Bug ID 642400: Path MTU discovery occasionally fails

Last Modified: Sep 13, 2023

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

Known Affected Versions:
11.6.1

Fixed In:
13.1.0, 13.0.0 HF1, 12.1.2 HF1, 11.6.2

Opened: Jan 31, 2017

Severity: 2-Critical

Symptoms

Connections using a TCP profile that receive an ICMP needsfrag message may incorrectly ignore the message. This may cause Path MTU discovery to fail.

Impact

The connection may stall as large TCP segments are continually retransmitted.

Conditions

TCP profile assigned to VIP. Smaller MTU on data path than on TCP endpoints.

Workaround

Configure the MSS in the TCP profile to match the lowest MSS. Use or disable Path MTU discovery with the tm.pathmtudiscovery database key.

Fix Information

Path MTU discovery functions correctly with the TCP profile.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips