SLIRP(1)                    General Commands Manual                   SLIRP(1)

       slirp - TCP/IP emulator

       slirp [options|commands]
       slirp help
       slirp "help cmd"

       Slirp is a TCP/IP emulator which turns an ordinary shell account into a
       (C)SLIP/PPP account. This allows shell users to use all the funky
       Internet applications like Netscape, Mosaic, CUSeeMe, etc.

       Slirp is copyright (c) 1995 Danny Gasparovski. All rights reserved.
       See the section COPYRIGHT for details.

       This manpage is organized as follows. First, basic usage is described
       very briefly. This is followed by details of configuration files,
       commands, and command-line options. Several sections discussing
       technical issues (special addresses, port redirection, baudrate
       setting) are next, followed by answers to frequently-asked questions
       and common problems. Contact information, acknowledgements and the
       copyright notice are at the end.

       Please read this manpage thoroughly before reporting problems!

       To run Slirp, simply type:


       (or whatever the full path to Slirp is). That's it. Now you activate
       your SLIP/PPP software, and start your applications.

       All you have to remember is this: Once you run Slirp, your shell
       account now looks exactly like a SLIP/PPP account (with some
       limitations of course). Any documentation that you have telling you how
       to connect to a SLIP/PPP account is completely valid for Slirp as well.

       To quit Slirp you simply kill your SLIP/PPP software and type five 0's
       (zeroes), with a 1 second gap between each zero. Slirp will then exit
       and you will be back at your shell prompt.

       You can also "disconnect" Slirp by typing five 1's (one's), with a 1
       second gap between each. This will disconnect Slirp from your shell's
       terminal and put Slirp in the background. Later, you can type

           slirp -l 0

       to "reconnect" Slirp again.

       Quick note for PDA users:  If you set SLIRP_TTY to the tty connected to
       your PDA (Palm, POSE emulator, etc.), Slirp will use that tty for
       communication.  You can use PPP without full masquerading, although you
       will be subject to the standard Slirp constraints.  You may need to
       experiment to find the correct baud rate.  Start with 19200 for Palms.
       If Slirp was not compiled with DO_CFSETSPEED, you'll need to set the
       speed on the tty manually.  Use an appropriate variant of "stty 19200 <
       /dev/pilot" after starting slirp.

       Slirp can be configured in 3 different ways: the command line, the
       configuration files, and "on-the-fly" configuration by telnet-ing to and entering the commands there (see "SPECIAL ADDRESSES,"

       The configuration file is located in your home directory (~) and is
       called ".slirprc", hence the path to your configuration file is

       Options which can appear in a configuration file can also be given on
       the command line.  E.g., If your .slirprc file looks like the

           redir 5022 21
           redir X

       you can achieve the same thing by running Slirp as:

           slirp "redir 5022 21" "redir X"

       (Notice the quotes, they ARE significant).  The reverse is also true.
       E.g., if you run slirp as:

           slirp -P -b 14400

       you can create your .slirprc file too look like the following:

           -b 14400

       (Notice that only ONE command per line is allowed in configuration
       files).  The 2 types of options can also be mixed. For example:

           In .slirprc:
               -b 14400
               redir 5022 21

           Command line:
               slirp -P -b 14400 "redir 5022 21"

       Note that on the command line, any command/option that does not begin
       with a '-' or '+', and has spaces in it, MUST be enclosed in quotes.
       E.g., The following are all legal:

           slirp -P "redir udp 5022 25" -vj -b 14400
           slirp "ppp" "baudrate 14400"
           slirp ppp "baudrate 14400"

       (Notice that even though "ppp" does not begin with a '-' or '+', it
       does not need to be enclosed in quotes because it has no spaces in it)

       The following are NOT legal:

           slirp baudrate 14400
           slirp "-b 14400"

       (Because "-b" starts with a '-' you must NOT enclose it in quotes.)
       Easy, eh?

       Note: Whenever Slirp expects an IP address as an argument (E.g., in the
       command "redir") and the IP address argument is not given, then the
       default used is different depending on where the command appeared; if
       it was in ~/.slirprc then the default is; if it was in a
       telnet, then the IP address used is the IP address from where
       the telnet connection was made. For example, if you have a LAN
       at home and telnet to from one of the hosts and issue a
       "redir" command, Slirp will use the IP address of the host from where
       you made the telnet connection. Also, if you use an IP address
       on your PC other than, you should include it as an argument
       whenever Slirp expects it, for example with the redir command:

           redir 5555 your.ip.address:5555

       A few notes on configuration:

         * You should have "ppp" or "-P" before any PPP options (because when
           Slirp parses -P or ppp, it will initialize all related fields,
           hence clearing anything that was parsed before it).

         * Upon startup, the configuration is done in this order:

           1) ~/.slirprc-N (if using Load-balancing or Link-resumption)

           2) ~/.slirprc

           3) Command-line options

           This is important because, for example, if you have "initiate-
           options" (a PPP option) in ~/.slirprc-0, and you run slirp with -P,
           "initiate-options" will not be valid, because -P will clear the
           fact that you want options initiated by Slirp (remember, -P should
           always come before any PPP options).

       Slirp includes an "online-help" facility. To get a list of commands
       accepted by Slirp give it the command "help". I.e, you can either run
       Slirp from your shell prompt as:

           slirp "help"

       or once Slirp is running, telnet to and type:


       To get a brief description of each command simply type "help COMMAND".

           slirp "help baudrate"

       from the command line, or

           help baudrate

       in telnet to

       In the following descriptions, items within square brackets are
       optional. "Usable" refers to where it can be used, ie: "command-
       line/config-file", "telnet", or "anywhere" (which means it can appear
       in either command-line/config-file or be given via telnet).  "Command-
       line" gives the command-line equivalent, where applicable.

       redir X [start N] [ADDR][:DISPLAY[.SCREEN]]
           Redirect a port for use with the X Window System.
           Usable: anywhere
           Command-line: -X

             start N
                 Tell slirp to start looking for free ports starting from N.
                 eg: if N = 2, slirp will try to grab port 6002 then 6003 etc.
                 this is useful for sites which sometimes run their own X
                 server and you don't want to nab their port 6000, which they
                 would naturally expect.

                 Our home ip address, or the address where the X server is (if
                 you have a LAN at home to connect more than one machine to
                 the net) (default when in ~/.slirprc, the source IP
                 address when in command-line).

                 Which display to redirect to (default :0).

                 Which screen to redirect to (default .0).

           Example: redir X

           Note: This will print the command needed to enter into each shell
           from where you launch your X apps.

           See also: show X.

       show X
           Show the command that needs to be given to your shell for any X
           port that has been redirected (in case you forget).

           Usable: telnet

           Example: show X

           Note: This is useful if you forget the command to give to your
           shell for X redirection.

           See also: redir X, log start.

       redir [once|time] [udp|tcp] PORT [to] [ADDRESS:]LPORT
           Redirect host port to local port using a selected protocol.
           Usable: anywhere

             once    Only allow one redirection [TCP only]

             time    Allow redirection to time out [UDP only]

             udp     Redirect a UDP port

             tcp     Redirect a TCP port [default]

             PORT    Port to use on host system

             ADDRESS Address of your home machine [default]

             LPORT   Port to redirect host port to on local system

           Example: redir tcp 5021 to 21
           Allow users to ftp to your local machine using your host's port 21.
           (ftp 5021).

           Note: if this command is in your .slirprc file and no address is
           specified, it will assume that your local IP address is
           If you enter the command from the slirp control telnet IP it will
           use the IP address you are accessing with.

       baudrate N
           Controls the allocation of time to communications across your
           serial link.  Higher values generally use more of the available
           bandwidth to your modem.  This is _only_ an internal control value
           and does _not_ change the physical settings for the host port or
           Usable: anywhere
           Command-line: -b

           Example: baudrate 14400

           Note: higher numbers generally allow better transfer rates for ftp
           sessions, but interactive sessions could become less responsive.
           the optimum value is *JUST* when ftp sessions reach maximum
           throughput, but this can be hard to find (especially on compressing
           modems) so you should choose the maximum throughput you would
           expect from your modem.

       special|control|host addr ADDRESS
           Set ip address aliases and others for slirp.
           Usable: anywhere

             special address
                 Set the network ip alias for slirp

             control address
                 Only allow access to slirp control address from ADDRESS.

             host address
                 Tell slirp the IP address of the host it's running on. Use
                 this only if slirp can't properly find the host's IP address.

           Example: special address

           Note: The ADDRESS for special must end in 0 (zero) and other
           addresses are classed from this.  The default special address is
  giving the following defined IP's:

                 slirp control telnet IP
                 slirp exec IP
                 slirp host alias
                   10.0.2.x        add [pty]exec optional address

       add [pty]exec PROGRAM:[ADDRESS:]PORT
           Set program to execute on host  when local machine attempts to
           connect to ADDRESS at port PORT.
           Usable: anywhere

             exec    Establish binary connection to program in the style of

             ptyexec Establish telnet connection to program using telnetd
                     helper application under a pseudo-terminal.

             PROGRAM Program to exec

             ADDRESS Optional address

             PORT    Port

           Example: add ptyexec csh:55
           A telnet connection to the slirp exec IP (default will
           start and connect you directly to the csh program on the host.
           (telnet 55).

           Example: add exec nntpd:
           A program that attempts to open port 119 at address will
           be connected to the nntpd program.

           Note: The use of the ptyexec form requires the slirp.telnetd helper
           application be available on your path.  Also note that ADDRESS must
           be of the form SPECIAL_ADDRESS.xx (10.0.2.xx by default).

           Force startup mode for slirp to SLIP or CSLIP.  This overrides the
           default automatic mode determination.

           Example: nocompress
           Start in SLIP mode.

           Example: compress
           Start in CSLIP mode.

           Note: The default method of operation generally performs well. You
           should only have to use this command if you find that your host and
           local system are failing synchronize the connection type.

       mtu N
           Controls the size of the IP packets sent across the serial IP link.
           Valid values are <= 1500.

           Example: mtu 1500 Set the mtu to its largest allowable size.

           Note: Larger values generally improve the performance of graphics
           web browsers and ftp transfers across the serial link, at the
           expense of interactive performance. The default value of 552 seems
           to be a reasonable compromise for connections at 14400 baud.

       shell PROGRAM
           Set program to execute on EXEC IP default telnet port (23).

           This is the same as

                   add ptyexec PROGRAM:23

           Note: By default slirp connects /bin/sh to the exec IP telnet port.

       help [COMMAND]
           Show a brief list of available commands, or more information on the
           named command.

       remove [pty]exec PROGRAM:[ADDRESS/]PORT
           Reverse the effect of "add [pty]exec".  see "add [pty]exec" for the
           options etc.

           Note: you must enter the options exactly as you entered it in add

           **This description is incomplete.**

       echo [on|off]
           Turn echo on or off, depending on how your client behaves.  "echo"
           by itself will show whether echo is currently on or off.

       kill N
           Kill the session which has a Socket no. of N.  to find the Socket
           no.  of a particular session, use the "stats socket" commands.  See
           "stats" below.

           Note: It is recommended you use "close N" instead, as this merely
           wipes out the session, whereas "close N" closes it properly, as a
           good little tcpip-emulator should :)

           "kill -1" shouldn't be used, it will kill the first session it
           finds with -1, which usually is the command-line connection.

       close N
           Close the session which has a Socket no. of N. same as "kill N",
           but closes it session gracefully. See "kill N".

       stats [ip|socket|tcp|vj|udp|mbuf|tty|alltty|others?]
           Show statistics on the given argument.

             ip     Show ip statistics.

             socket Show statistics on the currently active sockets. Use this
                    to find out which sessions to close/kill as it will also
                    show the FD of the session.

             tcp    Show tcp statistics (packets sent, received, etc).

             udp    Same as tcp but for udp.

             mbuf   Show how many mbufs were allocated, are in use, etc. If
                    the modem is idle, and there are more than 1 mbufs on the
                    used list, it suggests an mbuf leak.

