Subject: RE: more comments (questions) aboutdraft-draves-ipngwg-router-selection-01.txt

From: "Richard Draves" <[email-masked]>
Date: Thu, 26 Apr 2001 21:10:03 -0700

> I have a couple of questions on the draft:

Sorry for the delay...
These are good questions.

> 1. what should a host do when it receives an RA with the preference
>    field being set to 10 (i.e. reserved)?
>    - ignore the entire RA.
>    - accept the RA, but consider the preference value as 
> another value?
>      if so, high/medium/low?
>    - other option?

How about, treat the RA as if the RouterLifetime field is zero. I think
this will produce the best compatibility with future use of the reserved
preference value.

> 2. if the preference value for a router changes, does/should it
>    affect existing destination cache entries?  For example, consider
>    the following scenario:
>    - a host H receives an RA from a router R1 with the medium
>      preference.
>    - H sends a packet to an off-link destination D.  H uses R as the
>      next hop, and records H in the destination cache.
>    - a host A then receives an RA from another router R2 with the high
>      preference.
>    now, what should happen on the destination cache for D in H?
>    Should it be removed once, prompting H to do next hop determination
>    again (and to choose the more preferred router R2).  Or, should H
>    just keep the old cache and its next hop until it becomes
>    unreachable?

I think this is a quality of implementation issue that can be left
unspecified. 

My implementation will invalidate the destination cache appropriately
when the routing table changes.

Rich
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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Sat, 28 Apr 2001 15:26:28 +0900

>>>>> On Thu, 26 Apr 2001 21:10:03 -0700, 
>>>>> "Richard Draves" <[email-masked]> said:

> this will produce the best compatibility with future use of the reserved

Hmm, but, if all routers in a segment specify the reserved value, then
a host (which supports the router preference field, but does not
understand the reserved value yet) would never be able to make off-link
communications.  I don't think it's a happy story.  (Ignoring the RA
would also be a bad choice for the same reason.)

>> affect existing destination cache entries?

> when the routing table changes.

Okay, I don't mind to leave it unspecified, but it would be better to
mention the issue in the draft anyway.

Thanks,

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
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