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

Last Modified: Jan 20, 2023

Bug Tracker

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

Known Affected Versions:
16.1.0, 16.1.1, 16.1.2, 16.1.2.1, 16.1.2.2, 16.1.3, 16.1.3.1, 16.1.3.2, 16.1.3.3

Opened: Apr 09, 2020
Severity: 5-Cosmetic

Symptoms

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.

Impact

Retransmission might happen sooner than expected.

Conditions

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

Workaround

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

None

Behavior Change