DIP+SLiRP+CSLIP - almost a mini-HOWTO

DIP+SLiRP+CSLIP - almost a mini-HOWTO

Post by Zenon Fortu » Wed, 18 Oct 1995 04:00:00

I have promissed somebody to prepare a sort of a mini-HOWTO, summarizing
the basic steps with the installation of the CSLIP via dip+slirp.
Here it is:

====  available at ftp.netcom.com:/pub/ze/zenon/linux/DipSlirpCSLIP ====

                        Linux Dip+SLiRP+CSLIP mini-HOWTO
                 Zenon Fortuna (ze...@netcom.com)

Version: 1.0                                            October 15th '95

        0.      Why "Dip+SLiRP+CSLIP mini-HOWTO" ?
        1.      History of changes
        2.      Short description
        3.      Steps of the configuration
        3.1             Installing the SLiRP
        3.2             Testing the SLiRP
        3.3             Configuring your Linux system
        3.4             Testing your Linux system
        3.5             Installing the DIP
        3.6             Testing the DIP
        4.      Normal operation
        4.1             Adding a DNS capability

0.      Why "Dip+SLiRP+CSLIP mini-HOWTO" ?

        This document is for users, who don't want to read the NET-2-HOWTO
        with all its details, nor want to read the Dip/SLiRP documents, but
        would like to install a SLIP-like connection to the Internet, using
        available shell-only account.

        The above mentioned documents should be considered as more exhaustive,
        but also more exhausting.

        The dip337n-uri and slirp-0.95h packages were used to test the described
        functionality. The tests were verified under the stable (tm) Linux
        kernel version 1.2.13, installed under the Slackware 2.2.0 OS

1.      History of changes

        October 15th '95        Version: 1.0
            The initial version of the document.

2.      Short description

        - I assume, that the Linux system is able to dial-up a remote
          server of the ISP, where you have a shell-account. On this server
          we will install the "slirp" utility.

        - we would like to prepare the "dip" utility on the Linux system,
          along with a specialized script, to dial-up the remote server,
          and start the "slirp" on this remote system.

        - the running "dip" will configure the serial line parameters and
          will inform the Linux system about the IP mapping, performed by
          the remote "slirp".

        - as a result the TCP/IP packets sent over the serial-line/modem
          connection will be handled by the remote server as though being
          sent locally by this server.

        Miracle happens: we will get a TCP/IP connection of the Linux system
        to the Internet resources.

3.      Steps of the configuration
3.1             Installing the SLiRP

        - get the SLiRP distribution file, e.g. the slirp-0.95h.tar.gz,
          and compile the "slirp" program on your remote host (the system
          to which you will be dialing up). The SLiRP's docs/README.compiling
          explains the details.

          Instead, you can get the already precompiled binary from
          as it is explained in the Alt.dcom.slip-emulators FAQ, included
          with the docs.

        - move the "slirp" program to a better location, e.g. "./bin/slirp"
          or "./slirp" (i.e. at the $HOME directory)

        - at your $HOME directory create the ".slirprc" file.
          To keep it simple let's use only a few commands:
                #### .slirprc file ####
                add ptyexec /usr/bin/tcsh -l:
                baudrate 38400
                #### end

          The "compress" command ensures to use the CSLIP protocol.
          The "add ptyexec" command was used instead of the "shell"
          command (see the SLiRP's docs/CONFIG for a list of commands),
          because it is better to use the "tcsh -l" (for ".login" entry)
          and the "shell" command does not accept flags (I believe).
          You should use the remote system specific address of the "tcsh"
          program (or use another shell, if you prefer).

          The "baudrate" should be used with the speed proper for your modem

3.2             Testing the SLiRP

        Login to your remote site and type

                % bin/slirp     (or "./slirp", depending on the location)

        You should get a list of messages, with the following line at the end:
                [talking CSLIP, MTU 1500, MRU 1500, 38400 baud]

        To exit the "slirp" type slowly (>1 sec gap) five 0's (zeroes).

3.3             Configuring your Linux system

        Essentially, what you need to do is to prepare a kernel able
        to run network and the CSLIP. Then you should configure the network.
        Start the "make config" in the "src/linux" directory and set "y"
        to the following options:

                Networking support (CONFIG_NET) [y]
                TCP/IP networking (CONFIG_INET) [y]
                Assume subnets are local (CONFIG_INET_SNARL) [y]
                Network device support? (CONFIG_NETDEVICES) [y]
                Dummy net driver support (CONFIG_DUMMY) [y]
                SLIP (serial line) support (CONFIG_SLIP) [y]
                CSLIP compressed headers (CONFIG_SLIP_COMPRESSED) [y]
                PPP (point-to-point) support (CONFIG_PPP) [y]

        Now, I use the 3c509 Ethernet card, so my additional options are:

                3COM cards (CONFIG_NET_VENDOR_3COM) [y]
                3c509/3c579 support (CONFIG_EL3) [y]

        For the NFS installation you can add also:

                NFS filesystem support (CONFIG_NFS_FS) [y]

        Now, after successful "make config", complete the kernel generation
        with "make dep" and "make zImage".
        Then move the arch/i386/boot/zImage to your kernel location and
        run "lilo".

        To configure the network, first decide which IP address to use.
        In a lack of your special address, take, allowed for
        local networks by RFC1597.
        Of course, you should rather read the NET-2-HOWTO for correct
        information, but you can try to do the following:

        A. Give your system a network name, e.g. "hostname.linux.org",
           where all the three names could be chosen to your tastes.
           Place the above string (without the quotes) into the
           "/etc/HOSTNAME" file.

        B. Edit your "rc.inet1" from the /etc/rc.d directory (save the
           original somewhere :) and set
           Then, if you have a real Ethernet card on your system,
           uncomment the line
 /sbin/ifconfig eth0 ${IPADDR} netmask ${NETMASK} broadcast ${BROADCAST}
           and then the following line
 /sbin/route add -net ${NETWORK} netmask ${NETMASK}

        C. Edit your "/etc/hosts" file, adding
           The above "hostname" is the first name from the string chosen
           in the step A above.

        D. If you run local Ethernet edit also your "/etc/networks" file,
           adding a line:

        E. Place your domain name "linux.org" (compare the step A) into the
           "/etc/resolv.conf" file, as a line:
                domain  linux.org

        Now, reboot your system.

3.4             Testing your Linux system

        First of all watch the booting messages, or look into the
        "/usr/adm/messages" file, if your syslogd(8) is running.

        You should see messages like
                 IP Protocols: ICMP, UDP, TCP
                 PPP: version ...
                 TCP compression ...
                 PPP line discipline registered.
                 SLIP: version ...
                 CSLIP: code copyright ...
        If you have the Ethernet interface it should be recognized as well, e.g:
                 eth0: 3c509 at 0x280 ...

        Your network should be up and you could test it with a few commands:

        A. Run "ifconfig", without arguments.
           You should see the "lo" (loopback) interface activated, with its
           If you run a real Ethernet as well, you will see the information
           about the "eth0" interface as well, and you should notice the
           familiar addresses, like "inet addr:", etc.

        B. Run "route", without arguments.
           You should see a line about the "loopback" and maybe another one
           about the "yournet".

        OK, your Linux system is ready to work with the CSLIP as well.

3.5             Installing the DIP

        - it may happen, that your Linux system has already the "dip"
          binary. It would be nice to have the 3.3.7n version of it
          (it has the updated documentation).

        - otherwise, get the DIP distribution file, e.g. the dip337n-uri.tar.gz,
          and compile the "dip" program on your local Linux host.
          You do it by typing "make" in the dip-3.3.7n directory.

        - move the "dip" program to a better location which is in your PATH,
          e.g. /usr/local/bin/dip or $HOME/bin/dip.

        - at convenient location, e.g. your $HOME directory, create the dip's
          script file, for example "slirp.dip".

        The dip's script file is usually long and complex. There are some
        examples in the dip's "samples" directory (maybe installed as
        Anyway, I submit my "slirp.dip" file as an example.

#### slirp.dip file ####
# slirp.dip     Dialup IP script for use with SLiRP and netcom

  # Set netmask on sl0

  # Set the desired serial port and speed.
  # You may need to change ttyS2 to your modem device...
  # I am running the "mgetty" on this port as well, so I want to use
  # the "ttyS2" instead of the "cua2" device
  port ttyS2
  speed 38400

  # Reset the modem and terminal line.
  # This seems to cause trouble for some people!

  # Prepare for dialing.
  # Note your modem may need a different init string.
  # Mine is a WorldBlazer ...
  send AT S0=0 S11=70 S50=254 S58=2 Q0 V1 E1 X4\r
  wait OK 2
  if $errlvl != 0 goto modem_trouble

  # dial your POP#
  # The number below is for my local POP, your mileage may vary
  send ATDT 274 2900\r
  wait CONNECT 50
  if $errlvl != 0 goto dial_trouble

  # We are connected.  Login to the system.
  sleep 2
  send \n
  wait ogin: 20
  if $errlvl != 0 goto login_trouble
  print got the login prompt, OK
  # replace 'zenon' below with your remote login username
  sleep 2
  send \n
# I don't know why I had to add the extra "\n" before sending my login name,
# but otherwise it did not work.
  sleep 2
  send zenon\n
  print sent 'zenon', waiting for 'password' ...

