netdev - Re: [PATCH 1/1] netfilter: Add possibility to turn off netfilters defrag per netns

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Date:	Wed, 4 Jan 2012 10:03:49 +0100 (CET)
From:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
cc:	Patrick McHardy <kaber@...sh.net>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"jengelh@...ozas.de" <jengelh@...ozas.de>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"hans@...illstrom.com" <hans@...illstrom.com>
Subject: Re: [PATCH 1/1] netfilter: Add possibility to turn off netfilters
 defrag per netns

On Wed, 4 Jan 2012, Hans Schillstrom wrote:

> On Wednesday 04 January 2012 09:28:05 Jozsef Kadlecsik wrote:
> > 
> > On Wed, 4 Jan 2012, Hans Schillstrom wrote:
> > 
> > > In some cases it not desirable to have auto defrag.
> > > Ex. in a cluster where packets can arrive on different blades.
> > > In that case it is possible to use containers (LXC) and send
> > > all fragments to one place where defrag is enabled.
> > > 
> > > This patch makes it possible to turn off the defrag per network name space,
> > > by setting net.netfilter.nf_conntrack_nodefrag to 1.
> > > Both IPv4 and IPv6 is effected by this sysctl.
> > > Default is 0 which is defrag.
> > 
> > Conntrack assumes that the packets are defragmented and will drop any 
> > unfragmented one. So your patch results packet drops.
> 
> Hmmm, more work...
> > 
> > Also, if you want to disable defragmentation then why don't you simply 
> > "mark" the packets with the NOTRACK target?
> 
> I don't think that will work since NF_IP_PRI_CONNTRACK_DEFRAG is -400

Then change NF_IP_PRI_RAW so that it precedes NF_IP_PRI_CONNTRACK_DEFRAG. 
The raw table should be made possible to completely override conntack and 
defrag is implicit part of the latter.

Best regards,
Jozsef
-
E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.mta.hu
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : Wigner Research Centre for Physics, Hungarian Academy of Sciences
          H-1525 Budapest 114, POB. 49, Hungary
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