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

Last Modified: Jul 13, 2024

Affected Product(s):
BIG-IP All(all modules)

Known Affected Versions:
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

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips