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

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Date:	Wed, 4 Jan 2012 18:23:41 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
Cc:	Jan Engelhardt <jengelh@...ozas.de>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Patrick McHardy <kaber@...sh.net>,
	"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, Jan 04, 2012 at 10:47:53AM +0100, Hans Schillstrom wrote:
> On Wednesday 04 January 2012 10:32:14 Jan Engelhardt wrote:
> > On Wednesday 2012-01-04 10:03, Jozsef Kadlecsik wrote:
> > 
> > >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.
> > 
> > We've been there (me in the thread even) - defrag is running before raw,
> > because otherwise you could not select packets based upon L4 
> > parameters for non-defrag in the first place:
> > 
> > 	-t raw ... -p udp --dport 53 -j CT --notrack
> > 
> > Not that I overly care about whether defrag is before/after raw..
> > 
> What about a mod param for ip{6}table_raw so it could be changed ?

No obscure modparam tweaks, please.
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