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Network Working Group                                       P. MohapatraRequest for Comments: 5512                                      E. RosenCategory: Standards Track                            Cisco Systems, Inc.                                                              April 2009The BGP Encapsulation Subsequent Address Family Identifier (SAFI)and the BGP Tunnel Encapsulation AttributeStatus 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) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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   In certain situations, transporting a packet from one Border Gateway   Protocol (BGP) speaker to another (the BGP next hop) requires that   the packet be encapsulated by the first BGP speaker and decapsulated   by the second.  To support these situations, there needs to be some   agreement between the two BGP speakers with regard to the   "encapsulation information", i.e., the format of the encapsulation   header as well as the contents of various fields of the header.   The encapsulation information need not be signaled for all   encapsulation types.  In cases where signaling is required (such as   Layer Two Tunneling Protocol - Version 3 (L2TPv3) or Generic Routing   Encapsulation (GRE) with key), this document specifies a method by   which BGP speakers can signal encapsulation information to each   other.  The signaling is done by sending BGP updates using the   Encapsulation Subsequent Address Family Identifier (SAFI) and the   IPv4 or IPv6 Address Family Identifier (AFI).  In cases where no   encapsulation information needs to be signaled (such as GRE withoutMohapatra & Rosen           Standards Track                     [Page 1]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   key), this document specifies a BGP extended community that can be   attached to BGP UPDATE messages that carry payload prefixes in order   to indicate the encapsulation protocol type to be used.Table of Contents1. Introduction ....................................................22. Specification of Requirements ...................................43. Encapsulation NLRI Format .......................................44. Tunnel Encapsulation Attribute ..................................54.1. Encapsulation sub-TLV ......................................64.2. Protocol Type Sub-TLV ......................................74.3. Color Sub-TLV ..............................................84.3.1. Color Extended Community ............................84.4. Tunnel Type Selection ......................................84.5. BGP Encapsulation Extended Community .......................95. Capability Advertisement .......................................106. Error Handling .................................................107. Security Considerations ........................................108. IANA Considerations ............................................109. Acknowledgements ...............................................1110. References ....................................................1210.1. Normative References .....................................1210.2. Informative References ...................................121.  Introduction   Consider the case of a router R1 forwarding an IP packet P.  Let D be   P's IP destination address.  R1 must look up D in its forwarding   table.  Suppose that the "best match" route for D is route Q, where Q   is a BGP-distributed route whose "BGP next hop" is router R2.  And   suppose further that the routers along the path from R1 to R2 have   entries for R2 in their forwarding tables, but do NOT have entries   for D in their forwarding tables.  For example, the path from R1 to   R2 may be part of a "BGP-free core", where there are no BGP-   distributed routes at all in the core.  Or, as in [MESH], D may be an   IPv4 address while the intermediate routers along the path from R1 to   R2 may support only IPv6.   In cases such as this, in order for R1 to properly forward packet P,   it must encapsulate P and send P "through a tunnel" to R2.  For   example, R1 may encapsulate P using GRE, L2TPv3, IP in IP, etc.,   where the destination IP address of the encapsulation header is the   address of R2.   In order for R1 to encapsulate P for transport to R2, R1 must know   what encapsulation protocol to use for transporting different sorts   of packets to R2.  R1 must also know how to fill in the variousMohapatra & Rosen           Standards Track                     [Page 2]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   fields of the encapsulation header.  With certain encapsulation   types, this knowledge may be acquired by default or through manual   configuration.  Other encapsulation protocols have fields such as   session id, key, or cookie that must be filled in.  It would not be   desirable to require every BGP speaker to be manually configured with   the encapsulation information for every one of its BGP next hops.   In this document, we specify a way in which BGP itself can be used by   a given BGP speaker to tell other BGP speakers, "if you need to   encapsulate packets to be sent to me, here's the information you need   to properly form the encapsulation header".  A BGP speaker signals   this information to other BGP speakers by using a distinguished SAFI   value, the Encapsulation SAFI.  The Encapsulation SAFI can be used   with the AFI for IPv4 or with the AFI for IPv6.  