Re: [DNA] linkid [Was: Couple of points ondraft-jinchoi-dna-soln-frame-00.txt]

[Erik Nordmark <Erik.Nordmark@sun.com>]

> Really I was talking about a common (explicit)
> linkID, which could be configured on all
> routers. 
> 
> The existing 2461 statements about disjoint prefixes
> being allowed on a subnet would indicate that 
> routers will not be able to always agree on a 
> prefix which they can all advertise.

No matter how the linkid is picked (some local ID, a large random
number, or an existing prefix) the routers on a link would need to
agree on which number they advertise. Thus unless
you do manual config or the routers, there needs to be a router-to-router
protocol to agree on the number to advertise. (And DET also needs a 
router-to-router protocol for agreement about something else, so
one can probably do this in the same exchange.)

> If they did so, one or more routers would be
> advertising a global prefix they have no
> existing configuration knowledge of...

Yes, but that is true for a linkid which is a random number as well.

> This may be misleading or inappropriate
> when dealing with non-DNA ipv6 hosts.

I'm confused. I'm assuming there will be a new linkid option in the
RA with the semantics know to the host that "this uniquely identifies a link".
Thus non-DNA hosts would silently ignore that option.
Further, whether the number in the linkid option is a random number (which
the routers on the link agreed on), or a global prefix assigned to the link
(which the routers on the link agreed on) doesn't even have any impact
on DNA aware hosts. The only issue is whether
 - the probability of random numbers colliding should be of concern
 - the need to change a prefix-based linkid when the link is renumbered
   is of concern

> If we have a separate option which has
> a globally unique identifier (or even a locally
> unique one), then the information will have
> different semantics not tied to existing 
> prefix information option semantics.

Ah - you thought I wanted to use the prefix information option to carry
the linkid. I don't. But that explains the confusion.

> This may lead to additional information being
> transmitted in RAs though (the explicit 
> link identifier option).

Yes, but if we have a random number as the source for the linkid,
it might make sense to make that as large as 128 bits as well.
So the size of the linkid option might be the same whether random
or prefix-based.

   Erik