a host to the server, and the server doesn't have a static record for the PC making the request, an IP address may be assigned from a list of dynamic addresses. This simplifies server configuration, so that machines don't require prior IP address assignment. This is useful in environments such as university dormitories, where network service is provided, and the computers configurations change frequently. When the server list of free addresses reaches a minimum threshold, it will begin attempts to reclaim the address. The bootp client and server code are written according to RFC 951 and 1048. May 28, 1991 - 9 - 3.9.1. bootp [<net_name>] [silent] [noisy] Send a request to a bootp server, and wait for a reply. On receipt of the server reply, the information is used to configure the host. If a reply is not received, the command will time out. Without arguments, bootp sends a request to the first interface in the interface list. This command requires that there exist a routing entry for the IP broadcast address 255.255.255.255 pointing to the appropriate interface. If the interface uses ARP, there must also be an ARP entry that maps that address to the appropriate link level broad- cast address. For example, if you have an Ethernet interface named "ethernet", use the following commands before the bootp command: route add 255.255.255.255 ethernet arp add 255.255.255.255 ether ff:ff:ff:ff:ff:ff The following bootp subcommands are available: 3.9.1.1. bootp <net_name> Send a request over the specified network. 3.9.1.2. bootp silent Set bootp so that it will not print the configuration. 3.9.1.3. bootp noisy Set bootp so that it will print the configuration. 3.9.2. bootpd [start] [stop] [dns] [dynip] [host] [rmhost] [homedir] [defaultfile] [logfile] [logscreen] This command starts and stops the bootp server, and sets the con- figuration for the information it will provide in replies. If the file bootptab exists, it will read the file for configuration information. On receipt of a request, if bootptab has been changed, the server will reread the file for the changed configu- ration. The following subcommands are available: 3.9.2.1. bootpd start Start the bootp server, reading from the file bootptab for con- figuration information. 3.9.2.2. bootpd stop Stop the bootp server. 3.9.2.3. bootpd dns Print the address of the domain name servers supplied in replies. 3.9.2.4. bootpd dns <IP addr of domain name server>... Set the addresses. 3.9.2.5. bootpd dynip Print the range and use of the dynamic IP address. May 28, 1991 - 10 - 3.9.2.6. bootpd dynip <net_name> <IP address> <IP address> Set the range of IP address to be used for network netname. These address will be supplied to hosts that are not found in the static record. 3.9.2.7. bootpd dynip <netname> off Turn off dynamic ip for network interface netname. 3.9.2.8. bootpd host Print the information in the static host table. 3.9.2.9. bootpd host <hostname> ethernet|ax25 <ethernet addr>|<ax25 addr> <ip addr> [boot file] Add a host to the host table. The LANSTAR packet drivers provide an Ethernet interface to upper layer applications, so configure a LANSTAR network as an Ethernet. 3.9.2.10. bootpd rmhost <hostname> Remove host <hostname> from the static host tables. 3.9.2.11. bootpd homedir Print the default directory for the bootp file name used when the bootp file is not specified in the static host record, and when dynamic addresses are supplied. Default is the null string. 3.9.2.12. bootpd homedir <directory name> Set the default directory. 3.9.2.13. bootpd defaultfile Print the default file for the bootp file name used when the bootp file is not specified in the static host record, and when dynamic addresses are supplied. Default is the null string. 3.9.2.14. bootpd defaultfile <filename> Set the default file. 3.9.2.15. bootpd logfile Print the status of logging to a log file. 3.9.2.16. bootpd logfile <filename | default> on|off Sets the file for logging to <filename> or the default, bootplog. Turn logging to that file on or off. 3.9.2.17. bootpd logscreen Print the status of logging to the screen. 3.9.2.18. bootpd logscreen on|off Turn logging to the screen on or off. 3.10. cd [<dirname>] Change the current working directory, and display the new set- ting. Without an argument, cd simply displays the current direc- tory without change. The pwd command is an alias for cd. May 28, 1991 - 11 - 3.11. close [<session>] Close the specified session; without an argument, close the cur- rent session. On an AX.25 session, this command initiates a dis- connect. 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 initiate 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 outgoing 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. 3.12. connect <iface> <callsign> [<digipeater> ... ] Initiate a "vanilla" AX.25 session to the specified call sign 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 are 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 automati- cally added to the AX25 routing table as though the ax25 route add command had been given before issuing the connect command. 3.13. delete <filename> Delete a filename in the current working directory. 3.14. 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 inter- face are removed. 3.15. dialer <iface> <seconds> <hostid> <pings> <dialer-file> 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 con- tained 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 executed without pinging the <hostid>. The file may have any valid name, and must be located in the con- figuration directory (see the Installion section). The commands in the file are described in the Dialer Subcommands chapter. 3.16. 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 tempo- rary file, and then creating a more session to display it. After May 28, 1991 - 12 - this completes, the temporary file is deleted. 3.17. disconnect [<session #>] An alias for the close command (for the benefit of AX.25 users). 3.18. domain ... These commands control the operation of the Internet Domain Name Service (DNS). 3.18.1. domain addserver <hostid> Add one or more domain name server(s) to the list of name servers. 3.18.2. domain dropserver <hostid> Remove one or more domain name server(s) from the list of name servers. 3.18.3. 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. 3.18.4. domain query <hostid> Send a query to a domain server asking for all resource records associated with this <hostid>, and list the records. 3.18.5. domain retry [<count>] Display or set the number of attempts to reach each server on the list during one call to the resolver. If this count is exceeded, a failure indication is returned. If set to 0, the list will cycle forever; this may be useful for unattended operation. The default is 3. 3.18.6. domain suffix [<domain suffix>] 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 (eg. telnet foo.bar would NOT be turned into foo.bar.ampr.org). 3.18.7. 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. 3.18.8. domain cache ... These commands are used for the use of the resource record file domain.txt, and the local memory cache. May 28, 1991 - 13 - 3.18.8.1. domain cache clean [on | off] Display or set the flag controlling the removal of resource records from the domain.txt file whose time-to-live has reached zero. 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. 3.18.8.2. domain cache list List the current contents of the local memory cache. 3.18.8.3. domain cache size [<count>] 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.) 3.18.8.4. 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). 3.19. 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 negotiated 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 timesharing 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 ses- sion 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 congestion control algorithms 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.) May 28, 1991 - 14 - 3.20. 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 systems; 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. 3.21. escape [<char>] Display or set the current command-mode escape character in hex. (This command is not provided on the IBM-PC; on the PC, the escape char is always F10.) 3.22. etherstat Display 3-Com Ethernet controller statistics (if configured). 3.23. exit Exit the net.exe program and return to MS-DOS. 3.24. finger <user@hostid> [<user@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. 3.25. 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 the FTP Subcommands chapter for descriptions of the commands available in a FTP session. 3.26. help Display a brief summary of top-level commands. 3.27. hop ... These commands are used to test the connectivity of the network. 3.27.1. 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). 3.27.2. hop maxttl [<hops>] Display or set the maximum TTL value to be used in hop check ses- sions. This effectively bounds the radius of the search. 3.27.3. hop maxwait [<seconds>] Display or set the maximum interval that a hopcheck session will wait for responses at each stage of the trace. The default is 5 May 28, 1991 - 15 - seconds. 3.27.4. 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. 3.27.5. hop trace [on | off] Display or set the flag that controls the display of additional information during a hop check session. 3.28. 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>. 3.29. hs Display statistics about the HS high speed HDLC driver (if con- figured and active). 3.30. icmp ... These commands are used for the Internet Control Message Protocol service. 3.30.1. 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.) 3.30.2. icmp status Display statistics about the Internet Control Message Protocol (ICMP), including the number of ICMP messages of each type sent or received. 3.30.3. 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 routing, protocol or congestion problems. This option should be turned off before using the hop check facility because it relies on ICMP Time Exceeded messages, and the asynchronous display of these messages will be mingled with hop check command output. 3.31. ifconfig Display a list of interfaces, with a short status for each. 3.31.1. ifconfig <iface> Display an extended status of the interface. May 28, 1991 - 16 - 3.31.2. ifconfig <iface> broadcast <address> Set the broadcast address for the interface. The <address> takes the form of an IP address with 1's in the host part of the address. This is related to the netmask sub-command. See also the arp command. 3.31.3. ifconfig <iface> encapsulation <name> Not fully implemented. 3.31.4. ifconfig <iface> forward <forward-iface> Set a forwarding interface for multiple channel interfaces. To remove the forward, set <forward-iface> to <iface>. 3.31.5. ifconfig <iface> ipaddress <hostid> Set the IP address for this interface. It is standard Internet practice that each interface has its own address. For hosts with only one interface, the interface address is usually the same as the host address. See also the hostname and ip address commands. 3.31.6. ifconfig <iface> linkaddress <hardware-dependant> Set the hardware dependant address for this interface. 3.31.7. ifconfig <iface> mtu <mtu> Set the MTU for this interface. See the Setting ... MTU, MSS and Window chapter for more information. 3.31.8. 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. This is related to the broadcast sub-command. See also the route com- mand. 3.31.9. ifconfig <iface> rxbuf <?> Not yet implemented. 3.32. ip ... These commands configure the Internet Protocol (IP) service. 3.32.1. 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. 3.32.2. ip rtimer [<seconds>] Display or set the IP reassembly timeout. The default is 30 sec- onds. 3.32.3. ip status Display Internet Protocol (IP) statistics, such as total packet counts and error counters of various types. May 28, 1991 - 17 - 3.32.4. ip ttl [<hops>] Display or set the 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. 3.33. isat [on | off] Display or set the AT flag. Currently, there is no sure-fire way to determine the type of clock-chip being used. 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). 3.33.1. 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. 3.34. log [stop | <filename>] Display or set the filename for logging server sessions. If stop is given as the argument, logging is terminated (the servers themselves are unaffected). If a file name is given as an argu- ment, server session log entries will be appended to it. 3.35. mbox Display the status of the mailbox server system (if configured). 3.36. memory ... These commands are used to display memory allocation statistics. 3.36.1. memory free Display the storage allocator free list. Each entry consists of a starting address, in hex, and a size, in decimal bytes. 3.36.2. memory ibuffs Display or set the number of buffers on the interrupt buffer pool. The default is 5. 3.36.3. memory ibufsize Display or set the size of each buffer on the interrupt buffer pool. Since the interrupt buffer pool consists of fixed-size buffers, the value chosen must be large enough to satisfy the needs of the most demanding driver. The default is 2048. 3.36.4. memory sizes Display a histogram of storage allocator request sizes. Each his- togram bin is a binary order of magnitude (i.e., a factor of 2). 3.36.5. 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 May 28, 1991 - 18 - 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 subcom- mands. 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 allo- cation 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 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. 3.37. mkdir <dirname> Create a sub-directory in the current working directory. 3.38. 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 acknowledgements. 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 nec- essary. 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, how- ever, 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 whenever 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). 3.39. 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. The more command creates a session that you can suspend and resume just like any other session. May 28, 1991 - 19 - 3.40. param <iface> [<param> [value]] ... Invoke a device-specific control routine. The following parame- ter names are recognized by the parameter command, but not all are supported by each device type. Most commands deal only with half-duplex packet radio interfaces. TxDelay - transmit keyup delay Persist - P-persistence setting SlotTime - persistence slot time setting txTail - transmit done holdup delay FullDup - enable/disable full duplex Hardware - hardware specific command TxMute - experimental transmit mute command DTR - control Data Terminal Ready (DTR) signal to modem RTS - control Request to Send (RTS) signal to modem Speed - set line speed EndDelay Group Idle Min MaxKey Wait Down - drop modem control lines Up - raise modem control lines Return - return a KISS TNC to command mode Depending on the interface, some parameters can be read back by omitting a new value. This is not possible with KISS TNCs as there are no KISS commands for reading back previously sent parameters. On a KISS TNC interface, the param command generates and sends control packets to the TNC. Data bytes are treated as decimal. For example, param ax0 txdelay 255 will set the keyup timer (type field = 1) on the KISS TNC configured as ax0 to 2.55 sec- onds (255 x .01 sec). On all asy interfaces (slip, kiss/ax25, nrs, ppp) the param <iface> speed command allows the baud rate to be read or set. The implementation of this command for the various interface drivers is incomplete and subject to change. 3.41. ping <hostid> [<length> [<seconds> [<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 interval is specified, pings will be repeated indefinitely at the specified number of seconds; 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 ses- sion 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. May 28, 1991 - 20 - 3.42. ppp ... These commands are used to configure Point to Point Protocol interfaces. This implementation of PPP is designed to be as complete as pos- sible. 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 3.42.1. ppp <iface> Display the status of the PPP interface. 3.42.2. ppp <iface> lcp ... These commands are used for the LCP [Link Control Protocol] con- figuration. 3.42.2.1. ppp <iface> lcp close Shutdown the PPP interface. 3.42.2.2. 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. 3.42.2.2.1. ppp <iface> lcp local accm [ <bitmap> | allow [on | off] ] Display or set the Async Control Character Map. The default is 0xffffffff. 3.42.2.2.2. ppp <iface> lcp local authenticate [ pap | none | allow [on | off] ] Display or set the authentication protocol. The default is none. 3.42.2.2.3. 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 May 28, 1991 - 21 - for slow asynchronous links, and undesirable for fast or syn- chronous links. The default is off. 3.42.2.2.4. 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 asyn- chronous links, and undesirable for fast or synchronous links. The default is off. 3.42.2.2.5. ppp <iface> lcp local magic [ on | off | <value> | allow [on | off] ] Display or set the initial Magic Number. The default is off (zero). 3.42.2.2.6. ppp <iface> lcp local mru [ <size> | allow [on | off] ] Display or set the Maximum Receive Unit. The default is 1500. 3.42.2.2.7. ppp <iface> lcp local default Reset the options to their default values. 