netdev - Re: [PATCH net-next,v3 0/9] netfilter: flowtable bridge and vlan enhancements

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Date:   Sat, 21 Nov 2020 13:31:38 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Tobias Waldekranz <tobias@...dekranz.com>,
        netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, razor@...ckwall.org, jeremy@...zel.net
Subject: Re: [PATCH net-next,v3 0/9] netfilter: flowtable bridge and vlan
 enhancements

On Mon, Nov 16, 2020 at 11:56:58PM +0100, Pablo Neira Ayuso wrote:
> On Mon, Nov 16, 2020 at 02:45:21PM -0800, Jakub Kicinski wrote:
> > On Mon, 16 Nov 2020 23:36:15 +0100 Pablo Neira Ayuso wrote:
> > > > Are you saying A -> B traffic won't match so it will update the cache,
> > > > since conntrack flows are bi-directional?  
> > > 
> > > Yes, Traffic for A -> B won't match the flowtable entry, this will
> > > update the cache.
> > 
> > That's assuming there will be A -> B traffic without B sending a
> > request which reaches A, first.
> 
> B might send packets to A but this will not get anywhere. Assuming
> TCP, this will trigger retransmissions so B -> A will kick in to
> refresh the entry.
> 
> Is this scenario that you describe a showstopper?

I have been discussing the topology update by tracking fdb updates
with the bridge maintainer, I'll be exploring extensions to the
existing fdb_notify() infrastructure to deal with this scenario you
describe. On my side this topology update scenario is not a priority
to be supported in this patchset, but it's feasible to support it
later on.