Bug ID 439431: Some iRules can result in abandoned UDP flows.

Last Modified: Jul 12, 2023

Affected Product(s):
BIG-IP LTM(all modules)

Known Affected Versions:
11.4.0, 11.4.1, 11.5.0

Fixed In:
11.6.0, 11.5.1, 11.4.1 HF4, 11.4.0 HF6

Opened: Dec 02, 2013

Severity: 3-Major

Related Article: K15256


When asynchronous commands are used in iRules in both the SERVER_CLOSED and CLIENT_CLOSED, it is possible for the flows to be left allocated. These flows are left in the flow table (and will appear in tmsh show sys conn), and can possibly match new client flows but will not pass traffic.


Increased memory usage leading to a possible outage after time; new flows from the same client port may match this flow and be silently dropped by the BIG-IP.


Asynchronous commands must be executed in both SERVER_CLOSED and CLIENT_CLOSED on UDP VIPs.


Don't use asynchronous commands in iRules in both CLIENT_CLOSED and SERVER_CLOSED. After the error occurs, the only correction is to restart tmm.

Fix Information

Flows with asynchronous iRule commands in CLOSED events will be cleaned up normally, and will not match any new requests.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips