Bug ID 624846: TCP Fast Open does not work for Responses < 1 MSS

Last Modified: Sep 13, 2023

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

Known Affected Versions:
12.0.0, 12.0.0 HF1, 12.1.0 HF1, 12.0.0 HF2, 12.1.0 HF2, 12.0.0 HF3, 12.0.0 HF4, 12.1.1 HF1, 12.1.1 HF2, 12.1.2 HF1, 12.1.2 HF2, 12.1.0, 12.1.1, 12.1.2, 12.1.3,,,,,

Fixed In:

Opened: Oct 25, 2016

Severity: 3-Major


BIG-IP does not send the data until receiving the first client ACK.


Delayed completion of the connection.


TCP Fast Open requests an object of less than 1 MSS in size. Fast open and delayed acks enabled.


Disable delayed acks.

Fix Information

TCP sends SYN/ACK immediately after receiving the SYN, and the response as soon as it arrives from the server.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips