The SGI implementation of SLIP and PPP provides both RFC 1144 data compression and its own proprietary data compression, which compresses header framing, checksum, and TCP/IP information to three bytes. SLIP is part of the eoe software subsystem, and is installed via the eoe.sw.slip package. Use the versions command to see if you have SLIP installed on your system.

PPP offers substantially the same features as SLIP, but it is more flexible and robust. For this reason, PPP is usually preferred over SLIP (however, you must use SLIP if the system to which you are connecting supports SLIP and not PPP.) In addition to its use in dial-up connections over telephone lines and modems, PPP is also used in ISDN connections; however, this guide assumes that you are using PPP over a conventional serial line connection.

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Note: If you are connecting a remote host with ISDN, you might prefer to use the configuration instructions in the ISDN User's Guide instead of using the procedures in this chapter (also see the isdn(1M) reference page). You should use the information in this chapter for an understanding of PPP operation and maintenance, however.

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PPP is part of the eoe software subsystem, and is installed via the eoe.sw.ppp package. Use the versions command to check to see if you have PPP installed on your system.

Usually, a SLIP or PPP connection serves one of the following purposes:

A given SLIP or PPP link can be set up so that one system always initiates the connection (by dialing the other system), or so that either system can initiate the connection. In the case of a client-server connection, the client usually initiates the connection by dialing the server. However, the connection can be bi-directional as well. In the case of a connection between two networks, you can either choose one system to initiate connection, or allow either system to initiate the connection as needed.

Setting up an individual system as a SLIP or PPP client requires the following steps:

Setting up a system as a SLIP or PPP server requires the following steps:

Connecting two networks using SLIP or PPP requires the following steps:

Make sure you have the appropriate software installed: to use SLIP, you must have the eoe.sw.slip and eoe.sw.uucp subsystems installed. To use PPP, you must have the eoe.sw.ppp and eoe.sw.uucp subsystems installed. You should also install the corresponding reference pages (eoe.man subsystems). To verify whether these packages are installed, use the versions command. For example, to check whether you have PPP installed, use the following command:

% versions eoe.\*.{ppp,uucp}

If PPP and UUCP are installed, versions should produce output something like this:

I = Installed, R = Removed
 
   Name                 Date      Description
 
I  eoe                 09/24/96 IRIX Execution Environment, 6.3
I  eoe.man             09/24/96 IRIX Execution Environment Man Pages
I  eoe.man.ppp         09/24/96 Point-to-Point Protocol Man Pages
I  eoe.man.uucp        09/24/96 UNIX-to-UNIX Copy Man Pages
I  eoe.sw              09/24/96 IRIX Execution Environment Software
I  eoe.sw.ppp          09/24/96 Point-to-Point Protocol Software
I  eoe.sw.uucp         09/24/96 UUCP Utilities

For instructions on installing software, see IRIX Admin: Software Installation and Licensing . After installing the SLIP or PPP software, you must reboot your system to reconfigure the kernel.

A modem capable of at least 9600 bits per second (bps, sometimes referred to as “baud”) is required for use with SLIP or PPP. However, at this speed, your link will be quite slow. A good modem choice is any modem that supports the V.32bis or V.34 standards and a speed of 14,400 bps or greater. A half-duplex modem can be used but is less desirable for interactive tasks.

SGI does not manufacture these modems and cannot be responsible for changes to the modems. SGI cannot guarantee modem compatibility or the quality of the telephone line used with SLIP or PPP, but a separate data-grade telephone line is highly recommended.

If you are using a high-speed modem, be sure it supports hardware flow control using RTS/CTS. With such a modem, use the ttyf* device name.

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Note: SGI supports DSI, Inte, Telebit, ZyXEL U.S. Robotics, Hayes, and most Hayes compatible modems. While many others work, configuring them may be much more complicated and their operation is not guaranteed.

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For instructions on installing modems and configuring modems, see “Installing a Modem” in IRIX Admin: Peripheral Devices .

Each SLIP or PPP client needs an IP address and hostname for its SLIP or PPP interface. If it is also connected to one or more local area networks, it will also require an address and hostname for each of its other network interfaces. If you have had an address and hostname assigned to you by your system administrator or network service provider, you can use this information to configure your system.

Some network service providers use dynamic addressing, where each client is given a dynamically allocated IP address when it connects. IRIX PPP has support for dynamic addressing, but IRIX SLIP does not support dynamic addressing. See “Using Dynamic Address Allocation With PPP” for more information about dynamic addressing.

If you are setting up a SLIP or PPP server on your LAN, or are connecting two networks over a serial link, you should see “SLIP and PPP Routing and Address Allocation” for planning information.

Configuring SLIP or PPP for dial-out requires approximately the same steps:

PPP requires one additional step, setting up the /etc/ppp.conf file.

These sections explain how to configure SLIP and PPP for dial-out:

lynch Any ACUSLIP 38400 5551212 "" \r\c ogin:--ogin: slip-wenders \
asswd: hopper SLIP

type device null speed 212 x dialer

ACUSLIP ttyf2 null 38400 212 x t25slip

t2:23:off:/etc/getty ttyf2 co_38400         # port 2

t2:23:respawn:/usr/lib/uucp/uugetty -Nt 60 -it25in,conn ttyf2 dx_38400 

/etc/telinit q

salad     out remotehost=dial-in.salad.com 
          localhost=caesar.salad.com
          quiet add_route

salad Any ACUSLIP 38400 5551212 "" \r\c ogin:--ogin: slip-tuna \
asswd: celery SLIP

ACUSLIP ttyf2 null 38400 212 x t25slip

t2:23:off:/etc/getty ttyf2 co_38400         # port 2

% /usr/etc/slip -o -p comp -r salad 

salad     out remotehost=dial-in.salad.com 
          localhost=caesar.salad.com
          quiet add_route

salad Any ACUSLIP 38400 555-1212 "" @\r\c ogin--ogin: ppp-caesar \
ssword: mypasswd PPP

ACUSLIP ttyf2 null 38400 212 x t25slip

t2:23:off:/etc/uucp/uugetty ttyd2 dx_38400  # ppp modem

ppp -r salad

To configure any system for dial-in, you must have at least one port set up for dial-in use (or combination dial-in/dial-out use). Each system that can dial in requires an entry in the /etc/passwd file. In addition, SLIP connections may require an entry in the /usr/etc/remoteslip file, and PPP connections may require an entry in /etc/ppp.conf.

These sections describe how to configure SLIP and PPP for dial-in:

Configuring /etc/passwd for Dial-In With SLIP

SLIP requires an entry in /etc/passwd in order to log in. The user ID and group ID must both be zero (0). Instead of the shell specified at the end of a normal entry in /etc/passwd, SLIP uses the file /usr/etc/remoteslip. To allow tuna.salad.com to log in as “slip-tuna,” dial-in.salad.com should have this line in /etc/passwd:

slip-tuna:3RsB768WRAN2.:0:0:slip for tuna:/:/usr/etc/remoteslip

An entry like this one is necessary for each station that calls in by using SLIP. For maximum system security, the home directory for SLIP accounts should only be writable by the superuser. Using open directories such as /tmp opens your system up to a variety of threats.

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Note: The encrypted password in the example does not represent a real password. You must use the passwd command to set the password for the SLIP login. See the passwd(1) reference page for information on using passwd.