  wait ord: 30
  if $errlvl != 0 goto password_trouble
  # replace 'blablabla' below with your remote password
  send blablabla\r

  # We are now logged in, probably.
  # Substitute YOUR shell prompt below (mine is zenon@netcomNN n% )
  wait zenon 15
  if $errlvl != 0 goto prompt_error

  # SLiRP makes the IP of the remote machine
  get $remote

  # Make sure 'slirp' is found on netcom and is executable
  # Here I assume, that the "slirp" has been installed at the remote $HOME/bin
  # directory
  send exec bin/slirp\n

  # Set up the CSLIP operating parameters.
  get $mtu 1500
  # Ensure "route add -net default $remote" will be done
  # With the dip-3.3.7n it is simple, just say "default"

  # Say hello and fire up!
  print CONNECTED local: $locip ---> remote: $rmtip
  mode CSLIP
  goto exit

  print TIME-OUT waiting for SLIPlogin to fire up...
  goto error

  print Trouble waiting for the Login: prompt...
  goto error

  print Trouble waiting for the Password: prompt...
  goto error

  print Trouble occurred with the modem...
  goto error

  print Trouble occurred while dialing...
  print CONNECT FAILED to $remote

#### end

        COMMENT: There are some entries in the above script which should be
        adapted to your needs:
        - the port name (I use the ttyS2)
        - the port speed (I use 38400)
        - the modem initialization string (I have a WorldBlazer)
        - the POP's phone number (I hope yours is different :)
        - your remote login name
        - your password
        - your prompt (to confirm the successful login)
        - the location of your "slirp" (mine is in $HOME/bin)

3.6             Testing the DIP

        You can start the "dip" in a verbose mode with
                % dip -v slirp.dip

        The messages printed by the "dip" may suggest some modifications
        to the above "slirp.dip" script.

        If everything goes well, you should see the following message
        at the end:
                CONNECTED local: ---> remote:
        ... and the "dip" switches to a "daemon"-like execution, returning
        your prompt.
        BTW, to stop the "dip" now, type simple "dip -k", and all the action
        of the "dip" will be canceled, and the modem connection will be

4.      Normal operation

        A. Start your dip+slirp connection with typing

                % dip slirp.dip

        B. After successful connection and the "CONNECTED ..." message you have
           the CSLIP connection to the Internet via your remote ISP.

           Try first to connect to your remote server with the "telnet":

                % telnet

           Thanks to the ".slirprc" configuration file, this connection should
           activate the "tcsh -l" and you should get the remote login.
           Typing "ps" you may see the following output:
                 6019 s0 S     0:13 slirp
                 6075 sb IW    0:00 -/usr/bin/tcsh (tcsh)
                16721 t6 R     0:00 ps

        C. You can exit from the above telnet connection, or try from another
           virtual terminal (or X shell-window) the ftp connection:
                % ftp

           After the successful (?) anonymous connection you may discover, that
           you are ... at the "sunsite.unc.edu", Linux-archive site.

           If you got so far, you may start admiring the power of the dip+slirp
           connection: you are on the NET.

           Disconnect from the "sunsite" ASAP, coming back to your "hostname"
           Now, the question comes:

                Can we do simply "ftp sunsite.unc.edu" ?

           Not before activating the DNS (Domain Name Server).

        You may want to quit from the CSLIP at this moment:
        From your local prompt type

                % dip -k

4.1             Adding a DNS capability

        Apparently, your remote ISP has the DNS service (otherwise you would
        not be able to use the Internet connections in a reasonable way).
        Connect to the remote server once again, with the "dip slirp.dip"
        and "telnet", and read the file "/etc/resolv.conf".

        You should see a few lines like
                nameserver  <IP-address>
        where the <IP-address> will have a specific value.

        Copy at least one of those lines into your "/etc/resolv.conf" file
        on your local Linux system.

        Now, come back to this local system (without breaking the
        dip+slirp connection), and test if the DNS service works.
                % dnsquery sunsite.unc.edu

        If the output will inform about the sunsite's IP address, your
        DNS service is functioning.

        Now, you can use utilities like "lynx", "mosaic" and "netscape"
        directly from your Linux box.


        This simplified document was written as a summary of the basic
        dip+slirp installation, rather than as a tutorial.
        The intention was to help the potential CSLIP users with starting

        Therefore, if you see any obvious bugs in the above text, please
        let me know.
        After a while I would like to place this text as a mini-HOWTO
        document. For the time being it is available at my ftp directory at


        I want to thank the authors of the "dip" and "slirp" utilities
        for a wonderful utilities. I am impressed and grateful.

                Zenon Fortuna   (ze...@netcom.com)