I think it may be a naive question, but I also want to make sure of this; I'm wondering if this could affect pefromance of a tap or the program speed: I want to filter syn packets using(tcp.flags.syn==1), I know it is implicitly filter the tcp protocal, is there any need to mention the TCP protocol explicitly again inside the filter of the tap?? asked 05 Dec '12, 00:56  Leena edited 05 Dec '12, 04:53  Jasper ♦♦ |
One Answer:
You mean, do you need to filter on "tcp.flags.syn==1 and tcp"? No, tcp.flags.syn==1 is enough in itself, it will only look at the packets containing the TCP protocol layer. Speed-wise I don't think it makes much difference to additionally specifiy "tcp" since the filter checks that anyway, so I guess it gets optimized anyway. answered 05 Dec '12, 01:23 Jasper ♦♦ |
Thanks alot
@Jasper: I want to be sure of this although I checked on it by trials on wireshark, I need to filter ipv4 and in the filter I have ip address in ipv4(ip.src==172.16.0.0/12),so as the rule above it will implicitly filter the ipv4,right?? no need to write (ip) in the filter? Thanks a alot, and sorry to disturb you.
no, ip.src is enough to make sure the filter works. And you're not disturbing ;-)
@Jasper:Thanks a lot, but if I use (not ip.src==172.16.0.0/12)to filter inbound traffic I should mention ipv4 in the filter explicitly,right?? I tried it with just a display filter in a pcap and packets with ipv6 still there.
which makes sense, because all you're saying is "do not show me ipv4 addresses of the network 172.16.0.0/12". You need to add "and not ipv6" to also remove ipv6 traffic. Or just go "ip and not ip.src==172.16.0.0/12" to remove everything that is not IPv4 as well as the network you don't want.