netdev - Re: [PATCH nf-next 0/9] netfilter: remove per-netns conntrack tables, part 1

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Date:	Thu, 5 May 2016 22:54:18 +0200
From:	Florian Westphal <fw@...len.de>
To:	Brian Haley <brian.haley@....com>
Cc:	Florian Westphal <fw@...len.de>, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH nf-next 0/9] netfilter: remove per-netns conntrack
 tables, part 1

Brian Haley <brian.haley@....com> wrote:
> Openstack networking creates virtual routers using namespaces for isolation
> between users.  VETH pairs are used to connect the interfaces on these
> routers to different networks, whether they are internal (private) or
> external (public).  In most cases NAT is done inside the namespace as
> packets move between the networks.
> 
> I've seen cases where certain users are attacked, where the CT table is
> filled such that we start seeing "nf_conntrack: table full, dropping packet"
> messages (as expected).  But other users continue to function normally,
> unaffected.  Is this still the case - each netns has some limit it can't
> exceed?

The limit is global, the accounting per namespace.

If the bucket count (net.netfilter.nf_conntrack_buckets) is high enough
to accomodate the expected load and noone can create arbitrary number of
net namespaces things are fine.

I haven't changed the way this works yet because I did not have a better
idea so far.