TCP tracking states

[Henrik Nordstrom <hno@marasystems.com>]

The recent discussions and Oskar Andreassons work on a iptables 
tutorial made me take a closer look into the TCP tracking states, and 
I notices a couple of odd things that looks like they may be bugs..


1. What is the use of LAST_ACK? From what I can tell this state can 
only be reached if the connection is already in the LAST_ACK state..

2. The support for half-closed connections is very poor, and differs a 
lot depending on which side closed first.


To deal with 2, may I propose that the following symmetric FIN state 
machine is used instead of the odd assymetric one used today:


ESTABLISHED / FIN  -> FIN_WAIT

FIN_WAIT / ACK(R) -> CLOSE_WAIT

CLOSE_WAIT / FIN(R) -> TIME_WAIT (or a new FIN_WAIT2 state)

TIME_WAIT / ACK -> TIME_WAIT


And for completeness

FIN_WAIT / FIN(R) -> TIME_WAIT (or a new FIN_WAIT2 state)


Regards
Henrik