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

Last Modified: May 29, 2024

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

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.

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips