PPP permits the transfer of IP packets over a
serial line via a PPP network interface.
Packet filtering permits control of the traffic through a PPP
network interface
based on the contents of the packets passed to the interface.
Packet filter control is provided for these
interface functions:
bring up
By default, any packet passed to an outgoing link from a
dedicated serial or automatic dialup endpoint
will bring the interface up if it is down.
Packet filtering provides for specifying that only some types of packets
may bring up a PPP interface.
pass
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 packets
may pass through a PPP interface.
keep up
By default, any packet passed to an interface will reset the idle
timer for that interface.
(Expiration of the idle timer will cause the interface to be
automatically brought down.)
Packet filtering provides for specifying that only some types of packets
may reset the idle timer for a PPP interface.
Packets can be qualified or disqualified for:
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)
Packet filtering is specified on a per-endpoint basis, although more
than one endpoint may share the same packet filtering parameters.