I have checked the Web, Aruba documentation and this forum and there is no mention (at all) of TCP MSS adjustments. The reason to open this thread is to check whether anyone has had a look at this or whether this is something that gets sorted under the hood.
Recently troubleshooting a multi-vendor network I've noticed that for traffic connecting to the Aruba Controllers has the MTU Adjusted for all traffic that is tunneled between two Aruba Controllers.
Basically what I'm seeing is:
- Client sends TCP SYN with MSS=1460
- Server replies TCP SYNACK with MSS=986
Same server other vendor MSS stays 1460.
The traffic crosses a tunnel between 2 Aruba Controllers and there is no MTU defined and the Tunnel MTU is set to 1100 (based on a 'show interface tunnel x').
I'm wondering whether I'm seeing PMTUD at work - however my packet captures do not show any ICMP where the MTU is determined. Or is there a TCP MSS adjust/rewrite happening within the Aruba's ?
I'm hesitant on raising a TAC case - as it's not really a problem - it's more something that seems to be happening and we like better understand. Any ideas?