The IPv4 AFI is used   when the encapsulated packets are to be sent using IPv4; the IPv6 AFI   is used when the encapsulated packets are to be sent using IPv6.   In a given BGP update, the Network Layer Reachability Information   (NLRI) of the Encapsulation SAFI consists of the IP address (in the   family specified by the AFI) of the originator of that update.  The   encapsulation information is specified in the BGP "tunnel   encapsulation attribute" (specified herein).  This attribute   specifies the encapsulation protocols that may be used as well as   whatever additional information (if any) is needed in order to   properly use those protocols.  Other attributes, e.g., communities or   extended communities, may also be included.   Since the encapsulation information is coded as an attribute, one   could ask whether a new SAFI is really required.  After all, a BGP   speaker could simply attach the tunnel encapsulation attribute to   each prefix (like Q in our example) that it advertises.  But with   that technique, any change in the encapsulation information would   cause a very large number of updates.  Unless one really wants to   specify different encapsulation information for each prefix, it is   much better to have a mechanism in which a change in the   encapsulation information causes a BGP speaker to advertise only a   single update.  Conversely, when prefixes get modified, the tunnel   encapsulation information need not be exchanged.   In this specification, a single SAFI is used to carry information for   all encapsulation protocols.  One could have taken an alternative   approach of defining a new SAFI for each encapsulation protocol.   However, with the specified approach, encapsulation information can   pass transparently and automatically through intermediate BGP   speakers (e.g., route reflectors) that do not necessarily understand   the encapsulation information.  This works because the encapsulation   attribute is defined as an optional transitive attribute.  New   encapsulations can thus be added without the need to reconfigure anyMohapatra & Rosen           Standards Track                     [Page 3]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   intermediate BGP system.  If adding a new encapsulation required   using a new SAFI, the information for that encapsulation would not   pass through intermediate BGP systems unless those systems were   reconfigured to support the new SAFI.   For encapsulation protocols where no encapsulation information needs   to be signaled (such as GRE without key), the egress router MAY still   want to specify the protocol to use for transporting packets from the   ingress router.  This document specifies a new BGP extended community   that can be attached to UPDATE messages that carry payload prefixes   for this purpose.2.  Specification of Requirements   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 [RFC2119].3.  Encapsulation NLRI Format   The NLRI, defined below, is carried in BGP UPDATE messages [RFC4271]   using BGP multiprotocol extensions [RFC4760] with an AFI of 1 or 2   (IPv4 or IPv6) [IANA-AF] and a SAFI value of 7 (called an   Encapsulation SAFI).   The NLRI is encoded in a format defined inSection 5 of [RFC4760] (a   2-tuple of the form <length, value>).  The value field is structured   as follows:            +-----------------------------------------------+            |       Endpoint Address (Variable)             |            +-----------------------------------------------+   - Endpoint Address: This field identifies the BGP speaker originating     the update.  It is typically one of the interface addresses     configured at the router.  The length of the endpoint address is     dependent on the AFI being advertised.  If the AFI is set to IPv4     (1), then the endpoint address is a 4-octet IPv4 address, whereas     if the AFI is set to IPv6 (2), the endpoint address is a 16-octet     IPv6 address.   An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI   attribute with the Encapsulation SAFI MUST also carry the BGP   mandatory attributes:  ORIGIN, AS_PATH, and LOCAL_PREF (for IBGP   neighbors), as defined in [RFC4271].  In addition, such an update   message can also contain any of the BGP optional attributes, like the   Community or Extended Community attribute, to influence an action on   the receiving speaker.Mohapatra & Rosen           Standards Track                     [Page 4]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   When a BGP speaker advertises the Encapsulation NLRI via BGP, it uses   its own address as the BGP nexthop in the MP_REACH_NLRI or   MP_UNREACH_NLRI attribute.  The nexthop address is set based on the   AFI in the attribute.  For example, if the AFI is set to IPv4 (1),   the nexthop is encoded as a 4-byte IPv4 address.  If the AFI is set   to IPv6 (2), the nexthop is encoded as a 16-byte IPv6 address of the   router.  On the receiving router, the BGP nexthop of such an update   message is validated by performing a recursive route lookup operation   in the routing table.   Bestpath selection of Encapsulation NLRIs is governed by the decision   process outlined inSection 9.1 of [RFC4271].  The encapsulation data   carried through other attributes in the message are to be used by the   receiving router only if the NLRI has a bestpath.4.  Tunnel Encapsulation Attribute   The Tunnel Encapsulation attribute is an optional transitive   attribute that is composed of a set of Type-Length-Value (TLV)   encodings.  The type code of the attribute is 23.  Each TLV contains   information corresponding to a particular tunnel technology.  The TLV   is structured as follows:       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |    Tunnel Type (2 Octets)     |        Length (2 Octets)      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                                                               |      |                             Value                             |      |                                                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   * Tunnel Type (2 octets): identifies the type of tunneling technology     being signaled.  This document defines the following types:     - L2TPv3 over IP [RFC3931]: Tunnel Type = 1     - GRE [RFC2784]: Tunnel Type = 2     - IP in IP [RFC2003] [RFC4213]: Tunnel Type = 7     Unknown types are to be ignored and skipped upon receipt.   * Length (2 octets): the total number of octets of the value field.   * Value (variable): comprised of multiple sub-TLVs.  Each sub-TLV     consists of three fields: a 1-octet type, 1-octet length, and zero     or more octets of value.  The sub-TLV is structured as follows:Mohapatra & Rosen           Standards Track                     [Page 5]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009                     +-----------------------------------+                     |      Sub-TLV Type (1 Octet)       |                     +-----------------------------------+                     |     Sub-TLV Length (1 Octet)      |                     +-----------------------------------+                     |     Sub-TLV Value (Variable)      |                     |                                   |                     +-----------------------------------+   * Sub-TLV Type (1 octet): each sub-TLV type defines a certain     property about the tunnel TLV that contains this sub-TLV.  The     following are the types defined in this document:     - Encapsulation: sub-TLV type = 1     - Protocol type: sub-TLV type = 2     - Color: sub-TLV type = 4     When the TLV is being processed by a BGP speaker that will be     performing encapsulation, any unknown sub-TLVs MUST be ignored and     skipped.  However, if the TLV is understood, the entire TLV MUST     NOT be ignored just because it contains an unknown sub-TLV.   * Sub-TLV Length (1 octet): the total number of octets of the sub-TLV     value field.   * Sub-TLV Value (variable): encodings of the value field depend on     the sub-TLV type as enumerated above.  The following sub-sections     define the encoding in detail.4.1.  Encapsulation Sub-TLV   The syntax and semantics of the encapsulation sub-TLV is determined   by the tunnel type of the TLV that contains this sub-TLV.   When the tunnel type of the TLV is L2TPv3 over IP, the following is   the structure of the value field of the encapsulation sub-TLV:       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                      Session ID (4 octets)                    |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                                                               |      |                        Cookie (Variable)                      |      |                                                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Mohapatra & Rosen           Standards Track                     [Page 6]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   * Session ID: a non-zero 4-octet value locally assigned by the     advertising router that serves as a lookup key in the incoming     packet's context.   * Cookie: an optional, variable length (encoded in octets -- 0 to 8     octets) value used by L2TPv3 to check the association of a received     data message with the session identified by the Session ID.     Generation and usage of the cookie value is as specified in     [RFC3931].     The length of the cookie is not encoded explicitly, but can be     calculated as (sub-TLV length - 4).   When the tunnel type of the TLV is GRE, the following is the   structure of the value field of the encapsulation sub-TLV:       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                      GRE Key (4 octets)                       |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   * GRE Key: 4-octet field [RFC2890] that is generated by the     advertising router.  The actual method by which the key is obtained     is beyond the scope of this document.  The key is inserted into the     GRE encapsulation header of the payload packets sent by ingress     routers to the advertising router.  It is intended to be used for     identifying extra context information about the received payload.     Note that the key is optional.  Unless a key value is being     advertised, the GRE encapsulation sub-TLV MUST NOT be present.4.2.  Protocol Type Sub-TLV   The protocol type sub-TLV MAY be encoded to indicate the type of the   payload packets that will be encapsulated with the tunnel parameters   that are being signaled in the TLV.  The value field of the sub-TLV   contains a 2-octet protocol type that is one of the types defined in   [IANA-AF] as ETHER TYPEs.   For example, if we want to use three L2TPv3 sessions, one carrying   IPv4 packets, one carrying IPv6 packets, and one carrying MPLS   packets, the egress router will include three TLVs of L2TPv3   encapsulation type, each specifying a different Session ID and a   different payload type.  The protocol type sub-TLV for these will be   IPv4 (protocol type = 0x0800), IPv6 (protocol type = 0x86dd), and   MPLS (protocol type = 0x8847), respectively.  