SLIP packet filtering

SLIP permits the transfer of IP packets over a serial line via a SLIP network interface. Packet filtering permits control of the traffic through a SLIP network interface based on the contents of the packets passed to the interface. Unlike PPP, which allows ``keep up'' and ``bring up'' filtering as well, SLIP only provides ``pass'' filtering.

By default, any packet passed to an interface is allowed to pass through that interface. Packet filtering provides for specifying that only some types of packet may pass through a SLIP interface.

The following packet content can be used to qualify or disqualify a packet:

• transport level protocol type (that is, tcp, udp, icmp)

• IP destination or source fields

• destination or source port field in IP/TCP or IP/UDP packets

• packet length

• IP packet type (that is, broadcast or multicast)