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NET User Reference Manual (NOS Version) Phil Karn, KA9Q _1. _T_h_e _N_E_T._E_X_E _P_r_o_g_r_a_m 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. _I_n_s_t_a_l_l_a_t_i_o_n Net.exe uses the following directory structure: /net /net/spool /net/spool/help /net/spool/mail /net/spool/mqueue /net/spool/rqueue /net/spool/news The "/net" directory is not strictly necessary, and defaults to the root of the current drive. Any name may be chosen using the -d command-line option (described below). The alias, autoexec.net, dialer, domain.txt and ftpusers configuration files are located here. 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 2 - this file. _1._2. _n_e_t [-_b] [-_s <_s_o_c_k_e_t_s>] [-_d <_d_i_r_e_c_t_o_r_y>] [<_s_t_a_r_t_u_p _f_i_l_e>] _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. _1._2._2. -_s The -s option specifies the size of the _s_o_c_k_e_t 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. _S_t_a_r_t_u_p _f_i_l_e 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 3 - _2. _C_o_n_s_o_l_e _m_o_d_e_s The console may be in one of two modes: _c_o_m_m_a_n_d _m_o_d_e and _c_o_n_v_e_r_s_e _m_o_d_e. In _c_o_m_m_a_n_d _m_o_d_e, the prompt net> is displayed and any of the commands described in the Commands chapter may be entered. In _c_o_n_v_e_r_s_e _m_o_d_e, keyboard input is processed according to the _c_u_r_r_e_n_t _s_e_s_s_i_o_n. Sessions come in many types, including _T_e_l_n_e_t, _F_T_P, _A_X_2_5, _N_E_T_R_O_M, _P_i_n_g, _M_o_r_e, _H_o_p_c_h_e_c_k and _T_i_p. 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. The keyboard also has _c_o_o_k_e_d and _r_a_w states. In _c_o_o_k_e_d 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 _r_a_w state, each character is immediately passed to the application as it is typed. The keyboard is always in _c_o_o_k_e_d state in command mode. It is also _c_o_o_k_e_d 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 _c_o_m_m_a_n_d _m_o_d_e by hit- ting the F10 key. On other systems, the user must enter the _e_s_c_a_p_e character, which is by default control-] (hex 1d, ASCII GS). (Note that this is distinct from the ASCII character of the same name). The _e_s_c_a_p_e character can be changed (see the escape command). In the IBM PC version, each session (including the command "ses- sion") 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 4 - _3. _C_o_m_m_a_n_d_s 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 oth- ers that begin with the same series of letters. Parameters, how- ever, 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 chapter.) _3._1. <_C_R> Entering a carriage return (empty line) while in command mode puts you in converse mode with the current session. If there is no current session, net.exe remains in command mode. _3._2. ! An alias for the shell command. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 5 - _3._3. # Commands starting with the hash mark (#) are ignored. This is mainly useful for comments in the autoexec.net file. _3._4. _a_b_o_r_t [<_s_e_s_s_i_o_n #>] 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. _a_r_p Display the Address Resolution Protocol table that maps IP addresses to their subnet (link) addresses on subnetworks capable of broadcasting. For each IP address entry the subnet type (eg. Ethernet, AX.25), subnet address and time to expiration is shown. If the link address is currently unknown, the number of IP datagrams awaiting resolution is also shown. _3._5._1. _a_r_p _a_d_d <_h_o_s_t_i_d> _e_t_h_e_r_n_e_t | _a_x_2_5 <_e_t_h_e_r_n_e_t _a_d_d_r_e_s_s> | <_a_x_2_5__a_d_d_r_e_s_s> 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. _a_r_p _p_u_b_l_i_s_h <_h_o_s_t_i_d> _e_t_h_e_r_n_e_t | _a_x_2_5 <_e_t_h_e_r_n_e_t _a_d_d_r_e_s_s> | <_a_x_2_5__a_d_d_r_e_s_s> 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. _a_r_p _d_r_o_p <_h_o_s_t_i_d> _a_x_2_5 | _e_t_h_e_r_n_e_t Remove the specified entry from the ARP table. _3._5._4. _a_r_p _f_l_u_s_h Drop all automatically-created entries in the ARP table; per- manent entries are not affected. _3._6. _a_s_y_s_t_a_t 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 6 - configuration flags; these indicate whether the port is a 16550A chip, the _t_r_i_g_g_e_r _c_h_a_r_a_c_t_e_r if any, whether CTS flow control is enabled, whether RLSD (carrier detect) line control is enabled, and the speed in bits per second. (Receiving the _t_r_i_g_g_e_r _c_h_a_r_a_c_- _t_e_r 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 _h_i_g_h _w_a_t_e_r _m_a_r_k. 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 displayed on the RX status line. These are generated automati- cally 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 displayed. These indicate whether the <bufsize> parameter on the attach command needs to be adjusted (see the Attach Commands chapter). The third line shows transmit (TX) statistics, including a total count of transmit interrupts, transmitted characters, the length of the transmit queue in bytes, the number of status interrupts, and the number of THRE timeouts. The status interrupt count will be zero unless CTS flow control or RLSD line control has been enabled. The THRE timeout is a stopgap measure to catch lost transmit interrupts, which seem to happen when there is a lot of activity (ideally, this will be zero). _3._7. _a_t_t_a_c_h <_h_w _t_y_p_e> ... 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 7 - (eg. attach packet). This produces a usage message giving the complete command format. _3._8. _a_x_2_5 ... These commands are used for AX25 interfaces. _3._8._1. _a_x_2_5 _b_l_i_m_i_t [<_c_o_u_n_t>] 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 _b_i_n_a_r_y _e_x_p_o_n_e_n_t_i_a_l _b_a_c_k_- _o_f_f. 