Bug ID 578951: TCP Fast Open connection timeout during handshake does not decrement pre_established_connections

Last Modified: Oct 06, 2020

Bug Tracker

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

Known Affected Versions:
12.0.0, 12.0.0 HF1, 12.0.0 HF2, 12.0.0 HF3, 12.0.0 HF4, 12.1.0, 12.1.0 HF1, 12.1.0 HF2, 12.1.1, 12.1.1 HF1, 12.1.1 HF2

Fixed In:
13.0.0, 12.1.2

Opened: Mar 08, 2016
Severity: 3-Major


If a TCP connection is started and contains a valid Fast Open cookie, then times out during the three-way handshake, the failure is not accounted for properly. If this occurs more than a threshold number of times, BIG-IP will stop performing TCP Fast Open.


Each connection that times out in this fashion decreases the number of valid pre-established connections that the BIG-IP can support. If the number of connections timed out in this fashion rises above a threshold, BIG-IP will act as if TCP Fast Open is disabled. This threshold cannot be changed.


A TCP connection using TCP Fast Open with a valid Fast Open cookie times out during the three-way handshake.



Fix Information

Decrement the pre-established connections counter when a TCP Fast Open connection times out during the initial handshake.

Behavior Change