Subject: RE: draft-ietf-ipngwg-site-prefixes

From: Richard Draves <[email-masked]>
Date: Thu, 9 Dec 1999 19:10:08 -0800

I've been sitting for a while on some comments based on implementing (all
but reverse dns lookup) the 03 draft:

Should there be a validation for S-bit processing of Prefix Information
Options that the site prefix length is <= prefix length?

It's a bit unclear when a node auto-configures site-local addresses. I
assume that a Prefix Information Option with A bit and fec0 prefix is used?
(The alternative being that a Prefix Information Option with S and A bits
and global prefix results in configuring both a global address and a
site-local address.) The description of the S bit in section 4 ("used to
create site-local addresses") is confusing me on this point.

In section 8.1 - I'd rather keep both site-local and global addresses in the
returned address list and let the destination address ordering algorithm
apply.

I think there needs to be more in section 8.1 about site scope-ids. When a
site-local address is returned it needs a site scope-id value. I think this
can be derived by keeping track of what interface learned what Site
Prefixes, and using the site scope-id value associated with the interface of
the relevant Site Prefix.

It was enough code that I think it should be optional. So allow simple
implementations, when looking at an address list with both site-local and
global addresses, to just remove the site-local addresses without keeping
track of Site Prefixes.

Rich
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From: Erik Nordmark <[email-masked]>
Date: Thu, 9 Dec 1999 22:52:10 -0800 (PST)

> Options that the site prefix length is <= prefix length?

Well, if neither the L or the A bit are set then Prefix Length doesn't make
sense. Thus the check would be a bit complex.
And it seems better to keep things orthogonal.

> assume that a Prefix Information Option with A bit and fec0 prefix is used?

Correct. Nothing new here.
Is this something that it would make sense to clarify in the draft?

> create site-local addresses") is confusing me on this point.

Ah - that "create" would have made sense in -00.txt but is both incorrect and
confusing now. Something like "used to determine when to accept and prefer
site-local addresses over global addresses" is the intent.

> returned address list and let the destination address ordering algorithm

The disadvantage of doing that is that you can't ensure that site-local
communication uses site-local addresses. For instance if a router is broken
when the application tries to connect the application might fail to connect
using the site-local address. When it tries to connect using the global
address the router might be back up.

> the relevant Site Prefix.

Hmm - I wonder if this is the right document to wander into API land which
is where scope-ids appear.
Perhaps it can be phrased without using the term scope id.
Something along the lines of
	In multi-sited nodes the site-local addresses need to be associated
	with the set of interfaces that are connected to a site.
	[Some APIs do this using a scope-id concept - see XXX]
	This identification can be done by tracking the interface for which
	the site prefix matched in step 3) and use that interface
	to determine the associated attached site.

> global addresses, to just remove the site-local addresses without keeping

Sorry, what was enough code? 

Yes, simple implementations might want to
ignore site-local addresses unless the RRset contains only site-local
addresses i.e. the case when the site is not connected to the Internet.

   Erik

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From: Jim Bound <[email-masked]>
Date: Fri, 10 Dec 1999 11:47:15 -0500

Erik,

None of this should be mandatory.  In other words the user should have
a choice to not use your draft and it should not be the default.  The
default should be to use global addresses?

Do you agree?

thanks
/jim