Bug ID 648245: When using a route TMM may use a smaller MTU

Last Modified: Apr 28, 2025

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

Known Affected Versions:
13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1

Fixed In:
13.1.0

Opened: Mar 01, 2017

Severity: 2-Critical

Related Article: K29101604

Symptoms

TMM uses a smaller MTU when connecting to a device via a configured route.

Impact

Effective MTU when using the route will be limited to 1500 bytes. This includes derived MSS in TCP connections.

Conditions

- Larger than 1500 bytes MTU configured on VLAN. - Static, or dynamically learned route, to a destination, with no specific MTU defined.

Workaround

Specify the required MTU on routes.

Fix Information

TMM now by default uses VLAN-configured MTU when using a route to a destination.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips