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ACE default handling of the TCP Window Scale option

Level 1
Level 1

Can someone tell me a reasonable explanation why the default action of the ACE is to clear the window-scale option in SYN-segments? We were long baffled why some customers (specifically the ones with larger latencies) were suffering from poor TCP transfer speeds and resets. Packet captures confirmed the fact that the ACE was clearing window-scale options, causing the advertised receive windows to be remarkably small as the scaling factors were removed.

Isn't intermediate tampering with the window-scale option a widely known source for TCP performance problems? Window scaling is after all a widely used TCP extension. That's why I'm curious to know why such default behaviour from the ACE.

Our problem was of course finally resolved by explicitly allowing the window-scale option using a parameter map.

10 Replies 10


We are experiencing the same issue. Could you post your parameter map which changes this behaviur? As I understand I can actively set a new scaling-factor, but that is not what I want. I want it to just forward it untouched. Did you manage to accomplish that?