nfct - Man Page

command line tool to configure with the connection tracking system

Synopsis

nfct command subsystem [parameters]

Description

nfct is the command line tool that allows to configure the Connection Tracking System.

Commands

list: List the existing objects.
add: Add new object.
delete: Delete an object.
get: Get an existing object.
flush: Flush the accounting object table.
disable: This command is for the helper subsystem. It allows you to disable enqueueing packets to userspace for helper inspection.
default-set: This command is for the timeout subsystem. It allows you to set default protocol timeouts.
default-get: This command is for the timeout subsystem. It allows you to get the default protocol timeouts.

Subsys

By the time this manpage has been written, the supported subsystems are timeout and helper.

timeout: The timeout subsystem allows you to define fine-grain timeout policies.
helper: The helper subsystem allows you to configure userspace helpers.
version: Displays the version information.
help: Displays the help message.

Example

nfct add timeout test-tcp inet tcp established 100 close 10 close_wait 10

This creates a timeout policy for tcp using 100 seconds for the ESTABLISHED state, 10 seconds for CLOSE state and 10 seconds for the CLOSE_WAIT state.

Then, you can attach the timeout policy with the iptables CT target:

iptables -I PREROUTING -t raw -p tcp -j CT --timeout test-tcp

iptables -I OUTPUT -t raw -p tcp -j CT --timeout test-tcp

You can test that the timeout policy with:

conntrack -E -p tcp

It should display:

[UPDATE] tcp 6 100 ESTABLISHED src=192.168.39.100 dst=57.126.1.20 sport=56463 dport=80 src=57.126.1.20 dst=192.168.39.100 sport=80 dport=56463 [ASSURED]