Subject: WG ACTION: 2 weeks to discuss [LL56] Contradictory text?

From: Erik Guttman <[email-masked]>
Date: Wed, 5 May 2004 00:59:46 +0200

Please post discussion of this issue to the mailing list over the 
next two weeks
ending May 18, 2004.  In order to accept this issued, we will need a strong WG
consensus given that this is very late in the process.

Please see http://www.drizzle.org/~aboba/ZEROCONF/issues.html for a list of
current issues and their status.

[LL56]

Description of Issue:		Contradictory text?
Submitter Name:                 Stuart Cheshire
Submitter Email Address:        [email-masked]
Date first submitted:		04 May 04
Reference:
Comment Type ['t'ech|'e'dit]:	t
Prio ['S' Must|1 should|2 may]:	S
Section:			1.4, 1.8
Rationale/Explanation:
Lengthy Description:

[Stuart]

>         IPv4 addresses ...
>       ... which can only be resolved on the local link ...
>       ... SHOULD only be sent when a Link-Local address
>       is used as the source address.

Sent how? In the header? In the payload? Doesn't this contradict the text
later in the document that says:

>    There will be cases when devices with a configured Link-Local address
>    will need to communicate with a device with a routable address
>    configured on the same physical link, and vice versa.  The rules in
>    Section 2.6  allow this communication.

This says that link-local addresses *can* be used when the source address
is *not* link-local.

[Erik]

The IPv4 address would be sent in the LLMNR (DNS) payload.  I though
that was obvious due the the context in the paragraph.

The first paragraph refers to text in section 1.4.b which discuss
limitations of the use of IPv4 LL when used with LLMNR.  The second
paragraph is in section 1.8 which discusses general communication
between two hosts.  In the latter case, the text is definitely
appropriate.

I believe there is no contradiction.  1.4.b does not hinder the use of
LLMNR or IPv4 LL configuration except in one case:  A host implementor
is admonished (using SHOULD) to only hand out a LL address using LLMNR
when the host has a LL configuration and only from an interface which in
fact has been configured with an LL adddress.

[Stuart]

I disagee.

As stated, a device with a routable address, and a link-local-scope name
of some kind, is prohibited from answering queries for that name, because
the name can only be resolved on the local link, but the device doesn't
have a Link-Local address to use as the source IP address.

[Erik]

  The full quote is:

       IPv4 addresses and names which can only be resolved on the local
       link SHOULD NOT be forwarded, they SHOULD only be sent when a
       Link-Local address is used as the source address.  This strong
       advice should hinder limited scope addresses and names from
       leaving the context in which they apply.

     There is no prohibition.  There is only a 'SHOULD' implying that
     this is not a great idea.  The issue of 'leaving the context ni
     which they apply' is not very serious *today* since LLMNR has only
     LL scope.  In the future, LLMNR might be admin scope MNR.  In this
     case, we will need the SHOULD above - so that link-local scope
     identifiers (addresses and names) are properly contained.

Requested Change:

TEXT NEEDED

---

From: Ralph Droms <[email-masked]>
Date: Thu, 06 May 2004 06:38:00 -0400

I understand the issue but can't comment until the "Requested Change" is 
specified.

- Ralph

At 12:59 AM 5/5/2004 +0200, Erik Guttman wrote:
>Please post discussion of this issue to the mailing list over the next two 
>weeks

---

From: "Philip Nye" <[email-masked]>
Date: Fri, 7 May 2004 10:53:45 -0000

I support Erik's analysis.

The special case of having a routable address but only a locally resolvable name and particularly if there is some knowledge that the name will not be used off-link is sufficient justification for an implementer to reject the "SHOULD" and is why this is not "MUST".

Finally, I don't think this is a deal breaker and it should be too late to make a change.

Philip