Networking Guide
Chapter 10, Configuring the Serial Line Internet Protocol (SLIP)

Configuring packet filtering

Configuring packet filtering

To specify a packet filter for a SLIP link:

  1. 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.

  2. Perform one of the following actions:


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.