Bug ID 551614: MTU Updates should erase all congestion metrics entries

Last Modified: Sep 13, 2023

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

Known Affected Versions:
11.6.0, 12.0.0, 12.0.0 HF1, 12.1.0 HF1, 12.0.0 HF2, 12.1.0 HF2, 12.1.1 HF1, 12.1.1 HF2, 12.1.2 HF1, 12.1.2 HF2

Fixed In:
12.1.0, 12.0.0 HF3, 11.6.1

Opened: Oct 09, 2015

Severity: 4-Minor

Related Article: K10607444

Symptoms

MTU updates erase cwnd cache entries, but not ssthresh or RTT, while an MTU update generally indicates a path change, meaning that these values might be invalid.

Impact

Connection might use invalid congestion metrics.

Conditions

TCP cached congestion metrics from a previous connection, and subsequently receives an ICMP PMTU message.

Workaround

Disable cmetrics-cache, accept the suboptimal cached values, or write an iRule to purge the entry after path change.

Fix Information

MTU updates now erase all congestion metrics entries, which is correct behavior.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips