[Winpcap-users] Can I capture inbound packets only?

[Greg Watson]

Hello,

I saw this question asked a few months ago by someone else, but with no 
response. I'm hoping someone can provide a definitive answer.

I would like to set pcap to capture inbound packets only, not outbound.

Why? Because we use it to test Ethernet switches created by students: we 
use a 4-port NIC connected to a 4-port ethernet switch designed by the 
students (FPGAs).
                  +--------------+
NIC_port0 <----> | Switch_port0 |
NIC_port1 <----> | Switch_port1 |
NIC_port2 <----> | Switch_port2 |
NIC_port3 <----> | Switch_port3 |
                  +--------------+

We test the switch by sending packets to it and we capture the response 
packets. Because it is a switch then packets come back completely 
unmodified. Therefore we expect to receive packets we have sent, indeed 
we expect to receive ONLY packets we have sent.

It really complicates life if we capture the packets we send as we 
cannot tell if a captured packet was transmitted by us or received by us.

Note: we might well have a packet sent back to us ON THE SAME PORT that 
we sent it out on - this is an error (switches must not do this) but 
then these are student designs and sometimes they make mistakes.

Thanks for any help.

-Greg