BEHAVE Working Group D. Wing Internet-Draft Cisco Intended status: Informational March 4, 2009 Expires: September 5, 2009 Referrals Across a NAT64 draft-wing-behave-nat64-referrals-00 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 September 5, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes several scenarios where an IP address is referred across a NAT64 translator. Wing Expires September 5, 2009 [Page 1] Internet-Draft NAT64 Referrals March 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Application Referrals Across IP Address Families . . . . . . . 3 2.1. SIP . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1. SIP using a Media Relay . . . . . . . . . . . . . . . 4 2.1.2. SIP without a Media Relay . . . . . . . . . . . . . . 7 2.2. BitTorrent . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Security Considerations . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Normative References . . . . . . . . . . . . . . . . . . . 10 6.2. Informative References . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 Wing Expires September 5, 2009 [Page 2] Internet-Draft NAT64 Referrals March 2009 1. Introduction Historically, NATs (and firewalls) have been accused of "breaking referrals". At this point in time, the author is aware of two widely-available protocols that operate on the IPv4 Internet which perform referrals: SIP and BitTorrent. It is important that the community understand how referrals can work across an address family translator considering that existing IPv4 nodes do not understand IPv6 addresses, referrals to IPv6 nodes behind a NAT64 will not cause a DNS64 query, and other factors. This document describes how referrals work in BEHAVE's "An IPv6 network to the IPv4 Internet" scenario. In this BEHAVE scenario, an IPv6-only host utilizes a stateful NAT64 [I-D.bagnulo-behave-nat64] to communicate to an IPv4-only host on the Internet. After this communication is established, the document examines IPv6-only host refers the IPv4-only host to a variety of other hosts that are connected to the Internet. This document is intended to assist the IETF community to understand the scenarios where referrals across a NAT64 translator are successful. This document is not expected to be published as an RFC. This document is part of the consideration for a NAT64 prefix [I-D.miyata-behave-prefix64] [I-D.baker-behave-v4v6-framework]. 2. Application Referrals Across IP Address Families This section describes how SIP and BitTorrent perform referrals between IPv6 and IPv4, and between IPv4 and IPv6. 2.1. SIP A SIP call involves two the SIP signaling, sent to SIP proxies, and the media, sent directly between the SIP hosts. This is often referred to as the SIP "trapezoid", as shown in the following figure. This section shows that IPv4 addresses can be successfully referred to both IPv4 hosts and to IPv6 hosts, if those IPv6 hosts support the IPv6 transition strategy for SIP [I-D.ietf-sipping-v6-transition]. Because an IPv6 address is not referred, the success is not dependent on the NAT64 prefix (well-known prefix versus LIR prefix). Wing Expires September 5, 2009 [Page 3] Internet-Draft NAT64 Referrals March 2009 SIP signaling sip-proxy.example.com-------------------------sip-proxy.example.net / \ / \ / SIP signaling SIP signaling \ / \ / \ Host-A-----------------------------------------Host-B media path Figure 1: SIP Trapezoid It is the media path which is interesting for SIP referrals and is the subject of this section. The SIP signaling messages are exchanged on the upper part of the trapezoid and is not the subject of this section. The SIP signaling messages contain SDP [RFC4566] which conveys the IP address and UDP port of the hosts as well as other information (e.g., audio codec). The IPv6 transition strategy for SIP [I-D.ietf-sipping-v6-transition] states the requirements for the IPv6 transition: An IPv6 node SHOULD also be able to send and receive media using IPv4 addresses, but if it cannot, it SHOULD support STUN relay usage [I-D.ietf-behave-turn-ipv6]. Such a relay allows the IPv6 node to indirectly send and receive media using IPv4. Thus, all IPv6 nodes running SIP are expected to support ICE [I-D.ietf-mmusic-ice] which allows simultaneous referral of multiple IP addresses, even from different IP address families. IPv4-only endpoints do not have to support ICE, although such support assists both hosts by choosing the most optimal path (e.g., avoiding a media relay). There are two documented mechanisms for SIP endpoints to communicate across IP address families. The first mechanism uses uses media relays (TURN servers [I-D.ietf-behave-turn]) and is described in Section 2.1.1. The second documented mechanism uses NAT64 translators, does not use media relays, and is described in Section 2.1.2. 2.1.1. SIP using a Media Relay Section 4.2 of [I-D.ietf-sipping-v6-transition] documents how an IPv6-only SIP endpoint can use a media relay (a TURN-IPv6 server) to exchange media with an IPv4-only SIP endpoint. This can be accomplished using two methods. Wing Expires September 5, 2009 [Page 4] Internet-Draft NAT64 Referrals March 2009 The first method is shown in Figure 2, where the Host-A (IPv6-only) communicates with a TURN-IPV6 [I-D.ietf-behave-turn-ipv6] server directly (that is, using IPv6). In this communication, Host-A allocates a relayed-transport-address from the TURN server. This relayed-transport-address is an IPv4 address. Host-A learned Host-B's IPv4 address via SIP signaling. +------------+ ------ +------------+ | Host-A | +---------+ / IPv4 \ | Host-B | |SIP endpoint+---+TURN-IPv6+-----|SIP endpoint| | IPv6-only | | server | \______/ | IPv4-only | +------------+ +---------+ +------------+ <--IPv6----------------><---------- IPv4 ---------------> Figure 2: SIP using IPv6-capable Media Relay The second method is shown in Figure 3. This method is not mentioned in Section 4.2 of [I-D.ietf-sipping-v6-transition] because NAT-PT was deprecated at the time and NAT64 was not yet on the horizon. So it is discussed in this document. In this method, Host-A (IPv6-only) communicates across a NAT64 to an TURN server. This TURN server might be IPv4-only. Host-A allocates a relayed-transport-address IPv4 IPv4 address from the TURN server and uses that IPv4 address to communicate with Host-B. Host-A learned Host-B's IPv4 address via SIP signaling. +-------+ | IPv4 | +------------+ | media | ------ +------------+ | Host-A | +-----+ + relay | / IPv4 \ | Host-B | |SIP endpoint+---+NAT64+--+ (TURN +-----|SIP endpoint| | IPv6-only | +-----+ |server)| \______/ | IPv4-only | +------------+ +-------+ +------------+ <--IPv6------------><---------- IPv4 -------------------------> Figure 3: SIP using NAT64 and IPv4 Media Relay In both Figure 2 and Figure 3 Host-A (IPv6-only) obtains the IPv4 address of Host-B via SIP signaling and uses that address for any later referrals. Media is exchanged between Host-A and Host-B through the TURN server, which functions as a media relay. The following sections detail what occurs when Host-A refers Host-B's IP address to different hosts. These hosts are connected to the Internet in different ways: to the IPv6 internet (both with and without a NAT64) and to the IPv4 network. In a SIP referral, Host-A Wing Expires September 5, 2009 [Page 5] Internet-Draft NAT64 Referrals March 2009 sends a SIP message through SIP proxies to another host. As with most SIP messages, this SIP message contains an SDP [RFC4566] bodypart. The SDP has the IP address and UDP port of Host-B which is used to exchange media with Host-B. Note that, prior to the referral, Host-A does not know (and cannot learn) how other hosts are connected to the Internet. 2.1.1.1. Referring to IPv4-only host (Host-D) In both methods above, Host-A knows Host-B's IPv4 address. If Host-A (IPv6-only) refers Host-B's IPv4 address to an IPv4-only host, the referral will be successful. 2.1.1.2. Referring to IPv6-only or dual-stack host with NAT64 device (Host-B) If Host-A (IPv6-only) refers Host-B's IPv4 address to an IPv6-only host, the referral will succeed if Host-A's SIP stack understands IPv4 addresses and can obtain an IPv4 address from a media relay (similar to shown in Figure 3). As part of the IPv6 transition, IPv6-only SIP implementations need to understand IPv4 addresses, as already required (SHOULD) by IPv6 transition strategy for SIP [I-D.ietf-sipping-v6-transition]. Thus, this referral is also successful. 2.1.1.3. Referring to IPv6-only or dual-stack host without NAT64 device If Host-A (IPv6-only) refers Host-B's IPv4 address to an IPv6-only host, the referral will succeed if Host-A's SIP stack understands IPv4 addresses and can obtain an IPv4 address from a media relay (similar to shown in Figure 2). As part of the IPv6 transition, IPv6-only SIP implementations need to understand IPv4 addresses, as already required (SHOULD) by IPv6 transition strategy for SIP [I-D.ietf-sipping-v6-transition]. Thus, this referral is also successful. If Host-A (IPv6-only) refers Host-B's IPv4 address to an dual-stack host, it will succeed because the dual-stack host will be able to successfully use Host-B's IPv4 address. Wing Expires September 5, 2009 [Page 6] Internet-Draft NAT64 Referrals March 2009 2.1.2. SIP without a Media Relay Section 6.2 of [I-D.ietf-sipping-nat-scenarios] describes an IPv6- only SIP endpoint using a NAT64 to exchange media with an IPv4-only SIP endpoint. To do this, the IPv6-only SIP endpoint implements ICE [I-D.ietf-mmusic-ice] and is configured with a STUN server on the IPv4 side of the NAT64 translator (that is, on the IPv4 Internet). This section analyzes how such an IPv6-only SIP endpoint, exchanging media across a NAT64 translator with an IPv4-only SIP endpoint, would refer the synthesized IPv6 address to another SIP endpoint. [[Editor's note: which of the two diagrams, below, is clearer?]] In the following diagram all of the hosts belong to different ISPs: Host-A Host-B IPv6 only IPv6 only | | +----+----+ +-----+-----+ | IPv6 | | IPv6 | | Service | | Service | | Provider| | Provider | +-+-NAT64-+ +-NAT64---+-+ | | | | | +---------+ | | | IPv4| |IPv4 | IPv6| IPv6 | | | | +-------------------+ | | | | | | | | +--+---+-+ +---+-+---+ | IPv6 | | IPv4 | |Internet| | Internet| +-+----+-+ +-+-+---+-+ | | | | | | | +------+ | +---+ | | | | | Host-F | | Host-C Host-D IPv6-only | | IPv4-only IPv4-only | | Host-E dual-stack Wing Expires September 5, 2009 [Page 7] Internet-Draft NAT64 Referrals March 2009 In the following diagram all of the hosts belong to different ISPs: : IPv6 Internet : IPv4 Internet : : Host-A-------NAT64 Host-C IPv6-only : IPv4-only : Host-B-------NAT64 Host-D IPv6-only : IPv4-only : Host-F : IPv6-only : Host-E dual-stack : In the following scenarios, Host-A (IPv6-only) is communicating with Host-C through the NAT64 device. Host-A knows Host-C's synthetic IPv6 address (because it is sending traffic to it) and Host-C's IPv4 address (because it received Host-C's IPv4 address in SIP signaling). The following scenarios describe how referrals to other nodes would function. Note that, prior to the referral, Host-A does not know (and cannot learn) how other hosts are connected to the Internet. 2.1.2.1. Referring to IPv4-only host (Host-D) If Host-A refers to Host-D (IPv4-only), only the IPv4 address can be successfully referred. The IPv6 address cannot be successfully referred (no matter if well-known prefix or LIR prefix). Thus, this referral is successful. 