Subject: RE: DAD

From: "Brian Zill" <[email-masked]>
Date: Tue, 5 Jun 2001 16:51:53 -0700

Julian,

When this idea was suggested at the Interim Meeting, several people
expressed concern about needing to have a link-local address for every
interface identifier you might be using.  A node may want to have a
large number of global addresses, for example, and the overhead of
requiring that it keep a corresponding link-local address for each might
be prohibitive.  I think I'd prefer to just perfom DAD on all the global
addresses instead.  It's the same amount of DADing going on, and you
don't need to keep all those link-local addresses around.

--Brian

> -----Original Message-----
> From: Sellers, Julian P [mailto:[email-masked]] 
> Sent: Tuesday, 05 June, 2001 14:04
> To: 'Thomas Narten'
> Cc: [email-masked]'; [email-masked]'
> Subject: RE: DAD 
> 
> 
> Thomas,
> 
> Is there a problem with requiring nodes to perform DAD on the 
> link-local address generated from a given interface 
> identifier, even if they only want to use the site-local or 
> the global address?  That's what I thought the following 
> sentences from 5.4 of RFC 2462 required:
> 
>         Thus, for a set of addresses formed from the same
>         interface identifier, it is sufficient to check that the link-
>         local address generated from the identifier is unique on the
>         link. In such cases, the link-local address MUST be tested for
>         uniqueness, and if no duplicate address is detected, an
>         implementation MAY choose to skip Duplicate Address Detection
>         for additional addresses derived from the same interface
>         identifier.
> 
> It's not clear to me what the qualifier "In such cases" 
> refers to.  Maybe this paragraph just needs to state clearly that
> 
>      - If a node has successfully performed DAD on a 
> link-local address, the node has the
>        right to all addresses on the same link that contain 
> the same interface identifier.
>      - If a node has not performed DAD on the link-local 
> address, or if the link-local
>        address has failed DAD, the node must not use any 
> address on that link generated with
>        the same interface identifier.
> 
> Julian
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---

From: Markku Savela <[email-masked]>
Date: Wed, 6 Jun 2001 09:14:55 +0300

> From: "Brian Zill" <[email-masked]>

> don't need to keep all those link-local addresses around.

My proposal, doing the DAD related comparison only with the ID part,
solves the same problem, but lets you do single DAD / Id, regardless
of the number of prefixes you combine with this id. And, you don't
need to generate link-local address, if you are not using it.

There was some concern about the backwards compatibility, but I
*still* cannot see this introducing any more problems than what
already exists legally by the current specification, where you can
have hosts reserving ID for all combinations by DAD on link local, and
hosts that don't do that.

And, if you change specification, might as well change it to what I
proposed :-).

-- 
Markku Savela <[email-masked]>