3.42.2.3. ppp <iface> lcp open active | passive Wait for the physical layer to come up. If active, initiate con- figuration negotiation. If passive, wait for configuration nego- tiation from the remote. 3.42.2.4. 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 speci- fied, 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. 3.42.2.5. ppp <iface> lcp timeout [<seconds>] Display or set the interval to wait between configuration or ter- mination attempts. The default is 3 seconds. 3.42.2.6. ppp <iface> lcp try ... These commands are used for the various counters. 3.42.2.6.1. ppp <iface> lcp try configure [<count>] Display or set the number of configuration requests sent. The default is 10. 3.42.2.6.2. ppp <iface> lcp try failure [<count>] Display or set the number of bad configuration requests allowed from the remote. The default is 5. May 28, 1991 - 22 - 3.42.2.6.3. ppp <iface> lcp try terminate [<count>] Display or set the number of termination requests sent before shutdown. The default is 2. 3.42.3. 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). 3.42.3.1. 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. 3.42.3.1.1. 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. 3.42.3.1.2. 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 num- bers, so the default is 1. 3.42.3.2. 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 speci- fied, 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. 3.42.4. ppp <iface> pap ... These commands are used for the PAP [Password Authentication Pro- tocol] configuration. The timeout and try sub-commands are identical to the LCP (described above). However, the terminate counter is unused. May 28, 1991 - 23 - 3.42.4.1. 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. 3.42.5. 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. 3.43. 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 approximate. If this number reaches or exceeds the stksize figure, the system is almost certain to crash; the net.exe program should be recompiled to give the pro- cess 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 (Waiting for event) and S (Suspended). The I flag is set whenever a task has executed a pwait() call (wait for event) without first disabling hardware interrupts. 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.) 3.44. pwd [<dirname>] An alias for the cd command. 3.45. 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. 3.46. remote [-p <port>] [-k <key>] [-a <kickaddr>] <hostid> exit | reset | kick Send a UDP packet to the specified host commanding it to exit the May 28, 1991 - 24 - net.exe program, 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 target 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 con- nections that the remote node may have with the local node. If a connection is idle, a current ACK packet (without data) is sent. If the -a option is used, connections 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 net.exe program on a remote unattended system after the con- figuration file has been updated. The remote system should invoke the net.exe program automatically upon booting, preferably in an infinite loop. For example, under MS-DOS the boot disk should contain the following in autoexec.net: :loop net goto :loop 3.47. 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. 3.48. rename <oldfilename> <newfilename> Rename oldfilename to newfilename. 3.49. reset [<session>] Reset the specified session; if no argument is given, reset the current session. 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 automati- cally generated should the remote TCP send anything 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 connec- tion after a remote system has crashed.) 3.50. rip ... These commands are used for the RIP service. 3.50.1. rip accept <gateway> Remove the specified gateway from the RIP filter table, allowing future broadcasts from that gateway to be accepted. May 28, 1991 - 25 - 3.50.2. rip add <hostid> <seconds> [<flags>] Add an entry to the RIP broadcast table. The IP routing table will be sent to hostid every interval seconds. If flags is speci- fied 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 packets). 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 inter- face 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, and arp add 44.255.255.255 ax25 qst-0 for an AX25 packet radio channel. 3.50.3. rip drop <dest> Remove an entry from the RIP broadcast table. 3.50.4. 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 spe- cific 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 May 28, 1991 - 26 - entry. Note that the relative metrics of the entries are ignored. 3.50.5. 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. 3.50.6. 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. 3.50.7. rip status Display RIP status, including a count of the number of packets sent and received, the number of requests and responses, the num- ber 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. 3.50.8. 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 pack- ets 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. 3.51. rmdir <dirname> Remove a sub-directory from the current working directory. 3.52. route With no arguments, route displays the IP routing table. 3.52.1. route add <dest_hostid>[/bits] | default <iface> [<gateway_hostid> [<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 gateway_hostid may be omitted even if the target is non-local because this field is only used to determine the gate- way's link level address, if any. If the destination is directly reachable, gateway_hostid is also unnecessary since the destina- tion address is used to determine the interface link address). The optional /bits suffix to the destination host id specifies how many leading bits in the host id are to be considered signif- icant 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 respec- tively; the command route add 44/8 sl0 44.64.0.2 May 28, 1991 - 27 - 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 specifying a /bits suffix of /0 to any desti- nation 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 accidentally). The best way to use default routes is to pick one node in your network that has the "best" connections to the world outside your network. Create a spanning tree with that node as the root and have each node install a default route pointing in the direction of that node, with the exception of the root node. 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 3.52.2. 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. 3.52.3. 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. 3.53. session [<session #>] Without arguments, displays the list of current sessions, includ- ing session number, remote TCP or AX.25 address and the associ- ated socket index. An asterisk (*) is shown next to the current session; entering a blank line at this point puts you in converse mode with that session. Entering a session number as an argument May 28, 1991 - 28 - to the session command will put you in converse mode with that session. If the Telnet 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 con- verse with the remote user as though the session had been locally initiated. 3.54. shell Suspends net.exe and executes a sub-shell ("command processor" under MS-DOS). When the sub-shell exits, net.exe resumes (under MS-DOS, enter the exit command). 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. 3.55. smtp ... These commands control the operation of the Simple Mail Transfer Protocol (that is, mail). 3.55.1. 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 forwarding. 3.55.2. 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 net.exe is running. 3.55.3. 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. 3.55.4. smtp timer [<seconds>] Displays or sets the interval between "kicks" (scans) of the out- bound mail queue. For example, smtp timer 600 will cause the sys- tem to check for outgoing mail every 10 minutes and attempt to deliver anything it finds, subject of course to the smtp max- clients limit. Setting a value of zero disables queue scanning altogether, note that this is the default! This value is recom- mended for stand alone IP gateways that never handle mail, since it saves wear and tear on the floppy disk drive. 3.55.5. 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 tracing. 3.56. socket [<socket #>] 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 May 28, 1991 - 29 - 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 com- mand with the protocol control block address. 3.57. start ax25 | discard | echo | ftp | netrom | remote | smtp | telnet | ttylink Start the specified Internet server, allowing remote connection requests. 