Subject: [DNA] MUST NOT add DNA Option when landmark RA = NO? (draft-pentland-dna-protocol-00.txt)

From: Greg Daley <[email-masked]>
Date: Wed, 01 Jun 2005 13:46:00 +1000

I'm confused by this statement in the draft:

In Section 5.1.4:

"... If the RS contains a Landmark Option whose prefix does not
  match any of those in the interface's stored prefix list, then
  the Landmark option with the Landmark prefix is included in the
  RA but with the No flag set.  All fixed options (MTU,
  Advertisement Interval, flags, etc.) are added to the Router
  Advertisement.  Prefix Information Options for any explicitly
  configured prefixes SHOULD be added to the Router
  Advertisement, while the DNAO for learned prefixes MUST not be
  added."

Is there a reason why DNAO MUST NOT be sent in this case?

Isn't it useful to indicate immediately which of the
prefixes are available on the new link?

Greg

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From: Brett Pentland <[email-masked]>
Date: Wed, 01 Jun 2005 14:27:05 +1000

MUST NOT is probably too strong.  SHOULD NOT or even MAY NOT
might be ok.  I don't think there's much value
in the DNA option in this case, because the host cannot use the
prefixes in it for configuration. Those same prefixes
should arrive in PIOs in RAs from the router(s) where they are
explicitly configured, very soon anyway.

Brett.

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From: Greg Daley <[email-masked]>
Date: Wed, 01 Jun 2005 14:54:44 +1000

Hi Brett,

> explicitly configured, very soon anyway.

Can't the host use the prefixes learnt from the DNAO to not be
surprised by prefixes in responding RAs (which may not be DNA RAs)
to its existing solicitation?

Greg

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From: Ranjitsinh Wable <[email-masked]>
Date: Wed, 01 Jun 2005 10:24:47 +0530

Hi Greg,

I agree on your point. But as per my understanding this is the case when
the node has moved to the new link and want to configure
 the address and based on the source address of the RS
and ranking the router which decide to respond need to send its prefixes.
Router can send all the learned prefixes but at this point of time the
host will not be interested in learned prefix information unless host have
any preferences of prefixes and based on this information want to wait for 
more RAs.
So there is no point in adding this information and the consuming the 
bandwidth.

This is my understanding but its better if authors clear the point.

Thanks and Regards,

Wable R. U.
----- Original Message ----- 
From: "Greg Daley" <[email-masked]>
To: <[email-masked]>
Sent: Wednesday, June 01, 2005 9:16 AM
Subject: [DNA] MUST NOT add DNA Option when landmark RA = NO? 
(draft-pentland-dna-protocol-00.txt)

---

From: Brett Pentland <[email-masked]>
Date: Wed, 01 Jun 2005 15:50:16 +1000

> to its existing solicitation?

Yes, but the DNA router responses would usually be received first,
and the non-DNA router responses would have to be dealt with using
CPL logic anyway, and shouldn't cause confusion.

Brett.

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 01 Jun 2005 11:02:04 -0700

> to its existing solicitation?

What did you have in mind the host would actually do to be "less surprised"?

If it records the DNAO prefix somehow, what would it then do when it
  - receives an RA with a prefix which was recorded from the DNAO
  - receives an RA with a new prefix which was not recorded from a DNAO?

FWIW the conceptual data structures in RFC 2461 can only capture 
prefixes for which all the information in the PIO is present, i.e. the 
lifetimes and the flags must be includes.

    Erik

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From: Greg Daley <[email-masked]>
Date: Thu, 02 Jun 2005 11:05:52 +1000

Hi Brett,

> Greg Daley wrote:
[cut]
> CPL logic anyway, and shouldn't cause confusion.

As you know, I'm not arguing against the possibility of leaving
out the options per se, but I'd guess we  were trying to avoid
using CPL logic in most circumstances (wanting definitive
identification, rather than implicit).

If routers know there is limited cost to providing this, I guess
that there's no reason to prohibit them.

Greg

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From: Greg Daley <[email-masked]>
Date: Thu, 02 Jun 2005 12:12:18 +1000

Hi Erik,

> What did you have in mind the host would actually do to be "less 

I'm still cooking something, but to talk now on list
wouldn't really help the discussion

Please contact me if it's important to know now.

>  - receives an RA with a prefix which was recorded from the DNAO

It would be able to tell they belong to the same link.

>  - receives an RA with a new prefix which was not recorded from a DNAO?

That depends...

If it was 'surprised' I guess it would be treated as a hint of change
(like in CPL).

I think it's possible to do better than CPL with the learning phase
though (since you have an explicit CPL in the CompleteRA).

> lifetimes and the flags must be includes.

Yes, that's right.   It's not necessary to use exactly these
data structures, though if you're not using them for address
configuration, just for link identification.

(Though the link identification logic could be assisted if you
knew them).

Greg