Configuring SLIP for Dial-In

Configuring SLIP for Dial-In

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.

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.

/usr/etc/remoteslip

In the /etc/passwd entry for slip-tuna, the login shell is specified as the file /usr/etc/remoteslip. This file is used to invoke SLIP on a remote station. In /usr/etc/remoteslip, the slip command can specify the remote station's name and any other options appropriate to that connection.

/usr/etc/remoteslip is a Bourne shell script. You can add to the case statement as you would to any Bourne shell script case statement. The sh(1) reference page contains detailed information about shell script programming. Each SLIP connection should have an entry in the following format:

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

nodename is the name of the remote station. Options for slip are detailed in the slip(1M) reference page.

The /usr/etc/remoteslip file might contain this entry on the station dial-in.salad.com:

# 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

The connection between dial-in.salad.com and tuna uses the Silicon Graphics proprietary header prediction and compression for faster data transfer because the -p comp option is specified. To use RFC 1144 compression, use -p cslip instead. The option tells SLIP that the session is input from another station. The slip option, -r tuna, specifies the remote station's name. Note that this example also supplies a default case. If all of your SLIP clients use the same parameters, you can just modify the default case, instead of adding entries for each client.