2.1.2.2. Referring to IPv6-only or dual-stack host with NAT64 device (Host-B) If it refers to Host-B (IPv6-only, using a different NAT64 device) or to a dual-stack host (not shown) with a NAT64 device in the service provider, the IPv4 referral is also successful. It is successful because the IPv6-only host (with a NAT64 device) or the dual-stack host both have to be able to communicate with IPv4 hosts, as required by IPv6 transition strategy for SIP [I-D.ietf-sipping-v6-transition]. Wing Expires September 5, 2009 [Page 8] Internet-Draft NAT64 Referrals March 2009 2.1.2.3. Referring to IPv6-only or dual-stack host without NAT64 device (Host-F) If it refers to Host-F (IPv6-only, with no NAT64 device), the referral fails because Host-F cannot communicate with any IPv4 hosts. This failure is expected, because not only would a referral fail, but two hosts in two different IP address families cannot initiate their own communication -- they need an address family translator (or media relay) or one host needs to be dual-stack. If it refers to Host-E (dual-stack), the IPv4 address can be successfully referred. 2.2. BitTorrent BitTorrent trackers use HTTP URIs and DNS names. Thus, if an IPv6- only host running a web browser can connect to an IPv4-only web site using a translator (e.g., using NAT64 and DNS64), that same IPv6-only host running a BitTorrent client can connect to an IPv4-only BitTorrent tracker. While some BitTorrent trackers are beginning to track IPv6 addresses of BitTorrent peers, most trackers only track IPv4 peers. Most content is only available on IPv4. When an IPv6-only BitTorrent peer obtains IPv4 addresses from its tracker, it cannot use those IPv4 addresses. To do so, the BitTorrent client software would need to prefix the IPv4 address with the prefix of a NAT64 that will perform the necessary address family translation on behalf of the IPv6-only BitTorrent client. This could be done with updates to BitTorrent clients to prefix the IPv4 address with the IPv6 prefix of a NAT64 translator which will both authorize and route the communication to the IPv4 BitTorrent peer. BitTorrent clients do not perform this function today. 3. Security Considerations It is anticipated that an ISP would not allow non-customers to utilize the ISP's NAT64 device. 4. IANA Considerations There are no IANA considerations for this document. 5. Acknowledgements This draft was fostered by discussion with Marcelo Bagnulo Braun and Wing Expires September 5, 2009 [Page 9] Internet-Draft NAT64 Referrals March 2009 discussions on the BEHAVE mailing list. Thanks to Mohamed Boucadair and Philip Matthews for their review comments. 6. References 6.1. Normative References [I-D.bagnulo-behave-nat64] Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", draft-bagnulo-behave-nat64-02 (work in progress), November 2008. [I-D.baker-behave-v4v6-framework] Baker, F., Li, X., and C. Bao, "Framework for IPv4/IPv6 Translation", draft-baker-behave-v4v6-framework-02 (work in progress), February 2009. 6.2. Informative References [I-D.ietf-behave-turn] Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)", draft-ietf-behave-turn-13 (work in progress), February 2009. [I-D.ietf-behave-turn-ipv6] Camarillo, G. and O. Novo, "Traversal Using Relays around NAT (TURN) Extension for IPv4/IPv6 Transition", draft-ietf-behave-turn-ipv6-05 (work in progress), October 2008. [I-D.ietf-mmusic-ice] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", draft-ietf-mmusic-ice-19 (work in progress), October 2007. [I-D.ietf-sipping-nat-scenarios] Boulton, C., Rosenberg, J., Camarillo, G., and F. Audet, "Best Current Practices for NAT Traversal for Client- Server SIP", draft-ietf-sipping-nat-scenarios-09 (work in progress), September 2008. Wing Expires September 5, 2009 [Page 10] Internet-Draft NAT64 Referrals March 2009 [I-D.ietf-sipping-v6-transition] Camarillo, G., "IPv6 Transition in the Session Initiation Protocol (SIP)", draft-ietf-sipping-v6-transition-07 (work in progress), August 2007. [I-D.miyata-behave-prefix64] Miyata, H., "PREFIX64 Comparison", draft-miyata-behave-prefix64-00 (work in progress), October 2008. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. Author's Address Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing Expires September 5, 2009 [Page 11]