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rfc:rfc5512

Network Working Group P. Mohapatra Request for Comments: 5512 E. Rosen Category: Standards Track Cisco Systems, Inc.

                                                            April 2009
 The BGP Encapsulation Subsequent Address Family Identifier (SAFI)
             and the BGP Tunnel Encapsulation Attribute

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) 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

 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 without

Mohapatra & 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 Contents

 1. Introduction ....................................................2
 2. Specification of Requirements ...................................4
 3. Encapsulation NLRI Format .......................................4
 4. Tunnel Encapsulation Attribute ..................................5
    4.1. Encapsulation sub-TLV ......................................6
    4.2. Protocol Type Sub-TLV ......................................7
    4.3. Color Sub-TLV ..............................................8
         4.3.1. Color Extended Community ............................8
    4.4. Tunnel Type Selection ......................................8
    4.5. BGP Encapsulation Extended Community .......................9
 5. Capability Advertisement .......................................10
 6. Error Handling .................................................10
 7. Security Considerations ........................................10
 8. IANA Considerations ............................................10
 9. Acknowledgements ...............................................11
 10. References ....................................................12
    10.1. Normative References .....................................12
    10.2. Informative References ...................................12

1. 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 various

Mohapatra & 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 any

Mohapatra & 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 in Section 5 of [RFC4760] (a
 2-tuple of the form <length, value>).  The value field is structured
 as follows:
          +-----------------------------------------------+
          |       Endpoint Address (Variable)             |
          +-----------------------------------------------+
  1. 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 in Section 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:

  1. L2TPv3 over IP [RFC3931]: Tunnel Type = 1
  2. GRE [RFC2784]: Tunnel Type = 2
  3. 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:
  1. Encapsulation: sub-TLV type = 1
  2. Protocol type: sub-TLV type = 2
  3. 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 use

Mohapatra & 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 the Section 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                                     4

9. 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 2009

10. References

10.1. 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)", RFC
            3931, 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 2009

Authors' 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.com

Mohapatra & Rosen Standards Track [Page 13]

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