       [pty]exec PROGRAM
           This will execute PROGRAM, and the current command-line session
           will cease to exist, taken over by the PROGRAM. ie: when the
           program exits, you will not get the command-line back, the session
           will (should) close.

       socket [PORT,PASSWORD]
           Create a Unix-domain socket and listen() for more interfaces to
           connect.  This is also needed for restarting.  Give the arguments
           PORT,PASSWORD if you wish to use Internet-domain sockets instead of
           UNIX-domain sockets.

       log start
           Log all the startup output to the file .slirp_start.

       add emu SERVICE[:TYPE_OF_SERVICE] [lport:]fport
           Tell slirp to emulate SERVICE when on port lport/fport.

                    Can be: ftp, ksh, irc, none.

                    Can be: throughput, lowdelay.

             LPORT  Can be given if that service needs emulation for, say,

           Example: add emu ftp 8021
           If you wish to ftp to somewhere on port 8021.

           Example: add emu ftp 8021:0
           If your home ftp server is on port 8021. NOTE: this does NOT mean
           if you redirect port 8021 for your ftp daemon, it refers the the
           port AT HOME at which ftpd is listening to.

           Example: add emu none:lowdelay 8000
           If you telnet somewhere on port 8000, and you wish those packets to
           go on the fastq (ie: so they have a higher priority than, say, ftp
           packets). This tells slirp that any packets destined for port 8000
           will not have any emulation, but it will be set IPTOS_LOWDELAY.

       dns DNS_IP
           Give this to slirp if you want to use as an alias for DNS,
           AND slirp guesses wrong for the DNS on startup.

 Special Addresses
       All addresses of the form are special to Slirp (this can be
       changed with the "special addr" command).  The following is a
       description of what each of the addresses mean:
              This is the Slirp "on-line" configuration address.  When you
              telnet to you can close connections, configure Slirp,
              redirect ports, etc.  all while Slirp is running.  Please read
              the section "CONFIGURING SLIRP" for details on how to use this.
              This is the address used by Slirp to execute programs.  For
              example, if you give Slirp the command "add exec /bin/ls:23",
              when a connection is made to on port 23, Slirp will
              execute /bin/ls and redirect the output to that connection.
              E.g., with "add exec /bin/ls:23", if you telnet to
              (telnet uses port 23) you will get a list of files in the
              directory Slirp was started.  Another example could be "add exec
              /path/to/nntpd:119".  Now you can tell your News reader to use
     as the News host and it will actually connect to the
              running program "nntpd".
              This is an alias for the remote host.  When you connect to
     you will actually connect to the host Slirp is running
              on.  This is useful if your shell account can be on different
              hosts, will always mean the host Slirp is running on.
              This is an alias for your DNS.  Slirp will try to figure out
              your DNS address and all data sent to will be
              redirected to your DNS address, so you can tell your TCP/IP
              software to use as your DNS.  This can also be useful
              if your run Slirp from multiple hosts; you don't need to change
              your DNS for each host.
              This is the address recommended by Slirp to be used on your PC.
              However this is merely a suggestion, Slirp does not care what
              address you use.

 Port Redirection
       Port redirection is an important concept in TCP/IP emulators because it
       allows other people to connect to your PC, as well as allowing some
       programs to work which normally would not work.

  How do I Redirect a Port?
       First you need to realize that under Slirp, nobody on the Internet can
       address your PC directly, since you do NOT have an IP address that
       anybody else can see. The ONLY way they can contact you is through the
       remote host (where Slirp is running).

       What has this got to do with Port redirection?  Lots.  For other people
       on the Internet to be able to connect to your PC, Slirp needs to listen
       for connections on a specific port on the remote host, then "redirect"
       this connection and have it connect back to your PC.

