Subject: Re: A6 and Site / Link Local

From: "Matt Crawford" <[email-masked]>
Date: Mon, 07 Aug 2000 14:23:02 -0500

Mark explained this idea to me in Pittsburgh and once I finally
understood it, it seemed extremely useful at a very low cost.
Essentially, you'd leave the A6 records for the shortest global
prefixes alone, but put site-local and, if you wish, link-local
prefixes into your DNS, putting a DNS name of your choice into the
final A6 record with prefix length=0.  Example:

$ORIGIN example.com.
myhost          A6 64 ::1234:5678:9abc:def0 subnet-one.ip6
subnet-one.ip6  A6 48 0:0:0:1::  ip6
                A6  0 fe80:0:0:: link-one
ip6             A6 48 0::0       example-com-usa.ip6.my-isp.net.
                A6  0 fec0:0:0:: usa-hq
yourhost	A6 64 ::0246:8ace:1357:9bdf subnet-two.ip6
subnet-two.ip6  A6 48 0:0:0:2::  ip6
                A6  0 fe80:0:0:: link-two
herhost         A6 64 ::048c:159d:26ae:37bf subnet-eins.ip6
subnet-eins.ip6 A6 48 0:0:0:1    ip6de
                A6  0 fe80:0:0:: link-eins
ip6de           A6 48 0::0       example-com-de.ip6.andere-isp.de.
                A6  0 fec0:0:0:: de-site
usa-hq          TXT "There need not be any record at this label."
de-hq           TXT "There need not be any record at this label either."

So now if myhost looks up yourhost it gets a site-local address as
well as a global address.  The last RR of yourhost's site-local A6
chain has the same "prefix name" field as the last RR of myhost's
site-local A6 chain, so myhost can conclude that yourhost is on the
same site.  Similarly, it can conclude that yourhost is not on the
same link as my host, and that herhost is not on the same link or
site.

> 	Currently A6 records w/ prefix 0 do not have a prefix
> 	domain name.  Redefining A6 records with prefix 0 to
> 	have a domain name and to use this name as a site /
> 	link local identifier is still possible at this point
> 	in time.
> 
> 	Doing this would provide a mechanism to identify which
> 	of a number of addresses you which to use.

Today I thought of one possible simplification.  Couldn't the *owner
name* of the final A6 record in a chain be used for the same purpose?

______________________________________________________________________________
Matt Crawford                    [email-masked]                     Fermilab
"A5.1.5.2.7.1. Remove all classified and CCI boards from the COMSEC equipment,
thoroughly smash them with a hammer or an ax, and scatter the pieces."
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From: [email-masked]
Date: Fri, 04 Aug 2000 06:39:30 +1000

Mark

-- 
Mark Andrews, Nominum Inc.
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE:	+61 2 9871 4742		         INTERNET: [email-masked]

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From: [email-masked]
Date: Thu, 10 Aug 2000 01:12:54 +1000

> same link as my host, and that herhost is not on the same link or

	They can also be used to reference the appropriate value
	to fill in the sockaddr link field.
> name* of the final A6 record in a chain be used for the same purpose?

	I doesn't work where the chains are of length 1.

	Mark

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From: Jun-ichiro itojun Hagino <[email-masked]>
Date: Thu, 10 Aug 2000 05:41:34 +0900

>> same link as my host, and that herhost is not on the same link or

	Matt, did you intentionally pick linklocal address as the example
	above?  I don't think you should put linklocal address onto globally
	reachable DNS name tree.  even site-local is questionable too.
	or do you expect some magical code in name server to filter fe80::
	prefixes out from remote queries?

itojun

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From: [email-masked]
Date: Thu, 10 Aug 2000 12:32:45 +1000

> 	prefixes out from remote queries?

	No, but it is not unreasonable to have getipnodebyname() and / or
	getaddrinfo() use the "prefix" field to optionally filter non
	local addresses based on a local table of site / link local names
	and in getaddrinfo() case to fill in sin6_scope_id.

	Mark