Subject: RE: Making Autoconfig Optional [Was RE: draft-ietf-ipv6-cellular- host-00.txt -> wg last call?]

From: "Karim El-Malki (ERA)" <[email-masked]>
Date: Mon, 4 Mar 2002 10:44:01 +0100

Hi Margaret

 > My understanding is that the 3GPP group is actually migrating towards
 > a more standard IPv6 configuration mechanism, using router 
 > advertisements
 > and allowing hosts to generate their own interface IDs.

Yes, we all agree that was the right decision.

 > 
 > Currently the cellular hosts draft says:
 > 
 > "IPv6 Stateless Address Autoconfiguration [RFC-2462] MAY be 
 > supported."
 > 
 > However, I think that RFC 2462 should be a MUST for all IPv6 nodes.

I think this is related to 3GPP hosts in particular and it is the use of
DADs here that may be excluded. In the 3gpp-advice draft we basically
assign a /64 to the cellular host. That is, the upstream router (GGSN)
only advertises the /64 to one connection/host. A major reason to do that
was to forego a large number of (unreliable) DADs over lossy and expensive
wireless point-to-point links. Specifically, if we use unreliable DADs as a
way for the upstream router to know which addresses are in use there could be
problems. In the 3GPP case, even without DADs no duplication occurs on the
point-to-point link since the upstream router doesn't configure addresses
on the advertised /64 prefix.

Regards
/Karim
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From: Francis Dupont <[email-masked]>
Date: Mon, 04 Mar 2002 11:24:01 +0100

A way to solve your DAD/autoconf issue is to "delegate" the /64 prefix
and to keep only link-local addresses using link-layer negociated
interface IDs (negociation is very simple and just checks the interface
IDs of the both ends are different). The link has to be point-to-point
but this is the only constraint (you can even use PPP if you'd like).

Regards

[email-masked]

PS: prefix delegation should be one topic of the next IPv6 WG meeting.

---

From: Robert Elz <[email-masked]>
Date: Tue, 05 Mar 2002 14:39:51 +0700

Date:        Mon, 4 Mar 2002 10:44:01 +0100 
    From:        "Karim El-Malki (ERA)" <[email-masked]>
    Message-ID:  <795A014AF92DD21182AF0008C7A404320DFBEFB8@esealnt117>

  | I think this is related to 3GPP hosts in particular and it is the use of
  | DADs here that may be excluded. In the 3gpp-advice draft we basically
  | assign a /64 to the cellular host. That is, the upstream router (GGSN)
  | only advertises the /64 to one connection/host. A major reason to do that
  | was to forego a large number of (unreliable) DADs over lossy and expensive
  | wireless point-to-point links

I have seen this argument a couple of times now, and there's, I believe,
a degree of correctness about it.  Like others, I can see links where
address assignment policies don't require DAD to be used, and so where
using it would just be a waste of time (and bandwidth, which may or may
not matter).

But notice just what this is about - it is a property of the link technology
in use, and has absolutely nothing to do with the host that is connected
at the end of it.

That is, the proper place to make this kind of argument / statement, would
be in a draft with a title something like "IPv6 over 3GPP network links",
which would look very much like the "IPv6 over foobar" drafts/rfcs that
now abound.

It most certainly should not be in a "requirements for xxx hosts"
regardless of the value of xxx - even though a side effect of the
statement in a "IPv6 over 3GPP" draft might be that a host which only
implements a 3GPP interface might not need to implement DAD at all.

kre

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From: Margaret Wasserman <[email-masked]>
Date: Tue, 05 Mar 2002 09:57:43 -0500

I agree with Robert on this...

>which would look very much like the "IPv6 over foobar" drafts/rfcs that

Many of the specific technical issues raised in this "requirements"
document would be best handled in an "IPv6 over <foo>" document.
This document could cover the specific behaviour of IPv6 over a
cellular link.

We should also update some of the base IPv6 specs to expect that
certain portions of IPv6 behaviour (i.e. whether or not to use
DAD) will be dependent on the link type, and defined in the
"IPv6 over <foo>" documents for each link type.  Of course, we 
then have to define this behaviour for each of the link types 
that we've already specified (ethernet, PPP, etc.).

None of this is rocket science, but it will require some updates
to existing standards currently at DS.  Is this something that
we want to do at this point?

>implements a 3GPP interface might not need to implement DAD at all.

In fact, I am pretty certain that we _don't_ want to head down
the path of publishing an informational "Requirements for xxx Hosts"
document for every specialized host type...  Over time, it will 
be impossible to maintain these documents, and they will mislead
people regarding what the actual standards-based requirements are
for IPv6.

Margaret