Detect packet drops

elof2 at elof2 at
Tue Oct 25 10:17:17 EDT 2011

Hi Carter and list!

Is there any way to easily detect loss in SPAN-traffic?

If I mirror two 1 Gbps full-duplex ports to a 1 Gbps SPAN port, in theory 
the switch could try to copy 4 Gbps onto it, resulting in dropped packets.

The sniffer machine receiving the mirrored traffic could be heavily loaded 
and drop packets.

In protocols such as TCP, these drops are detectable, due to gaps in the 
sequence counters.

Generating a pcap-file, scp:ing it to a machine running wireshark and then 
looking at the expert info is such a hassle. I'm looking for a commandline 
tool that show me when packets are missing (by printing a * for every 
missed packet) or giving me an estimated ratio of drops per minute.

Is there such a tool?

I'm guessing that argus can't help me, since it doesn't distinguish 
between loss and retransmissions in the 'flgs' field:
                *     -  Both Src and Dst loss/retransmission
                s     -  Src loss/retransmissions
                d     -  Dst loss/retransmissions


More information about the argus mailing list