Re: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt

JINMEI Tatuya / 神明達哉 <Jinmei_Tatuya@isc.org> Fri, 18 July 2008 02:10 UTC

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Date: Thu, 17 Jul 2008 19:11:07 -0700
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From: JINMEI Tatuya / =?ISO-2022-JP?B?GyRCP0BMQEMjOkgbKEI=?= <Jinmei_Tatuya@isc.org>
To: Erik Nordmark <erik.nordmark@sun.com>
Subject: Re: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt
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At Mon, 14 Jul 2008 03:22:44 -0700,
Erik Nordmark <erik.nordmark@sun.com>; wrote:

> > BSD variants have in fact supported this behavior for years: I've just
> > tested this with a FreeBSD 7.0 box and confirmed it (that is, if that
> > host receives an NS from an address that is not covered by "on-link"
> > prefixes advertised by RAs, it will create a specific neighbor cache
> > entry for that address).  I've also quickly checked that Linux
> > (seemingly) supports this behavior, too.
> 
> Did you verify that it in fact treats the source of the NS as on-link as 
> a result?

Yes.

> I don't have an issue with creating a neighbor cache entry; that has no 
> security implications because it does impact anything but the neighbor 
> cache on the interface where the NS was received. The question is about 
> on-link determination.
> Thus will the source of the NS be treated as on-link? Is the behavior of 
> the implementations different if the source of the NS falls in a prefix 
> which is already considered on-link on some other interface?

Ah, that's an interesting point.  To be clear, you're asking about a
case like this

- the receiving node has two interfaces, I1 and I2
- the node regards prefix P as on-link on interface I1
- the node receives an NS from P::X on interface I2

right?  I've not tested that case, but according to the source code,
I guess the following will happen:

- if the node has already a neighbor cache entry for P::x on interface
  I1, it does nothing about the source address of that NS
- if the node does not have any neighbor cache entry for P::x on any
  interface, it will create a new neighbor cache entry on interface
  I2.

But, this is a tricky case, so I may be wrong.

---
JINMEI, Tatuya
Internet Systems Consortium, Inc.
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