From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: jch@irif.fr
Received: from krantz.zx2c4.com (localhost [127.0.0.1])
 by krantz.zx2c4.com (ZX2C4 Mail Server) with ESMTP id 89a4e360
 for <wireguard@lists.zx2c4.com>; Sat, 8 Apr 2017 17:08:44 +0000 (UTC)
Received: from korolev.univ-paris7.fr (korolev.univ-paris7.fr [194.254.61.138])
 by krantz.zx2c4.com (ZX2C4 Mail Server) with ESMTP id 7836a2a8
 for <wireguard@lists.zx2c4.com>; Sat, 8 Apr 2017 17:08:43 +0000 (UTC)
Date: Sat, 08 Apr 2017 19:15:04 +0200
Message-ID: <87d1cm2547.wl-jch@irif.fr>
From: Juliusz Chroboczek <jch@irif.fr>
To: Dan =?ISO-8859-1?Q?L=FCdtke?= <mail@danrl.com>
Subject: Re: [RFC] Multicast and IPv6 Link Local Addresses
In-Reply-To: <E60CF446-DDB2-4C66-B221-FBDCA346E461@danrl.com>
References: <CAHmME9poZPFbYhitnK8UvDB-32hLRcTFc4vAwaUPwGEz0wY+Yg@mail.gmail.com>
 <E60CF446-DDB2-4C66-B221-FBDCA346E461@danrl.com>
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Cc: Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@toke.dk>,
 Dave =?ISO-8859-1?Q?T=E4ht?= <dave@taht.net>,
 WireGuard mailing list <wireguard@lists.zx2c4.com>
List-Id: Development discussion of WireGuard <wireguard.lists.zx2c4.com>
List-Unsubscribe: <https://lists.zx2c4.com/mailman/options/wireguard>,
 <mailto:wireguard-request@lists.zx2c4.com?subject=unsubscribe>
List-Archive: <http://lists.zx2c4.com/pipermail/wireguard/>
List-Post: <mailto:wireguard@lists.zx2c4.com>
List-Help: <mailto:wireguard-request@lists.zx2c4.com?subject=help>
List-Subscribe: <https://lists.zx2c4.com/mailman/listinfo/wireguard>,
 <mailto:wireguard-request@lists.zx2c4.com?subject=subscribe>

> - Scalability: I agree with what George said. Broadcast does not scale
>   nicely, and IPv6 multicast is intended to help scaling things by
>   reaching exactly the node that need to get a copy of a particular
>   packet.

Not necessarily.  IPv6 link-local multicast replaces IPv4 link-local
broadcast.  Implementing link-local multicast as broadcast, while
suboptimal, is good enough to get IPv6 to work.

> - Multicast is not the everyday use case,

That's IPv4 thinking.  In IPv6, multicast is a basic, compulsory part of
the protocol.  A number of very basic IPv6 protocols fail to work if
link-local multicast is not functional.

See the IPv6 over NMBA (MARS, not LANE) specification for the kind of
horrors that are required to work around link layers that don't support
multicast.

> - IPv6 link-local addressing: For me it is a perfect example for "the
>   right amount of magic". It would make (at least my) life so much
>   easier. Filling the neighbor cache would require WireGuard to provide
>   (simulated or real) solicited node multicast addresses routing, right?

Yes, IPv6 neighbour discovery is one of those protocols that rely on
link-local multicast.

-- Juliusz