Bug ID 515915: Server side timewait close state causes long establishment under port reuse

Last Modified: Nov 07, 2022

Bug Tracker

Affected Product:  See more info
BIG-IP All(all modules)

Known Affected Versions:
11.5.1, 11.5.1 HF1, 11.5.1 HF10, 11.5.1 HF11, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.10, 11.5.2, 11.5.2 HF1, 11.5.3, 11.5.3 HF1, 11.5.3 HF2, 11.5.4, 11.5.4 HF1, 11.5.4 HF2, 11.5.4 HF3, 11.5.4 HF4, 11.6.0, 11.6.0 HF1, 11.6.0 HF2, 11.6.0 HF3, 11.6.0 HF4, 11.6.0 HF5, 11.6.0 HF6, 11.6.0 HF7, 11.6.0 HF8, 11.6.1, 11.6.1 HF1, 11.6.1 HF2, 11.6.2, 11.6.2 HF1

Fixed In:
12.0.0, 11.6.3, 11.5.5

Opened: Apr 02, 2015
Severity: 2-Critical
Related Article:
K47804233

Symptoms

When the server TCP connection is under timewait closing state, if a new client connection is initiated toward the server under the BIG-IP SYN-Cookie mode, the server respond with ACK instead of SYN+ACK for the SYN received. The BIG-IP system drops this ACK and retransmit the SYN, till timeout occurs.

Impact

Longer establishment time and retry.

Conditions

-- FastL4 is under SYN-Cookie mode. -- The previous server connection is under time wait close state. -- New client connection is reusing the port to get to the same server TCP connection.

Workaround

None.

Fix Information

When ACK is received instead of SYN+ACK in this case, the system resets the server side to quick recovery, ensuring a quick recovery.

Behavior Change