Bug ID 897437: First retransmission might happen after syn-rto-base instead of minimum-rto.

Last Modified: Apr 24, 2024

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

Known Affected Versions:
14.1.0,,,,,, 14.1.2,,,,,,,,, 14.1.3,, 14.1.4,,,,,,, 14.1.5,,,,,, 15.1.0,,,,,, 15.1.1, 15.1.2,, 15.1.3,, 15.1.4,, 15.1.5,, 15.1.6,, 15.1.7, 15.1.8,,, 15.1.9,, 15.1.10,,,, 16.1.0, 16.1.1, 16.1.2,,, 16.1.3,,,,,, 16.1.4,,,

Opened: Apr 09, 2020

Severity: 5-Cosmetic


If a TCP profile is configured with a syn-rto-base value that is lower than minimum-rto, the first retransmission might happen after syn-rto-base. This behavior is encountered only if the BIG-IP system is unable to compute the new RTO value before the retransmission timer expires, meaning: -- The BIG-IP system has not received a packet with a TCP timestamp reply. -- The BIG-IP system has not received an ACK for a timed sequence number.


Retransmission might happen sooner than expected.


Configured value of syn-rto-base is lower than minimum-rto.


There are two possible workarounds: -- Avoid using a syn-rto-base value that is lower than the minimum-rto value (the default values are 3 seconds for syn-rto-base and 1 second for minimum-rto). -- Consider enabling timestamps to allow faster RTT measurement.

Fix Information


Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips