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

Last Modified: Dec 07, 2023

Affected Product(s):
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:
17.1.0, 16.1.4,

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

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips