Bug ID 503257: Persistence, connection limits and HTTP::respond or HTTP::redirect may result in RST

Last Modified: Sep 13, 2023

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

Known Affected Versions:
11.5.1 HF1, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.1 HF10, 11.5.1 HF11, 11.5.2 HF1, 11.5.3 HF1, 11.5.3 HF2, 11.5.4 HF1, 11.5.4 HF2, 11.5.4 HF3, 11.5.4 HF4, 11.2.1, 11.3.0, 11.4.0, 11.4.1, 11.5.0, 11.5.1, 11.5.2, 11.5.3, 11.6.0, 11.6.1, 11.6.2, 11.6.3,,,,, 11.6.4, 11.6.5,,,, 12.0.0, 12.0.0 HF1, 12.1.0 HF1, 12.0.0 HF2, 12.1.0 HF2, 12.1.1 HF1, 12.1.1 HF2, 12.1.2 HF1, 12.1.2 HF2

Fixed In:
12.1.0, 12.0.0 HF3, 11.6.1 HF1, 11.5.4

Opened: Jan 27, 2015

Severity: 3-Major

Related Article: K17054


Client connections to a virtual server with persistence, connection limits, and an iRule that issues an HTTP response may receive a RST with a cause of "pmbr enqueue failed" even though connection queuing is not enabled.


Clients may receive a RST and fail to connect to an available pool member under some traffic patterns.


This can happen if the connection makes an HTTP request and an iRule directly responds to the first request on the connection. A future request on that TCP connection would be reset if it is persisted to a pool member that is at its connection limit. The iRule would use HTTP::respond (without "connection close") or HTTP::redirect.


If using HTTP::respond or HTTP::redirect in an iRule, change to HTTP::respond with the "Connection close" option in order to force the connection to terminate and the client to start a new connection after the redirect is sent.

Fix Information

Persistence, connection limits and HTTP::respond or HTTP::redirect no longer result in RST.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips