Subject: Re: Why I support deprecating SLs

From: Dan Lanciani <[email-masked]>
Date: Thu, 3 Apr 2003 17:44:27 -0500 (EST)

|Thomas Narten <[email-masked]> wrote:
|
|> 	- Site-locals should be retained as a means for internal
|> 		connections to survive global prefix renumbering.
|
|4) This is strikes me as a nice requirement, but something we don't
|   have a solution for, even with SLs. We need to accept that we have
|   no solution and SL is doesn't really seem to be a help here.

Please explain why you feel that internal connections using site-locals will
not survive global prefix renumbering.

				Dan Lanciani
				ddl@danlan.*com
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From: Thomas Narten <[email-masked]>
Date: Thu, 03 Apr 2003 20:16:35 -0500

> not survive global prefix renumbering.

Internal connections using SLs will survive renumbering. But that is
the easy part and by itself is largely uninteresting.

The tough question is, how do we get applications in general to prefer
SLs for local communication. Note that it is not enough for a handful
of applications to use SLs and survive renumbering, my assumption is
you want pretty much all intra-site communication to use SLs. I.e., if
only 30% of your intra-site traffic is using SLs, and a renumbering
takes place, 70% of your traffic is still potentially impacted. That
doesn't seem like much of a real solution to me.

I have yet to see what I believe is a credible approach to getting
applications to prefer SLs across the board. Some people suggest we
need to do split DNS. But their is no real consensus in the community
for doing this. For example, I'll note that the DNS community has
never been willing to officially bless split DNS behavior. They
understand folks use it, but there are problems with the approach, and
the DNS community has never had consensus that the benefits outweighed
the problems. Hence, no IETF spec officially advocates split DNS,
AFAIK. So, approaches that rely heavily on split DNS being even more
widely deployed that it is already (e.g., in homes and other places
with no clueful operations support) seems like an uphill fight at best

There was some work done a few years ago
(draft-ietf-ipngwg-site-prefixes-xx.txt) that tried to come up with a
way of getting intra-site traffic to favor SLs. But the author
eventually concluded their were problems with the approach and
abandoned it. Plus, it required everyone implement the draft, and
we've long since missed the window for making this happen.

So, IMO, the notion that SLs protect a site agains the impact of a
renumbering event is one of those IPv6 myths for which there is no
real story to back up the desire. I wish it were otherwise.

Thomas