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Date:   Wed, 11 Jan 2023 19:08:18 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Jeremy Sowden <jeremy@azazel.net>,
        Netfilter Devel <netfilter-devel@vger.kernel.org>
Subject: Re: [libnetfilter_conntrack PATCH] conntrack: increase the length of
 `l4proto_map`
Message-ID: <20230111180818.GD27644@breakpoint.cc>
References: <20221223123806.2685611-1-jeremy@azazel.net>
 <Y7758rNEafF9XurG@salvia>
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Fri, Dec 23, 2022 at 12:38:06PM +0000, Jeremy Sowden wrote:
> > With addition of MPTCP `IPPROTO_MAX` is greater than 256, so extend the
> > array to account for the new upper bound.
> 
> Applied, thanks.
> 
> I don't expect we will ever see IPPROTO_MPTCP in this path though.
> To my understanding, this definition is targeted at the
> setsockopt/getsockopt() use-case. IP headers and the ctnetlink
> interface also assumes 8-bits protocol numbers.

Yes, this is an uapi thing:

socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); vs.
socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);

Only second version results in a multipath-tcp aware socket.

If mptcp is active (both peers need to support it), tcp frames will
have an 'mptcp' option, but its still tcp (6) on wire.