Bug ID 1076785: Virtual server may not properly exit from hardware SYN Cookie mode

Last Modified: Mar 31, 2023

Bug Tracker

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

Known Affected Versions:
14.0.0,,,,,, 14.0.1,, 14.1.0,,,,,, 14.1.2,,,,,,,,, 14.1.3,, 14.1.4,,,,,,, 14.1.5,,,, 15.0.0, 15.0.1,,,,, 15.1.0,,,,,, 15.1.1, 15.1.2,, 15.1.3,, 15.1.4,, 15.1.5, 16.0.0,, 16.0.1,,, 16.1.0, 16.1.1, 16.1.2,,, 16.1.3,,,, 17.0.0,,

Fixed In:

Opened: Jan 30, 2022
Severity: 3-Major


Virtual servers do not exit hardware SYN Cookie mode even after the SYN flood attack stops. The TMSH 'show ltm virtual' output shows 'full hardware' mode.


The affected virtual server would not receive the TCP SYN packets until a TMM restart. The limited range of MSS values in SYN Cookie mode may slightly affect performance.


Selected HSB platforms where TMM is attached to multiple HSB modules. This depends on platform, BIG-IP version and selected Turboflex profile where applicable.


Disable hardware SYN Cookie mode on all virtual servers.

Fix Information

Virtual server is now fully exits hardware SYN Cookie mode once a SYN flood attack stops.

Behavior Change