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slip-nodename )
    exec /usr/etc/slip options
    ;;

# Edit the case statement as required. 
case $USER in
       slip-tuna)
              exec /usr/etc/slip -p comp -i -r tuna 
              ;;
       *)
              exec /usr/etc/slip -i -r $USER
              ;;
esac

Configuring /etc/passwd for Dial-In With PPP

Like SLIP, PPP requires an entry in /etc/passwd in order to log in. The user ID and group ID must both be zero (0). Instead of the shell specified at the end of a normal entry in /etc/passwd, PPP uses the command /usr/etc/ppp. To allow the system caesar.salad.com to log in as “ppp-caesar,” dial-in.salad.com should have this line in /etc/passwd:

ppp-caesar:3RsB768WRAN2.:0:0:PPP for caesar:/:/usr/etc/ppp

An entry like this one is necessary for each station that calls in by using PPP. For maximum system security, the home directory for PPP accounts should be writable only by the superuser. Using open directories such as /tmp exposes your system to a variety of threats.

---

Note: The encrypted password in the example does not represent a real password. You must use passwd to set the password for the PPP login. See the passwd(1) reference page for information on using passwd.

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If the default parameters are acceptable, you don't even need an entry in /etc/ppp.conf for a client. You may want to add a minimal entry, such as this:

ppp-caesar in remotehost=caesar.salad.com

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Note: You should never use the add-route keyword by itself on a server system.

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There are three basic ways to deal with routing over a SLIP or PPP link, depending on the circumstances.

In all cases, the server should run the routing daemon, routed, unless you have a very small network and use static routing. For more information, see the routed(1M) and route(1M) reference pages. You can turn routed on using the chkconfig command:

# chkconfig routed on

Standalone clients should not run routed.

route add net default server-address 1

arp -s client-hostname server--ethernet-address pub

% arp dial-in.salad.com
dial-in.salad.com (192.70.79.7) at 8:0:69:9:4f:ef

#!/bin/sh
#
# starting up local networking stuff
#
 
IS_ON=/etc/chkconfig
CONF=/etc/config
SERV_ADDR=8:0:69:9:4f:ef 
 
if $IS_ON verbose ; then
        ECHO=echo
        VERBOSE=-v
else            # For a quiet startup and shutdown
        ECHO=:
        VERBOSE=
fi
 
case "$1" in
  'start')
      # setup proxy ARP for the dialin hosts
      # if this host has more than one interface,
      # you will need to hard-code the Ethernet MAC address
      # instead of letting it be determined at run time.
      # note that 4DDN (among others) may change the MAC address from default!
      # and some AppleTalk packages change the output of `netstat -ian`!
      arp -s client1 $SERV_ADDR pub
      arp -s client2 $SERV_ADDR pub
      arp -s client3 $SERV_ADDR pub
      ;;
  'stop')
      # be nice and delete the ARP entries
      arp -d client1
      arp -d client2
      arp -d client3
      ;;
  *)
        echo "usage: $0 {start|stop}"
        ;;
esac
exit 0
#

ln -s /etc/init.d/network.local /etc/rc2.d/S31netlocal
ln -s /etc/init.d/network.local /etc/rc0.d/K39netlocal

% chkconfig network off

A simple SLIP or PPP link, in which one station must always initiate the connection, can be changed to allow either station to initiate the connection.

The first step is to establish a link in one direction. Once that link is working correctly, set up the link in the reverse direction. You should be able to use the same ppp.conf entry for both dial-in and dial-out.

To have a SLIP or PPP connection between networks start automatically, create a local network script, /etc/init.d/network.local, for that purpose. The script resides on the station where you want to initiate the link and should be linked to appropriate files in the /etc/rc2.d and /etc/rc0.d directories. For example, to automatically start the demand-dialed PPP link described in “Sample PPP Configuration for Dial-Out”, you would create a local network script on caesar.salad.com. The script should start PPP when called with the argument start, and terminate it when called with the argument stop.

