Bug ID 467274: In SYN_SENT state, TCP retransmit timer may fail to back off.

Last Modified: Mar 12, 2019

Bug Tracker

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

Known Affected Versions:
10.2.2, 10.2.3, 10.2.4, 11.0.0, 11.1.0, 11.2.0, 11.2.1, 11.3.0, 11.4.0, 11.4.1, 11.5.0, 11.5.1, 11.5.1 HF1, 11.5.1 HF10, 11.5.1 HF11, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.2, 11.5.2 HF1, 11.5.3, 11.5.3 HF1, 11.5.3 HF2, 11.5.4, 11.5.4 HF1, 11.5.4 HF2, 11.5.4 HF3, 11.5.4 HF4, 11.5.5, 11.5.6, 11.5.7, 11.5.8, 11.5.9, 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, 11.6.1, 11.6.1 HF1, 11.6.1 HF2, 11.6.2, 11.6.2 HF1, 11.6.3, 11.6.3.1, 11.6.3.2, 11.6.3.3, 11.6.3.4

Fixed In:
12.0.0

Opened: Jun 13, 2014
Severity: 3-Major
Related AskF5 Article:
K16181

Symptoms

When configured with a tcp profile, virtual servers attempting to egress initial SYN (i.e., TCP is in SYN_SENT state) may exhibit a re-transmission behavior which is inconsistent with current RFCs. Rather than backing off, re-transmission rate (RTO) may increase.

Impact

Slightly increased network congestion.

Conditions

Configure virtual server with tcp profile.

Workaround

In versions which support the option, specify a TCP profile syn-rto-base value other than 0 or 3000 (e.g., 3001).

Fix Information

Virtual servers configured to use a TCP profile no longer retransmit initial TCP SYN packets at a slightly more aggressive rate than current RFC algorithms.

Behavior Change