Configuring the Serial Line Internet Protocol (SLIP)

Advanced SLIP configuration

Advanced configuration consists of using the Advanced Options or directly editing the slattach entry in /etc/tcp to configure:

Configuring proxy address resolution

To configure proxy address resolution, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set Proxy ARP to On or Off.
Edit the slattach line in /etc/tcp or the incoming login script to contain the +a flag.

Configuring TCP/IP header compression

To configure TCP/IP header compression, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set TCP/IP header compression and Auto detect header compression to On or Off.
Edit the slattach line in /etc/tcp or the incoming login script to contain the c or e flags.
With the flag +c set, the compression mode is turned on. The interface sends compressed packets.
With the flag +e set, the interface attempts to detect compressed packets and, if it detects such packets, to respond with compressed packets.
The +c flag overrides any setting of the e flag.

Configuring flow control

To configure hardware flow control, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set Hardware flow control On or Off.
Edit the slattach line in /etc/tcp or the incoming login script to contain the f flag.
Setting the flag to +f enables hardware flow control. -f disables flow control.

Configuring ICMP packet suppression

To configure ICMP packet suppression, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set ICMP packet suppression On or Off.
Edit the slattach line in /etc/tcp or the incoming login script to contain the i flag.
Setting the flag to +i suppresses ICMP packets. -i allows them through the interface.

Configuring the maximum transmission unit

To configure the maximum transmission unit (MTU) for each link, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set the Maximum transmission unit (MTU) to the desired value in bytes.
Edit the slattach line in /etc/tcp or the incoming login script to contain the -m flag. This flag is in the form -m value, where value is a number in bytes.

The default MTU value is 296. Increasing this value may increase throughput as packets can contain more data. However, it may also decrease throughput if packets are routed through systems with lower MTU values, as each packet is split (fragmented) into smaller packets for transmittal. You can experiment with this value to obtain the most desirable results.

NOTE: The suggested value for the MTU is 40 plus some power of 2. For example, the default value, 296, is 40 plus 2^8. Other possible values include 552, 1064, and 2088.

Configuring SLIP debugging messages

To configure debugging mode, perform one of these actions:

In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set Debugging to On.
Edit the slattach line in /etc/tcp or the incoming login script to contain the v flag.
Setting the flag to +v enables verbose mode. Each time a SLIP link is initiated, various messages about the status of the link appear on the console. Setting the flag to -v removes this behavior.

Configuring packet filtering

To specify a packet filter for a SLIP link:

Create a filter entry in the file /etc/pppfilter. See the packetfilter(SFF) manual page for a description of the format for the filter file.
Perform one of the following actions:
- In the Network Configuration Manager's Advanced Options window for SLIP link configuration, set the Filter file tag name to match that found in /etc/pppfilter.
- Edit the slattach line in /etc/tcp or the incoming login script to contain the -p filter_tag entry, where filter_tag matches the name of the entry you created in pppfilter.

NOTE: Two or more SLIP link configurations may specify the same filter file entry. Also, a SLIP link may share a filter file entry with a PPP link. If the entry contains the bringup or keepup keywords for use in filtering PPP packets, SLIP ignores these parts of the entry.

If /etc/pppfilter does not exist or no filter file entry is specified for a link, then all packets are passed.

Following is an example filter entry:

   # tag      keyword     filter
   sample     pass        !port ntp and !port who and !port timed

The above specification does not allow ntp, who, and timed packets to pass through the network interface. For this packet filter to apply to a SLIP link, the tag ``sample'' must be specified on the slattach command line with the -p option.