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