3.58. stop ax25 | discard | echo | ftp | netrom | remote | smtp | telnet | ttylink Stop the specified Internet server, rejecting any further remote connect requests. Existing connections are allowed to complete normally. 3.59. tcp ... These commands are used for the Transmission Control Protocol service. 3.59.1. tcp irtt [<milliseconds>] Display or set the initial round trip time estimate, in millisec- onds, 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 caches 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 mentioned above is used, along with a MDEV of 0. This feature is fully automatic, and it can improve performance greatly when a series of connections are opened and closed to a given destination (eg. a series of FTP file transfers or directory listings). 3.59.2. tcp kick <tcb_addr> If there is unacknowledged data on the send queue of the speci- fied TCB, this command forces an immediate retransmission. 3.59.3. 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. 3.59.4. tcp reset <tcb_addr> Deletes the TCP control block at the specified address. May 28, 1991 - 30 - 3.59.5. tcp rtt <tcb_addr> <rtt> <mdev> Replaces the automatically computed round trip time and mean deviation values in the specified TCB with new values in mil- liseconds. 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. 3.59.6. tcp status [<tcb_addr>] 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 con- nection state. If tcb_addr is specified, a more detailed dump of the specified TCB is generated, including send and receive sequence numbers and timer information. 3.59.7. 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. 3.60. telnet <hostid> Creates a Telnet session to the specified host and enters con- verse mode. 3.61. tip <iface> Creates a tip session that connects to the specified interface in "dumb terminal" mode. The interface must have already been attached with the attach command. Any packet traffic (IP data- grams, etc) routed to the interface while this session exists will be discarded. To close a tip session, use the reset com- mand. 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. 3.62. trace [<iface> [off | <btio> [<tracefile>]]] Controls packet tracing by the interface drivers. Specific bits enable tracing of the various interfaces and the amount of infor- mation produced. Tracing is controlled on a per-interface basis; without arguments, trace gives a list of all defined interfaces and their tracing status. Output can be limited 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: May 28, 1991 - 31 - 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. 3.63. udp status Displays the status of all UDP receive queues. 3.64. upload [<filename>] Opens filename and sends it on the current session as though it were typed on the terminal. 3.65. 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 supported 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 net.exe usually has no stopwatch calls. 3.66. ? 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 net.exe 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 speci- fies the largest packet that may be received on the interface. This should be set by mutual agreement 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 May 28, 1991 - 32 - 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 informa- tion field. For AX.25 I frames, however, the ax25 paclen parame- ter 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> [<ip_addr>] Attach a 3Com 3C501 Ethernet interface. qlen is the maximum allowable transmit queue length. If the ip_addr 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> [<crv>] 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 con- trol header are added to the front of the datagram before SLIP encoding. Either UI (connectionless) 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. May 28, 1991 - 33 - 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 commu- nication, 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 opera- tion on point-to-point lines and is compatible with 4.2BSD UNIX SLIP. 4.2.5. <crv> The optional flags are a string of characters "crv": c enables RTS/CTS detection, r enables RLSD (Carrier Detect) physical line sensing, v enables Van Jacobson TCP/IP Header Compression, and is valid only for SLIP. 4.3. attach drsi <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <ch_a_speed> <ch_b_speed> 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. ch_a_speed and ch_b_speed are the speeds, in bits/sec, for the A and B channels, respectively. 4.4. attach eagle <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <speed> WA3CVG/NG6Q driver for the Eagle Computer card (Zilog 8530). 4.5. 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 carrier sense multiple access (CSMA) mode or in full duplex. 4.6. attach hs <ioaddr> <vector> ax25 <iface> <bufsize> <mtu> <keyup_delay> <p> Attach a DRSI PCPA or Eagle Computer interface card using a spe- cial "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 keyup_delay parameter specifies the transmitter keyup delay in milliseconds. The p value specifies the transmitter persis- tence 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. May 28, 1991 - 34 - 4.7. attach packet <intvec> <iface> <txqlen> <mtu> Attach a separate software "packet driver" meeting the FTP Soft- ware, Inc, Software Packet Driver specification. The driver must have already been installed as a TSR (e.g., by invocation in autoexec.bat). 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. 4.8. attach pc100 <ioaddr> <vector> ax25 <iface> <bufsize> <speed> Driver for the PACCOMM PC-100 (Zilog 8530) card. Only AX.25 operation is supported. 4.9. 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: 4.9.1. <devices> The number of SCC chips to support. 4.9.2. <addr> The base address of the first SCC chip (hex). 4.9.3. <spacing> The spacing between the SCC chip base addresses. 4.9.4. <Aoff> The offset from a chip's base address to its channel A control register. 4.9.5. <Boff> The offset from a chip's base address to its channel B control register. 4.9.6. <Dataoff> The offset from each channel's control register to its data reg- ister. 4.9.7. <intack> The address of the INTACK/Read Vector port. If none, specify 0 to read from RR3A/RR2B. 4.9.8. <vec> The CPU interrupt vector for all connected SCCs. 4.9.9. <clock> The clock frequency (PCLK/RTxC) of all SCCs in hertz. Prefix with 'p' for PCLK, 'r' for RTxC clock (for baudrate gen). May 28, 1991 - 35 - 4.9.10. <hdwe> Optional hardware type. The following values are currently sup- ported: 1 - Eagle card, 2 - PACCOMM PC-100, 4 - PRIMUS-PC card (DG9BL), 8 - DRSI PCPA card. 4.9.11. <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 inter- faces are actually attached with the following command. 4.10. attach scc <chan> slip | kiss | nrs | ax25 <iface> <mtu> <speed> <bufsize> [<call>] Attach an initialized SCC port to the system. The parameters are as follows: 4.10.1. <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. 4.10.2. slip | kiss | nrs | ax25 The operating mode of the interface. slip, kiss and nrs all oper- ate the port hardware in asynchronous mode; slip is Internet- standard serial line IP mode, kiss generates SLIP frames contain- ing KISS TNC commands and AX.25 packets and nrs uses NET/ROM local serial link framing conventions to carry NET/ROM packets. Selecting ax25 mode puts the interface into synchronous HDLC mode that is suitable for direct connection to a half duplex radio modem. 4.10.3. <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. 4.11. Attach Examples Here are some examples of the attach command: May 28, 1991 - 36 - # 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 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 com- mand. If not, the line is passed intact to the remote server on the control channel. If it is one of the following commands, how- ever, it is executed locally. (Note that this generally 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 com- mand; this can be a specific file or subdirectory that is mean- ingful to the remote file system. If two arguments are given, the second is taken as the local file into which the directory list- ing 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 May 28, 1991 - 37 - 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 com- mands 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 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 transferring text between dissimilar systems (eg. 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 (eg. 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 fol- lows: May 28, 1991 - 38 - 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 rec- ognized locally, the response is always displayed, regardless of the setting of verbose. 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 section (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 "atdt555-1212\r" wait 45000 "CONNECT " speed wait 2000 # PAD specific initialization send "\r" wait 15000 "Terminal =" send "ppp\r" wait 10000 "\r\n" 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 inter- face. The string quote marks are required, and the string may not contain embedded control characters. However, the standard C string escape sequences are recognized (\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 available 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 interface. If the string is not detected within the desired May 28, 1991 - 39 - time, the autodialer will reset. The string quote marks are required, and the string may not contain embedded control charac- ters. However, the standard C string escape sequences are recog- nized (\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. The speed feature is useful for reading back the CONNECT <speed> message generated by Hayes- compatible modems. 7. The /ftpusers File Since MS-DOS is a single-user operating system (some might say it is a glorified 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.exe 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 commands, 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; therefore it is not a good idea to give general read per- mission to the root directory. A password of '*' (a single asterisk) means that any password is acceptable. /path is the allowable prefix on accessible files. Before any file or directory 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 redundant /'s, recog- nized 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. 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 pre- fix 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 sub- ject to the path name prefix restrictions. Permissions may be combined by adding bits, for example, 0x3 (= 0x2 + 0x1) means May 28, 1991 - 40 - that the user is given read and create permission, but not over- write/delete permission. For example, suppose /ftpusers on machine pc.ka9q.ampr.org con- tains 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 3 # User "guest" with password "bletch" may read # any file under /g/bogus 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 reposi- tory of public files; in particular, the username "anonymous" is an established ARPA convention. 8. The domain.txt File Net.exe 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. When- ever 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.net file are in IP address format, then it is possible to start with a completely empty domain.txt file and have net.exe build it for you. However, you may wish to May 28, 1991 - 41 - add your own entries to domain.txt, either because you prefer to use symbolic domain names in your /autoexec.net 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 any combination of tabs or spaces. For example: 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 system with (primary, or canonical) domain name "pc.ka9q.ampr.org." When a domain name having a CNAME record is given to net.exe, the system automatically follows the reference to the canonical name and returns the IP address associated with that entry. Entries added automatically by net.exe 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 net.exe) 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 net.exe 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 MX (mail exchanger), NS (name server) and SOA (start of authority) may appear in domain.txt from remote server responses. Only MX is currently used by net.exe (in the mailbox). The others are retained for future development (such as the incorporation of a smarter resolver or a full-blown domain name server). 9. Setting Bufsize, Paclen, Maxframe, MTU, MSS and Window Many net.exe users are confused by these parameters and do not know how to set them properly. This chapter will first review these parameters and then discuss how to choose values for them. Special emphasis is given to avoiding interoperability problems that may appear when communicating with non-net.exe implementa- tions of AX.25. May 28, 1991 - 42 - 9.1. Hardware Parameters 9.1.1. Bufsize This parameter is required by most of net.exe'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. 9.2. AX25 Parameters 9.2.1. 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. 9.2.2. Maxframe This parameter controls the number of I-frames that net.exe 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 net.exe is 1. 9.3. IP and TCP Parameters 9.3.1. MTU The MTU (Maximum Transmission Unit) is an interface parameter that limits the size of the largest IP datagram that it may han- dle. 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 belong- ing to the original datagram have arrived. Then they are reassem- bled back into the complete, 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 net.exe; it must be explicitly speci- fied for each interface as part of the attach command. 9.3.2. 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 net.exe implementation of TCP, the MSS actually used by TCP is further reduced in order May 28, 1991 - 43 - 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. 9.3.3. 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 acknowledgement. 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. 9.4. Discussion 9.4.1. IP Fragmentation vs AX.25 Segmentation IP-level fragmentation often makes it possible to interconnect two dissimilar networks, but it is best avoided whenever possi- ble. 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 allocation 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 net.exe 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 belonging to a datagram arrive within a single timeout interval, only that the interval between fragments be less than the time- out. Most subnetworks that carry IP have MTUs of 576 bytes or more, so interconnecting them with subnetworks having smaller values can result in considerable fragmentation. For this reason, IP imple- mentors working with links or subnets having unusually small packet size limits are encouraged to use transparent fragmenta- tion, 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 orig- inal, whole IP datagram without the use of IP-level fragmenta- tion. Such a scheme is provided 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 segments), 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 May 28, 1991 - 44 - implemented; in fact, net.exe is so far the only known implemen- tation. This creates some interoperability problems between net.exe and non-net.exe 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. 9.4.2. 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 over- head. 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 net.exe can handle much larger values, some other AX.25 implemen- tations (including digipeaters) cannot and this may cause inter- operability problems. Even net.exe may have trouble with certain 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. Net.exe'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 possi- ble 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 digipeaters, 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 configured by the memory nibufs and memory ibufsize commands. ibufsize defaults to 2048 bytes. The setting of ibufsize 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 run- ning the memory status command and looking for a non-zero count of Ibuffail events, although these events can also occur occa- sionally during normal operation. One of the drawbacks of AX.25 that there is no way for one sta- tion to tell another how large a packet it is willing to accept. This requires the stations sharing a channel to agree beforehand on a maximum packet size. TCP is different, as we shall see. 9.4.3. 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 Net- working Conference in 1986. May 28, 1991 - 45 - 9.4.4. Setting MTU TCP/IP header overhead considerations similar to those of the AX.25 layer when setting paclen apply when choosing an MTU. How- ever, certain subnetwork types supported by net.exe 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 net.exe has no hard wired limit on the size of a received SLIP frame, this is not true for other systems. Interoperability problems may there- fore result if larger MTUs are used in net.exe. Choosing an MTU for an AX.25 interface is more complex. When the interface operates in datagram (UI-frame) mode, the paclen param- eter 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 ear- lier, net.exe is so far the only known implementation of the new AX.25 segmentation procedure. This is fine as long as all of the NET/ROM nodes along a path are running net.exe, but since the main reason net.exe 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 run- ning 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 net.exe 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 whatever paclen value is appropriate for the link. 9.4.5. 