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Date:      Mon, 16 Jan 2012 11:16:19 -0800
From:      Matt Mullins <mokomull@gmail.com>
To:        Freek Dijkstra <public@macfreek.nl>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Disable auto_linklocal
Message-ID:  <CAPyT1SETL7+A3rgMWhwpFaD7HNCcp1FvT6ekzP2p0kpfOY2X6A@mail.gmail.com>
In-Reply-To: <4F12F04B.2080504@macfreek.nl>
References:  <4F12F04B.2080504@macfreek.nl>

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On Sun, Jan 15, 2012 at 7:27 AM, Freek Dijkstra <public@macfreek.nl> wrote:
> The link-local addresses don't really harm, but I found them confusing,
> as the host is running as a router, and rtadv announces the link-local
> address by default.

IPv6-standards-wise, this is the correct thing to do.  Router
advertisements should contain link-local source addresses and
advertise the link-local address as the router; the globally-routable
prefix that is being advertised is a completely different field in
those messages.  I'm not too sure of the reasons behind this, other
than eliminating some need for carp(4): you can have multiple routers
on a subnet and if one goes down, clients will just pick up the
other's router advertisements.

It's atypical that one would want to disable link-local addressing,
since it's one of the core differences from IPv4 that adds some
benefit and flexibility.

References:
http://tools.ietf.org/html/rfc4861#section-4.2
      Source Address
                     MUST be the link-local address assigned to the
                     interface from which this message is sent."
--
Matt Mullins



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