BEHAVE D. Wing Internet-Draft Cisco Systems Intended status: Best Current May 17, 2007 Practice Expires: November 18, 2007 Multicast Requirements for a Network Address Port Translator (NAPT) draft-ietf-behave-multicast-06 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 November 18, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document specifies requirements for a Network Address Translator (NAT) and Network Address and Port Translator (NAPT) that supports any-source multicast or single-source multicast. A multicast-capable NAPT device that adheres to the requirements of this document can optimize the operation of multicast applications that are generally unaware of multicast NAPT devices. Wing Expires November 18, 2007 [Page 1]
Internet-Draft NAPT Multicast Requirements May 2007 Table of Contents 1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Background . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Conventions Used in this Document . . . . . . . . . . . . . . 5 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 5 4.2. IGMPv1 and IGMPv2 NAPTs . . . . . . . . . . . . . . . . . 5 4.3. IGMPv3 NAPT . . . . . . . . . . . . . . . . . . . . . . . 5 4.4. UDP mapping lifetime with ASM transmission . . . . . . . . 5 4.5. Considerations for Source-Specific Multicast (SSM) . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.2. Informational References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 10 Wing Expires November 18, 2007 [Page 2]
Internet-Draft NAPT Multicast Requirements May 2007 1. Problem Statement In order for multicast applications to function well over NATs, multicast UDP must work as seamlessly as unicast UDP. However, NATs have little consistency in multicast operation which results in inconsistent user experiences and failed multicast operation. 2. Introduction This document describes how an IGMP/MLD proxy device [RFC4605] can NAPT multicast traffic so that existing any-source multicast applications and single-source multicast applications can function without awareness of NAPT device. Such a NAPT device will send and receive IGMP membership reports and queries. When it does so, it functions exactly like a non-NAPTted IGMP/MLD Proxy [RFC4605]. This is because IGMP packets are link local, and for IGMPv3 are not forwarded (but rather aggregated) by the device's IGMP/MLD Proxying function. For example, when the IGMPv3 proxying device receives an IGMP membership on an inside interface, it creates its own IGMP proxying membership state and its own IGMP/MLD forwarding table. It then creates an independent IGMP membership report on its outside interface reporting the multicast groups/channels -- but there is no direct relationship or "relaying" of IGMP membership reports or queries across the interfaces. The NAPT device will subsequently receive a multicast data packet on the outside ('public') interface and forward the multicast packet to inside ('internal') interfaces based on its IGMP/MLD forwarding table. As with normal NAPT operation for unicast flows, multicast packets received from the outside interface and forwarded to the inside interface do not have their source IP addresses changed. Such multicast packets do not need to have their destination IP address changed (unless the NAT device wishes to establish septate multicast domains, but this is not the typical operation). As with normal NAPT operation for unicast flows, multicast packets received from an inside interface and forwarded to the public interface do have their source IP address changed to the public IP interface of the NAPT and their source UDP port changed to a port selected by the NAPT. This NAPT is commonly called a 'mapping'. 2.1. Scope This document describes the behavior of a device providing any-source multicast or source-specific multicast proxy functions as described Wing Expires November 18, 2007 [Page 3]
Internet-Draft NAPT Multicast Requirements May 2007 in [RFC4605] using IGMPv1 [RFC1112], or IGMPv2 [RFC2236], or IGMPv3 [RFC3376] and that additionally functions as a Network Address and Port Translator (NAPT), as described in section 4.1.2 of [RFC2663]. Out of scope of this document are PIM-SM [RFC4601] and IPv6 [RFC2460]. The IGMP Proxy devices that are scoped in this document do not forward PIM-SM. IPv6 is out of scope because NAPT is not considered necessary with IPv6. This document is a companion document to "NAT Behavioral Requirements for Unicast UDP" [RFC4787]. 2.2. Background 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 | +------------+ +-------------+ Figure 1: Network without NATting IGMP Proxy The primary functions of an IGMP proxy device are to collect IGMP traffic from the 'inside' interface, aggregate them, and transmit the aggregated IGMP membership information to the 'outside' interface. Additionally, multicast traffic is accepted from the 'inside' and (more typically) from the 'outside' interface and routed to the other interface(s) based on forwarding state established by the IGMP/MLP proxy routing. Packets with a multicast destination IP address do not have their destination IP address changed by a NAPT. However, their source IP address and source UDP port is changed if the packet goes from an 'inside' interface of a NAPT to the 'outside' interface of a NAPT -- similar to the behavior of a unicast packet across those same interfaces. +----+ +-------------+ |host+---+ +---------+ | +-----------+ +----+ | |Multicast| | | DSL modem | +------------+ | | Proxy | +--+ or +-//-+ WAN Router | inside | +---------+ | |cable modem| +------------+ interfaces | | +-----------+ | +------+ | +----+ | | NAPT | | outside |host+---+ +------+ | interfaces +----+ +-------------+ Wing Expires November 18, 2007 [Page 4]
