Bug ID 818833: TCP re-transmission during SYN Cookie activation results in high latency

Last Modified: Sep 23, 2021

Bug Tracker

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

Known Affected Versions:
13.1.0,,,,,,,,, 13.1.1,,,,, 13.1.3,,,,,,, 13.1.4,, 14.1.0,,,,,, 14.1.2,,,,,,,,, 14.1.3,, 14.1.4,,,, 15.0.0, 15.0.1,,,,, 15.1.0,,,,,, 15.1.1, 15.1.2,, 15.1.3,

Fixed In:
16.0.0, 15.1.4,

Opened: Aug 29, 2019
Severity: 3-Major


Issue is reported at the following system setup: client <-> BIG-IP <-> concentrator <-> proxy <-> BIG-IP nat gateway <-> Internet -- SYN Cookie got activated on F5 nat gateway. -- Latency from 'Internet' (public host) is observed at 'Proxy' device sitting before F5 nat gw. -- During the latency issue, SYN Cookie was active and evicting connections. -- When SYN Cookie is enabled, it switches to l7 delayed binding as expected but it is not sending ACK for HTTP request so the client sends it again and again.


High latency is observed.


Haredware SYN Cookie is enabled on FastL4 profile


Disable the SYN Cookie on the FastL4 profile

Fix Information


Behavior Change