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 automatically lowered according to the MTU of the local interface when a connection is created. Although this is, strictly speaking, a protocol layering violation (TCP is not sup- posed 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 May 28, 1991 - 46 - 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 Discov- ery" procedure to determine the largest datagram that may be sent over a given path without fragmentation, but it is not yet com- plete.) 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 generate 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 largest MTU on your system, with the 40-byte margin allowing for the TCP and IP headers. For exam- ple, 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, assum- ing the path to your system does not have any bottleneck subnets with smaller MTUs. 9.4.6. 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 controls 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. Net.exe includes them, and you can watch them in action with the tcp status <tcb> or socket <sockno> commands. Look at the cwind (congestion win- dow) value. In most cases it is safe to set the TCP window to a small integer multiple of the MSS (eg. 4 times), 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 avail- able for incoming data. Net.exe does not actually preallocate this space; it keeps it in a common pool and may well "overbook" it, exploiting the fact that many TCP connections are idle for long periods and gambling that most applications will read incom- ing data from an active connection as soon as it arrives, thereby quickly freeing the buffer memory. However, it is possible to run net.exe out of memory if excessive TCP window sizes are advertised 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 May 28, 1991 - 47 - 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 collisions. In particular, collisions between data packets and returning acknowledgements 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. 9.5. Summary In most cases, the default values provided by net.exe for each of these parameters will work correctly and give reasonable perfor- mance. 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. 10. Mail Forwarding 10.1. Intended audience This section is intended for the NOS system operator desiring to enable the forwarding of mail to other systems. They are NOT intended as a user guide for the mail capabilities of NOS. 10.2. Background This section of the NOS docs deals with the intricacies of mail forwarding. You should read and understand this documentation thoroughly before attempting to forward mail through your NOS box to the AX.25 BBS world, otherwise you might grossly misconfigure your system and be the unhappy recipient of flames from BBS sysops. This section does NOT deal with the minutae of the mailbox and its various commands; it assumes that you understand concepts such as user areas (both public and private) and how to list and send mail. If you need help with these, please look elsewhere in the NOS docs. Apart from the usual domain.txt and other files necessary for ordinary functionality of NOS, three files are important in the mail forwarding process. These are: /spool/forward.bbs, /alias and /spool/rewrite. The contents of these will now be addressed individually. 10.3. /spool/forward.bbs This file describes the actions taken by NOS in forwarding to AX.25 BBSes. The file contains a series of forwarding records, each record being separated by a line containing two or more hyphens. The template for a forwarding record is: BBS callsign Connection route Connection commands <zero or more lines> List of areas to be forwarded <one per line> May 28, 1991 - 48 - ------------ <end of record> 10.4. BBS callsign This is simply the ordinary call of the remote BBS. A typical (but not random!) entry might be simply the line: sm0rgv The callsign may be followed, on the same line, by a comma sepa- rated list of valid intervals when forwarding is to take place. Each valid interval is a four digit number: the first two digits are the beginning hour of the valid interval, the last two digits are the final hour of the valid interval. For example, if the first line of a forwarding record looks like: sm0rgv 0006,1414 then forwarding to sm0rgv will take place only during hours num- bered 00, 01, 02, 03, 04, 05, 06 and 14. Ticks of the mbox timer outside of these times will not cause mail to be forwarded to sm0rgv. The default interval for forwarding is 0023. 10.5. Connection route This is the method by which communication is to be established with the remote BBS. The first token on the line is the type of protocol to be used. This is one of ax25, netrom or tcp. Follow- ing this is whatever further information the chosen protocol requires to make the connection. An example connection route for a simple ax25 connection on interface ax0 is: ax25 ax0 g3dlh 10.6. Connection commands Connection commands may, optionally, follow the connection route. These take the form of a full stop (period), followed by the com- mand which will be transmitted once the connection defined in the first line of the connection route is established. For example, suppose that we wish to establish a netrom connec- tion with sm0rgv-2, through the netrom node #sth67. Then the con- nection route and connection command portion of the record would look like: netrom #sth67 .c sm0rgv-2 [ Please note that the full stop would be placed at the beginning of the line; I have placed it here indented by one column simply so that gateways which handle this message do not complain at having a line beginning with a full stop; this convention is followed throughout this documentation] If the station is reached through digipeating, then the digi- peater callsigns should be in the ax25 route to the destination callsign. That is, if you wish to forward traffic to w0ljf, May 28, 1991 - 49 - using k2na as a digipeater, then you should have the line: ax25 route add w0ljf k2na in your autoexec file. 10.7. List of areas to be forwarded This is a list, one per line, of entries in the /spool/mail directory which will be forwarded to the remote BBS. An entry of the form: callsign will cause the file /spool/mail/callsign.txt to be scanned for unread messages. Any such messages are sent to the remote BBS and deleted from the file. One can also forward user areas using this mechanism. To do this, simply place a line containing the name of the area in the record. So, to forward amsat bulletins to the BBS, one would have a line: amsat This will search the /spool/mail/amsat.txt file; any messages contained therein which have not been forwarded to the BBS in question will be forwarded. They will NOT be deleted. The deter- mining factor as to whether or not entries are deleted is that if the filename is present in the /spool/areas file, then there is NO deletion, otherwise there is. Please note that ONLY FILES IN /spool/mail are checked. In par- ticular, the outbound SMTP mail queue is NOT checked. 10.8. Changing the recipient address Normally, NOS uses the information in the To: header line to determine the parameters used by the "S" command during BBS for- warding. As the To: header is unchanged by all /alias and /spool/rewrite machinations, the mail will be sent to the BBS addressed precisely as the originator of the message typed it. Occasionally, one might want to change this behaviour. In this case, a line of the form: area new_address in the list of areas to be forwarded will replace the originally typed destination with the string new_address instead. 