ACK sequence number

[Mitchyban]

I have a strange issue that's causing us grief.

We have two servers that are identical for failover purposes. When traffic is routed through Server A (the shorter path in terms of hops), there is a great deal of latency even when there are a handful of users using connections.

However, on Server A, there is no latency.

Checking sniffer logs for the server A throws up an interesting situation that I'm having trouble explaining.

The client sends a SYN, which is then met with an ACK instead of the expected SYNACK. An RST is then sent, and the conversation carries on normally.

Looking at the full conversation history for the port, it appears the first ACK received is from the previous conversation's FIN, ACK, and that's what's causing the RST. But from what I can see, the ports are being released without problem, and TIMEWAIT is 60 seconds. So not sure what to think.

I've also reviewed the TCP stack on both, and they match line for line.

Any ideas?!

Thanks in advance.

 

[VinceWhirlwind]

Get on the switch where these servers are patched and do a "show int..." for each switchport. Also do a "show run int..." for each of them while you're at it.