BEHAVE D. Wing Internet-Draft Cisco Systems Expires: March 18, 2007 September 14, 2006 Multicast Requirements for a Network Address Port Translator (NAPT) draft-ietf-behave-multicast-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. This Internet-Draft will expire on March 18, 2007. 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 Internet Group Management Protocol (IGMP) proxy. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this Wing Expires March 18, 2007 [Page 1]
Internet-Draft NAPT Multicast Requirements September 2006 document are to be interpreted as described in RFC 2119 [RFC2119]. Table of Contents 1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 3 3. NAPT Multicast Requirements . . . . . . . . . . . . . . . . . . 4 3.1. NAPT Inbound Refresh Behavior . . . . . . . . . . . . . . . 4 3.2. Extend Mapping Refresh . . . . . . . . . . . . . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informational References . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Wing Expires March 18, 2007 [Page 2]
Internet-Draft NAPT Multicast Requirements September 2006 1. Problem Statement For users to accept and enjoy multicast, multicast UDP must work as seamlessly as unicast UDP. However, NATs have 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 proxy functions as described in [RFC4605] 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 PIM-SM [RFC2362], IPv6, and IGMPv1 [RFC1112]. 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 NAPT is not considered necessary with IPv6. IGMPv1 is not significantly deployed on the Internet. This document does not describe how to implement multicast, IGMPv2 [RFC2236], or IGMPv3 [RFC3376] in an IGMP Proxy device. Rather, it provides requirements for an IGMP Proxy device so that hosts behind the NAPT can receive multicast traffic without any knowledge of the IGMP Proxy. 2.1. Background 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 that interface 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 | +------------+ +-------------+ Wing Expires March 18, 2007 [Page 3]
Internet-Draft NAPT Multicast Requirements September 2006 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 Behavioral Requirements for Unicast UDP" [I-D.ietf-behave-nat-udp]. 3. NAPT Multicast Requirements The NAPTed hosts will periodically send IGMP Report messages to indicate continued interest in receiving the multicast traffic. Per IGMPv3 [RFC3376], the default transmission interval for the periodic Membership Report is one second. Per IGMPv2 [RFC2236], the default transmission interval for the periodic Unsolicited Report Interval is 10 seconds. If a NAPTed host no longer sends its periodic messages within those timeframes, the NAPT device MAY consider the host no longer wants to receive the multicast traffic and can inform the upstream WAN router and close the NAPT mapping. However, it is RECOMMENDED that the NAPT wait until 3 missing unsolicited reports (to account for packet loss on the LAN, especially wireless LANs), or that the NAPT first query the host using IGMPv2 or IGMPv3. In addition to the above requirements, the NAPT device MUST also: o follow the RFC2119 requirements of [RFC4605], and; o have "NAT Inbound Refresh Behavior", as described in [I-D.ietf- behave-nat-udp] (see Section 3.1), and; o extend the Mapping Refresh Timer, as described in [I-D.ietf- behave-nat-udp], to 60 minutes for UDP packets originating from hosts receiving any multicast stream that are sent to UDP ports above 1023 (see Section 3.2). 3.1. NAPT Inbound Refresh Behavior Multicast traffic arrives only outside-to-inside. Thus, a NAPT needs to also meet REQ-6a of NAT UDP requirements [I-D.ietf-behave-nat-udp] because multicast traffic typically only flows ouside-to-inside. Wing Expires March 18, 2007 [Page 4]
Internet-Draft NAPT Multicast Requirements September 2006 3.2. Extend Mapping Refresh RTP [RFC3550] uses the source transport address (source IP address and source UDP port), in addition to the the RTP/RTCP SSRC value, to identify session members. If a session member sees the same SSRC arrive from a different transport address, that session member will perform RTP collision detection (section 8.2 of [RFC3550]). If a NAPT followed the requirements of [I-D.ietf-behave-nat-udp] (and timed out a UDP session after 2 minutes of inactivity) and the multicast group is sufficiently large (approximately 300 members with a normal 50kbps audio RTP stream), the elapsed time between a NAPTed host sending its RTCP Receiver Reports would exceed 2 minutes, causing an unnecessary RTP collision detection to be performed by other session members. To prevent this unnecessary RTP collision detection by other session members, the other session members need to see the same source transport address for the RTP and RTCP traffic from the NAPTed host. This requires the NAPT not assign a new UDP source port for that traffic. A NAPT is unable to associate a received multicast session with its unicasted RTCP Receiver Reports. Thus, this document requires the NAPT to extend its UDP mapping refresh timer. This requirement also facilitates other, non-RTP multicast applications. This requirement applies to ports above 1023 because RTP and RTCP are only used on ports above 1023. Other, non-RTP multicast feedback protocols are also expected to use ports above 1023. If a NAPT has exhausted its resources, the NAPT MAY time out a mapping before 60 minutes have elapsed. However, a NAPT is still required to follow the minimum mapping duration of [I-D.ietf-behave- nat-udp] in order to comply with that specification. 4. Security Considerations Compliance with this specification does not increase security risks beyond those already discussed in the Security Considerations section of IGMPv3 [RFC3376] and IGMP/MLD Proxying [RFC4605]. 5. IANA Considerations This document does not require any IANA registrations. 6. Acknowledgments Wing Expires March 18, 2007 [Page 5]
Internet-Draft NAPT Multicast Requirements September 2006 Thanks to Bryan McLaughlin and Yiqun Cai for their assistance in writing this document. 7. References 7.1. 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. [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, August 2006. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. [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. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. 7.2. Informational References [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. [RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112, August 1989. Wing Expires March 18, 2007 [Page 6]
Internet-Draft NAPT Multicast Requirements September 2006 Author's Address Dan Wing Cisco Systems 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing Expires March 18, 2007 [Page 7]
Internet-Draft NAPT Multicast Requirements September 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Wing Expires March 18, 2007 [Page 8]