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. _a_x_2_5 _d_i_g_i_p_e_a_t [_o_n | _o_f_f] Display or set the digipeater enable flag. _3._8._3. _a_x_2_5 _f_l_u_s_h Clear the AX.25 "heard" list (see ax25 heard). _3._8._4. _a_x_2_5 _h_e_a_r_d 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 local station always appears first in the listing; the packet count actually reflects the number of packets transmitted. This entry is always present even if no packets have been sent. _3._8._5. _a_x_2_5 _i_r_t_t [<_m_i_l_l_i_s_e_c_o_n_d_s>] Display or set the initial value of smoothed round trip time to be used when a new AX25 connection is created. The value is in milliseconds. The actual round trip time will be learned by measurement once the connection has been established. _3._8._6. _a_x_2_5 _k_i_c_k <_a_x_c_b> Force a retransmission on the specified AX.25 control block. _3._8._7. _a_x_2_5 _m_a_x_f_r_a_m_e [<_c_o_u_n_t>] 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 8 - _3._8._8. _a_x_2_5 _m_y_c_a_l_l [<_c_a_l_l>] 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._9. _a_x_2_5 _p_a_c_l_e_n [<_s_i_z_e>] Limit the size of I-fields on new AX.25 connections. If IP datagrams or fragments larger than this are transmitted, they will be transparently 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._1_0. _a_x_2_5 _p_t_h_r_e_s_h [<_s_i_z_e>] 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._1_1. _a_x_2_5 _r_e_s_e_t <_a_x_c_b> Delete the AX.25 connection control block at the specified address. _3._8._1_2. _a_x_2_5 _r_e_t_r_y [<_c_o_u_n_t>] Limit the number of successive unsuccessful retransmission attempts on new AX.25 connections. If this limit is exceeded, link re-establishment is attempted. If this fails retry times, then the connection is abandoned and all queued data is deleted. _3._8._1_3. _a_x_2_5 _r_o_u_t_e Display the AX.25 routing table that specifies the digipeaters to updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 9 - be used in reaching a given station. _3._8._1_3._1. _a_x_2_5 _r_o_u_t_e _a_d_d <_t_a_r_g_e_t> [_d_i_g_i_s ... ] Add an entry to the AX.25 routing table. An automatic ax25 route add is executed if digipeaters are specified in an AX25 connect 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._1_3._2. _a_x_2_5 _r_o_u_t_e _d_r_o_p <_t_a_r_g_e_t> Drop an entry from the AX.25 routing table. _3._8._1_4. _a_x_2_5 _s_t_a_t_u_s [<_a_x_c_b>] 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._1_5. _a_x_2_5 _t_3 [<_m_i_l_l_i_s_e_c_o_n_d_s>] Display or set the AX.25 idle "keep alive" timer. Value is in milliseconds. _3._8._1_6. _a_x_2_5 _v_e_r_s_i_o_n [_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._1_7. _a_x_2_5 _w_i_n_d_o_w [<_s_i_z_e>] 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. _c_d [<_d_i_r_n_a_m_e>] 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. _3._1_0. _c_l_o_s_e [<_s_e_s_s_i_o_n>] Close the specified session; without an argument, close the updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 10 - current session. On an AX.25 session, this command initiates a disconnect. On a FTP or Telnet session, this command sends a FIN (i.e., initiates a close) on the session's TCP connection. This is an alternative to asking the remote server to 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._1_1. _c_o_n_n_e_c_t <_i_f_a_c_e> <_c_a_l_l_s_i_g_n> [<_d_i_g_i_p_e_a_t_e_r> ... ] 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._1_2. _d_e_l_e_t_e <_f_i_l_e_n_a_m_e> Delete a filename in the current working directory. _3._1_3. _d_e_t_a_c_h <_i_f_a_c_e> 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._1_4. _d_i_a_l_e_r <_i_f_a_c_e> <_s_e_c_o_n_d_s> <_h_o_s_t_i_d> <_p_i_n_g_s> <_d_i_a_l_e_r-_f_i_l_e> 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 11 - _3._1_5. _d_i_r [<_d_i_r_n_a_m_e>] 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 tem- porary file, and then creating a more session to display it. After this completes, the temporary file is deleted. _3._1_6. _d_i_s_c_o_n_n_e_c_t [<_s_e_s_s_i_o_n #>] An alias for the close command (for the benefit of AX.25 users). _3._1_7. _d_o_m_a_i_n ... These commands are used for access to the Domain Name Service. _3._1_7._1. _d_o_m_a_i_n _a_d_d_s_e_r_v_e_r <_h_o_s_t_i_d> Add one or more domain name server(s) to the list of name servers. _3._1_7._2. _d_o_m_a_i_n _d_r_o_p_s_e_r_v_e_r <_h_o_s_t_i_d> Remove one or more domain name server(s) from the list of name servers. _3._1_7._3. _d_o_m_a_i_n _l_i_s_t_s_e_r_v_e_r_s 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._1_7._4. _d_o_m_a_i_n _q_u_e_r_y <_h_o_s_t_i_d> Send a query to a domain server asking for all resource records associated with this <hostid>, and list the records. _3._1_7._5. _d_o_m_a_i_n _r_e_t_r_y [<_c_o_u_n_t>] 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._1_7._6. _d_o_m_a_i_n _s_u_f_f_i_x [<_d_o_m_a_i_n _s_u_f_f_i_x>] 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). updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 12 - _3._1_7._7. _d_o_m_a_i_n _t_r_a_c_e [_o_n | _o_f_f] 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._1_7._8. _d_o_m_a_i_n _c_a_c_h_e ... These commands are used for the use of the resource record file domain.txt, and the local memory cache. _3._1_7._8._1. _d_o_m_a_i_n _c_a_c_h_e _c_l_e_a_n [_o_n | _o_f_f] 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._1_7._8._2. _d_o_m_a_i_n _c_a_c_h_e _l_i_s_t List the current contents of the local memory cache. _3._1_7._8._3. _d_o_m_a_i_n _c_a_c_h_e _s_i_z_e [<_c_o_u_n_t>] 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._1_7._8._4. _d_o_m_a_i_n _c_a_c_h_e _w_a_i_t [<_s_e_c_o_n_d_s>] 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._1_8. _e_c_h_o [_a_c_c_e_p_t | _r_e_f_u_s_e] 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 13 - 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 Nagle tinygram algorithm in TCP). While this mode is just fine across an Ethernet, it is clearly inefficient and painful across slow paths like packet radio channels. Specifying echo refuse causes an incoming WILL ECHO offer to be answered with a DONT ECHO; the client Telnet session remains in the local echo mode. Sessions already in the remote echo mode are unaffected. (Note: Berkeley Unix has a bug in that it will still echo input even after the client has refused the WILL ECHO offer. To get around this problem, enter the stty -echo command to the shell once you have logged in.) _3._1_9. _e_o_l [_u_n_i_x | _s_t_a_n_d_a_r_d] 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._2_0. _e_s_c_a_p_e [<_c_h_a_r>] 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._2_1. _e_t_h_e_r_s_t_a_t Display 3-Com Ethernet controller statistics (if configured). _3._2_2. _e_x_i_t Exit the net.exe program and return to MS-DOS. _3._2_3. _f_i_n_g_e_r <_u_s_e_r@_h_o_s_t_i_d> [<_u_s_e_r@_h_o_s_t_i_d> ...] 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 14 - _3._2_4. _f_t_p <_h_o_s_t_i_d> 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._2_5. _h_e_l_p Display a brief summary of top-level commands. _3._2_6. _h_o_p ... These commands are used to test the connectivity of the network. _3._2_6._1. _h_o_p _c_h_e_c_k <_h_o_s_t_i_d> Initiate a _h_o_p_c_h_e_c_k 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 _t_r_a_c_e_r_o_u_t_e facility. ICMP message tracing should be turned off before this command is executed (see the icmp trace command). _3._2_6._2. _h_o_p _m_a_x_t_t_l [<_h_o_p_s>] Display or set the maximum TTL value to be used in hop check ses- sions. This effectively bounds the radius of the search. _3._2_6._3. _h_o_p _m_a_x_w_a_i_t [<_s_e_c_o_n_d_s>] Display or set the maximum interval that a hopcheck session will wait for responses at each stage of the trace. The default is 5 seconds. _3._2_6._4. _h_o_p _q_u_e_r_i_e_s [<_c_o_u_n_t>] Display or set the number of UDP probes that will be sent at each stage of the trace. The default is 3. _3._2_6._5. _h_o_p _t_r_a_c_e [_o_n | _o_f_f] Display or set the flag that controls the display of additional information during a hop check session. _3._2_7. _h_o_s_t_n_a_m_e [<_n_a_m_e>] 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 15 - 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._2_8. _h_s Display statistics about the HS high speed HDLC driver (if con- figured and active). _3._2_9. _i_c_m_p ... These commands are used for the Internet Control Message Protocol service. _3._2_9._1. _i_c_m_p _e_c_h_o [_o_n | _o_f_f] 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._2_9._2. _i_c_m_p _s_t_a_t_u_s Display statistics about the Internet Control Message Protocol (ICMP), including the number of ICMP messages of each type sent or received. _3._2_9._3. _i_c_m_p _t_r_a_c_e [_o_n | _o_f_f] 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._3_0. _i_f_c_o_n_f_i_g Display a list of interfaces, with a short status for each. _3._3_0._1. _i_f_c_o_n_f_i_g <_i_f_a_c_e> Display an extended status of the interface. _3._3_0._2. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _b_r_o_a_d_c_a_s_t <_a_d_d_r_e_s_s> 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._3_0._3. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _e_n_c_a_p_s_u_l_a_t_i_o_n <_n_a_m_e> Not fully implemented. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 16 - _3._3_0._4. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _f_o_r_w_a_r_d <_f_o_r_w_a_r_d-_i_f_a_c_e> Set a forwarding interface for multiple channel interfaces. To remove the forward, set <forward-iface> to <iface>. _3._3_0._5. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _i_p_a_d_d_r_e_s_s <_h_o_s_t_i_d> 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._3_0._6. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _l_i_n_k_a_d_d_r_e_s_s <_h_a_r_d_w_a_r_e-_d_e_p_e_n_d_a_n_t> Set the hardware dependant address for this interface. _3._3_0._7. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _m_t_u <_m_t_u> Set the MTU for this interface. See the Setting ... MTU, MSS and Window chapter for more information. _3._3_0._8. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _n_e_t_m_a_s_k <_a_d_d_r_e_s_s> 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._3_0._9. _i_f_c_o_n_f_i_g <_i_f_a_c_e> _r_x_b_u_f <?> Not yet implemented. _3._3_1. _i_p ... These commands are used for the Internet Protocol service. _3._3_1._1. _i_p _a_d_d_r_e_s_s [<_h_o_s_t_i_d>] 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._3_1._2. _i_p _r_t_i_m_e_r [<_s_e_c_o_n_d_s>] Display or set the IP reassembly timeout. The default is 30 seconds. _3._3_1._3. _i_p _s_t_a_t_u_s Display Internet Protocol (IP) statistics, such as total packet counts and error counters of various types. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 17 - _3._3_1._4. _i_p _t_t_l [<_h_o_p_s>] 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._3_2. _i_s_a_t [_o_n | _o_f_f] 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._3_2._1. _k_i_c_k [<_s_e_s_s_i_o_n>] 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._3_3. _l_o_g [_s_t_o_p | <_f_i_l_e_n_a_m_e>] 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._3_4. _m_b_o_x Display the status of the mailbox server system (if configured). _3._3_5. _m_e_m_o_r_y ... These commands are used for memory allocation. _3._3_5._1. _m_e_m_o_r_y _f_r_e_e Display the storage allocator free list. Each entry consists of a starting address, in hex, and a size, in decimal bytes. _3._3_5._2. _m_e_m_o_r_y _s_i_z_e_s 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._3_5._3. _m_e_m_o_r_y _s_t_a_t_u_s Display a summary of storage allocator statistics. The first line shows the base address of the heap, its total size, the amount of heap memory available in bytes and as a percentage of the total updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 18 - 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._3_6. _m_k_d_i_r <_d_i_r_n_a_m_e> Create a sub-directory in the current working directory. _3._3_7. _m_o_d_e <_i_f_a_c_e> [_v_c | _d_a_t_a_g_r_a_m] 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 mechan- isms, 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 necessary. In both modes, ARP is used to map IP to AX.25 addresses. The defaults can be overridden with the type-of-service (TOS) bits in the IP header. Turning on the "reliability" bit causes I frames to be used, while turning on the "low delay" bit uses UI frames. (The effect of turning on both bits is undefined and subject to change). In both modes, IP-level fragmentation is done if the datagram is larger than the interface MTU. In virtual circuit mode, 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). updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 19 - _3._3_8. _m_o_r_e <_f_i_l_e> [<_f_i_l_e> ...] 