Subject: link-local address on loopback interface

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 17 Jun 2005 08:02:15 +0900

This should be way too delayed for ipv6-addr-arch-v4 (already approved
by the IESG), but...

I happen to find one possible clarification which could have been in
the latest address architecture document.  In a previous discussion
back in 2002, we seem to have agreed the loopback interface does not
have to have a link-local address (with the "fe80::/10" prefix):

http://www.atm.tut.fi/list-archive/ipng/msg02583.html

...despite the requirement in Section 2.1 of
draft-ietf-ipv6-addr-arch-v4-04.txt:

   All interfaces are required to have at least one link-local unicast
   address (see Section 2.8 for additional required addresses).

(this should be generally interpreted that even the loopback interface
are required to have at least one fe80::xxx address)

It would be great if this clarification could be incorporated into the
forthcoming RFC in the editorial stage, but I'm afraid this is beyond
a purely editorial change.  (And if so, I won't push it.  We'll simply
wait for the time when we work on addr-arch-v5...)

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

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From: Bob Hinden <[email-masked]>
Date: Thu, 16 Jun 2005 16:56:27 -0700

Jinmei,

At 04:02 PM 06/16/2005, 
>This should be way too delayed for ipv6-addr-arch-v4 (already approved

Agreed!

>are required to have at least one fe80::xxx address)

Possibly, however from Section 2.5.3 "The Loopback Address" it says:

    The unicast address 0:0:0:0:0:0:0:1 is called the loopback address.
    It may be used by a node to send an IPv6 packet to itself.  It must
    not be assigned to any physical interface.   It is treated as having
    link-local scope, and may be thought of as the link-local unicast
    address of a virtual interface (typically called "the loopback
    interface") to an imaginary link that goes nowhere.

I read this as saying the loopback address is the link-local unicast 
address of the loopback interface and thus meets the requirement in section 
2.8.

Does this resolve the issue you are raising?

Bob

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 17 Jun 2005 14:40:00 +0900

>>>>> On Thu, 16 Jun 2005 16:56:27 -0700, 
>>>>> Bob Hinden <[email-masked]> said:

> Does this resolve the issue you are raising?

Ah, yes, and I should have been more careful before sending the
message...RFC3513(addr-arch-v3) already has this change, which is not
in RFC2372 and is probably a result of the previous discussion.

Thanks for the clarification, and sorry about the noise.

					JINMEI, Tatuya

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 17 Jun 2005 14:47:33 +0900

>>>>> On Fri, 17 Jun 2005 08:16:50 +0300, 
>>>>> Markku Savela <[email-masked]> said:

> Hmm.. i've missed this. For me loopback address has always had a "node
> local" scope, and it seems to work fine logically.

We should first note that the notion of "node local" scope was
deprecated in RFC3513.  But I suspect there is almost no difference in
practice between (now deprecated) "node-local" and "link-local of the
loopback link", in that addresses of those scopes should not be leaked
outside the node.  (So, it's not surprising that "it seems to work
fine", whether the official definition is "node-local" or "link-local
of the loopback link").

					JINMEI, Tatuya

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From: Bob Hinden <[email-masked]>
Date: Fri, 17 Jun 2005 07:32:27 -0700

Jinmei,

>Thanks for the clarification, and sorry about the noise.

No problem.  I was glad to find the text too :-)

Bob

---

From: Markku Savela <[email-masked]>
Date: Fri, 17 Jun 2005 08:16:50 +0300

> From: Bob Hinden <[email-masked]>

---

From: Vlad Yasevich <[email-masked]>
Date: Fri, 17 Jun 2005 11:17:29 -0400

> local" scope, and it seems to work fine logically.

But it works equally well with it being a link-local addresses belonging
to a virtual loopback link.

I've updated one implementation to use this new scoping.  The change was
minimal and actually made things easier.

-vlad

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From: Markku Savela <[email-masked]>
Date: Fri, 17 Jun 2005 21:12:03 +0300

> From: JINMEI Tatuya / =?ISO-2022-JP?B?GyRCP0BMQEMjOkgbKEI=?=
> 	<[email-masked]>

> outside the node.

I have to keep using the "node-local scope", because implementation
architecture puts it into good use internally.

There is some difference in link local and node local:

- link local addresses can actually appear on the link, outside the
  node itself.

- link local addresses need the scope id to be unique

- node local addresses can never escape the node itself.

So, I'm a bit puzzled why node-local was deprecated. It's a useful
concept, even if all implementations do not put it into any good use.

I guess I have to view it as internal implementation issue, and keep
using it.

---

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Sat, 18 Jun 2005 09:49:41 +0900

>>>>> On Fri, 17 Jun 2005 21:12:03 +0300, 
>>>>> Markku Savela <[email-masked]> said:

> concept, even if all implementations do not put it into any good use.

Node-local was deprecated by interface-local as per RFC3513.
Interface-local has all the properties for the 'good use' you
indicated above.  This is also the case for "link-local of the link
attached to a loopback interface'.

I don't know if this answers your comment, though.  But in any event,
I believe the slight difference between node-local and interface-local
doesn't matter for most users.

					JINMEI, Tatuya