Subject: LLMNR Issue 80: Conflicts and Addresses

From: Bernard Aboba <[email-masked]>
Date: Thu, 3 Mar 2005 18:55:53 -0800 (PST)

Issue 80: Conflicts and Addresses
Submitter: Bernard Aboba
Submitter email address: [email-masked]
Date first submitted: March 3, 2005
Reference:
Document: LLMNR-38
Comment type: E
Priority: 1
Section:  4.2
Rationale/Explanation of issue:

When LLMNR messages are sent over multiple protocols (IPv4 and IPv6),
some interesting conflict scenarios can arise.

For example:
Host A supports both IPv4 and IPv6 but only sends and responds to LLMNR
queries over IPv6. Host B supports IPv4 only and sends and responds to LLMNR
queries only over IPv4. What happens if Host A and B configure the same
name?

A sender (Host C) will send an LLMNR query and will get a single response,
whether the query is sent over IPv4 or IPv6. However, when it sends a
query over IPv6, Host A could respond with an A RR conflicting with the A
RR that Host B would respond with if the query were sent over IPv4.

Since a sender only gets a single response, it never sends a query with
the 'C' bit set. The responders never detect a conflict via the uniqueness
verification mechanism either.

Yet a conflict does exist.  What can we do about this?

My suggestion is that a host should only respond with resource records
corresponding to protocols that it supports for use with LLMNR.
So if Host A only supports LLMNR over IPv6, it should not configure an A
RR, even if it has an IPv4 address. Similarly, if Host A only supports
LLMNR over IPv4, it should not configure a AAAA RR.

Does this make sense?

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