Last Modified: Aug 19, 2026
Affected Product(s):
BIG-IP LTM
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, 12.0.0, 12.0.0 hf1, 12.0.0 hf2, 12.0.0 hf3, 12.0.0 hf4
Fixed In:
12.1.0, 11.6.1
Opened: Oct 09, 2015 Severity: 4-Minor Related Article:
K10607444
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.
Connection might use invalid congestion metrics.
TCP cached congestion metrics from a previous connection, and subsequently receives an ICMP PMTU message.
Disable cmetrics-cache, accept the suboptimal cached values, or write an iRule to purge the entry after path change.
MTU updates now erase all congestion metrics entries, which is correct behavior.