       For example, say you are running an FTP server on your PC and you want
       others to be able to connect to it, get files, upload files, etc.  What
       you need to do is pick a port number, any port number above 1024 (for
       security reasons), and tell Slirp that any connections on that port are
       really connections to your FTP server.  You do this with the "redir"

       For this example, say you choose 5555 as the port to redirect (this can
       be ANY number, provided nobody else is using it).  You simply give
       Slirp the command:

           redir 5555 21

       The second argument, 21, is the port that is used by FTP.  You could
       have also used the command:

           redir 5555 ftp

       and Slirp will figure out that "ftp" means 21.  This command is
       basically telling Slirp "any connections to this host (where Slirp is
       running) on port 5555 are really connections to the home PC on port 21
       (the port used by the FTP server)".

       Now you simply tell others to connect to the Remote Host (where Slirp
       is running), which IS visible on the Internet, on port 5555 and they
       will be connected to your FTP server.

       This same technique is used when a program uses a specific port for
       communication, for example Kali, an IPX emulator over TCP/IP allowing
       users to run IPX games over the Internet.  Kali uses UDP port 2213 for
       communication so for others to be able to send a packet to your PC on
       UDP port 2213 you need to do the following:

           redir udp 2213 2213

       All packets now destined for the Remote Host on UDP port 2213 will be
       sent to your PC on port 2213.

  Common Port Redirections
       Here is a list of programs which need a port redirection to work.
       YOUR_PC_ADDRESS refers to the IP address you assigned to your PC. If it
       is not supplied, is assumed.

          redir udp 2213 YOUR_PC_ADDRESS:2213
          (Note: you MUST also set your PC's IP address to the same IP address
          as the Remote Host (where Slirp is running))

          redir udp 22555 YOUR_PC_ADDRESS:22555

          redir udp 8000 YOUR_PC_ADDRESS:8000
          (the 8000 is configurable)

          redir tcp 13223 YOUR_PC_ADDRESS:13223

          redir tcp 21845 YOUR_PC_ADDRESS:21845
          redir udp 21845 YOUR_PC_ADDRESS:21845
          (Note: WebPhone uses BOTH tcp and udp port 21845. In addition, you
          probably need to set your PC's address to the same IP address as the
          RemoteHost in order to get full functionality)

       Please let me know of other programs which require redirection like the
       above.  See "GETTING HELP" for details on how to contact me.

 Setting The baudrate Option
       Slirp's "baudrate" option has caused some confusion.  This section will
       explain exactly what it's for and how to use it.

       When sending data over the modem to your PC, Slirp needs to know how
       much data it can send over without "saturating" the link.  If Slirp was
       to send as much data as it could, the Operating System would buffer a
       LOT of it - 20k is not uncommon.  This could severely "lag" any telnet
       connections if you happen to be FTP-ing a file at the same time.  This
       is because when you type a character, you will not see that character
       on the screen until the the other end sends you the "echo", so if there
       is 20k worth of data buffered you will need to wait until 20k of data
       is received before you see that character on your screen.

       To counter this, Slirp uses the "baudrate" option to limit the amount
       of data it sends over the link to prevent the Operating System from
       buffering too much of it.  So if you give Slirp a "baudrate" of 14400,
       Slirp will send data at a rate of 14400 Baud modem (with no

       In general, the baud rate at which the connection was made should be
       the "baudrate" you give to Slirp.  So, for example, if you connected at
       14400 Baud, you should give Slirp the option "baudrate 14400".
       However, since most modems today do compression (v.42bis), it is very
       difficult for Slirp know how much data to send to keep the link "full",
       yet prevent too much buffering by the Operating system.

       Therefore you should choose a "baudrate" appropriate to your needs: if
       you use telnet a lot while downloading compressed files, you should set
       your "baudrate" to the same as the CONNECT speed of your modem.
       Downloading compressed files should not suffer, and telnet sessions
       will be far more responsive.  However, sending text over the modem will
       not be as fast, because your modem will compress the data and send it
       faster than Slirp expects.  Giving a "baudrate" the same as the CONNECT
       speed will effectively turn off modem compression.

       If you do not use telnet very much, you should set your "baudrate" to
       the maximum theoretical speed your modem can do.  For example, if you
       connect at 14400 and use v.42bis compression, which can compress up to
       4x, you should set your "baudrate" to 14400*4 = 57600.  This will
       ensure any compressible data will get compressed, and a maximum
       throughput will be attained, at the expense of telnet sessions which
       will be almost unusable if you happen to be downloading files at the
       same time.

       Note however that you can change the "baudrate" setting at any time.
       Simply telnet to and enter "baudrate XXX" and Slirp will
       change the rate at which data is sent.  This can be useful for example
       if you're downloading a lot of compressed files, but in the middle of
       the download you want to read mail.  Simply change the "baudrate" to
       the CONNECT speed, and when you're finished, change it back to the
       maximum theoretical speed.

       Also, keep in mind that the "baudrate" is also used for other
       calculations.  For example, if there are many connections, Slirp will
       try to be fair and send one packet per connection in a round-robin
       fashion.  This makes all connections "smooth" instead of sending a
       bunch of packets for one connection, then a bunch of packets for
       another connection, etc.  But if the "baudrate" is too high, the is
       exactly what will happen.  Packet priority selection also uses the
       "baudrate"; I.e., if there are packets queued ready for sending from
       both an FTP connection and a telnet connection, the telnet packets will
       be sent first.  But again, this will only work if the "baudrate"
       reflects the amount of data Slirp can send, and generally won't work if
       you set it to the maximum theoretical connection speed.

       So here are my tips:

         * If you download a lot of compressed files and occasionally use
           telnet, or other "interactive" programs, set your "baudrate" to
           your CONNECT speed (because already compressed files won't compress
           any more with the modem compression, so you're unlikely to get
           faster download's as a result of modem compression);

         * If you mainly use telnet, or other "interactive" programs, and you
           occasionally download some compressed files, set your "baudrate" to
           the maximum theoretical speed (because telnet sessions are usually
           text, which compresses very well, hence screen updates will be
           faster.  Only when downloading compressed files will you experience
           severe lag);

         * If you mainly browse the Web (E.g., using Netscape, etc.), then you
           should set your "baudrate" to the theoretical maximum speed
           (because there's lots of text in Web documents which is very
           compressible, and there's no telnet sessions so lag will not be a

       I personally have by baudrate set at 14400, the speed at which my modem
       connects, even though the modems do v.42bis compression.  Compressed
       file downloads are just as fast, and telnet sessions during FTP
       downloads are surprisingly responsive.  Try it yourself, there's a
       world of difference.

 Which programs do not work over Slirp?
       Any programs that bind()'s a port, then tell the other end of the
       connection where they should connect() to this bound port.

       For example, when you "get" a file during an FTP session, the FTP
       client bind()'s a socket, has a look at which port the socket is bound
       to, then tells the FTP server the address and port of this socket (with
       the PORT command). The FTP server then connect()'s to this
       address/socket pair.

       Now, since your machine isn't really on the Internet, this connect()
       request will not arrive to your host, so it will not work.

       Slirp emulates this by bind()ing it's own port on the server that *is*
       on the Internet, and tells the FTP server about *that* address/socket
       pair.  When the server connect()'s to it, Slirp will then connect back
       to your machine.

       At present, the following programs are emulated:

            irc (for /dcc)

              The connection will "freeze".  E.g., while downloading a picture
              on WWW it will stop halfway and no connections will continue.

               You probably don't have an 8bit clean link.

       Cure:  You should try and find out from your sysadmin which characters
              need to be "escaped", then tell Slirp about them using the
              "asyncmap" and "escape" commands.  Note that you need to use PPP
              for this to work.  (One way to test for 8bit cleanliness is to
              download a BINARY file with Z-Modem.  If the file doesn't make
              it, you have a "dirty" link).

              One thing you might try is run Slirp as:

                  slirp "asyncmap ffffffff" "escape ff"

              (quotes included!) This will tell Slirp to escape the most
              common "nasty characters.

              You can connect to hosts using numerical addresses (of the form
     but you cannot connect to hosts when you use their
              hostname (E.g.:  It usually times out with a DNS

              You probably did not set your DNS address properly.

       Cure:  Try setting your DNS address to  This should work for
              most situations.  If that fails, go to your shell prompt and
              type "nslookup".  This should print the address and hostname of
              your DNS server.  Use the numerical IP address as your DNS.  Do
              NOT use the hostname.

              If you still can't find your DNS address, ask your sysadmin for

 Answers to Frequently Asked Questions (FAQs)
       Q1.    Can I use Slirp through Telnet or Rlogin?

       A1.    Yes, usually.  But this is highly dependent on your situation.

              The reason Slirp usually doesn't work through telnet is because
              of the ^] character is interpreted by the telnet client, and
              0xff interpreted by the server.  While you can tell Slirp to
              escape these characters while using PPP, it may not be possible
              to get your local PPP software to escape characters greater than
              ASCII 31.  Rlogin also interprets the ~ character, which may
              interfere with PPP (especially considering ~ is ASCII 0x7e which
              is used by PPP as the "end of packet" character").

              If your PPP software is unable to escape these characters, or
              you're using (C)SLIP (which must have an 8bit clean link), your
              best bet is to try and make the link 8bit clean.  For example,
              on some systems you can give telnet the -8 flag to make the link
              8bit, and -E to stop it from interpreting the ^] character.
              Similarly for rlogin; -8 to make the link 8bit, -E to stop
              rlogin from interpreting the ~ character.  You should look at
              the telnet and rlogin manual pages ("man telnet" and "man
              rlogin" respectively) to see if your telnet/rlogin has similar

              Another possible solution is to use Slirp's ability to work over
              multiple hosts.  See the slirp.doc documentation for more

       Q2.    How do I run an X program on another host and have it display on
              my PC?

       A2.    Use the "redir X" command in ~/.slirprc.  This will redirect a
              port for use with X programs.

              On startup, Slirp should print something like:

                  X Redir: In sh/bash/zsh/etc. type: DISPLAY=IP.ADDRESS:X.Y; export DISPLAY
                  X Redir: In csh/tcsh/etc. type:    setenv DISPLAY IP.ADDRESS:X.Y

              Now, when you telnet to the host you wish to run the X programs
              from, you should do as Slirp suggest above; type either of the
              two commands, depending on which shell you are using.  You could
              also run the X program as "xprog -display IP.ADDRESS:X.Y" as
              printed above.

              If you missed what Slirp displayed on startup, you can telnet to
     and give Slirp the command "show X", and the above will
              be printed.

              Note that you also have to make sure your X server will accept
              the connection.  See the man page for xhost and Xsecurity.  Be
              careful with issuing commands like "xhost +", this will allow
              anyone to connect to your X server and do basically anything
              they want.

       Q3.    When I run "talk" or "wintalk", etc. I am able to send requests
              to other people but they cannot send requests to me.  Why?

       A3.    You won't be able to receive talk requests, period.  This is
              because Slirp never see's the incoming talk request; it is sent
              directly over the modem, most likely corrupting any incoming
              packet with it (which will have to be retransmitted).  Slirp
              turns off your messages so the person who tries to talk to you
              should receive a "User is refusing messages" error.

       Q4.    I can't telnet to, the Slirp control address.  What's

       A4.    See the answer to this question in slirp.doc and recompile

       Q5.    I'm having a few problems with Slirp and want to try and find
              the problem myself.  Does Slirp have any debugging facilities?

       A5.    Yes. See slirp.doc for compile-time debug options.

       Q6.    My ISP logs me out if I idle too long.  How can I get Slirp to
              prevent this?

       A6.    First of all, the idle-logout mechanism is used for a reason: to
              prevent people from hogging a modem which is not in use.  So if
              you're idle, logout and give others chance to logon.

              Having said that, you can make Slirp use TCP keep-alive timers
              to regularly probe each TCP connection.  To activate this, add:


              to your ~/.slirprc file.  This will make Slirp probe each TCP
              connection every minute or so.  You can change this interval by
              giving keepalive the number of seconds:

                  keepalive SECONDS

              Note that no probes will be sent if there are no TCP
              connections.  So you need at least one active TCP connection for
              this to work.

