Re: Link-local IPv6 addresses in the DNS

Kerry Lynn <> Tue, 22 November 2011 21:56 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 4F53D1F0C6D for <>; Tue, 22 Nov 2011 13:56:38 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -4.478
X-Spam-Status: No, score=-4.478 tagged_above=-999 required=5 tests=[AWL=1.120, BAYES_00=-2.599, GB_I_LETTER=-2, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-1]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id KzI5OLFjgm6Y for <>; Tue, 22 Nov 2011 13:56:37 -0800 (PST)
Received: from ( []) by (Postfix) with ESMTP id 80BDA1F0C6B for <>; Tue, 22 Nov 2011 13:56:37 -0800 (PST)
Received: by yenm7 with SMTP id m7so816024yen.31 for <>; Tue, 22 Nov 2011 13:56:37 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=SDehWm+5GdZFBE04A0qrmEdXRwkrjHBpTKwBFweTzqM=; b=gXrlk2YcXctnXbiC7e6qWFMdD1VxpY1HDrzsZs3TiqjLe7NcWV+0PPwcUhFzIgToIg ywIedVOImaY3YHPomanSga5OYRFY4XaSCh/a65eKblhwVTIzO6aS/t6CT+YDh4m3ZoMz z8eKwFJlnvEagnwSFlnekzGw8nh4QOH3gU/wo=
MIME-Version: 1.0
Received: by with SMTP id c37mr1139217eec.88.1321998996528; Tue, 22 Nov 2011 13:56:36 -0800 (PST)
Received: by with HTTP; Tue, 22 Nov 2011 13:56:36 -0800 (PST)
In-Reply-To: <>
References: <> <>
Date: Tue, 22 Nov 2011 16:56:36 -0500
Message-ID: <>
Subject: Re: Link-local IPv6 addresses in the DNS
From: Kerry Lynn <>
To: Mark Andrews <>
Content-Type: multipart/alternative; boundary="0016e659fe0c94dedc04b259e0a0"
X-Mailman-Approved-At: Wed, 23 Nov 2011 05:29:02 -0800
Cc: 6man <>, Philip Homburg <>, Brian E Carpenter <>, Tomoyuki Sahara <>
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 22 Nov 2011 21:56:38 -0000

On Tue, Nov 22, 2011 at 3:52 PM, Brian E Carpenter <> wrote:

> On 2011-11-23 05:34, Philip Homburg wrote:
> > In your letter dated Tue, 22 Nov 2011 14:30:03 +1100 you wrote:
> >> On a related issue to link locals in URI's, we don't currently have
> >> a good method of supporting link locals in the DNS.  Sure we can
> >> add them as AAAA records but they are essentially useless as the
> >> scope information is lost.  People keep saying use LL for disconnected
> >> but it just doesn't work without more support.
> Other people keep saying "use ULA for disconnected". The fact
> that you can put ULA into (er, local) DNS without any fancy
> stuff is a distinct advantage.
> IMHO link-local should be used only for bootstrapping a host and
> for diagnostic purposes. I guess I could statically configure a
> printer on fe00::a%1 if I really had no choice.
> This is a distinctly different problem than the one that kicked off the
local discussion.  In the web browser case, you know the link-local
destination address of the server a priori but it only has validity with
respect to a particular link, and there's no way to indicate the zone
index to the browser (assuming multi-homed client here).  The once-
existing capability was removed because there is no RFC support for it.

The DNS case seems like a server-side issue.  In the case of link-
local adresses stored in AAAA records, the zone index would seem to
indicate the corresponding interface with respect to the *server* (assuming
a multi-homed server here).  What's more, the DNS server would need to
keep track of the interface on which the query arrived and only respond
with a link-local address if the client and server are on the same

Some additional observations:
- If you want to stay with link-local addresses then perhaps multicast
  DNS is the best solution for you.
- If you want to stay with unicast DNS, then ULAs have the advantage
  of being routable and the problem goes away.
- If you want to stay with link-local addresses *and* DNS, then perhaps
  you need to engage dnsext WG to discuss the server-side issues.


> >
> > For disconnected operation, why not have getaddrinfo fill in the scope?
> > Just set it to the interface over which the DNS reply arrived.
> >
> > I have to admit that this may become a bit tricky if the DNS resolver is
> local
> > or if interface information is lost in some other way.
> >
> >