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Note The pid, sid and command matching is broken in SMP kernels since they use different process lists for each processor. It might be fixed in the future however
Packet type match
The packet type match is used to match packets based on their type. I.e., are they destined to a specific person, to everyone or to a specific group of machines or users. These three groups are generally called unicast, broadcast and multicast, as discussed in the TCP/IP repetition chapter. The match is loaded by using -m pkttype.
Table 10-25. Packet type match options
Match--pkt-typeKernel2.3, 2.4, 2.5 and 2.6Exampleiptables -A OUTPUT -m pkttype --pkt-type unicastExplanationThe --pkt-type match is used to tell the packet type match which packet type to match. It can either take unicast , broadcast or multicast as an argument, as in the example. It can also be inverted by using a ! like this: -m pkttype --pkt-type ! broadcast, which will match all other packet types.