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

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Message-ID: <201201041248.36881.hans.schillstrom@ericsson.com>
Date:	Wed, 4 Jan 2012 12:48:35 +0100
From:	Hans Schillstrom <hans.schillstrom@...csson.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Patrick McHardy <kaber@...sh.net>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"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 Wednesday 04 January 2012 12:17:18 Jan Engelhardt wrote:
> On Wednesday 2012-01-04 11:18, Hans Schillstrom wrote:
> 
> >On Wednesday 04 January 2012 10:03:49 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.
> >> 
> >
> >An other idea, turn off both conntrack and defrag
> >i.e. do like NOTRAC and rename the flag  ?
> 
> Or just add a new table - that one we can remove/stash
> when I get my xt2 patches out.
> 
I like that idea, an "early" table at prio -500 with PREROUTING.
There is also a need for a new flag "--allfrags"
i.e. all fragments needs to be sorted out and sent to same dest for defrag.

ex.
iptables -t early -A PREROUTING -i eth0 --allfrags -j NOTRACK


-- 
Regards
Hans Schillstrom <hans.schillstrom@...csson.com>
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