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Versions: (draft-wing-behave-multicast) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5135

BEHAVE                                                           D. Wing
Internet-Draft                                             Cisco Systems
Expires: December 18, 2006                                 June 16, 2006


  Multicast Requirements for a Network Address Port Translator (NAPT)
                     draft-ietf-behave-multicast-02

Status of this Memo

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   This Internet-Draft will expire on December 18, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document places requirements on a Network Address Translator
   (NAT) and Network Address and Port Translator (NAPT) that supports IP
   multicast by implementing an IGMP proxy.

Requirements Language

   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 [RFC2119].



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Table of Contents

   1.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Background  . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  NAPT Multicast Requirements . . . . . . . . . . . . . . . . . . 4
     3.1.  Keep NAT Binding Open . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7






































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1.  Problem Statement

   For users to accept and enjoy multicast, multicast UDP must work as
   seamlessly as unicast UDP.  However, today's equipment has little
   consistency in multicast operation which results in inconsistant user
   experiences and failed multicast operation.


2.  Introduction

   This document describes the behavior of a device providing multicast
   functions similar to [I-D.ietf-magma-igmp-proxy] and that
   additionally functions as a Network Address and Port Translator
   (NAPT), as described in section 4.1.2 of [RFC2663].

   Specifically out of scope of this document are:

      *  sending multicast traffic,
      *  PIM-SM [RFC2362],
      *  IPv6, and,
      *  IGMPv1.

   Sending multicast traffic is out of scope because it requires NATting
   the source IP address of such transmitted multicast traffic.
   Similarly, PIM is used only between routers and the IGMP Proxy
   devices that are scoped in this document do not function as routers.
   IPv6 is out of scope because NAT is not considered necessary with
   IPv6.  IGMPv1 is not significantly deployed on the Internet.

   This document does not describe how to implement multicast, IGMPv2,
   or IGMPv3 in an IGMP Proxy device.  Rather, it provides requirements
   for an IGMP Proxy device so that hosts behind the NAT can receive
   multicast traffic without any knowledge of the IGMP Proxy.

2.1.  Background

   As detailed in the Document Scope section, the primary functions of
   an IGMP proxy device are to collect IGMP traffic from one interface
   and relay it to another interface, and accept multicast traffic from
   thatinterface and route -- or replicate it -- to other interface(s).

   When a NAPT isn't used, a host might be connected to the Internet in
   a configuration such as this:

                +-------------+
     +------+   |  DSL modem  |        +------------+
     | host +---+     or      +---//---+ WAN Router |
     +------+   | cable modem |        +------------+



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                +-------------+

   When an IGMP Proxy device is added to such a network, its behavior is
   identical towards the upstream (WAN) router.  Specifically, when
   dealing with multicast, the IGMP Proxy has the same behavior towards
   the WAN as if it was a host.

     +------+  +------------+   +-------------+
     | host +--+            |   |  DSL modem  |        +------------+
     +------+  | IGMP Proxy +---+     or      +---//---+ WAN Router |
     +------+  |   (NAPT)   |   | cable modem |        +------------+
     | host +--+            |   +-------------+
     +------+  +------------+

   This document is a companion document to "NAT/Firewall Behavioral
   Requirements" [I-D.ietf-behave-nat-udp].


3.  NAPT Multicast Requirements

   All requirements of [I-D.ietf-magma-igmp-proxy] apply equally to
   NAPTs and are incorporated herein by reference.

   Additionally, there are some requirements particular to NATs that
   implement IGMP proxies:

3.1.  Keep NAT Binding Open

   The NAT UDP requirements [I-D.ietf-behave-nat-udp] document only
   requires that a NAT binding be kept open for inside-to-outside UDP
   flows.  However, with multicast traffic, UDP traffic will only arrive
   outside-to-inside.

   Hosts will periodically send IGMP Report messages to indicate
   continued interest in receiving the multicast traffic.  As long as
   the IGMP Proxy sees a host is interested in receiving the flow, the
   NAT MUST continue to receive multicast traffic from the WAN and send
   it to the interfaces with interested hosts.

   Per IGMPv3, the default transmission interval for the periodic
   Membership Report is one second.  Per IGMPv2, the default
   transmission interval for the periodic Unsolicited Report Interval is
   10 seconds.  If a host no longer sends its periodic messages within
   those timeframes, the NAT MAY consider the host no longer wants to
   receive the multicast traffic and can inform the upstream WAN router
   and close the NAT binding.  However, it is suggested that the NAT
   wait until 3 missing unsolicited reports (to account for packet loss
   on the LAN, especially wireless LANs), or that the NAT first query



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   the host using IGMPv2 or IGMPv3.


4.  Security Considerations

   Compliance with this specification does not increase security risks
   beyond those already discussed in the Security Considerations section
   of IGMPv3 [RFC3376].


5.  IANA Considerations

   This document does not require any IANA registrations.


6.  Acknowledgments

   Thanks to Bryan McLaughlin and Yiqun Cai for their assistance in
   writing this document.

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [I-D.ietf-magma-igmp-proxy]
              Fenner, B., He, H., Haberman, B., and H. Sandick, "IGMP/
              MLD-based Multicast Forwarding ('IGMP/MLD Proxying')",
              draft-ietf-magma-igmp-proxy-06 (work in progress),
              April 2004.

   [RFC2362]  Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering,
              S., Handley, M., and V. Jacobson, "Protocol Independent
              Multicast-Sparse Mode (PIM-SM): Protocol Specification",
              RFC 2362, June 1998.

   [I-D.ietf-behave-nat-udp]
              Audet, F. and C. Jennings, "NAT Behavioral Requirements
              for Unicast UDP", draft-ietf-behave-nat-udp-07 (work in
              progress), June 2006.



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Author's Address

   Dan Wing
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: dwing@cisco.com










































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Acknowledgment

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   Internet Society.




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