From: "Paul A. Fischer, Sr UNIX Sys Consultant" <paul@openage.com>
Subject: RE: Experiences with Slip and ODT 1.1
Resent-From: mmdf@xenitec.on.ca
Submit-To: scogen@xenitec.on.ca
Organization: [resent by] The SCOGEN gateway and Propagation Society
Date: Wed, 18 Nov 1992 19:58:51 GMT
Precedence: bulk

>I am attempting slip connections with a 486-50 running SCO ODT 1.1.
>I seem to be only able to get one slip connection at a time.  sl0 seems
>to go without a hitch, but then it skips to sl2 with a lot of errors.  If
>someone email me their experiences, hints, suggestions, etc for slip
>under ODT 1.1 I would appreciate it.


What is SLIP? How many SLIP connections are supported?

KEYWORDS: slip connections supported tcp/ip subnet ipcnt configure kernel dialup

RELEASE:  SCO TCP/IP Generic 

PROBLEM:  What is SLIP? How many SLIP connections are supported?

SOLUTION: SLIP stands for Serial Line IP.  SLIP provides a way of connecting
          two systems together to run TCP/IP without requiring a network card,
          such as a wdn8003 or 3COM card.  Instead of the network card and 
          ethernet cable, you will use the serial port and a standard serial
          (RS-232) cable.  I have used SLIP to speeds of 9600 baud.  Although 
          I have not used them, in the code there is support for 19.2 kbaud, 
          as well as 38.4.  These speeds will NOT work if your serial port 
          does not support these speeds.
  
          The default TCP/IP parameters are configured to support eight open 
          file descriptors.  Each ethernet card will require one file 
          descriptor, and each SLIP line requires two file descriptors.  So 
          this means, at most, 4 SLIP lines can be configured at one time 
          using default configurations.

          It is possible to configure more than that by increasing kernel
          parameters. You will need to increase four kernel parameters.  
          They are:

   IPCNT        --      /etc/conf/pack.d/ip/space.c
        number of open file descriptors in IP driver.  Default value of 8.
   IPPROVCNT    --      /etc/conf/pack.d/ip/space.c 
        Should be 2x IPCNT.  Default value of 16.
   NSLPHYS      --      /etc/conc/pack.d/slip/space.c o
        number of simultaneous SLIP connections.  Default value of 8.
   NSLUNIT      --      /etc/conf/pack.d/slip/space.c
        number of open file descriptors for SLIP.  Should be 2x NSLPYSH.
        Default value of 16.

          Since each SLIP line requires 2 file descriptors, and the default
          limit of file descriptors is 8 (IPCNT), the maximum number of SLIP 
          lines is four.  By increasing IPCNT to 2x the number of SLIPS, and 
          IPPROVCNT to be 2x IPCNT, you will be allowed to have up up NSLPYSH 
          SLIPS.
  
          As an example, if I wanted to configure 12 SLIP lines, I would then
          configure these values to:

           IPCNT        26
           IPPROVCNT    52
           NSLPHYS      12
           NSLUNIT      24

          You may have to increase STREAMS parameters to be able to get this
          number of SLIPS configured at one time.  Once you have changed these
          values you will need to relink and reboot.

          - Is it possible to configure dialup SLIP?
          Dialup SLIP allows you to configure SLIP across standard telephone
          lines via a modem.  Configuring SLIP is described in the Release
          and Installation Notes for TCP/IP.  The section is also included
          here:

          Supporting Dialup SLIP        Lines

          SCO TCP/IP does not directly support dialup SLIP lines.  However, 
          it is possible to implement a workaround as the following example
          shows.

          If machine A wishes to connect to machine B via a dialup SLIP 
          connection, machine B must already have executed a slattach command.
          The following example for machine B can be executed at the super 
          user's shell prompt or via the /etc/tcp script.  Refer to the 
          slattach manual page for more information.

          (stty 1200; echo "ATE0\r" > /dev/tty1a) < /dev/tty1a
          slattach /dev/tty1a slipb slipa 1200

          The first command puts the modem in non-echo mode.  This is
          important if the SLIP connection is to be used correctly.  Note 
          that the device special file chosen must be a non-modem control 
          one (that is, /dev/tty1a instead of /dev/tty1A for COM1). Be sure 
          that the modem is attached to the appropriate port specified in the 
          slattach command.

          Machine A must dial machine B before performing a slattach. The 
          following example for machine A can be entered at a root shell
          prompt or in a shell script:

          (stty 1200; echo "ATE0\r" > /dev/tty1a) < /dev/tty1a
          /usr/lib/uucp/dialHA12 /dev/tty1a 5551212 1200

          if [ $? ]
          then
          slattach /dev/tty1a slipa slipb 1200
          else
          echo "Error dialing\n"
          fi

          The first command puts the modem in non-echo mode.  This is
          important if the SLIP connection is to be used correctly.  In 
          the above script, /usr/lib/uucp/dialHA12 returns 0 (TRUE) if 
          dialing is successful.  Note that the dialer program (dialHA12) 
          is part of the operating system's UUCP package.  If it is not 
          installed, you can use the custom utility to do so.  Refer to 
          your operating system documentation for more details.

          Also note that each machine's slattach command must have matching,
          supported baud rates.  It is important to remember that only the 
          super user can attach or detach a network interface.  The tty lines 
          used for the SLIP connection must be dedicated only to this task.

          Be sure to start /etc/routed after and not before /etc/slattach.  If
          routed is started before slattach, the following message appears on
          the console at roughly one-minute intervals:

          routed: packed from unknown router <net address>


          - I have two SLIP lines coming out of one system.  Host A will talk 
          with Host B, and Host C will talk with Host B, but Host A will not 
          be able to talk with Host C.  What am I doing wrong?

          The configuration looks like this:

          Host A ------ Host B ------ Host C

          The most common error when configuring this type of network is not
          realizing each SLIP is considered a subnet.  So in order to handle
          this type of setup, you will have to configure your network for 
          subnetting.  Once you have changed your system to handle subnetting,
          reboot the three systems so the route tables will be handled properly.
   
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Paul A. Fischer           | Open Age Inc.  | paul@openage.com
Sr. UNIX Sys. Consultant  | (301) 948-6422 | (301) 948-9644 Fax