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Date: Fri, 19 May 2023 12:53:48 +0200
From: Florian Westphal <fw@strlen.de>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Florian Westphal <fw@strlen.de>, netdev@vger.kernel.org,
	Eric Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	netfilter-devel <netfilter-devel@vger.kernel.org>,
	Jeremy Sowden <jeremy@azazel.net>
Subject: Re: [PATCH net-next 3/9] netfilter: nft_exthdr: add boolean DCCP
 option matching
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Jakub Kicinski <kuba@kernel.org> wrote:
> On Thu, 18 May 2023 12:07:53 +0200 Florian Westphal wrote:
> > From: Jeremy Sowden <jeremy@azazel.net>
> > 
> > The xt_dccp iptables module supports the matching of DCCP packets based
> > on the presence or absence of DCCP options.  Extend nft_exthdr to add
> > this functionality to nftables.
> 
> Someone is actually using DCCP ? :o

Don't know but its still seeing *some* activity.
When I asked the same question I was pointed at

https://multipath-dccp.org/

respectively the out-of-tree implementation at
https://github.com/telekom/mp-dccp/

There is also some ietf activity for dccp, e.g.
BBR-like CC:
https://www.ietf.org/archive/id/draft-romo-iccrg-ccid5-00.html