Subject: Re: M & O Bits was: draft-ietf-ipv6-node-requirements-01.txt

From: Tim Hartrick <[email-masked]>
Date: Tue, 18 Feb 2003 12:23:54 -0800 (PST)

Fred,

I have myself been confused by the L bit in the past but I don't think
there is anywhere near as much ambiguity here as you.  And, if there is
the node requirements document isn't the place to fix it.

> 
> I'm still of the opinion that some ambiguity exists. Namely, if a prefix
> option has the Autonomous flag ("A" bit) set and the on-link flag ("L" bit)
> NOT set, one could infer from reading RFC 2462, section 5.5 that it is OK
> to go ahead and configure an address from the (off-link) prefix as specified
> in 5.5.3 d). But then, which link would one derive an interface identifier
> from in order to form an address? (And, which interface would one assign
> the address to?)
>

It is correct to infer that one should configure an address from a prefix
option with the A bit set and the L bit clear.  Is it really necessary to
spell out that the address should be configured on the interface on which
the advertisement was received?  What would justify making any other choice? 

Tim Hartrick
Mentat Inc.
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From: "Fred L. Templin" <[email-masked]>
Date: Tue, 18 Feb 2003 13:56:36 -0800

Tim,

> the advertisement was received?  What would justify making any other choice?

Right now, all RFC 2462 (section 5.3.3) says is to go ahead and configure
addresses for prefix options with the "A" bit set; the "L" bit is don't-care.
But, RFC 2461 (section 6.3.4) says that "a prefix information option with the
on-link flag set to zero conveys no information concerning on-link determination",
i.e., you can't tell whether the prefix is on/off link. But, if you configure an
address from a prefix option with the "L" bit set to zero and assign it to the
interface the RA arrived on, you are in effect declaring that at least one /128
chunk of the prefix is on-link. But, I don't see any text in RFC 2461 that says
you can assume this. This is where I see the ambiguity.

Fred
[email-masked]

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From: JINMEI Tatuya / 神明達哉 <[email-masked]>
Date: Wed, 19 Feb 2003 12:12:25 +0900

>>>>> On Tue, 18 Feb 2003 13:56:36 -0800, 
>>>>> "Fred L. Templin" <[email-masked]> said:

>>> from in order to form an address? (And, which interface would one assign

I agree with Tim (and perhaps Thomas).  I don't see any ambiguity in
RFC 2461 and RFC 2462 on this point.

> you can assume this. This is where I see the ambiguity.

I don't see why we need to declare one /128 chunk.  Perhaps you are
just confused about a "on-link" prefix and a prefix (of the same
length) as a base of address configuration.  These two are, at least
conceptually, orthogonal, which is very clear to me from the spec.

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