Internet-Draft NAPT Multicast Requirements May 2007 IGMP Proxy NAPT Device Figure 2: Network with NAPTing IGMP Proxy 3. Conventions Used in this Document 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]. 4. Requirements 4.1. IGMP/MLD Proxy REQ-1: A device compliant with this specification MUST implement [RFC4605]. 4.2. IGMPv1 and IGMPv2 NAPTs REQ-2: If a NAPT supports IGMPv1 and/or IGMPv2 (but not IGMPv3), it MAY simply receive IGMP membership reports on the inside interface, NAT them, and relay the IGMP membership report. That is, the NAPT does not need to do any aggregation of IGMP messages. 4.3. IGMPv3 NAPT REQ-3: If a NAPT supports IGMPv3, the NAPT MUST aggregate the IGMPv3 membership reports, and report the aggregated information upstream. Failure to do this aggregation will cause undesired temporary blackholing of multicast traffic. For example, consider two hosts behind the same NAPT. If one host is joining a session at the same time another is lesaving the session, and the NAPT merely relays the join and leave upstream, the session will be terminated and the join and leave announcements do not comply with section 5 of [RFC3376]. 4.4. UDP mapping lifetime with ASM transmission Any-sosurce multicast (ASM) uses the IP addresses in the 224.0.0.0 - 239.255.255.255 range [IANA-ALLOC]. Wing Expires November 18, 2007 [Page 5]
Internet-Draft NAPT Multicast Requirements May 2007 REQ-4: If a host on the inside interface of a NAPT belongs to an any-source multicast host group and sends a UDP packet to the same group, the NAPT MUST have a UDP mapping timer of 60 minutes for that mapping. a. This UDP mapping SHOULD be destroyed when the host leaves that host group. b. If a NAPT has exhausted its resources, the NAPT MAY time out that mapping before 60 minutes have elapsed, but this is discouraged. Note that even in a situation with resource exhaustion, a NAPT is still required to follow the minimum mapping duration of 2 minutes (REQ-5 of [RFC4787]). Discussion: If a NAPT merely followed the requirements of [RFC4787] it could cause problems for RTP [RFC3550]. RTP uses the source transport address (source IP address and source UDP port) and 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 merely followed the requirements of [RFC4787] and timed out a UDP session after 2 minutes of inactivity and RTCP receiver reports are sent less often than every 2 minutes, RTP collision detection would be performed by other session members sharing the same SSRC, complicating diagnostic tools and potentially interfering with jitter buffer algorithms. This situation can occur, for example, with a multicast group of approximately 300 members with a normal 50kbps audio RTP stream. 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 to assign the same UDP source port for that RTCP traffic. This requirement also facilitates other, non-RTP multicast applications which may function similarly. 4.5. Considerations for Source-Specific Multicast (SSM) Source-specific multicast uses the IP addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range [IANA-ALLOC]. REQ-5: When implementing a NAPT that operates with Source-Specific Multicast [RFC4607], the NAPT MUST: Wing Expires November 18, 2007 [Page 6]
Internet-Draft NAPT Multicast Requirements May 2007 a. implement IGMPv3 according to section 4.2 of [RFC4607], and; b. follow the requirements in section Section 4.3 of this document. Primarily due to NAPTs functioning as IGMP/MLD proxies with multiple receivers behind the NAT, multicast applications are encouraged to use identifiers, rather than IP addresses and UDP ports, to identify specific multicast receivers (e.g., [I-D.ietf-avt-rtcpssm] encourages SSM applications to not rely exclusively on transport addresses for collision detection). As compared to any-source multicast, the use of such receiver identifiers removes the need for the NAT to have long mapping timers; instead, the timers in [RFC4787] are used when a host transmits to a single-source multicast address. 5. 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]. 6. IANA Considerations This document does not require any IANA registrations. 7. Acknowledgments Thanks to Yiqun Cai, Stephen Casner, Remi Denis-Courmont, Toerless Eckert, Alfred Hines, Marcus Maranhao, Bryan McLaughlin, and Magnus Westerlund for their assistance in writing this document. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version Wing Expires November 18, 2007 [Page 7]
Internet-Draft NAPT Multicast Requirements May 2007 3", RFC 3376, October 2002. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [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. [RFC4787] Audet, F. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, January 2007. 8.2. Informational References [I-D.ietf-avt-rtcpssm] Chesterfield, J., "RTCP Extensions for Single-Source Multicast Sessions with Unicast Feedback", draft-ietf-avt-rtcpssm-13 (work in progress), March 2007. [IANA-ALLOC] Internet Assigned Numbers Authority, "Internet Multicast Addresses", <http://www.iana.org/assignments/multicast-addresses>. [RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112, August 1989. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations", RFC 2663, August 1999. [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, August 2006. Wing Expires November 18, 2007 [Page 8]
Internet-Draft NAPT Multicast Requirements May 2007 Author's Address Dan Wing Cisco Systems 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing Expires November 18, 2007 [Page 9]
Internet-Draft NAPT Multicast Requirements May 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 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, THE IETF TRUST 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. Intellectual Property 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Wing Expires November 18, 2007 [Page 10]
