Bug ID 773421: Server-side packets dropped with ICMP fragmentation needed when a OneConnect profile is applied

Last Modified: Sep 13, 2023

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

Known Affected Versions:
13.1.0,,,,,,,,, 13.1.1,,,,, 13.1.3,, 14.0.0,,,,,, 14.0.1,, 14.1.0,,,,,, 14.1.2, 15.0.0, 15.0.1

Fixed In:

Opened: Apr 16, 2019

Severity: 3-Major


When OneConnect is applied to a virtual server, the server-side packets larger than the client-side MTU may be dropped.


The BIG-IP system rejects server-side ingress packets larger than the client-side MTU, with an ICMP fragmentation needed message. Connections could hang if the server ignores ICMP fragmentation needed and still sends TCP packets with larger size.


-- If the client-side MTU is smaller than server-side (either via Path MTU Discovery (PMTUD), or by manually configuring the client-side VLAN). -- OneConnect is applied. -- proxy-mss is enabled (the default value starting in v12.0.0).


Disable proxy-mss in the configured TCP profile.

Fix Information

OneConnect prevents sending ICMP fragmentation needed messages to servers.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips