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Message-ID: <572BC7A5.1060503@hpe.com> Date: Thu, 5 May 2016 18:22:29 -0400 From: Brian Haley <brian.haley@....com> To: Florian Westphal <fw@...len.de> Cc: netfilter-devel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH nf-next 0/9] netfilter: remove per-netns conntrack tables, part 1 On 05/05/2016 04:54 PM, Florian Westphal wrote: > 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. So this is a change from existing. > 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. In my case we can't control the number of namespaces, each user will get one as a virtual router is created. We could change how we size things, but that doesn't stop one user from consuming larger than their 1/N share of entries. Typically we just increase the number of systems hosting these "routers" when we hit a limit, which decreases the netns count per node. > I haven't changed the way this works yet because I did not have a better > idea so far. Creating a per-netns maximum seems doable, but maybe not practical from the accounting side of things. Can't think of anything else at the moment. -Brian
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