Subject: Proposed Resolution to LLMNR Issue 6: IPv6 Multicast Groups

From: Bernard Aboba <[email-masked]>
Date: Wed, 16 Apr 2003 09:28:24 -0700 (PDT)

During the LLMNR Issue Conference call of 4/16/03, it was
noted that use of multiple multicast groups requires that
the name be canonicalized prior to computing the hash to
determine what multicast group is to be used. In the past,
canonicalization has been the source of issues, so requiring
that it be done correctly is likely to result in interoperability
problems.

Also, each responder will need to listen both on the
"node information" IPv6 multicast addresses used for
A/AAAA queries as well as on the single multicast address
used for other queries. This means that a sender could send to the
single multicast address that all responders must listen on,
and it would work. Therefore, implementers looking to simplify their
senders will choose only send to a single multicast group anyway.

Given that multiple multicast groups results in interoperability
and is likely to be bypassed by implementers, the
recommended resolution is to use a single multicast group
with IPv6 as well as IPv4.

In Section 1, Change:

"LLMNR queries are sent to and received on port TBD using a link-scope
multicast address as specified in "Administratively Scoped IP Multicast"
[RFC2365] for IPv4.  The LLMNR link-scope multicast address to be used
for IPv4 is 224.0.0.251.  For IPv6, the "solicited name" link-scope
multicast addresses are used for A/AAAA queries, and a separate link-
scope multicast address TBD for all other queries.  Link-scope multicast
addresses are used to prevent propagation of LLMNR traffic across
routers, potentially flooding the network; for details, see Section 2.4.
In circumstances described in Section 2.3, LLMNR queries can also be
sent to a unicast address."

To:

"LLMNR queries are sent to and received on port TBD using a link-scope
multicast address as specified in "Administratively Scoped IP Multicast"
[RFC2365] for IPv4.  The LLMNR link-scope multicast address to be used
for IPv4 is 224.0.0.251.  For IPv6, the LLMNR link-scope multicast
address is TBD.  Link-scope multicast addresses are used to prevent
propagation of LLMNR traffic across routers, potentially flooding the
network; for details, see Section 2.4.  In circumstances described in
Section 2.3, LLMNR queries can also be sent to a unicast address."

Change Section 2.4 from:

"The IPv4 link-scope multicast address a given responder listens to, and
to which a sender sends all queries, is 224.0.0.251.  The IPv6 link-
scope multicast address a given responder  listens to, and to which a
sender sends A/AAAA queries, is formed as follows: The name of the
resource record in question is expressed in its canonical form (see
[RFC2535], section 8.1), which is uncompressed with all alphabetic
characters in lower case.

The first label of the FQDN in the query is then hashed using the MD5
algorithm, described in [RFC1321].  The first 32 bits of the resultant
128-bit hash is then appended to the prefix FF02:0:0:0:0:2::/96 to yield
the 128-bit "solicited name multicast address".  (Note: this procedure
is intended to be the same as that specified in section 3 of "IPv6 Node
Information Queries" [NodeInfo]).  A responder that listens for queries
for multiple names with different first labels will necessarily listen
to multiple of these solicited name multicast addresses.
"

To:

"The IPv4 link-scope multicast address a given responder listens to, and
to which a sender sends all queries, is 224.0.0.251.  The IPv6 link-
scope multicast address a given responder  listens to, and to which a
sender sends all queries, is TBD."

Section 6 from:

"This specification does not create any new name spaces for IANA
administration.  LLMNR requires allocation of a port TBD for both TCP
and UDP.  Assignment of the same port for both transports is requested.
LLMNR utilizes a link-scope multicast IPv4 address (224.0.0.251) that
has been previously allocated to LLMNR by IANA.  It also requires
allocation of a link scope multicast IPv6 address, for use with queries
of types other than A/AAAA."

To:

"This specification does not create any new name spaces for IANA
administration.  LLMNR requires allocation of a port TBD for both TCP
and UDP.  Assignment of the same port for both transports is requested.
LLMNR utilizes a link-scope multicast IPv4 address (224.0.0.251) that
has been previously allocated to LLMNR by IANA.  It also requires
allocation of a link-scope multicast IPv6 address."

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