Subject: RE: My Thoughts on Site-Locals

From: "Michel Py" <[email-masked]>
Date: Thu, 3 Apr 2003 15:53:08 -0800

> Margaret Wasserman wrote:
> Bill Fenner, Alex Zinin, Steve Deering, Bob Hinden and I
> (along with a variety of other folks) spent a long time
> discussing this in various fora of the past two years,
> and we have not come up with any way to ensure that the
> internal path will be the shortest path (== site is
> "convex") without requiring that site boundaries be on
> routing area or AS boundaries.

Why don't you simply make this a requirement? I have heard many times
that issue about the convexity although I don't remember opposition to
coupling the site boundaries with the AS or routing area.

This is the way I would do it anyway. I understand that we should not
put restrictions when there is no need for them, but if putting a
restriction allows something to work there is nothing wrong with it.

Michel.

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From: Margaret Wasserman <[email-masked]>
Date: Thu, 03 Apr 2003 18:59:19 -0500

>coupling the site boundaries with the AS or routing area.

We probably would have...  Except that around the time that we actually
formulated the correct solution, the WG started doubting the validity
of site-border routers and started considering various alternatives for
limiting site-local usage.

The scoped addressing architecture has basically been on-hold ever
since, waiting for us to make up our collective minds about site-locals.

If the consensus to deprecate them does not hold, I'm not quite sure
what we are going to do...  We certainly don't have consensus to do
any further work on site-locals, and it isn't clear how we can
ever finalize the scoped addressing architecture without some type
of decision on this issue.  Perhaps we can break out the non-contentious
parts and advance those parts?

Well, we'll see what happens...

Margaret

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From: Alex Zinin <[email-masked]>
Date: Fri, 4 Apr 2003 00:00:50 -0800

Michel,

> coupling the site boundaries with the AS or routing area.

You can't oppose it--it just won't work otherwise (RIP being an
exception) :)

The problem or rather inconvenience with tieing site boundaries and
area/domain boundaries is that they are driven by different factors.
Imagine, for instance, that your site that is currently implemented as
an OSPF area is growing so big that you need to split it into multiple
areas to give your routers a break. Because your site boundaries are
driven by non-routing considerations (you just want your network to
continue working as it used to), you don't want to split the site into
two, so what you end up with is removing that big site from the OSPF
domain in a separate one and splitting it into its own areas, while
normally you would just have one more area in the OSPF domain.
Operationally, this might be a headache.

> restriction allows something to work there is nothing wrong with it.

I don't think this is _the_ problem. This only contributes to the list
of complications. Also count modifications to RIB, FIB management, the
forwarding process, making pings, traceroutes, etc site-aware... It's
not impossible, in fact we know exactly how to do this, it just that
complexity adds up to one side of the equation, and you really want to
avoid extra complexity in routing and below...

Alex

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From: Mike Saywell <[email-masked]>
Date: Fri, 4 Apr 2003 18:50:45 +0100

> parts and advance those parts?

It seems to me that the way out of this is to find some mechanism by which
site-locals can be considered reasonably unique.  I think it would be
sensible to define several different mechanisms for this (perhaps each
with a different prefix) as cases can be made for choosing uniqeness
based on time, geography, mac address etc.

e.g. geographical prefixes allow a degree of control and aggregation,
time or mac-address prefixs are more suiteed to zero-conf etc

If they're recommended and easy to use then I see no reason why network
managers would choose not to use them, as it's a benefit for them.

I admit I'm not an expert with regards to the scoping issues here, but
personally I don't see that these private-unique prefixes need to be
given any special treatment other than that they're the least preferred
prefix used.

Personally I do not give the "site locals + nat will be used because
re-numbering is hard" argument much credit, that's a re-numbering
issue not a site-local one.  I think it's reasonable to expect an "ipv6
renumber" command in routers, at least if re-numbering is going to be
a major concern, and for DNS I'm sure something similar can be done.

Well that's my take on it anyway :)

Cheers,

Mike