       There are several sources of help.  First, read the previous sections
       "Troubleshooting" and "Answers to Frequently Asked Questions (FAQs)".

       If that fails, try the Slirp Home Page at:


       There are lots of neat links there to other pages which have specific
       configuration information.

       There is also a Newsgroup dedicated to SLIP-emulators called
       alt.dcom.slip-emulators. You will find lots of discussion about Slirp
       and other "SLIP-emulators". The FAQ (Frequently Asked Questions) for
       alt.dcom.slip-emulators is included in the "docs" directory, I would
       suggest reading this as well.

       If all else fails, send me e-mail to with
       the following information:

         * Output of the command "uname -a" on the remote system;

         * Operating System name and version you run on your PC;

         * Version of Slirp you are using (IMPORTANT!!!);

         * If you managed to get Slirp running, run Slirp as "slirp -S" then
           try whatever failed.  When you exit Slirp, you should have a file
           called "slirp_stats".  Send me this file; and

         * Anything else you consider relevant.

       *PLEASE* include all the above information. If you do not, I may simply
       press "d". I can't guarantee a response, but I will try my best.

       A big "THANK YOU!" goes to the following people for their help in
       creating Slirp.

       Juha Pirkola, Gregory M. Christy, The Regents of the University of
       California, Carnegie Mellon University, The Australian National
       University, and RSA Data Security, Inc. whose source code is used
       throughout Slirp.  Slirp would not be without them.

       Thanks to all the contributors who helped with bugs, suggestions, code,
       etc.  Read the file ChangeLog to see exactly who helped with what.

       A special thanks goes to Chris Metcalf and Juha Pirkola for their
       contributions (see ChangeLog).  They put in extra effort and Slirp
       wouldn't be the same without their help.  Thanks guys!

       Thanks to all the people who sent very kind and encouraging e-mail,
       it's sincerely appreciated.

       Thanks to all the admins and Head Honcho's at UCNet, the University of
       Canberra Computer Club ("blitzen") who gave me some real-estate on
       their machine ( to work with (thanks to Tony
       Delroy for giving me the account originally).  Hey! Why don't you check
       out their home page at

       Thanks to Brazil for coffee (and Sepultura! :)

       Thanks to the laws of physics, the building blocks of the universe.

       Slirp was written by Danny Gasparovski.

       Copyright (c) 1995 Danny Gasparovski.  All Rights Reserved.

       Slirp is free software; "free" as in you don't have to pay for it, and
       you are free to do whatever you want with it. I do not accept any
       donations, monetary or otherwise, for Slirp. Instead, I would ask you
       to pass this potential donation to your favorite charity. In fact, I
       encourage *everyone* who finds Slirp useful to make a small donation to
       their favorite charity (for example, GreenPeace). This is not a
       requirement, but a suggestion from someone who highly values the
       service they provide.

       Redistribution and use in source and binary forms, with or without
       modification, are permitted provided that the following conditions are

       1. Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.

       2. Redistributions in binary form must reproduce the above copyright
          notice, this list of conditions and the following disclaimer in the
          documentation and/or other materials provided with the distribution.

       3. All advertising materials mentioning features or use of this
          software must display the following acknowledgment: This product
          includes software developed by Danny Gasparovski.


       This basically means you can do anything you want with the software,
       except 1) call it your own, and 2) claim warranty on it.  There is no
       warranty for this software.  None.  Nada.  If you lose a million
       dollars while using Slirp, that's your loss not mine.  So, ***USE AT
       YOUR OWN RISK!***.

       If these conditions cannot be met due to legal restrictions (E.g. where
       it is against the law to give out Software without warranty), you must
       cease using the software and delete all copies you have.

       Slirp uses code that is copyrighted by the following

           Juha Pirkola.
           Gregory M. Christy.
           The Regents of the University of California.
           Carnegie Mellon University.
           The Australian National University.
           RSA Data Security, Inc.

       Please read the top of each source file for the details on the various

       Slirp was written by Danny Gasparovski.

       Manpage by George Ferguson,, based on Slirp
       1.0b documentation.

Version 1.0b                      9 Jan 1996                          SLIRP(1)