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

From: Tim Hartrick <[email-masked]>
Date: Tue, 18 Feb 2003 14:25:47 -0800 (PST)

Fred,

> 
> 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.
> 

Sure, that is what assigning an address to an interface means.  Are you saying
that you want to send datagrams that are destined to an address which is
assigned to a local interface, to a router, just because the advertised prefix
from which the address was derived had the "L" bit clear?  If one were trying
to implement the "L" bit to a fault, one might consider doing this but it is
hard to see this being the first implementation choice that would occur to
someone.  Typically the act of assigning an address to a local interface
implies node-local reachability.  If there are implementations that don't
assume this, I have never seen them.

Tim Hartrick
Mentat Inc.
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From: "Fred L. Templin" <[email-masked]>
Date: Tue, 18 Feb 2003 15:03:55 -0800

Tim,

Tim Hartrick wrote:
> from which the address was derived had the "L" bit clear? 

No; I'm not saying that. I don't see any ambiguity in accepting the /128
resulting from address autoconfiguration as being "on-node"; i.e., it seems
clear enough that packets sent by the node to the autoconfigured address
should be looped back internally and not sent to a router. But, I still see
it as ambiguous as to whether the /128 must be "on-link" with the interface
the RA arrived on.

Thanks,

Fred
[email-masked]