Bug ID 642400: Path MTU discovery occasionally fails

Last Modified: Nov 07, 2022

Bug Tracker

Affected Product:  See more info
BIG-IP All(all modules)

Known Affected Versions:
11.6.0, 11.6.0 HF1, 11.6.0 HF2, 11.6.0 HF3, 11.6.0 HF4, 11.6.0 HF5, 11.6.0 HF6, 11.6.0 HF7, 11.6.0 HF8, 11.6.1, 11.6.1 HF1, 11.6.1 HF2, 12.1.0, 12.1.0 HF1, 12.1.0 HF2, 12.1.1, 12.1.1 HF1, 12.1.1 HF2, 12.1.2, 13.0.0

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

Opened: Jan 31, 2017
Severity: 2-Critical


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


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


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


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