Symptoms
Client enables Window Scale in the first SYN packet with a specific factor value, however the BIG-IP system disables Window Scale in its SYN/ACK response.
Instead, disabling the Window Scale TCP option in both peer BIG-IPs, TMM honors the Window Scale presented by the client in the first SYN, whereas client assumes Window Scale is disabled. This will cause BIG-IP to send data payload bytes exceeding the client's Windows Size.
Impact
This can cause performance issues because some packets could need to be retransmitted.
In rare cases where client TCP stack is configured to abort
the connection when it receives a window overflow, the connection will be RST by the client.
Conditions
Below conditions must be met in order to match this issue:
- Client and server enables timestamp TCP option.
- Client enables Window Scale TCP option.
- SYN Cookie HW is activated in BIG-IP.
Workaround
The preferred workaround is changing to Software SYN Cookie mode.
Fix Information
Correct server-side Window Scale behavior is provided when:
- Client and server enables timestamp TCP option
- Client enables Window Scale TCP option
- SYN Cookie HW is activated in BIG-IP
