Bug ID 975597: Using global variables in iRules causes TCP connections to reset with msg 'No flow found for ACK'

Last Modified: May 29, 2024

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

Known Affected Versions:, 13.1.3,,,,,,, 13.1.4,, 13.1.5,, 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,, 15.1.6,, 15.1.7, 15.1.8,,, 15.1.9,, 15.1.10,,,, 16.0.0,, 16.0.1,,, 16.1.0, 16.1.1, 16.1.2,,, 16.1.3,,,,,, 16.1.4,,,

Opened: Dec 21, 2020

Severity: 3-Major


When source port is reused toward a TCP virtual server with CMP disabled or in single-CPU mode, a RST might be returned with a cause 'No flow found for ACK'.


Unexpected RST events occur on the client side.


-- TCP virtual server with CMP disabled, or in single-CPU mode. (For example, configuring an iRule that uses global variables is one way to put the system into single-CPU mode.) -- The client connection reuses the same TCP port as it used for a recently closed connection.


You can use either of the following workarounds: -- Enable CMP. -- Modify the iRule (e.g., use a static namespace instead) to make it CMP capable.

Fix Information


Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips