Bug ID 505089: Spurious ACKs result in SYN cookie rejected stat increment.

Last Modified: Feb 13, 2019

Bug Tracker

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

Known Affected Versions:
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, 11.6.0, 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, 12.0.0, 12.0.0 HF1, 12.0.0 HF2, 12.0.0 HF3, 12.0.0 HF4

Fixed In:
12.1.0, 11.6.1, 11.5.4 HF2

Opened: Feb 05, 2015
Severity: 3-Major
Related AskF5 Article:
K13627243

Symptoms

Sending unsolicited ACK to a virtual server increments the counter 'Total Software Rejected' from tmsh show ltm virtual 'name_of_virtual_server' when syn cookie status is not activated.

Impact

Potentially inaccurate statistics in tmsh show ltm virtual.

Conditions

This has been observed under the following conditions: 1. The client sends a SYN, the LTM sends an SYN/ACK and then the client sends a bad ACK. 2. A client sends an ACK for a connection that does not exist in the connection table (either it never existed or had been closed).

Workaround

None.

Fix Information

In this release, the system increments the syncookie reject stat only if a bad ACK could correspond to a syncookie the system issued.

Behavior Change