Subject: Proposed resolution of LLMNR Issue 7

From: Bernard Aboba <[email-masked]>
Date: Mon, 17 Mar 2003 09:48:02 -0800 (PST)

For a list of LLMNR issues, please see:

http://www.drizzle.com/~aboba/DNSEXT/llmnrissues.html

Issue 7: Advertisement of LL addresses
Submitter: Erik Nordmark
Submitter email address: [email-masked]
Date first submitted: November 4, 2002
Reference: <[email-masked]>
Document: LLMNR-12
Comment type: T
Priority: S
Section:
Rationale/Explanation of issue:

> Since automatic IPv6 DNS configuration mechanisms such as [DHCPv6DNS]
> and [DNSDisc] are not yet widely deployed, and not all DNS servers
> support IPv6, "partial configuration" may be common in the short
> term, and LLMNR may prove useful in enabling linklocal name resolution
> over IPv6. However, in the long term, IPv6 DNS configuration, and DNS
> support over IPv6 will become more common so that LLMNR usage will
> typically be
> restricted to adhoc networks in which neither IPv4 nor IPv6 DNS servers
> are configured, and situations in which DNS servers do not respond to
> queries."

The above doesn't speculate about a future where names to global
addresses can be resolved using DNS, but names to link-local
addresses can only be resolved using LLMNR.
The high-order question is whether the LLMNR spec should speculate
about this future or not.
[BA Comment]:
Currently, the draft doesn't state what addresses an LLMNR responder will
include in its A/AAAA RR query response. Are you suggesting that it should
respond *only* with a linklocal address?

[Erik Nordmark Comment]:
I'm suggesting that we don't know the answer to that question yet.
And the draft, by saying that the applicability is likely to be
limited to adhoc networks, says that we do know the answer to the
question.

So leaving the applicability a bit more open-ended might be useful.

Note that ideally we'd use global addresses for all application use,
since limited scope addresses can cause problems for applications.
But the thing I don't know is whether this will always be sufficient
or whether there will be cases where it makes sense to use LLMNR to
get a link-local address back even in cases when the network is
connected to the Internet.

Erik
[BA comment]:
It seems unwise to advertise a LL address (IPv4 or IPv6) in an LLMNR
Response if a routable address is available. This will only encourage the querier
to contact the responder on the LL address.

Add the following text to section 4:

"[4] A responder with both linklocal and routable addresses
    SHOULD respond only to LLMNR queries for A/AAAA RRs for
    the routable address. This encourages use of the routable
    address for establishment of new connections."

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