Subject: comments on draft-kohno-ipv6-prefixlen-p2p-00.txt

From: JINMEI Tatuya / 神明達哉 <[email-masked]>
Date: Mon, 09 Nov 2009 14:19:44 +0900

I've read this draft.  I don't have a strong opinion on the proposal
per se, but have a couple of minor comments:

1. In Section 4, the draft says:

   However, Subnet-router
   anycast address has not been implemented and in practice, this has
   not been a problem.

I'm afraid "has not been implemented" is too strong.  In fact, we have
"implemented" it in the KAME/BSD IPv6 stack in that we implemented
special restrictions (at that time) on anycast addresses and had
experimentally assigned subnet-router anycast addresses on PC-based
IPv6 routers.  In general, it's difficult to declare something hasn't
been implemented because it eliminates any minor implementation
activity, which is almost impossible to prove.

I have no objection to the conclusion itself (i.e. not a problem in
practice) and would rephrase it to something like this:

   However, Subnet-router anycast addresses have not been (widely)
   deployed, and this has not been a problem in practice.

2. In section 5, it states:

         1) A rule described in ICMPv6 [RFC4443] indicates that a
         Destination Unreachable (Code 3) message should be sent by a
         router rather than forwarding packets back onto point-to-point
         links from which they were received if their destination
         address belongs to the link itself.

This sentence is clear, but IMO is not perfectly accurate because an
address doesn't belong t(or isn't assigned to) a *link*; it's assigned
to an interface.  The corresponding text of RFC4443 reads:

   One specific case in which a Destination Unreachable message is sent
   with a code 3 is in response to a packet received by a router from a
   point-to-point link, destined to an address within a subnet assigned
   to that same link (other than one of the receiving router's own
   addresses).

where it's a *subnet* that is assigned to the link.  So, to be very
accurate, I'd propose to revise the text (e.g.) as follows:

         1) A rule described in ICMPv6 [RFC4443] indicates [...]
         if their destination address matches a subnet that belongs to
         the link itself.

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

---

From: Pekka Savola <[email-masked]>
Date: Tue, 10 Nov 2009 09:07:52 +0200 (EET)

> activity, which is almost impossible to prove.

I agree that the wording is a bit strong, and I'm ok with weakening 
it, but I've yet to see an implementation that enables it by default 
or even by an enable/disable configuration directive.

AFAIK, on KAME/BSD it's "implemented" in such a fashion that the 
operator must manually configure it with "ifconfig".  I wouldn't call 
that "implemented" myself. At least on my FreeBSD 7.2 router, subnet 
router anycast address isn't configured automatically and I don't even 
see system configuration parameters (e.g. in init scripts) which would 
change this.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: JINMEI Tatuya / 神明達哉 <[email-masked]>
Date: Wed, 11 Nov 2009 18:51:09 +0900

At Tue, 10 Nov 2009 09:07:52 +0200 (EET),

> see system configuration parameters (e.g. in init scripts) which would 

I won't try to win the debate of the definition of implementation.
It was not my point that the KAME/BSD may implement it.  The point is
that the original wording of the draft was unnecessarily strong.  And
since we both seem to agree on that point, I think we are done.

---
JINMEI, Tatuya