11. /alias The alias file is used to map LOCAL names to other names, which may be either local or remote; additionally, from a single input message, the alias file permits one to produce multiple output messages. Thus, typical uses for the /alias file are: converting May 28, 1991 - 50 - one local name to another, converting a local name to a remote name, and exploding a mail message so that it is passed on to several recipients. The format of a record in the alias file is very simple: aliasname recipient1 recipient2 recipient3 <tab> or <SP> recipient4 ... recipientN There is no separation between records in the /alias file other than a newline. The aliasname is a local username; that is, it does not contain an "@" symbol. When the alias file is processed, if the destina- tion of the message matches precisely the aliasname, then the mail is redirected to ALL of the alieased recipients. Scanning of the /alias file is performed by the SMTP server. The SMTP timer (which controls the SMTP client) is kicked whenever the mailbox or SMTP server queues something for delivery by SMTP. Mail transport within a single NOS system is performed through the SMTP client/server mechanism. The result of these facts is that as soon as a piece of mail is entered to the mailbox, the SMTP client is kicked and attempts to deliver the mail (which has already been scanned by the rewrite mechanism - see below). If the mail is local to the NOS system (i.e. no "@" sign in the address), then the /alias file will be scanned and the name map- pings take place. A few lines in the /alias file might look something like: bdale bdale@n3eua local fred@k0yum bdale@n3eua bill@ai0c.co.usa.na n5op@n5op jim@k0jtz n0esg@n0esg g4bki g4bki@gb7bil._2712.gbr.eu The system must know how to deliver traffic to each of the indi- vidual addresses in the style in which they are entered in the /alias file. If the system does not know how to deliver one of the new addresses, then it will send it to the SMTP gateway sta- tion defined by the 'smtp gateway' command. Note that it is reasonable, and sometimes desireable, to have alias records of the form: area area dest1 dest2 ... As the /alias file is scanned only once (see below), this does not result in an infinite recursion. 12. /spool/rewrite The rewrite file is used to perform a one-to-one mapping between destination addresses as received by NOS and destination May 28, 1991 - 51 - addresses as actually used by NOS. Each record within the rewrite file comprises a single line, containing either two or three entries separated by spaces. The first field is the template field; if a destination address matches the template, it is replaced by the second field. The third field, which is optional, is the single letter "r", which, if present, tells NOS to rescan the rewrite file, using the new destination address to attempt to match against the templates. A template may contain asterisks. These stand for a match of any number of characters (including zero). In the second field, the character "$", followed by a single digit in the range 1 to 9, represents the string that matched the respective asterisk in the template. By way of example, suppose that there is a line in the rewrite file which looks like: *@* $1%$2@g1emm.ampr.org Then, any traffic reaching the system through the mailbox or the SMTP server, but which is supposed to go to a remote system, will be redirected to go through g1emm.ampr.org. Suppose that a user logs on, and sends a message to n0gbe@nq0i. Then the rewrite file attempts to match "n0gbe@nq0i" against the entry *@*. It matches, and assignes $1 the value n0gbe, and $2 the value nq0i. The mail file as written to the disk will no longer be to n0gbe@nq0i, but, rather, to n0gbe%nq0i@g1emm.ampr.org. [The nomenclature sta- tion1%station2@station3 means the final destination is sta- tion1@station2, and this traffic is to be routed through the gateway station3.] As soon as a template match is found, the conversion is performed and scanning is stopped, unless the third "r" field is present, in which case scanning restarts from the top of the file. N.B. It is a good idea to have a line of the form: *@*.ampr.org $1@$2.ampr.org at the beginning of your rewrite file. This will cause all ampr- net traffic to be caught early in the rewrite scan, and no fur- ther scanning (and, hence, no unexpected substitutions) will take place. 12.1. Scanning procedure The two files which are used to determine the disposition of traffic are scanned under slightly different circumstances. Note that neither the /alias nor the /spool/rewrite scan makes any actual changes to the contents of the traffic. In particular, the To: field remains exactly as it was first entered into the sys- tem. There are four possible entry routes for traffic into the system: SMTP, through the mailbox by a user, through the mailbox by a BBS, and via an external program (like BM) or creation of the May 28, 1991 - 52 - files manually. NOS determines if a piece of traffic was entered into the system by a BBS by looking for a BBS system ID (like the "[NET-H$]" block issued by NOS) on the incoming connection prior to messages being uploaded. 12.2. Traffic received by SMTP server 1. The rewrite file is scanned and any changes applied (unless the traffic was recieved through the local mailbox; in that case, this step does not occur); 2. If the traffic appears to be local then the alias file is scanned and any changes or explosions applied. 3. Any copies local to the system are delivered; copies for remote delivery are placed in the SMTP queue. 12.3. Traffic received by mailbox from user 1. The rewrite file is scanned and any changes applied; 2. The traffic is passed to the SMTP client. 12.4. Traffic received by mailbox from BBS 1. The rewrite file is scanned and any changes applied; 2. The traffic is passed to the SMTP client. 12.5. Traffic entered by external mechanism 1. No scanning occurs; 2. The traffic is passed to the SMTP client. 12.6. Headers Appropriate RFC-822 headers are added to all incoming traffic. Traffic entering through the mailbox recieves a full complement of RFC-822 headers; traffic coming through the SMTP server has only a "Received:" header applied. On forwarding to a BBS, if an item of traffic contains BBS R: headers, the RFC-822 header is converted to an appropriate R: line at the time that NOS forwards the message. (This change only occurs for BBS forwarding; for- warding by SMTP retains the RFC-822 headers.) 12.7. Bulletin Identifiers (BIDs) The AX.25 BBS system has evolved a reasonably efficient way of reducing overhead when forwarding bulletins. When a bulletin is originated on a BBS, it is given a unique bulletin identifier (BID). This BID should (theoretically) travel with the bulletin, and should never be changed during the distribution of the bul- letin. Each system keeps track of all received BIDs. If a for- warding station wishes to forward a bulletin to a BBS, then the receiving station checks its local list of known BIDs and informs the transmitting station if it already posesses the bulletin in question. The NOS mailbox conforms to this protocol. Received BIDs are stored in the file /spool/history, and are encoded in the Message-ID: header line of the message by NOS. Messages for- warded from areas listed in the /areas file will have their BID (re)generated from the Message-ID: line. Note that ALL messages from public areas are forwarded with a BID, whether or not the message was produced with the "SB" command. Like other BBSes, NOS will inform a transmitting station not to transmit a bulletin if May 28, 1991 - 53 - it is one that NOS already has locally; likewise, it understands similar messages from other stations to which it tries to for- ward. Note that the BID mechanism is not a part of the SMTP world. If you are forwarding bulletins through SMTP, there is no mechanism by which the receiving station can reject the attempted delivery of a bulletin, even if it already exists on the recipient system. (Note that a possible workaround is to deliver bulletins to TCP/IP stations using TCP instead of SMTP. Alternatively, one could use NNTP, as NNTP commands utilise the Message-ID: line, from which the BID is derived.) The BID is preserved no matter which mechanism is used to deliver the bulletin. 12.8. Traffic in practice Now, the big question is, how does one set up these various files to perform intelligent manipulation of mail? A number of examples follow. Note that, often, there is more than one way to accom- plish an objective. The following are merely examples (and not necessarily the most efficient method possible for any given case). The format used will be: typed destination -> intended destination followed by the necessary entries in the alias (/alias), rewrite (/spool/rewrite) and forwarding (/spool/forward.bbs) files. 12.9. Using familiar names - SMTP destination bdale -> bdale@n3eua.ampr.org alias: bdale bdale@n3eua.ampr.org rewrite: forward: 12.10. Exploding local mail sysops -> nq0i, n5op@n5op.ampr.org alias: sysops nq0i n5op@n5op@ampr.org rewrite: forward: 12.11. Using familiar names - BBS forwarding g4bki -> g4bki@gb7bil._2712.gbr.eu, to be forwarded by ai0c alias: rewrite: May 28, 1991 - 54 - forward: ai0c ax25 ax1 ai0c g4bki g4bki@gb7bil._2712.gbr.eu ai0c 12.12. Handling incoming bulletins by subject tcpip@* -> nq0i, tcpip, bdale@n3eua.ampr.org, ai0c@ai0c [a BBS] alias: tcpip nq0i tcpip bdale@n3eua.ampr.org ai0c rewrite: tcpip@* tcpip forward: ai0c ax25 ai0c ai0c Let's walk through the above example. An incoming item comes in addressed to TCPIP@ALLUS. A scan is made through the rewrite file, and a match is found. The item is redirected to tcpip. The alias file is scanned; a total of four copies of the item exist after this, three in local areas tcpip, nq0i and ai0c, and one on the SMTP queue (for bdale@n3eua.ampr.org). When the mailbox timer next ticks, the mail in the local ai0c area will be forwarded on the ax1 interface to ai0c. 12.13. Routing based on Hierarchical addressing Wyoming -> KE7VS (SMTP) Nebraska -> AG0N (BBS over the NETROM, NETROM ID WNBBS) Europe -> W0LJF (BBS over AX.25) alias: rewrite: *.noam $1.na r *.us $1.usa.na r *.usa $1.usa.na r *.ne $1.ne.usa.na r *.wy $1.wy.usa.na r *@*.