Bug ID 789857: "TCP half open' reports drops made by LTM syn-cookies mitigation.

Last Modified: Sep 30, 2019

Bug Tracker

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

Known Affected Versions:
14.1.0,,,,,,, 14.1.2,, 15.0.0, 15.0.1

Opened: Jun 04, 2019
Severity: 3-Major


'TCP half open' reports drops in logs/tmctl/AVR even though it is configured in detect-only mode.


It will appear that 'TCP half open' is doing mitigation, but it is actually LTM syn-cookies dropping the connections.


-- 'TCP half open' attack is being actively detected. -- LTM syn-cookie mitigation is enabled. -- This is triggered when LTM syn-cookies mitigation begins.


If LTM syn-cookies are not needed, disable the option: modify ltm global-settings connection default-vs-syn-challenge-threshold infinite global-syn-challenge-threshold infinite

Fix Information


Behavior Change