Bug ID 1053149: A FastL4 TCP connection which is yet to fully establish fails to update its internal SEQ space when a new SYN is received.

Last Modified: Nov 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, 13.1.5, 13.1.5.1, 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, 14.1.4.5, 14.1.4.6, 14.1.5, 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, 15.1.5, 15.1.5.1, 15.1.6, 16.1.0, 16.1.1, 16.1.2, 16.1.2.1, 16.1.2.2, 16.1.3

Fixed In:
17.0.0, 16.1.3.1, 15.1.6.1, 14.1.5.1

Opened: Oct 07, 2021
Severity: 3-Major

Symptoms

Depending on the software version running on the BIG-IP system, this issue can manifest in one of two ways: - Versions with the fix for ID1008077 will fail to forward the client's final ACK (from the TCP 3-way handshake) to the server. Eventually, once the TCP handshake timeout expires, the BIG-IP system will reset both sides of the connection. - Versions without the fix for ID1008077 will forward the traffic correctly, but will not advance the internal FastL4 state for the connection. Given enough traffic for the same 4-tuple, the connection may never expire. Traffic for subsequent connections will appear to be forwarded correctly, but no load-balancing will occur due to the original connection not having expired yet.

Impact

Traffic failures (intended as either connections failing to establish, or improper load-balancing occurring).

Conditions

A FastL4 TCP connection not completing the TCP handshake correctly, and the client retrying with a new (different SEQ number) SYN.

Workaround

None

Fix Information

A FastL4 TCP connection which is yet to fully establish now correctly updates its internal SEQ space when a new SYN is received. This means the connection advances as it should through internal FastL4 states, and is removed from the connection table when the connection closes.

Behavior Change