Hi,

So we´ve been having this performance issue, and on the capture I can see that maybe 50% of the DC to Core traffic are Out ot Order and TCP Retransmissions. Cisco Nexus device also shows many of these in the Socket Statistics (does someone know how the N5k actually manages to qualify them as retransmissions, how fiable is this?).

I do have the same TCP flow going over the same psyical link towards the Checkpoint FW and back to the Core, and then over to the server... but how can I actually be sure if the TCP Retransmissions are not just the members of the same IP flow but detected twice? How does Wireshark detect the Out of order and Retransmission, there is no flag for that, so... some inside intelligence? And even if WireShark is wrong... is Nexus wrong too showing 50% packets as retransmissions in "show socket statistics" output?