Reset conntrack...

Sven Anders anders at
Fri Dec 3 12:11:01 CET 2004

Hash: SHA1

Patrick Schaaf wrote:
|>Is it possible to reset the conntrack list or set any entry to the state
|>NEW to force a recheck against new filter rules?
|>~  If I set the (new) filtering rules with the target DROP, I want old
|>~  (existing) connections to be dropped immediatly.
| Consider using REJECT. This has two advantages: it gives the end
| systems you are now blocking a chance at state cleanup (instead of
| needlessly wasting memory and CPU resources on a connection that you
| now elect to forbit). But, the greater advantage: the packets that
| the end systems exchange in response to the connection teardown,
| are JUST what you need to get rid of their conntracks.

This is not exactly what I'm meant...

Consider the following scenario:

~ 1. Set firewall rules
~     with:
~      a) ACCEPT on all --state RELATED,ESTABLISHED
~      b) with ACCEPT on ports 22 and 80

~ 2. Remote client creates connection through the firewall
~     on the port 80 (CONNTRACK state is: NEW)
~     It will be allowed due to the ACCEPT policy...

~ 3. Server answers and connection CONNTRACK state will be changed

~ 4. Set new firewall rules:
~      Changed b) to only allow port 22

~ 5. The connection to port 80 will continue to exists, because
~    it CONNTRACK state did not change and we have rule a)...

Possible solutions:

~ 1) Recheck all CONNTRACK entries against the new firewall rules.

~ 2) Set all CONNTRACK entries with states RELATED or ESTABLISHED to
~     NEW, to force the recheck.

Is there any way to accomplish this?

~ Sven

- --
~ Sven Anders <anders at>

~ ANDURAS service solutions AG
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