#!/bin/sh
# ppp boot startup script
case $1 in
   start)
       /etc/killall ppp
       if /etc/chkconfig ppp && test -x /usr/etc/ppp -a -s /etc/ppp.conf
       then
           /usr/etc/ppp -r salad &
       fi
       ;;
   stop)
       /etc/killall -TERM ppp
       ;;
   *)
       echo “usage: $0 {start|stop}”
       ;;
esac

This script should be linked to the appropriate filenames in the /etc/rc2.d and /etc/rc0.d directories:

ln -s /etc/init.d/network.local /etc/rc2.d/S31netlocal
ln -s /etc/init.d/network.local /etc/rc0.d/K39netlocal

If you have a SLIP or PPP link that is used irregularly but frequently, it is likely to be economical for you to make that link a demand-dialing link. With demand dialing, the system makes the telephone connection as needed, when there is network traffic to be transmitted, and it drops the connection when there is no traffic. By default, much of the non-essential network traffic does not cause a link to be established. For example, the traffic generated by the time daemon (timed) would not cause a call to be placed, but a request for file transfer would cause the connection to be made.

To use demand-dialing, add the -q option to your slip command on the system that initiates the connection. Demand-dialing mode is also known as “quiet” mode. For complete information on this and other options, see the slip(1M) reference page.

PPP can be configured to use demand dialing by adding the “quiet” keyword to the ppp.conf file.

When using demand-dialing, it makes sense to start SLIP or PPP automatically at boot time, as described in “Starting SLIP or PPP at Boot Time”.

Note that the link is initiated only when there is traffic on the initiating end of the link.

You can run NFS over a SLIP or PPP link. NFS will be very slow because of the amount of information transferred in NFS transactions. You may be able to improve performance with these measures:

File transfer over a serial link may be slow if other demanding utilities share the link. For faster file transfer, try using uucp. Using uucp is effective if you do not want to share the line with other utilities.

If your SLIP or PPP link seems to be connecting, but you can't reach systems on the remote network, you might have a routing problem. Try to reach the remote system with ping:

% ping -c 10 dial-in.salad.com

If the connection is working, you should see output something like this:

PING dial-in.salad.com (128.70.79.52): 56 data bytes
64 bytes from 128.70.79.52: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 128.70.79.52: icmp_seq=1 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=2 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=3 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=4 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=5 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=6 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=7 ttl=255 time=1 ms
64 bytes from 128.70.79.52: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 128.70.79.52: icmp_seq=9 ttl=255 time=1 ms
 
 
----dial-in.salad.com PING Statistics----
10 packets transmitted, 10 packets received, 0% packet loss

If the connection is not working, you should see output like this:

PING dial-in.salad.com (128.70.79.52): 56 data bytes
 
 
----dial-in.salad.com PING Statistics----
10 packets transmitted, 0 packets received, 100% packet loss

If you can contact the remote host, but not other systems on the network, you probably have a routing problem. Check that your routing is set up as described in “SLIP and PPP Routing and Address Allocation”.

If you aren't getting any connection at all, test the line with another utility. If you are familiar with uucp, you may want to establish a uucp link between the stations as a means of testing the connection. Most users will find that cu is an easier way to debug the link.

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Note: cu requires a direct entry in the /etc/uucp/Devices file. Refer to “UUCP Devices File” in Chapter 8, for more details.

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When debugging a SLIP connection, check each station separately. First check the port and modem on the local station by using a cu command like this:

cu -d -s speed -l port 

For example, to test the port and modem installed on the station tuna.salad.com, you would use this cu command:

cu -d -s 38400 -l ttyf2 

(It may be necessary to turn off the (uu)getty first by changing respawn to off on the line for the port in the file /etc/inittab.)

The modem should respond. Many modems respond by printing AT. If the modem does not respond as expected, review the SLIP configuration procedure for the local station and review the modem configuration and documentation. If the modem does respond as expected, disconnect from cu by typing a tilde followed by a dot:

~. 

Connect the stations you want to link as you would for the SLIP link. On the local station, use cu to call the remote station through the port and connection you have already verified with cu.

Check the connection to the remote station with a cu command like this:

cu -d -sspeed telno 

For example, to test the connection between tuna and dial-in.salad.com, you would call dial-in from tuna with this cu command:

cu -d -s38400 5552002 

You should see the local station tell the modem to call the remote station. Eventually, you should see the login prompt. Type the send strings from the /etc/uucp/Systems file in response to the expect strings.