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Network Working Group                                      Bernard Aboba
INTERNET-DRAFT                                              Levon Esibov
Category: Standards Track                                    Dave Thaler
<draft-aboba-dhc-mdns-conf-00.txt>                             Microsoft
20 February 2000

                     Multicast DNS Node Type Option

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet- Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

1.  Copyright Notice

Copyright (C) The Internet Society (2000).  All Rights Reserved.

2.  Abstract

This document defines a new DHCP option which is passed from the DHCP
Server to the DHCP Client to specify the multicast DNS configuration.

3.  Introduction

Multicast DNS was first defined in [5], and behavior was further
specified in [3]. The Dynamic Host Configuration Protocol (DHCP)[1]
provides a framework for passing configuration information to hosts on a
TCP/IP network. RFC 2132 [2] allows DHCP servers to specify
configuration information for various kinds of name servers to be passed
to DHCP clients. However, no information is provided as to the
configuration desired for multicast DNS. The purpose of  this document
is to allow DHCP servers to specify the multicast DNS configuration to
be used by DHCP clients.





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3.1.  Requirements terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [4].

3.2.  DHCP terminology

This document uses the following terms:

DHCP client
          DHCP client or "client" is an Internet host using DHCP to
          obtain configuration parameters such as a network address.

DHCP server
          A DHCP server or "server" is an Internet host that returns
          configuration parameters to DHCP clients.

4.  Format of the mDNS node type option

The following diagram defines the format of the mDNS configuration
option:

 0                   1                   2
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |     Length    |  Node Type    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   TBD

Length

   1















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INTERNET-DRAFT     Multicast DNS Configuration Option   20 February 2000


Node type

   The node type field, which is one octet, describes how the host
   should behave as an mDNS querier and listener. Values are defined as
   follows:

   Value         Node Type
   -----         ---------
   0x1           B-node
   0x2           P-node
   0x3           Reserved
   0x4           M-node
   0x5 - 0x7     Reserved
   0x8           H-node
   0x9 - 0xFF    Reserved

4.1.  B-node

B-nodes act as multicast DNS queriers and listeners, but do not send
unicast DNS queries. As a result, they are unable to resolve non-local
names.

4.2.  P-node

P-nodes only send unicast DNS queries, and MUST NOT listen for mDNS
queries or respond to them in any way. Hosts configured as P-nodes MUST
NOT send multicast DNS queries for any purpose, including DNS server
location. Thus, if no DNS server option is provided, a P-node host will
be unable to resolve names.

4.3.  M-node

M-nodes use multicast DNS queries for resolving local names prior to
querying the unicast DNS server, but use the unicast DNS server
exclusively for resolving non-local names. M-nodes not configured with
the address of a unicast DNS server will send only multicast DNS
queries, and will be unable to resolve non-local names.

Hosts configured as M-nodes MUST listen for mDNS queries on both the
linklocal and local scopes, and MUST respond to mDNS queries for their
own name, via unicast. M-nodes MUST NOT send unicast DNS queries for
local names without first sending an mDNS linklocal and then local query
for the name.

If a host receives an mDNS node type option corresponding to an M-node
without receiving a DNS server option, then the host SHOULD send an mDNS
query in order to locate a local DNS server, as described in [5].




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4.4.  H-nodes

H-nodes send multicast DNS queries only if they have not been able to
resolve the name via a query to a unicast DNS server. H-nodes not
configured with the address of a unicast DNS server will send only
multicast DNS queries, and will be unable to resolve non-local names.

Hosts configured as H-nodes MUST listen for mDNS queries on both the
linklocal and local scopes, and MUST respond to mDNS queries for their
own name, via unicast. H-nodes MUST NOT send mDNS queries without first
querying the unicast DNS server if one is available.

If a host receives an mDNS node type option corresponding to an H-node
without receiving a DNS server option, then the host SHOULD send an mDNS
query in order to locate a local DNS server, as described in [5].

5.  References

[1]  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
     1997.

[2]  Alexander, S., Droms, R., "DHCP Options and BOOTP Vendor
     Extensions", RFC 2132, March 1997.

[3]  Woodcock, B., Manning, B., "Multicast Discovery of DNS Services",
     Internet draft (work in progress), draft-manning-multicast-
     dns-01.txt, October 1998.

[4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.

[5]  Braden, R., "Requirements for Internet Hosts -- Application and
     Support", RFC 1123, October 1989.

6.  Security Considerations

The option described in this draft may be used in situations where DHCP
is authenticated or unauthenticated. In situations where authenticated
DHCP is not used, it is possible for a rogue DHCP server to respond to
the DHCP client with an inappropriate mDNS configuration option. For
example, the rogue DHCP server could specify an mDNS configuration
option of 0x1. This would cause the host to become both an mDNS querier
and listener (B-node). Were hosts to be widely configured this way, this
could result in propagation of mDNS queries throughout the enterprise.







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7.  IANA Considerations

This draft does not create any new number spaces for IANA
administration.

8.  Acknowledgements

This draft has been enriched by comments from Rick Lamb of Microsoft.

9.  Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 (425) 936-6605
EMail: bernarda@microsoft.com

Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 (425) 703-8835
EMail: dthaler@microsoft.com

Levon Esibov
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 (425) 936-2464
EMail: levone@microsoft.com


10.  Full Copyright Statement

Copyright (C) The Internet Society (2000).  All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implmentation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works.  However, this document itself
may not be modified in any way, such as by removing the copyright notice
or references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in



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which case the procedures for copyrights defined in the Internet
Standards process must be followed, or as required to translate it into
languages other than English.  The limited permissions granted above are
perpetual and will not be revoked by the Internet Society or its
successors or assigns.  This document and the information contained
herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

11.  Expiration Date

This memo is filed as <draft-aboba-dhc-mdns-conf-00.txt>,  and  expires
September 1, 2000.




































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