*.wy.usa.na $1%$2.$3.wy.usa.na@ke7vs *@*.wy.usa.na $1%$2.wy.usa.na@ke7vs *.ne.usa.na ag0n *.eu w0ljf forward: May 28, 1991 - 55 - ag0n netrom ax0 wnbbs ag0n ---------- w0ljf ax25 ax1 w0ljf w0ljf ---------- Why is the example rewrite file apparently so complicated? This is to handle poorly constructed hierarchical addresses in a rea- sonable way. A full U.S. hierarchical address has the form: callsign@BBS.#localid.state.usa.na. Many states have no #localid field. In the example rewrite file above, the first three lines convert non-standard, but frequently used, U.S. designators to the more standard format. It is common for users not to use a full hierarchical address if the destination is relatively local. For eample, a user might easily use only .wy instead of the full grouping of two lines handles this problem. Note the third, "r", field in all the entries so far. The remainder of the file handles properly formatted hierarchical addresses. The two Wyoming entries handle the cases with and without a #localid field. Differentiation between these cases is not necessary for BBS forwarding. 12.14. General bulletin handling The details of bulletin handling will vary somewhat from place to place, as there are several distinct styles of bulletin handling currently in use in the AX.25 BBS world. In general, it is neces- sary to arrange one's system so that it accepts bulletins from BBSes, forwards them to one or more stations, and also handles intelligently bulletins input by users into NOS. Suppose that we sish to handle bulletins @JUNK. We are to deposit them locally in the junk area, and also forward to BBS g4bki. We also know that we generally receive @JUNK bulletins from g4amj, a local BBS which handles much bulletin traffic. alias: rewrite: *@junk junk forward: g4bki ax25 ax1 g4bki g4bki junk ---------- g4amj ax25 ax1 g4amj g4amj junk ---------- May 28, 1991 - 56 - All incoming @JUNK traffic is written to the junk area (which should be an explicit entry in the /spool/areas file). Each tick of the mailbox timer, NOS scans the junk area for traffic not forwarded to g4bki or g4amj and attempts to deliver unforwarded bulletins. Usually, g4amj will respond with a "Have it" message and the bulletin will not be forwarded. Any bulletins @JUNK deposited locally by users will automatically be sent to both g4bki and g4amj. 13. Questions and Answers Q. Under what circumstances does NOS request reverse forwarding from a BBS? A. NOS requests a reverse forward after completing any forwards of its own to the BBS. If no traffic was queued for a given BBS, then no connection is attempted, so no reverse forward request is issued. Q. What kinds of message types does the NOS mbox support? A. Basically, NOS supports all two letter commands starting with an "S". If the mailbox has not received an SID banner (the "[NET- H$]") from a connected station, then an SF command will send a followup to the address specified on the command line. The SR command will send a reply to the current message. One can also issue the command "SR <number>", where <number> is the number of the message to which you want to generate a reply. All other variations cause an X-BBS-Msg-Type: header to be added to the message. When a message with such a line is forwarded to a BBS, it is sent to the BBS with the appropriate message type as the second letter in the "S" command to the BBS. If NOS has received a valid SID, then ALL S commands are handled by the X-BBS-Msg-Type: mechanism outlined above. May 28, 1991 - 57 - 14. Logic map of the mailbox ============== AX.25 === NET/ROM === Ethernet === Loopback ================= | | | | | | | | +--------------+ +--------------+ +--------------+ +--------------+ | | | | | | | | | Mailbox | | SMTP client | | SMTP server | | BBS Forward | | | | | | | | | +--------------+ +--------------+ +--------------+ +--------------+ | ^ | ^ | | | | v | v | +--------------+ +--------------+ +--------------+ +--------------+ | | | | | | | | | Add RFC822 | | Use MX or A | | Add Received | | Add own R: | | header suite | | type records | | line | +>| line | | | | | | | | | | +--------------+ +--------------+ +--------------+ | +--------------+ | ^ | | ^ | | | | | v | v | | +--------------+ +--------------+ +--------------+ | +--------------+ | | | | | | | | | | Get Rewrite | | Use optional | | Apply Rewrite| | | Strip RFC822 | | file address | | SMTP gateway | | file address | | | header suite | | | | | | | | | | +--------------+ +--------------+ +--------------+ | +--------------+ | ^ | | ^ | | | | | Yes v | v | | +--------------+ | +--------------+ | +--------------+ | | No | | | | | | | Local addr? |-------+ | | Alias file | +-| Any R: lines?| | | | | | | No | | +--------------+ | | +--------------+ +--------------+ | | | | | | ^ | Yes | | | | | | v | | v v v | +--------------+ v | +--------------+ +--------------+ | | +--------------+ | | | | | Apply Rewrite| | | No | Local |Yes | /spool/mail/ | | file address |--->| SMTP queue |<---| address? |--->| directory | | | | | | | | | +--------------+ +--------------+ +--------------+ +--------------+ 15. Credits Several people have contributed to this manual. I would particu- larly like to thank Bill Simpson and Michael Westerhof, KA9WSB, for their significant editorial contributions to this document. Deborah Swanberg wrote the original BOOTP documentation,. and G4AMJ/NQ0I and SM0RGV contributed the section on mail forwarding. Although I am the primary author of this software package, many others have contributed substantial additions and refinements. May 28, 1991 - 58 - Here is a partial list; additions and corrections are welcome. See the individual source code files for additional authorship details. 15.1. ARCNET Written by Russ Nelson of Clarkson University. 15.2. Autodialer Bill Simpson substantially rewrote my original version and cre- ated a much improved control file format. 15.3. Bootstrap Protocol (BOOTP) Written by Deborah Swanberg of the University of Michigan. 15.4. Domain resolver Bill Simpson substantially extended my original version, adding record caching and automatic expiration. 15.5. DRSI driver Written by Stu Phillips, N6TTO. 15.6. Eagle 8530 board driver Written by Art Goldman, WA3CVG, and Richard Bisbey, NG6Q. 15.7. HAPN 8273 HDLC board driver Written by Jon Bloom, KE3Z, with fixes by John Tanner, VK2ZXQ. 15.8. Hop Check utility Written by Katie Stevens of UC Davis; enhancements by Bill Simp- son. 15.9. Mailbox server & SMTP My original, primitive SMTP server was vastly enhanced and expanded by Bdale Garbee, N3EUA and Dave Trulli, NN2Z. Anders Klemets, SM0RGV, wrote the first "mailbox" specifically for AX.25; he then expanded it into a full-blown bulletin board sys- tem and integrated it with the SMTP facilities. 15.10. NET/ROM The original NET/ROM code was done by Dan Frank, W9NK. It was ported to the NOS platform by Anders Klemets, SM0RGV. 15.11. Netnews Transfer Protocol (NNTP) Written by Anders Klements, SM0RGV, with help from Bernie Roehl and Gerard Van Der Grinten, PA0GRI. 15.12. Packet Drivers Although not really part of this package, the Clarkson Packet Driver Collection by Russ Nelson of Clarkson University has enor- mously enhanced the utility of this package by allowing it to use virtually every PC Ethernet controller board on the market. May 28, 1991 - 59 - 15.13. PI 8530 DMA HDLC driver Written by Dave Perry, VE3IFB. 15.14. Post Office Protocol (POP) Originally authored by Mike Stockett, WA7DYX. Updates and modifi- cations by Allen Gwinn, N5CKP, Gerard Van Der Grinten, PA0GRI, and Mark Edwards, WA6SMN. 15.15. Point to Point Protocol (PPP) Written by Katie Stevens of UC Davis, based on the original implementation by Drew Perkins of CMU. Updated by Bill Simpson and Glenn McGregor of the University of Michigan. 15.16. Routing Information Protocol (RIP) Original (pre-NOS) version written by Al Broscious N3FCT. 15.17. SCC - Generic 8530 driver Originally written for the old "NET" code by Rob Janssen, PE1CHL. Ported to NOS by Ken Mitchum, KY3B. 15.18. Socket-level stream compression Written by Anders Klemets, SM0RGV 15.19. TCP/IP Header Compression Adapted from Van Jacobson's original BSD UNIX implementation by Katie Stevens of UC Davis. Updated by Bill Simpson. May 28, 1991