Bug ID 1015133: Tail loss can cause TCP TLP to retransmit slowly.

Last Modified: Jun 07, 2022

Bug Tracker

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

Known Affected Versions:
13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 13.1.3, 13.1.3.1, 13.1.3.2, 13.1.3.3, 13.1.3.4, 13.1.3.5, 13.1.3.6, 13.1.4, 13.1.4.1, 14.1.0, 14.1.0.1, 14.1.0.2, 14.1.0.3, 14.1.0.5, 14.1.0.6, 14.1.2, 14.1.2.1, 14.1.2.2, 14.1.2.3, 14.1.2.4, 14.1.2.5, 14.1.2.6, 14.1.2.7, 14.1.2.8, 14.1.3, 14.1.3.1, 14.1.4, 14.1.4.1, 14.1.4.2, 14.1.4.3, 14.1.4.4, 15.1.0, 15.1.0.1, 15.1.0.2, 15.1.0.3, 15.1.0.4, 15.1.0.5, 15.1.1, 15.1.2, 15.1.2.1, 15.1.3, 15.1.3.1, 15.1.4, 15.1.4.1, 16.1.0, 16.1.1, 16.1.2

Fixed In:
17.0.0, 16.1.2.1, 15.1.5, 14.1.4.5, 13.1.5

Opened: Apr 28, 2021
Severity: 3-Major

Symptoms

If a long tail loss occurs during transmission, TCP might be slow to recover.

Impact

BIG-IP retransmits one packet per RTT, causing a long recovery. The impact is more pronounced if an entire window is lost.

Conditions

-- A virtual server is configured with the TCP profile attached. -- SACK and TLP are enabled. -- A tail loss of multiple packets sent by the BIG-IP occurs.

Workaround

Disabling TLP may improve performance in this particular case, but may degrade performance in other situations.

Fix Information

A new sys db key was added: tm.tcpaggressivepartialack (disabled by default). When enabled, more data is retransmitted every RTT, similar to slow-start.

Behavior Change

A new sys db key was added: tm.tcpaggressivepartialack (disabled by default). When enabled, more data is retransmitted every RTT, similar to slow-start.