This informs the   ingress routers of the appropriate encapsulation information to useMohapatra & Rosen           Standards Track                     [Page 7]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   with each of the given protocol types.  Insertion of the specified   Session ID at the ingress routers allows the egress to process the   incoming packets correctly, according to their protocol type.   Inclusion of this sub-TLV depends on the tunnel type.  It MUST be   encoded for L2TPv3 tunnel type.  On the other hand, the protocol type   sub-TLV is not required for IP in IP or GRE tunnels.4.3.  Color Sub-TLV   The color sub-TLV MAY be encoded as a way to color the corresponding   tunnel TLV.  The value field of the sub-TLV contains an extended   community that is defined as follows:4.3.1.  Color Extended Community   The Color Extended Community is an opaque extended community   [RFC4360] with the following encoding:           0                   1                   2                   3           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          |       0x03    |     0x0b      |           Reserved            |          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          |                          Color Value                          |          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The value of the high-order octet of the extended type field is 0x03,   which indicates it is transitive.  The value of the low-order octet   of the extended type field for this community is 0x0b.  The color   value is user defined and configured locally on the routers.  The   same Color Extended Community can then be attached to the UPDATE   messages that contain payload prefixes.  This way, the BGP speaker   can express the fact that it expects the packets corresponding to   these payload prefixes to be received with a particular tunnel   encapsulation header.4.4.  Tunnel Type Selection   A BGP speaker may include multiple tunnel TLVs in the tunnel   attribute.  The receiving speaker MAY have local policies defined to   choose different tunnel types for different sets/types of payload   prefixes received from the same BGP speaker.  For instance, if a BGP   speaker includes both L2TPv3 and GRE tunnel types in the tunnel   attribute and it also advertises IPv4 and IPv6 prefixes, the ingress   router may have local policy defined to choose L2TPv3 for IPv4   prefixes (provided the protocol type received in the tunnel attribute   matches) and GRE for IPv6 prefixes.Mohapatra & Rosen           Standards Track                     [Page 8]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   Additionally, the Encapsulation SAFI UPDATE message can contain a   color sub-TLV for some or all of the tunnel TLVs.  The BGP speaker   SHOULD then attach a Color Extended Community to payload prefixes to   select the appropriate tunnel types.   In a multi-vendor deployment that has routers supporting different   tunneling technologies, including color sub-TLV to the Encapsulation   SAFI UPDATE message can serve as a classification mechanism (for   example, set A of routers for GRE and set B of routers for L2TPv3).   The ingress router can then choose the encapsulation data   appropriately while sending packets to an egress router.   If a BGP speaker originates an update for prefix P with color C and   with itself as the next hop, then it MUST also originate an   Encapsulation SAFI update that contains the color C.   Suppose that a BGP speaker receives an update for prefix P with color   C, that the BGP decision procedure has selected the route in that   update as the best route to P, and that the next hop is node N, but   that an Encapsulation SAFI update originating from node N containing   color C has not been received.  In this case, no route to P will be   installed in the forwarding table unless and until the corresponding   Encapsulation SAFI update is received, or the BGP decision process   selects a different route.   Suppose that a BGP speaker receives an "uncolored" update for prefix   P, with next hop N, and that the BGP speaker has also received an   Encapsulation SAFI originated by N, specifying one or more   encapsulations that may or may not be colored.  In this case, the   choice of encapsulation is a matter of local policy.  The only   "default policy" necessary is to choose one of the encapsulations   supported by the speaker.4.5.  BGP Encapsulation Extended Community   Here, we define a BGP opaque extended community that can be attached   to BGP UPDATE messages to indicate the encapsulation protocol to be   used for sending packets from an ingress router to an egress router.   Considering our example from theSection 1, R2 MAY include this   extended community, specifying a particular tunnel type to be used in   the UPDATE message that carries route Q to R1.  This is useful if   there is no explicit encapsulation information to be signaled using   the Encapsulation SAFI for a tunneling protocol (such as GRE without   key).Mohapatra & Rosen           Standards Track                     [Page 9]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009        0                   1                   2                   3        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |       0x03    |      0x0c     |           Reserved            |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |            Reserved           |          Tunnel Type          |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The value of the high-order octet of the extended type field is 0x03,   which indicates it's transitive.  The value of the low-order octet of   the extended type field is 0x0c.   The last two octets of the value field encode a tunnel type as   defined in this document.   For interoperability, a speaker supporting Encapsulation SAFI MUST   implement the Encapsulation Extended Community.5.  Capability Advertisement   A BGP speaker that wishes to exchange tunnel endpoint information   must use the Multiprotocol Extensions Capability Code as defined in   [RFC4760], to advertise the corresponding (AFI, SAFI) pair.6.  Error Handling   When a BGP speaker encounters an error while parsing the tunnel   encapsulation attribute, the speaker MUST treat the UPDATE as a   withdrawal of existing routes to the included Encapsulation SAFI   NLRIs, or discard the UPDATE if no such routes exist.  A log entry   should be raised for local analysis.7.  Security Considerations   Security considerations applicable to softwires can be found in the   mesh framework [MESH].  In general, security issues of the tunnel   protocols signaled through Encapsulation SAFI are inherited.   If a third party is able to modify any of the information that is   used to form encapsulation headers, to choose a tunnel type, or to   choose a particular tunnel for a particular payload type, user data   packets may end up getting misrouted, misdelivered, and/or dropped.8.  IANA Considerations   IANA assigned value 7 from the "Subsequent Address Family" Registry,   in the "Standards Action" range, to "Encapsulation SAFI", with this   document as the reference.Mohapatra & Rosen           Standards Track                    [Page 10]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009   IANA assigned value 23 from the "BGP Path Attributes" Registry, to   "Tunnel Encapsulation Attribute", with this document as the   reference.   IANA assigned two new values from the "BGP Opaque Extended Community"   type Registry.  Both are from the transitive range.  The first new   value is called "Color Extended Community" (0x030b), and the second   is called "Encapsulation Extended Community"(0x030c).  This document   is the reference for both assignments.   IANA set up a registry for "BGP Tunnel Encapsulation Attribute Tunnel   Types".  This is a registry of two-octet values (0-65535), to be   assigned on a first-come, first-served basis.  The initial   assignments are as follows:      Tunnel Name                             Type      ---------------                         -----      L2TPv3 over IP                            1      GRE                                       2      IP in IP                                  7   IANA set up a registry for "BGP Tunnel Encapsulation Attribute Sub-   TLVs".  This is a registry of 1-octet values (0-255), to be assigned   on a "standards action/early allocation" basis.  This document is the   reference.  The initial assignments are:      Sub-TLV name                            Type      -------------                           -----      Encapsulation                             1      Protocol Type                             2      Color                                     49.  Acknowledgements   This specification builds on prior work by Gargi Nalawade, Ruchi   Kapoor, Dan Tappan, David Ward, Scott Wainner, Simon Barber, and   Chris Metz.  The current authors wish to thank all these authors for   their contribution.   The authors would like to thank John Scudder, Robert Raszuk, Keyur   Patel, Chris Metz, Yakov Rekhter, Carlos Pignataro, and Brian   Carpenter for their valuable comments and suggestions.Mohapatra & Rosen           Standards Track                    [Page 11]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 200910.  References10.1.  Normative References   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A              Border Gateway Protocol 4 (BGP-4)",RFC 4271, January              2006.   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,              "Multiprotocol Extensions for BGP-4",RFC 4760, January              2007.   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended              Communities Attribute",RFC 4360, February 2006.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3931]  Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,              "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",RFC3931, March 2005.   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.              Traina, "Generic Routing Encapsulation (GRE)",RFC 2784,              March 2000.   [RFC2890]  Dommety, G., "Key and Sequence Number Extensions to GRE",RFC 2890, September 2000.   [RFC2003]  Perkins, C., "IP Encapsulation within IP",RFC 2003,              October 1996.   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms              for IPv6 Hosts and Routers",RFC 4213, October 2005.10.2.  Informative References   [IANA-AF]  "Address Family Numbers,"http://www.iana.org.   [MESH]     Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh              Framework," Work in Progress, February 2009.Mohapatra & Rosen           Standards Track                    [Page 12]

RFC 5512    BGP Encapsulation SAFI and Tunnel Encapsulation   April 2009Authors' Addresses   Pradosh Mohapatra   Cisco Systems, Inc.   170 Tasman Drive   San Jose, CA, 95134   EMail: pmohapat@cisco.com   Eric Rosen   Cisco Systems, Inc.   1414 Massachusetts Avenue   Boxborough, MA, 01719   EMail: erosen@cisco.comMohapatra & Rosen           Standards Track                    [Page 13]