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. _3._3_9. _p_a_r_a_m <_i_f_a_c_e> [<_p_a_r_a_m> ...] Invoke a device-specific control routine. On a KISS TNC inter- face, this sends control packets to the TNC. Data bytes are treated as decimal. For example, param ax0 1 255 will set the keyup timer (type field = 1) on the KISS TNC configured as ax0 to 2.55 seconds (255 x .01 sec). On a SLIP interface, the param command allows the baud rate to be read (without arguments) or set. The implementation of this command for the various inter- face drivers is incomplete and subject to change. _3._4_0. _p_i_n_g <_h_o_s_t_i_d> [<_l_e_n_g_t_h> [<_s_e_c_o_n_d_s> [<_i_n_c_f_l_a_g>]]] 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. _3._4_1. _p_p_p ... These commands are used for 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: updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 20 - 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._4_1._1. _p_p_p <_i_f_a_c_e> Display the status of the PPP interface. _3._4_1._2. _p_p_p <_i_f_a_c_e> _l_c_p ... These commands are used for the LCP [Link Control Protocol] con- figuration. _3._4_1._2._1. _p_p_p <_i_f_a_c_e> _l_c_p _c_l_o_s_e Shutdown the PPP interface. _3._4_1._2._2. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l ... 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._4_1._2._2._1. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _a_c_c_m [ <_b_i_t_m_a_p> | _a_l_l_o_w [_o_n | _o_f_f] ] Display or set the Async Control Character Map. The default is 0xffffffff. _3._4_1._2._2._2. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _a_u_t_h_e_n_t_i_c_a_t_e [ _p_a_p | _n_o_n_e | _a_l_l_o_w [_o_n | _o_f_f] ] Display or set the authentication protocol. The default is none. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 21 - _3._4_1._2._2._3. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _c_o_m_p_r_e_s_s _a_d_d_r_e_s_s/_c_o_n_t_r_o_l [ _o_n | _o_f_f | _a_l_l_o_w [_o_n | _o_f_f] ] Display or set the option to compress the address and control fields of the PPP HLDC-like header. This is generally desirable for slow asynchronous links, and undesirable for fast or synchro- nous links. The default is off. _3._4_1._2._2._4. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _c_o_m_p_r_e_s_s _p_r_o_t_o_c_o_l [ _o_n | _o_f_f | _a_l_l_o_w [_o_n | _o_f_f] ] 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._4_1._2._2._5. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _m_a_g_i_c [ _o_n | _o_f_f | <_v_a_l_u_e> | _a_l_l_o_w [_o_n | _o_f_f] ] Display or set the initial Magic Number. The default is off (zero). _3._4_1._2._2._6. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _m_r_u [ <_s_i_z_e> | _a_l_l_o_w [_o_n | _o_f_f] ] Display or set the Maximum Receive Unit. The default is 1500. _3._4_1._2._2._7. _p_p_p <_i_f_a_c_e> _l_c_p _l_o_c_a_l _d_e_f_a_u_l_t Reset the options to their default values. _3._4_1._2._3. _p_p_p <_i_f_a_c_e> _l_c_p _o_p_e_n _a_c_t_i_v_e | _p_a_s_s_i_v_e 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._4_1._2._4. _p_p_p <_i_f_a_c_e> _l_c_p _r_e_m_o_t_e ... 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._4_1._2._5. _p_p_p <_i_f_a_c_e> _l_c_p _t_i_m_e_o_u_t [<_s_e_c_o_n_d_s>] Display or set the interval to wait between configuration or ter- mination attempts. The default is 3 seconds. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 22 - _3._4_1._2._6. _p_p_p <_i_f_a_c_e> _l_c_p _t_r_y ... These commands are used for the various counters. _3._4_1._2._6._1. _p_p_p <_i_f_a_c_e> _l_c_p _t_r_y _c_o_n_f_i_g_u_r_e [<_c_o_u_n_t>] Display or set the number of configuration requests sent. The default is 10. _3._4_1._2._6._2. _p_p_p <_i_f_a_c_e> _l_c_p _t_r_y _f_a_i_l_u_r_e [<_c_o_u_n_t>] Display or set the number of bad configuration requests allowed from the remote. The default is 5. _3._4_1._2._6._3. _p_p_p <_i_f_a_c_e> _l_c_p _t_r_y _t_e_r_m_i_n_a_t_e [<_c_o_u_n_t>] Display or set the number of termination requests sent before shutdown. The default is 2. _3._4_1._3. _p_p_p <_i_f_a_c_e> _i_p_c_p ... 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._4_1._3._1. _p_p_p <_i_f_a_c_e> _i_p_c_p _l_o_c_a_l ... 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._4_1._3._1._1. _p_p_p <_i_f_a_c_e> _i_p_c_p _l_o_c_a_l _a_d_d_r_e_s_s [ <_h_o_s_t_i_d> | _a_l_l_o_w [_o_n | _o_f_f] ] 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._4_1._3._1._2. _p_p_p <_i_f_a_c_e> _i_p_c_p _l_o_c_a_l _c_o_m_p_r_e_s_s [ _t_c_p <_s_l_o_t_s> [<_f_l_a_g>] | _n_o_n_e | _a_l_l_o_w [_o_n | _o_f_f] ] 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 23 - The tcp <flag> is 0 (don't compress the slot number) or 1 (OK to compress the slot number). KA9Q can handle compressed slot numbers, so the default is 1. _3._4_1._3._2. _p_p_p <_i_f_a_c_e> _i_p_c_p _r_e_m_o_t_e ... 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._4_1._4. _p_p_p <_i_f_a_c_e> _p_a_p ... 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. _3._4_1._4._1. _p_p_p <_i_f_a_c_e> _p_a_p _u_s_e_r [ <_u_s_e_r_n_a_m_e> [<_p_a_s_s_w_o_r_d>] ] 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._4_1._5. _p_p_p <_i_f_a_c_e> _t_r_a_c_e [<_f_l_a_g_s>] 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._4_2. _p_s 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 24 - 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 runn- able. 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._4_3. _p_w_d [<_d_i_r_n_a_m_e>] An alias for the cd command. _3._4_4. _r_e_c_o_r_d [_o_f_f | <_f_i_l_e_n_a_m_e>] 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._4_5. _r_e_m_o_t_e [-_p <_p_o_r_t>] [-_k <_k_e_y>] [-_a <_k_i_c_k_a_d_d_r>] <_h_o_s_t_i_d> _e_x_i_t | _r_e_s_e_t | _k_i_c_k Send a UDP packet to the specified host commanding it to exit the 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 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 25 - 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._4_6. _r_e_m_o_t_e -_s <_k_e_y> 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 _n_o_t yet supported by any other TCP/IP implementation. _3._4_7. _r_e_n_a_m_e <_o_l_d_f_i_l_e_n_a_m_e> <_n_e_w_f_i_l_e_n_a_m_e> Rename oldfilename to newfilename. _3._4_8. _r_e_s_e_t [<_s_e_s_s_i_o_n>] 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._4_9. _r_i_p ... These commands are used for the RIP service. _3._4_9._1. _r_i_p _a_c_c_e_p_t <_g_a_t_e_w_a_y> Remove the specified gateway from the RIP filter table, allowing future broadcasts from that gateway to be accepted. _3._4_9._2. _r_i_p _a_d_d <_h_o_s_t_i_d> <_s_e_c_o_n_d_s> [<_f_l_a_g_s>] 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 26 - "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._4_9._3. _r_i_p _d_r_o_p <_d_e_s_t> Remove an entry from the RIP broadcast table. _3._4_9._4. _r_i_p _m_e_r_g_e [_o_n | _o_f_f] This flag controls an experimental feature for consolidating redundant entries in the IP routing table. When rip merging is enabled, the table is scanned after processing each RIP update. An entry is considered redundant if the target(s) it covers would be routed identically by a less "specific" entry already in the table. That is, the target address(es) specified by the entry in question must also match the target addresses of the less specific entry and the two entries must have the same interface and gateway fields. For example, if the routing table contains Dest Len Interface Gateway Metric P Timer Use 1.2.3.4 32 ethernet0 128.96.1.2 1 0 0 0 1.2.3 24 ethernet0 128.96.1.2 1 0 0 0 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 27 - then the first entry would be deleted as redundant since packets sent to 1.2.3.4 will still be routed correctly by the second entry. Note that the relative metrics of the entries are ignored. _3._4_9._5. _r_i_p _r_e_f_u_s_e <_g_a_t_e_w_a_y> 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._4_9._6. _r_i_p _r_e_q_u_e_s_t <_g_a_t_e_w_a_y> Send a RIP Request packet to the specified gateway, causing it to reply with a RIP Response packet containing its routing table. _3._4_9._7. _r_i_p _s_t_a_t_u_s Display RIP status, including a count of the number of packets sent and received, the number of requests and responses, the number of unknown RIP packet types, and the number of refused RIP updates from hosts in the filter table. A list of the addresses and intervals to which periodic RIP updates are being sent is also shown, along with the contents of the filter table. _3._4_9._8. _r_i_p _t_r_a_c_e [_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._5_0. _r_m_d_i_r <_d_i_r_n_a_m_e> Remove a sub-directory from the current working directory. _3._5_1. _r_o_u_t_e With no arguments, route displays the IP routing table. _3._5_1._1. _r_o_u_t_e _a_d_d <_d_e_s_t__h_o_s_t_i_d>[/_b_i_t_s] | _d_e_f_a_u_l_t <_i_f_a_c_e> [<_g_a_t_e_w_a_y__h_o_s_t_i_d> [<_m_e_t_r_i_c>]] 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 gateway's link level address, if any. If the destination is directly reachable, gateway_hostid is also unnecessary since the destination address is used to determine the interface link updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 28 - address). The optional /bits suffix to the destination host id specifies how many leading bits in the host id are to be considered signi- ficant 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 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). 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 29 - _3._5_1._2. _r_o_u_t_e _a_d_d_p_r_i_v_a_t_e <_d_e_s_t _h_o_s_t_i_d>[/_b_i_t_s] | _d_e_f_a_u_l_t <_i_f_a_c_e> [<_g_a_t_e_w_a_y _h_o_s_t_i_d> [<_m_e_t_r_i_c>]] 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._5_1._3. _r_o_u_t_e _d_r_o_p <_d_e_s_t _h_o_s_t_i_d> 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._5_2. _s_e_s_s_i_o_n [<_s_e_s_s_i_o_n #>] Without arguments, displays the list of current sessions, includ- ing session number, remote TCP or AX.25 address and the address of the TCP or AX.25 control block. 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 to the session command will put you in _c_o_n_- _v_e_r_s_e 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 converse with the remote user as though the session had been locally initiated. _3._5_3. _s_h_e_l_l 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._5_4. _s_m_t_p ... These commands are used for the Simple Message Transport Protocol service (that is, mail). _3._5_4._1. _s_m_t_p _g_a_t_e_w_a_y [<_h_o_s_t_i_d>] 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._5_4._2. _s_m_t_p _k_i_c_k 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 30 - _3._5_4._3. _s_m_t_p _m_a_x_c_l_i_e_n_t_s [<_c_o_u_n_t>] 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._5_4._4. _s_m_t_p _t_i_m_e_r [<_s_e_c_o_n_d_s>] Displays or sets the interval between scans of the outbound mail queue. For example, smtp timer 600 will cause the system to check for outgoing mail every 10 minutes and attempt to deliver any- thing it finds, subject of course to the smtp maxclients limit. Setting a value of zero disables queue scanning altogether, note that this is the default! This value is recommended for stand alone IP gateways that never handle mail, since it saves wear and tear on the floppy disk drive. _3._5_4._5. _s_m_t_p _t_r_a_c_e [<_v_a_l_u_e>] 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._5_5. _s_o_c_k_e_t [<_s_o_c_k_e_t #>] Without an argument, displays all active sockets, giving their index and type, the address of the associated protocol control block and the and owner process ID and name. If the index to an active socket is supplied, the status display for the appropriate protocol is called. For example, if the socket refers to a TCP connection, the display will be that given by the tcp status com- mand with the protocol control block address. _3._5_6. _s_t_a_r_t _a_x_2_5 | _d_i_s_c_a_r_d | _e_c_h_o | _f_t_p | _n_e_t_r_o_m | _r_e_m_o_t_e | _s_m_t_p | _t_e_l_n_e_t | _t_t_y_l_i_n_k Start the specified Internet server, allowing remote connection requests. _3._5_7. _s_t_o_p _a_x_2_5 | _d_i_s_c_a_r_d | _e_c_h_o | _f_t_p | _n_e_t_r_o_m | _r_e_m_o_t_e | _s_m_t_p | _t_e_l_n_e_t | _t_t_y_l_i_n_k Stop the specified Internet server, rejecting any further remote connect requests. Existing connections are allowed to complete normally. _3._5_8. _t_c_p ... These commands are used for the Transmission Control Protocol service. _3._5_8._1. _t_c_p _i_r_t_t [<_m_i_l_l_i_s_e_c_o_n_d_s>] Display or set the initial round trip time estimate, in updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 31 - milliseconds, to be used for new TCP connections until they can measure and adapt to the actual value. The default is 5000 mil- liseconds (5 seconds). Increasing this when operating over slow channels will avoid the flurry of retransmissions that would oth- erwise occur as the smoothed estimate settles down at the correct value. Note that this command should be given before servers are started in order for it to have effect on incoming connections. TCP also keeps a _c_a_c_h_e of measured round trip times and mean deviations (MDEV) for current and recent destinations. Whenever a new TCP connection is opened, the system first looks in this cache. If the destination is found, the cached IRTT and MDEV values are used. If not, the default IRTT value 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._5_8._2. _t_c_p _k_i_c_k <_t_c_b__a_d_d_r> If there is unacknowledged data on the send queue of the speci- fied TCB, this command forces an immediate retransmission. _3._5_8._3. _t_c_p _m_s_s [<_s_i_z_e>] 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._5_8._4. _t_c_p _r_e_s_e_t <_t_c_b__a_d_d_r> Deletes the TCP control block at the specified address. _3._5_8._5. _t_c_p _r_t_t <_t_c_b__a_d_d_r> <_m_i_l_l_i_s_e_c_o_n_d_s> Replaces the automatically computed round trip time in the speci- fied TCB with the rtt in milliseconds. This command is useful to speed up recovery from a series of lost packets since it provides a manual bypass around the normal backoff retransmission timing mechanisms. _3._5_8._6. _t_c_p _s_t_a_t_u_s [<_t_c_b__a_d_d_r>] 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 32 - _3._5_8._7. _t_c_p _w_i_n_d_o_w [<_s_i_z_e>] Displays or sets the default receive window size in bytes to be used by TCP when creating new connections. Existing connections are unaffected. _3._5_9. _t_e_l_n_e_t <_h_o_s_t_i_d> Creates a Telnet session to the specified host and enters con- verse mode. _3._6_0. _t_i_p <_i_f_a_c_e> 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 datagrams, 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._6_1. _t_r_a_c_e [<_i_f_a_c_e> [_o_f_f | <_b_t_i_o> [<_t_r_a_c_e_f_i_l_e>]]] 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: 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 33 - _3._6_2. _u_d_p _s_t_a_t_u_s Displays the status of all UDP receive queues. _3._6_3. _u_p_l_o_a_d [<_f_i_l_e_n_a_m_e>] Opens filename and sends it on the current session as though it were typed on the terminal. _3._6_4. _w_a_t_c_h 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._6_5. ? Same as the help command. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 34 - _4. _A_t_t_a_c_h _C_o_m_m_a_n_d_s 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. <_b_u_f_s_i_z_e> 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 mar- gin. 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. <_i_o_a_d_d_r> The base address of the interface's control registers, in hex. _4._0._3. <_v_e_c_t_o_r> The interface's hardware interrupt (IRQ) vector, in hex. _4._0._4. <_i_f_a_c_e> 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. <_m_t_u> 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). updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 35 - _4._0._6. <_s_p_e_e_d> The speed in bits per second (eg. 2400). _4._1. _a_t_t_a_c_h _3_c_5_0_0 <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_r_p_a <_i_f_a_c_e> <_q_l_e_n> <_m_t_u> [<_i_p__a_d_d_r>] 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. _a_t_t_a_c_h _a_s_y <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 | _n_r_s | _p_p_p | _s_l_i_p <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_m_t_u> <_s_p_e_e_d> [<_c_r_v>] Attach a standard PC "com port" (asynchronous serial port), using the National 8250 or 16550A chip. Standard values on the IBM PC and clones for ioaddr and vector are 0x3f8 and 4 for COM1, and 0x2f8 and 3 for COM2. If the port uses a 16550A chip, it will be detected automatically and the FIFOs enabled. _4._2._1. _a_x_2_5 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. _n_r_s Use the NET/ROM asynchronous framing technique for communication with a local NET/ROM TNC. _4._2._3. _p_p_p Point-to-Point-Protocol. Encapsulates datagrams in an HDLC-like frame. This is a new Internet standard for point-to-point com- munication, compatible with CCITT standards. _4._2._4. _s_l_i_p 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. <_c_r_v> 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 36 - valid only for SLIP. _4._3. _a_t_t_a_c_h _d_r_s_i <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_m_t_u> <_c_h__a__s_p_e_e_d> <_c_h__b__s_p_e_e_d> 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. _a_t_t_a_c_h _e_a_g_l_e <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_m_t_u> <_s_p_e_e_d> WA3CVG/NG6Q driver for the Eagle Computer card (Zilog 8530). _4._5. _a_t_t_a_c_h _h_a_p_n <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_m_t_u> _c_s_m_a | _f_u_l_l 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. _a_t_t_a_c_h _h_s <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_m_t_u> <_k_e_y_u_p__d_e_l_a_y> <_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 byte time intervals. The p value specifies the transmitter persistence value in the range 1-255; the corresponding slot time is fixed at one hardware clock tick, about 55 ms on the PC. As with the other 8530 drivers, this driver actually attaches two interfaces, one for each 8530 channel. _4._7. _a_t_t_a_c_h _p_a_c_k_e_t <_i_n_t_v_e_c> <_i_f_a_c_e> <_t_x_q_l_e_n> <_m_t_u> Driver for use with separate software "packet drivers" meeting the FTP Software, Inc, Software Packet Driver specification. The driver must have already been installed before the attach command is given. Packet drivers in the Ethernet, ARCNET, SLIP, SLFP, and KISS/AX25 classes are supported. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 37 - 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. _a_t_t_a_c_h _p_c_1_0_0 <_i_o_a_d_d_r> <_v_e_c_t_o_r> _a_x_2_5 <_i_f_a_c_e> <_b_u_f_s_i_z_e> <_s_p_e_e_d> Driver for the PACCOMM PC-100 (Zilog 8530) card. Only AX.25 operation is supported. _4._9. _a_t_t_a_c_h _s_c_c <_d_e_v_i_c_e_s> _i_n_i_t <_a_d_d_r> <_s_p_a_c_i_n_g> <_A_o_f_f> <_B_o_f_f> <_D_a_t_a_o_f_f> <_i_n_t_a_c_k> <_v_e_c> [_p|_r]<_c_l_o_c_k> [<_h_d_w_e>] [<_p_a_r_a_m>] PE1CHL driver to initialize a generic SCC (8530) interface board prior to actually attaching it. The parameters are as follows: _4._9._1. <_d_e_v_i_c_e_s> The number of SCC chips to support. _4._9._2. <_a_d_d_r> The base address of the first SCC chip (hex). _4._9._3. <_s_p_a_c_i_n_g> The spacing between the SCC chip base addresses. _4._9._4. <_A_o_f_f> The offset from a chip's base address to its channel A control register. _4._9._5. <_B_o_f_f> The offset from a chip's base address to its channel B control register. _4._9._6. <_D_a_t_a_o_f_f> The offset from each channel's control register to its data register. _4._9._7. <_i_n_t_a_c_k> The address of the INTACK/Read Vector port. If none, specify 0 to read from RR3A/RR2B. _4._9._8. <_v_e_c> The CPU interrupt vector for all connected SCCs. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 38 - _4._9._9. <_c_l_o_c_k> The clock frequency (PCLK/RTxC) of all SCCs in hertz. Prefix with 'p' for PCLK, 'r' for RTxC clock (for baudrate gen). _4._9._1_0. <_h_d_w_e> 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._1_1. <_p_a_r_a_m> 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._1_0. _a_t_t_a_c_h _s_c_c <_c_h_a_n> _s_l_i_p | _k_i_s_s | _n_r_s | _a_x_2_5 <_i_f_a_c_e> <_m_t_u> <_s_p_e_e_d> <_b_u_f_s_i_z_e> [<_c_a_l_l>] Attach an initialized SCC port to the system. The parameters are as follows: _4._1_0._1. <_c_h_a_n> 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._1_0._2. _s_l_i_p | _k_i_s_s | _n_r_s | _a_x_2_5 The operating mode of the interface. slip, kiss and nrs all operate the port hardware in asynchronous mode; slip is Internet-standard serial line IP mode, kiss generates SLIP frames containing KISS TNC commands and AX.25 packets and nrs uses NET/ROM local serial link framing conventions to carry NET/ROM packets. Selecting ax25 mode puts the interface into synchronous HDLC mode that is suitable for direct connection to a half duplex radio modem. _4._1_0._3. <_s_p_e_e_d> 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 39 - _4._1_1. _A_t_t_a_c_h _E_x_a_m_p_l_e_s Here are some examples of the attach command: # Attach a 3Com Ethernet controller using the standard 3Com address and # vector (i.e., as it comes out of the box) to use ARPA-standard encapsulation. # The receive queue is limited to 5 packets, and outgoing packets larger # than 1500 bytes will be fragmented attach 3c500 0x300 3 arpa ec0 5 1500 # Attach the PC asynch card normally known as "com1" (the first controller) # to operate in point-to-point slip mode at 9600 baud, calling it "sl0". # A 1024 byte receiver ring buffer is allocated. Outgoing packets larger # than 256 bytes are fragmented. attach asy 0x3f8 4 slip sl0 1024 256 9600 # Attach the secondary PC asynch card ("com2") to operate in AX.25 mode # with an MTU of 576 bytes at 9600 baud with a KISS TNC, calling it "ax0". # By default, IP datagrams are sent in UI frames attach asy 0x2f8 3 ax25 ax0 1024 576 9600 # Attach the packet driver loaded at interrupt 0x7e # The packet driver is for an Ethernet interface attach packet 0x7e ethernet 8 1500 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 40 - _5. _F_T_P _S_u_b_c_o_m_m_a_n_d_s 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. _d_i_r [<_f_i_l_e> | <_d_i_r_e_c_t_o_r_y> [<_l_o_c_a_l _f_i_l_e>]] 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. _g_e_t <_r_e_m_o_t_e _f_i_l_e> [<_l_o_c_a_l _f_i_l_e>] 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. _h_a_s_h A synonym for the verbose 3 command. _5._4. _l_s [<_f_i_l_e> | <_d_i_r_e_c_t_o_r_y> [<_l_o_c_a_l _f_i_l_e>]] ls is identical to the dir command except that the "NLST" command is sent to the server instead of the "LIST" command. This results in an abbreviated directory listing, i.e., one showing only the file names themselves without any other information. _5._5. _m_g_e_t <_f_i_l_e> [<_f_i_l_e> ...] 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. _m_k_d_i_r <_r_e_m_o_t_e _d_i_r_e_c_t_o_r_y> Creates a directory on the remote machine. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 41 - _5._7. _m_p_u_t <_f_i_l_e> [<_f_i_l_e> ...] 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. _p_u_t <_l_o_c_a_l _f_i_l_e> [<_r_e_m_o_t_e _f_i_l_e>] 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. _r_m_d_i_r <_r_e_m_o_t_e _d_i_r_e_c_t_o_r_y> Deletes a directory on the remote machine. _5._1_0. _t_y_p_e [_a | _i | _l <_b_y_t_e_s_i_z_e>] 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 _i_m_a_g_e, 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._1_1. _v_e_r_b_o_s_e [_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: 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 42 - If a command is sent to the remote server because it is not recognized locally, the response is always displayed, regardless of the setting of 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 43 - _6. _D_i_a_l_e_r _S_u_b_c_o_m_m_a_n_d_s 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" wait 45000 "CONNECT " speed wait 2000 # PAD specific initialization send "" wait 15000 "Terminal =" send "ppp" wait 10000 " _6._0._1. _c_o_n_t_r_o_l _d_o_w_n | _u_p Control asy interface. The down option drops DTR and RTS. The up option asserts DTR and RTS. _6._0._2. _s_e_n_d "_s_t_r_i_n_g" 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. _s_p_e_e_d [ _9_6_0_0 | _4_8_0_0 | _2_4_0_0 | _1_2_0_0 | _3_0_0 ] 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. _w_a_i_t <_m_i_l_l_i_s_e_c_o_n_d_s> [ "_t_e_s_t _s_t_r_i_n_g" ] [ _s_p_e_e_d ] 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 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). updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 44 - Finally, if the _s_p_e_e_d 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 45 - _7. _T_h_e /_f_t_p_u_s_e_r_s _F_i_l_e 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 _n_o 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 that the user is given read and create permission, but not overwrite/delete permission. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 46 - 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 47 - _8. _T_h_e domain.txt _F_i_l_e 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 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 _c_l_a_s_s of the record. It means _I_n_t_e_r_n_e_t, and it will be found in all entries. A is the _t_y_p_e of the record, and it means that this is an _a_d_d_r_e_s_s 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 _c_a_n_o_n_i_c_a_l) 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 48 - This is the _t_i_m_e-_t_o-_l_i_v_e value, in seconds, associated with the record received from the server. Clients (such as net.exe) cach- ing 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 _T_T_L value is missing (as in the examples above), the record will never expire, and must be managed by hand. Since domain.txt is a plain text file, it may be easily edited by the user to add, change or delete records. Additional types of records, include NS (name server) and SOA (start of authority) may appear in domain.txt from remote server responses. These are not currently used by net.exe but are retained for future development (such as the incorporation of a domain name server into net.exe itself). updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 49 - _9. _S_e_t_t_i_n_g _B_u_f_s_i_z_e, _P_a_c_l_e_n, _M_a_x_f_r_a_m_e, _M_T_U, _M_S_S _a_n_d _W_i_n_d_o_w 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. _9._1. _H_a_r_d_w_a_r_e _P_a_r_a_m_e_t_e_r_s _9._1._1. _B_u_f_s_i_z_e 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. _A_X_2_5 _P_a_r_a_m_e_t_e_r_s _9._2._1. _P_a_c_l_e_n Paclen limits the size of the data field in an AX.25 I-frame. This value does _n_o_t 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. _M_a_x_f_r_a_m_e 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 _n_o_t apply to unconnected mode. The default value of maxframe in net.exe is 1 frame. _9._3. _I_P _a_n_d _T_C_P _P_a_r_a_m_e_t_e_r_s _9._3._1. _M_T_U The MTU (Maximum Transmission Unit) is an interface parameter updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 50 - 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 _f_r_a_g_m_e_n_t_s. 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 (frag- ment) 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. _M_S_S MSS (Maximum Segment Size) is a TCP-level parameter that limits the amount of data that the _r_e_m_o_t_e 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 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. _W_i_n_d_o_w 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 _e_f_f_e_c_t_i_v_e _w_i_n_d_o_w. This is the smaller of two values: the window advertised by the remote TCP minus the unacknowledged data in flight, and the _c_o_n_g_e_s_t_i_o_n _w_i_n_d_o_w, an automatically computed time-varying estimate of how much data the network can handle. The default value of Window is 2048 bytes. _9._4. _D_i_s_c_u_s_s_i_o_n _9._4._1. _I_P _F_r_a_g_m_e_n_t_a_t_i_o_n _v_s _A_X._2_5 _S_e_g_m_e_n_t_a_t_i_o_n 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 51 - 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 pro- gress is made in reassembling a datagram (i.e., a new fragment is received). It is not necessary that all of the fragments belong- ing to a datagram arrive within a single timeout interval, only that the interval between fragments be less than the timeout. Most subnetworks that carry IP have MTUs of 576 bytes or more, so 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 _t_r_a_n_s_p_a_r_e_n_t _f_r_a_g_m_e_n_t_a_- _t_i_o_n, 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 ori- ginal, 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 imple- mented; in fact, net.exe is so far the only known implementation. 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. _S_e_t_t_i_n_g _p_a_c_l_e_n _a_n_d _b_u_f_s_i_z_e 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 intero- perability 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 updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 52 - 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 currently fixed in size to 2048 bytes and this can be changed only by editing config.h and recompiling NOS. This limits buf- size; 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. _S_e_t_t_i_n_g _M_a_x_f_r_a_m_e For best performance on a half-duplex radio channel, maxframe should always be set to 1. The reasons are explained in the paper _L_i_n_k _L_e_v_e_l _P_r_o_t_o_c_o_l_s _R_e_v_i_s_i_t_e_d by Brian Lloyd and Phil Karn, which appeared in the proceedings of the ARRL 5th Computer Net- working Conference in 1986. _9._4._4. _S_e_t_t_i_n_g _M_T_U 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 _c_o_n_n_e_c_t_i_o_n_s are automatically segmented into I-frames no updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 53 - 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. _S_e_t_t_i_n_g _M_S_S 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 been opened and the new local interface has a smaller MTU than the previous one, IP fragmentation may occur in the local system. The only drawback to setting a large MSS is that it might cause avoidable fragmentation at some other point within the network path if it includes a "bottleneck" subnet with an MTU smaller than that of the local interface. (Unfortunately, there is presently no way to know when this is the case. There is ongoing work within the Internet Engineering Task Force on a "MTU Discovery" procedure to determine the largest datagram that may be sent over a given path without fragmentation, but it is not yet complete.) Also, since the MSS you specify is sent to the remote system, and not all other TCPs do the MSS-lowering pro- cedure yet, this might cause the remote system to generate IP fragments unnecessarily. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 54 - 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. _S_e_t_t_i_n_g _W_i_n_d_o_w 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 control- ling 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 window) 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 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991 - 55 - _9._5. _S_u_m_m_a_r_y 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. updated by Bill SimpsonMarch 7, 1991 March 3, 1991