cnetwork-programmingtcplibpcap

How can I use libpcap to filter only client packets?

I am using libpcap to capture packet with the following filter:

"tcp[tcpflags] & (tcp-syn) != 0 and not net 127.0.0.1"

But I actually want to get the packet only if the sender is the client (SYN-SENT).

Basically what I am trying to do is to get inform only for new connection and not multiple time for every connection.

Is there a way to do that?

Solution

  • If you only want the SYN from the client but not the SYN+ACK from the server use:

     tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn