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Network Working Group                                       J. De ClercqRequest for Comments: 4798                                Alcatel-LucentCategory: Standards Track                                        D. Ooms                                                              OneSparrow                                                              S. Prevost                                                                      BT                                                          F. Le Faucheur                                                                   Cisco                                                           February 2007Connecting IPv6 Islands over IPv4 MPLS UsingIPv6 Provider Edge Routers (6PE)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The IETF Trust (2007).Abstract   This document explains how to interconnect IPv6 islands over a   Multiprotocol Label Switching (MPLS)-enabled IPv4 cloud.  This   approach relies on IPv6 Provider Edge routers (6PE), which are Dual   Stack in order to connect to IPv6 islands and to the MPLS core, which   is only required to run IPv4 MPLS.  The 6PE routers exchange the IPv6   reachability information transparently over the core using the   Multiprotocol Border Gateway Protocol (MP-BGP) over IPv4.  In doing   so, the BGP Next Hop field is used to convey the IPv4 address of the   6PE router so that dynamically established IPv4-signaled MPLS Label   Switched Paths (LSPs) can be used without explicit tunnel   configuration.De Clercq, et al.           Standards Track                     [Page 1]

RFC 4798                          6PE                      February 2007Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................42. Protocol Overview ...............................................43. Transport over IPv4-signaled LSPs and IPv6 Label Binding ........54. Crossing Multiple IPv4 Autonomous Systems .......................75. Security Considerations ........................................106. Acknowledgements ...............................................107. References .....................................................117.1. Normative References ......................................117.2. Informative References ....................................111.  Introduction   There are several approaches for providing IPv6 connectivity over an   MPLS core network [RFC4029] including (i) requiring that MPLS   networks support setting up IPv6-signaled Label Switched Paths (LSPs)   and establish IPv6 connectivity by using those LSPs, (ii) use   configured tunneling over IPv4-signaled LSPs, or (iii) use the IPv6   Provider Edge (6PE) approach defined in this document.   The 6PE approach is required as an alternative to the use of standard   tunnels.  It provides a solution for an MPLS environment where all   tunnels are established dynamically, thereby addressing environments   where the effort to configure and maintain explicitly configured   tunnels is not acceptable.   This document specifies operations of the 6PE approach for   interconnection of IPv6 islands over an IPv4 MPLS cloud.  The   approach requires that the edge routers connected to IPv6 islands be   Dual Stack Multiprotocol-BGP-speaking routers [RFC4760], while the   core routers are only required to run IPv4 MPLS.  The approach uses   MP-BGP over IPv4, relies on identification of the 6PE routers by   their IPv4 address, and uses IPv4-signaled MPLS LSPs that do not   require any explicit tunnel configuration.   Throughout this document, the terminology of [RFC2460] and [RFC4364]   is used.   In this document an 'IPv6 island' is a network running native IPv6 as   per [RFC2460].  A typical example of an IPv6 island would be a   customer's IPv6 site connected via its IPv6 Customer Edge (CE) router   to one (or more) Dual Stack Provider Edge router(s) of a Service   Provider.  These IPv6 Provider Edge routers (6PE) are connected to an   IPv4 MPLS core network.De Clercq, et al.           Standards Track                     [Page 2]

RFC 4798                          6PE                      February 2007            +--------+            |site A  CE---+  +-----------------+            +--------+    |  |                 |       +--------+                         6PE-+  IPv4 MPLS core +-6PE--CE site C |            +--------+    |  |                 |       +--------+            |site B  CE---+  +-----------------+            +--------+             IPv6 islands          IPv4 cloud       IPv6 island            <-------------><---------------------><-------------->                                  Figure 1   The interconnection method described in this document typically   applies to an Internet Service Provider (ISP) that has an IPv4 MPLS   network, that is familiar with BGP (possibly already offering   BGP/MPLS VPN services), and that wants to offer IPv6 services to some   of its customers.  However, the ISP may not (yet) want to upgrade its   network core to IPv6, nor use only IPv6-over-IPv4 tunneling.  With   the 6PE approach described here, the provider only has to upgrade   some Provider Edge (PE) routers to Dual Stack operations so that they   behave as 6PE routers (and route reflectors if those are used for the   exchange of IPv6 reachability among 6PE routers) while leaving the   IPv4 MPLS core routers untouched.  These 6PE routers provide   connectivity to IPv6 islands.  They may also provide other services   simultaneously (IPv4 connectivity, IPv4 L3VPN services, L2VPN   services, etc.).  Also with the 6PE approach, no tunnels need to be   explicitly configured, and no IPv4 headers need to be inserted in   front of the IPv6 packets between the customer and provider edge.   The ISP obtains IPv6 connectivity to its peers and upstreams using   means outside of the scope of this document, and its 6PE routers   readvertise it over the IPv4 MPLS core with MP-BGP.   The interface between the edge router of the IPv6 island (Customer   Edge (CE) router) and the 6PE router is a native IPv6 interface which   can be physical or logical.  A routing protocol (IGP or EGP) may run   between the CE router and the 6PE router for the distribution of IPv6   reachability information.  Alternatively, static routes and/or a   default route may be used on the 6PE router and the CE router to   control reachability.  An IPv6 island may connect to the provider   network over more than one interface.   The 6PE approach described in this document can be used for customers   that already have an IPv4 service from the network provider and   additionally require an IPv6 service, as well as for customers that   require only IPv6 connectivity.De Clercq, et al.           Standards Track                     [Page 3]

RFC 4798                          6PE                      February 2007   The scenario is also described in [RFC4029].   Note that the 6PE approach specified in this document provides global   IPv6 reachability.  Support of IPv6 VPNs is not within the scope of   this document and is addressed in [RFC4659].   Deployment of the 6PE approach over an existing IPv4 MPLS cloud does   not require an introduction of new mechanisms in the core (other than   potentially those described at the end ofSection 3 for dealing with   dynamic MTU discovery).  Configuration and operations of the 6PE   approach have a lot of similarities with the configuration and   operations of an IPv4 VPN service ([RFC4364]) or IPv6 VPN service   ([RFC4659]) over an IPv4 MPLS core because they all use MP-BGP to   distribute non-IPv4 reachability information for transport over an   IPv4 MPLS Core.  However, the configuration and operations of the 6PE   approach is somewhat simpler, since it does not involve all the VPN   concepts such as Virtual Routing and Forwarding (VRFs) tables.1.1.  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 inRFC 2119 [RFC2119].2.  Protocol Overview   Each IPv6 site is connected to at least one Provider Edge router that   is located on the border of the IPv4 MPLS cloud.  We call such a   router a 6PE router.  The 6PE router MUST be dual stack IPv4 and   IPv6.  The 6PE router MUST be configured with at least one IPv4   address on the IPv4 side and at least one IPv6 address on the IPv6   side.  The configured IPv4 address needs to be routable in the IPv4   cloud, and there needs to be a label bound via an IPv4 label   distribution protocol to this IPv4 route.   As a result of this, every considered 6PE router knows which MPLS   label to use to send packets to any other 6PE router.  Note that an   MPLS network offering BGP/MPLS IP VPN services already fulfills these   requirements.   No extra routes need to be injected in the IPv4 cloud.   We call the 6PE router receiving IPv6 packets from an IPv6 site an   ingress 6PE router (relative to these IPv6 packets).  We call a 6PE   router forwarding IPv6 packets to an IPv6 site an egress 6PE router   (relative to these IPv6 packets).De Clercq, et al.           Standards Track                     [Page 4]

RFC 4798                          6PE                      February 2007   Interconnecting IPv6 islands over an IPv4 MPLS cloud takes place   through the following steps:   1. Exchange IPv6 reachability information among 6PE routers with MP-      BGP [RFC2545]:      The 6PE routers MUST exchange the IPv6 prefixes over MP-BGP      sessions as per [RFC2545] running over IPv4.  The MP-BGP Address      Family Identifier (AFI) used MUST be IPv6 (value 2).  In doing so,      the 6PE routers convey their IPv4 address as the BGP Next Hop for      the advertised IPv6 prefixes.  The IPv4 address of the egress 6PE      router MUST be encoded as an IPv4-mapped IPv6 address in the BGP      Next Hop field.  This encoding is consistent with the definition      of an IPv4-mapped IPv6 address in [RFC4291] as an "address type      used to represent the address of IPv4 nodes as IPv6 addresses".      In addition, the 6PE MUST bind a label to the IPv6 prefix as per      [RFC3107].  The Subsequence Address Family Identifier (SAFI) used      in MP-BGP MUST be the "label" SAFI (value 4) as defined in      [RFC3107].  Rationale for this and label allocation policies are      discussed inSection 3.   2. Transport IPv6 packets from the ingress 6PE router to the egress      6PE router over IPv4-signaled LSPs:      The ingress 6PE router MUST forward IPv6 data over the IPv4-      signaled LSP towards the egress 6PE router identified by the IPv4      address advertised in the IPv4-mapped IPv6 address of the BGP Next      Hop for the corresponding IPv6 prefix.   As required by the BGP specification [RFC4271], PE routers form a   full peering mesh unless Route Reflectors are used.3.  Transport over IPv4-signaled LSPs and IPv6 Label Binding   In this approach, the IPv4-mapped IPv6 addresses allow a 6PE router   that has to forward an IPv6 packet to automatically determine the   IPv4-signaled LSP to use for a particular IPv6 destination by looking   at the MP-BGP routing information.   The IPv4-signaled LSPs can be established using any existing   technique for label setup [RFC3031] (LDP, RSVP-TE, etc.).   To ensure interoperability among systems that implement the 6PE   approach described in this document, all such systems MUST support   tunneling using IPv4-signaled MPLS LSPs established by LDP [RFC3036].   When tunneling IPv6 packets over the IPv4 MPLS backbone, rather than   successively prepend an IPv4 header and then perform label impositionDe Clercq, et al.           Standards Track                     [Page 5]

RFC 4798                          6PE                      February 2007   based on the IPv4 header, the ingress 6PE Router MUST directly   perform label imposition of the IPv6 header without prepending any   IPv4 header.  The (outer) label imposed MUST correspond to the IPv4-   signaled LSP starting on the ingress 6PE Router and ending on the   egress 6PE Router.   While this approach could theoretically operate in some situations   using a single level of labels, there are significant advantages in   using a second level of labels that are bound to IPv6 prefixes via   MP-BGP advertisements in accordance with [RFC3107].   For instance, the use of a second level label allows Penultimate Hop   Popping (PHP) on the IPv4 Label Switch Router (LSR) upstream of the   egress 6PE router, without any IPv6 capabilities/upgrades on the   penultimate router; this is because it still transmits MPLS packets   even after the PHP (instead of having to transmit IPv6 packets and   encapsulate them appropriately).   Also, an existing IPv4-signaled LSP that is using "IPv4 Explicit NULL   label" over the last hop (e.g., because that LSP is already being   used to transport IPv4 traffic with the Pipe Diff-Serv Tunneling   Model as defined in [RFC3270]) could not be used to carry IPv6 with a   single label since the "IPv4 Explicit NULL label" cannot be used to   carry native IPv6 traffic (see [RFC3032]), while it could be used to   carry labeled IPv6 traffic (see [RFC4182]).   This is why a second label MUST be used with the 6PE approach.   The label bound by MP-BGP to the IPv6 prefix indicates to the egress   6PE Router that the packet is an IPv6 packet.  This label advertised   by the egress 6PE Router with MP-BGP MAY be an arbitrary label value,   which identifies an IPv6 routing context or outgoing interface to   send the packet to, or MAY be the IPv6 Explicit Null Label.  An   ingress 6PE Router MUST be able to accept any such advertised label.   [RFC2460] requires that every link in the IPv6 Internet have an MTU   of 1280 octets or larger.  Therefore, on MPLS links that are used for   transport of IPv6, as per the 6PE approach, and that do not support   link-specific fragmentation and reassembly, the MTU must be   configured to at least 1280 octets plus the encapsulation overhead.   Some IPv6 hosts might be sending packets larger than the MTU   available in the IPv4 MPLS core and rely on Path MTU discovery to   learn about those links.  To simplify MTU discovery operations, one   option is for the network administrator to engineer the MTU on the   core facing interfaces of the ingress 6PE consistent with the core   MTU.  ICMP 'Packet Too Big' messages can then be sent back by the   ingress 6PE without the corresponding packets ever entering the MPLSDe Clercq, et al.           Standards Track                     [Page 6]

RFC 4798                          6PE                      February 2007   core.  Otherwise, routers in the IPv4 MPLS network have the option to   generate an ICMP "Packet Too Big" message using mechanisms as   described inSection 2.3.2, "Tunneling Private Addresses through a   Public Backbone" of [RFC3032].   Note that in the above case, should a core router with an outgoing   link with an MTU smaller than 1280 receive an encapsulated IPv6   packet larger than 1280, then the mechanisms of [RFC3032] may result   in the "Packet Too Big" message never reaching the sender.  This is   because, according to [RFC4443], the core router will build an ICMP   "Packet Too Big" message filled with the invoking packet up to 1280   bytes, and when forwarding downstream towards the egress PE as per   [RFC3032], the MTU of the outgoing link will cause the packet to be   dropped.  This may cause significant operational problems; the   originator of the packets will notice that his data is not getting   through, without knowing why and where they are discarded.  This   issue would only occur if the above recommendation (to configure MTU   on MPLS links of at least 1280 octets plus encapsulation overhead) is   not adhered to (perhaps by misconfiguration).4.  Crossing Multiple IPv4 Autonomous Systems   This section discusses the case where two IPv6 islands are connected   to different Autonomous Systems (ASes).   Like in the case of multi-AS backbone operations for IPv4 VPNs   described inSection 10 of [RFC4364], three main approaches can be   distinguished:   a. eBGP redistribution of IPv6 routes from AS to neighboring AS      This approach is the equivalent for exchange of IPv6 routes to      procedure (a) described inSection 10 of [RFC4364] for the      exchange of VPN-IPv4 routes.      In this approach, the 6PE routers use IBGP (according to [RFC2545]      and [RFC3107] and as described in this document for the single-AS      situation) to redistribute labeled IPv6 routes either to an      Autonomous System Border Router (ASBR) 6PE router, or to a route      reflector of which an ASBR 6PE router is a client.  The ASBR then      uses eBGP to redistribute the (non-labeled) IPv6 routes to an ASBR      in another AS, which in turn distributes them to the 6PE routers      in that AS as described earlier in this specification, or perhaps      to another ASBR, which in turn distributes them etc.De Clercq, et al.           Standards Track                     [Page 7]

RFC 4798                          6PE                      February 2007      There may be one, or multiple, ASBR interconnection(s) across any      two ASes.  IPv6 needs to be activated on the inter-ASBR links and      each ASBR 6PE router has at least one IPv6 address on the      interface to that link.      No inter-AS LSPs are used.  There is effectively a separate mesh      of LSPs across the 6PE routers within each AS.      In this approach, the ASBR exchanging IPv6 routes may peer over      IPv6 or IPv4.  The exchange of IPv6 routes MUST be carried out as      per [RFC2545].      Note that the peering ASBR in the neighboring AS to which the IPv6      routes were distributed with eBGP, should in its turn redistribute      these routes to the 6PEs in its AS using IBGP and encoding its own      IPv4 address as the IPv4-mapped IPv6 BGP Next Hop.   b. eBGP redistribution of labeled IPv6 routes from AS to neighboring      AS      This approach is the equivalent for exchange of IPv6 routes to      procedure (b) described inSection 10 of [RFC4364] for the      exchange of VPN-IPv4 routes.      In this approach, the 6PE routers use IBGP (as described earlier      in this document for the single-AS situation) to redistribute      labeled IPv6 routes either to an Autonomous System Border Router      (ASBR) 6PE router, or to a route reflector of which an ASBR 6PE      router is a client.  The ASBR then uses eBGP to redistribute the      labeled IPv6 routes to an ASBR in another AS, which in turn      distributes them to the 6PE routers in that AS as described      earlier in this specification, or perhaps to another ASBR, which      in turn distributes them, etc.      There may be one, or multiple, ASBR interconnection(s) across any      two ASes.  IPv6 may or may not be activated on the inter-ASBR      links.      This approach requires that there be label switched paths      established across ASes.  Hence the corresponding considerations      described for procedure (b) inSection 10 of [RFC4364] apply      equally to this approach for IPv6.      In this approach, the ASBR exchanging IPv6 routes may peer over      IPv4 or IPv6 (in which case IPv6 obviously needs to be activated      on the inter-ASBR link).  When peering over IPv6, the exchange of      labeled IPv6 routes MUST be carried out as per [RFC2545] and      [RFC3107].  When peering over IPv4, the exchange of labeled IPv6De Clercq, et al.           Standards Track                     [Page 8]

RFC 4798                          6PE                      February 2007      routes MUST be carried out as per [RFC2545] and [RFC3107] with      encoding of the IPv4 address of the ASBR as an IPv4-mapped IPv6      address in the BGP Next Hop field.   c. Multi-hop eBGP redistribution of labeled IPv6 routes between      source and destination ASes, with eBGP redistribution of labeled      IPv4 routes from AS to neighboring AS.      This approach is the equivalent for exchange of IPv6 routes to      procedure (c) described inSection 10 of [RFC4364] for exchange of      VPN-IPv4 routes.      In this approach, IPv6 routes are neither maintained nor      distributed by the ASBR routers.  The ASBR routers need not be      dual stack, but may be IPv4/MPLS-only routers.  An ASBR needs to      maintain labeled IPv4 /32 routes to the 6PE routers within its AS.      It uses eBGP to distribute these routes to other ASes.  ASBRs in      any transit ASes will also have to use eBGP to pass along the      labeled IPv4 /32 routes.  This results in the creation of an IPv4      label switched path from the ingress 6PE router to the egress 6PE      router.  Now 6PE routers in different ASes can establish multi-hop      eBGP connections to each other over IPv4, and can exchange labeled      IPv6 routes (with an IPv4-mapped IPv6 BGP Next Hop) over those      connections.      IPv6 need not be activated on the inter-ASBR links.      The considerations described for procedure (c) inSection 10 of      [RFC4364] with respect to possible use of multi-hop eBGP      connections via route-reflectors in different ASes, as well as      with respect to the use of a third label in case the IPv4 /32      routes for the PE routers are NOT made known to the P routers,      apply equally to this approach for IPv6.      This approach requires that there be IPv4 label switched paths      established across the ASes leading from a packet's ingress 6PE      router to its egress 6PE router.  Hence the considerations      described for procedure (c) inSection 10 of [RFC4364], with      respect to LSPs spanning multiple ASes, apply equally to this      approach for IPv6.      Note also that the exchange of IPv6 routes can only start after      BGP has created IPv4 connectivity between the ASes.De Clercq, et al.           Standards Track                     [Page 9]

RFC 4798                          6PE                      February 20075.  Security Considerations   The extensions defined in this document allow BGP to propagate   reachability information about IPv6 routes over an MPLS IPv4 core   network.  As such, no new security issues are raised beyond those   that already exist in BGP-4 and use of MP-BGP for IPv6.   The security features of BGP and corresponding security policy   defined in the ISP domain are applicable.   For the inter-AS distribution of IPv6 routes according to case (a) ofSection 4 of this document, no new security issues are raised beyond   those that already exist in the use of eBGP for IPv6 [RFC2545].   For the inter-AS distribution of IPv6 routes according to case (b)   and (c) ofSection 4 of this document, the procedures require that   there be label switched paths established across the AS boundaries.   Hence the appropriate trust relationships must exist between and   among the set of ASes along the path.  Care must be taken to avoid   "label spoofing".  To this end an ASBR 6PE SHOULD only accept labeled   packets from its peer ASBR 6PE if the topmost label is a label that   it has explicitly signaled to that peer ASBR 6PE.   Note that for the inter-AS distribution of IPv6 routes, according to   case (c) ofSection 4 of this document, label spoofing may be more   difficult to prevent.  Indeed, the MPLS label distributed with the   IPv6 routes via multi-hop eBGP is directly sent from the egress 6PE   to ingress 6PEs in another AS (or through route reflectors).  This   label is advertised transparently through the AS boundaries.  When   the egress 6PE that sent the labeled IPv6 routes receives a data   packet that has this particular label on top of its stack, it may not   be able to verify whether the label was pushed on the stack by an   ingress 6PE that is allowed to do so.  As such, one AS may be   vulnerable to label spoofing in a different AS.  The same issue   equally applies to the option (c) ofSection 10 of [RFC4364].  Just   as it is the case for [RFC4364], addressing this particular security   issue is for further study.6.  Acknowledgements   We wish to thank Gerard Gastaud and Eric Levy-Abegnoli who   contributed to this document.  We also wish to thank Tri T. Nguyen,   who initiated this document, but unfortunately passed away much too   soon.  We also thank Pekka Savola for his valuable comments and   suggestions.De Clercq, et al.           Standards Track                    [Page 10]

RFC 4798                          6PE                      February 20077.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6              (IPv6) Specification",RFC 2460, December 1998.   [RFC2545]  Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol              Extensions for IPv6 Inter-Domain Routing",RFC 2545, March              1999.   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack              Encoding",RFC 3032, January 2001.   [RFC3036]  Andersson, L., Doolan, P., Feldman, N., Fredette, A., and              B. Thomas, "LDP Specification",RFC 3036, January 2001.   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in              BGP-4",RFC 3107, May 2001.   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing              Architecture",RFC 4291, February 2006.   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,              "Multiprotocol Extensions for BGP-4",RFC 4760, January              2007.7.2.  Informative References   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol              Label Switching Architecture",RFC 3031, January 2001.   [RFC3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,              P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-              Protocol Label Switching (MPLS) Support of Differentiated              Services",RFC 3270, May 2002.   [RFC4029]  Lind, M., Ksinant, V., Park, S., Baudot, A., and P.              Savola, "Scenarios and Analysis for Introducing IPv6 into              ISP Networks",RFC 4029, March 2005.   [RFC4182]  Rosen, E., "Removing a Restriction on the use of MPLS              Explicit NULL",RFC 4182, September 2005.De Clercq, et al.           Standards Track                    [Page 11]

RFC 4798                          6PE                      February 2007   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway              Protocol 4 (BGP-4)",RFC 4271, January 2006.   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private              Networks (VPNs)",RFC 4364, February 2006.   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control              Message Protocol (ICMPv6) for the Internet Protocol              Version 6 (IPv6) Specification",RFC 4443, March 2006.   [RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,              "BGP-MPLS IP Virtual Private Network (VPN) Extension for              IPv6 VPN",RFC 4659, September 2006.De Clercq, et al.           Standards Track                    [Page 12]

RFC 4798                          6PE                      February 2007Authors' Addresses   Jeremy De Clercq   Alcatel-Lucent   Copernicuslaan 50   Antwerpen  2018   Belgium   EMail: jeremy.de_clercq@alcatel-lucent.be   Dirk Ooms   OneSparrow   Belegstraat 13   Antwerpen  2018   Belgium   EMail: dirk@onesparrow.com   Stuart Prevost   BT   Room 136 Polaris House, Adastral Park, Martlesham Heath   Ipswich Suffolk IP5 3RE   England   EMail: stuart.prevost@bt.com   Francois Le Faucheur   Cisco   Domaine Green Side, 400 Avenue de Roumanille   Biot, Sophia Antipolis  06410   France   EMail: flefauch@cisco.comDe Clercq, et al.           Standards Track                    [Page 13]

RFC 4798                          6PE                      February 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.De Clercq, et al.           Standards Track                    [Page 14]