Networking Guide
Chapter 9, Configuring the Point-to-Point Protocol (PPP)

Creating a packet filter

Creating a packet filter

Packet filter entries must be edited into the /etc/pppfilter file. Two or more PPP endpoint configurations can share the same entry.

If /etc/pppfilter does not exist or no filter file entry is specified for an endpoint, then all packets bring up the interface, all packets are passed, and all packets reset the idle timer.

The following filter entry describes the default behavior of a PPP link:

   # tag    keyword  filter
   

default bringup !port ntp and !port who and !port route\ and !port timed and !port bgp and !ip proto 8\ and !ip proto 63 and !ip proto 89 and icmp[20]!=9\ and icmp[20]!=10 pass \ keepup !port ntp and !port who and !port route\ and !port timed and !port bgp and !ip proto 8\ and !ip proto 63 and !ip proto 89 and icmp[20]!=9\ and icmp[20]!=10

This specification does not allow ntp, rwhod, routed, timed, gated, or irdd, packets to bring up or keep up the link, but it does allow all packets to pass the link.

See the packetfilter(SFF) manual page for a description of the format for the filter file.