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5.3.4 Using dip


    dip can simplify the process of connecting to a SLIP server, logging in, and configuring the SLIP device. Unless you have a leased line running to your SLIP server, dip is the way to go.

  To use dip, you'll need to write a ``chat script'' which contains a list of commands used to communicate with the SLIP server at login time. These commands can automatically send your username/password to the server, as well as get information on your IP address from the server.

Here is an example dip chat script, for use with a dynamic IP address server. For static servers, you will need to set the variables $local and $remote to the values of your local IP address and server IP address, respectively, at the top of the script. See the dip man page for details.

  # Set Maximum Transfer Unit. This is the maximum size of packets 
  # transmitted on the SLIP device. Many SLIP servers use either 1500 or
  # 1006; check with your network admins when in doubt. 
  get $mtu 1500

  # Make the SLIP route the default route on your system.

  # Set the desired serial port and speed.
  port cua03
  speed 38400

  # Reset the modem and terminal line. If this causes trouble for you,
  # comment it out.

  # Prepare for dialing. Replace the following with your 
  # modem initialization string.
  send ATT&C1&D2\\ N3&Q5%M3%C1N1W1L1S48=7\r
  wait OK 2
  if $errlvl != 0 goto error
  # Dial the SLIP server
  dial 2546000
  if $errlvl != 0 goto error
  wait CONNECT 60
  if $errlvl != 0 goto error

  # We are connected.  Login to the system.
  sleep 3
  send \r\n\r\n
  # Wait for the login prompt
  wait login: 10
  if $errlvl != 0 goto error

  # Send your username
  send USERNAME\n

  # Wait for password prompt
  wait ord: 5
  if $errlvl != 0 goto error

  # Send password.
  send PASSWORD\n

  # Wait for SLIP server ready prompt
  wait annex: 30
  if $errlvl != 0 goto error

  # Send commands to SLIP server to initate connection. 
  send slip\n
  wait Annex 30

  # Get the remote IP address from the SLIP server. The `get...remote' 
  # command reads text in the form, and assigns it
  # to the variable given as the second argument (here, $remote).
  get $remote remote
  if $errlvl != 0 goto error
  wait Your 30

  # Get local IP address from SLIP server, assign to variable $local.
  get $local remote
  if $errlvl != 0 goto error

  # Fire up the SLIP connection
  print CONNECTED to $remote at $rmtip
  print GATEWAY address $rmtip
  print LOCAL address $local
  mode SLIP
  goto exit
  print SLIP to $remote failed.


dip automatically executes ifconfig and route commands based on the values of the variables $local and $remote. Here, those variables are assigned using the get...remote command, which obtains text from the SLIP server and assigns it to the named variable.

If the ifconfig and route commands that dip runs for you don't work, you can either run the correct commands in a shell script after executing dip, or modify the source for dip itself. Running dip with the -v option will print debugging information while the connection is being set up, which should help you to determine where things might be going awry.

Now, in order to run dip and open the SLIP connection, you can use a command such as:

/etc/dip/dip -v /etc/dip/mychat 2>&1

Where the various dip files, and the chat script (mychat.dip), are stored in /etc/dip.    

The above discussion should be enough to get you well on your way to talking to the network, either via Ethernet or SLIP. Again, we strongly suggest looking into a book on TCP/IP network configuration, especially if your network has any special routing considerations, other than those mentioned here.            

next up previous contents index
Next: 5.4 Networking with UUCP Up: 5.3 Networking with TCP/IP Previous: Dynamic IP address

Matt Welsh