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Provider Provisioned VPN WG                           Hamid Ould-Brahim
Internet Draft                                            Bryan Gleeson
draft-ietf-ppvpn-bgpvpn-auto-01.txt                 Peter Ashwood-Smith
Expiration Date: April 2002                             Nortel Networks


                                                          Eric C. Rosen
                                                          Cisco Systems


                                                          Yakov Rekhter
                                                       Juniper Networks


                                                            Luyuan Fang
                                                                   AT&T


                                                       Jeremy De Clercq
                                                                Alcatel


                                                           Riad Hartani
                                                       Caspian Networks

                                                          November 2001





                     Using BGP as an Auto-Discovery
                    Mechanism for Network-based VPNs





Status of this Memo

   This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026 [RFC-2026].

   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."


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Internet-Draft   draft-ietf-ppvpn-bgpvpn-auto-01.txt    November 2001


   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.



Abstract

   In any Network-Based VPN (NBVPN) scheme, the Provider Edge (PE)
   routers attached to a common VPN must exchange certain information
   as a prerequisite to establish VPN-specific connectivity. In
   [RFC2547-bis], VPN-specific routes are exchanged, along with the
   information needed to enable a PE to determine which routes belong
   to which VPNs. In [VPN-VR], VR addresses must be exchanged, along
   with the information needed to enable the PEs to determine which VRs
   are in the same VPN ("membership"), and which of those VRs are to
   have VPN connectivity ("topology"). Once the VRs are reachable
   through the tunnels, routes ("reachability") are then exchanged by
   running existing routing protocol per VPN basis. The purpose of this
   draft is to define a common BGP based auto-discovery mechanism used
   for both the virtual router [VPN-VR] and [RFC2547-bis]
   architectures. Each scheme uses the mechanism to automatically
   discover the information needed by that particular scheme.
   Interworking scenarios between [RFC2547-bis] and the virtual router
   models are also discussed.


ID Summary

   RELATED DOCUMENTS

   http://www.ietf.org/internet-drafts/draft-rosen-rfc2547bis-03.txt
   http://www.ietf.org/internet-drafts/draft-ouldbrahim-vpn-vr-03.txt


   WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK

   Fits the PPVPN box.

   WHY IS IT TARGETED AT THIS WG

   This ID describes an auto-discovery mechanism for both RFC2547 and
   virtual router schemes which are considered by PPVPN working group.

   JUSTIFICATION

   This work highlights explicitly the VPN auto-discovery PPVPN layer-3
   solutions. More than that it also addresses interworking scenarios
   between RFC2547 and virtual router solutions.



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Internet-Draft   draft-ietf-ppvpn-bgpvpn-auto-01.txt    November 2001

1. Introduction

   In any Network-Based VPN (NBVPN) scheme, the Provider Edge (PE)
   routers attached to a common VPN must exchange certain information
   as a prerequisite to establish VPN-specific connectivity. In
   [RFC2547-bis], VPN-specific routes are exchanged, along with the
   information needed to enable a PE to determine which routes belong
   to which VPNs. In [VPN-VR], virtual router (VR) addresses must be
   exchanged, along with the information needed to enable the PEs to
   determine which VRs are in the same VPN ("membership"), and which of
   those VRs are to have VPN connectivity ("topology"). Once the VRs
   are reachable through the tunnels, routes ("reachability") are then
   exchanged by running existing routing protocols per VPN basis.

   The purpose of this draft is to define a common BGP based auto-
   discovery mechanism used for both the virtual router [VPN-VR] and
   [RFC2547-bis] architectures. Each scheme uses the mechanism to
   automatically discover the information needed by that particular
   scheme. The BGP multiprotocol extension attributes are used to carry
   either the virtual router or the RFC2547 auto-discovery information.
   Interworking scenarios between [RFC2547-bis] and the virtual router
   models are also discussed.



2. Network Based VPNs Reference Model

   Both the virtual router and [RFC2547-bis] architectures are using a
   network reference model as illustrated in figure 1.


                     PE                         PE
               +--------------+             +--------------+
   +--------+  | +----------+ |             | +----------+ | +--------+
   |  VPN-A |  | |  VPN-A   | |             | |  VPN-A   | | |  VPN-A |
   |  Sites |--| |Database /| |  BGP route  | | Database/| |-|  sites |
   +--------+  | |Processing| |<----------->| |Processing| | +--------+
               | +----------+ | Distribution| +----------+ |
               |              |             |              |
   +--------+  | +----------+ |             | +----------+ | +--------+
   | VPN-B  |  | |  VPN-B   | |  --------   | |   VPN-B  | | |  VPN-B |
   | Sites  |--| |Database /| |-(Backbones)-| | Database/| |-|  sites |
   +--------+  | |Processing| |  --------   | |Processing| | +--------+
               | +----------+ |             | +----------+ |
               |              |             |              |
   +--------+  | +----------+ |             | +----------+ | +--------+
   | VPN-C  |  | |  VPN-C   | |             | |   VPN-C  | | |  VPN-C |
   | Sites  |--| |Database /| |             | | Database/| |-|  sites |
   +--------+  | |Processing| |             | |Processing| | +--------+
               | +----------+ |             | +----------+ |
               +--------------+             +--------------+



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Internet-Draft   draft-ietf-ppvpn-bgpvpn-auto-01.txt    November 2001

                Figure 1: Network based VPN Reference Model


   It is assumed that the PE routers can use BGP to distribute
   information to each other. This may be via direct IBGP peering, via
   direct EBGP peering, via multihop BGP peering, through
   intermediaries such as Route Reflectors, through a chain of
   intermediate BGP connections, etc. It is assumed also that the PE
   knows what architecture it is supporting (either the virtual router,
   or [RFC2547-bis] architectures, or both).


3. Carrying VPN information in BGP Multi-Protocol Extension Attributes

   The BGP-4 multiprotocol extensions are used to carry various
   information about VPNs for both architectures. This is done as
   follows.  The NLRI is a VPN-IP address or a labeled VPN-IP address.
   VPN-specific information associated with the NLRI is encoded either
   as attributes of the NLRI, or as part of the NLRI itself, or both.

   The address prefix in the NLRI field is ALWAYS within the VPN
   address space, and therefore MUST be unique within the VPN. The
   address specified in the BGP next hop attribute, on the other hand,
   is in the service provider addressing space.

   In the case of the virtual router, the NLRI address prefix is an
   address of one of the virtual routers configured on the PE. Thus
   this mechanism allows the virtual routers to discover each other, to
   set up adjacencies and tunnels to each other, etc. In the case of
   [RFC2547-bis], the NLRI prefix represents a route to an arbitrary
   system or set of systems within the VPN.


4. Interpretation of VPN Information in the [RFC2547-bis] model

   The [RFC2547-bis] model interprets the NLRI reachability
   information. The BGP attributes (in particular, the Route Target
   Extended Community) are used by the PE routers to assign the routes
   to particular VPN database/processing contexts, and hence implicitly
   determine the topology. The BGP Next Hop attribute specifies the
   remote end point of the tunnel to be used when sending packets whose
   destination addresses match the corresponding NLRI. For details, see
   [RFC2547-bis].

5. Interpretation of VPN Information in the [VPN-VR] model

5.1 Membership Discovery

   The VPN-ID format as defined in [RFC-2685] is used to identify a
   VPN. All virtual routers that are members of a specific VPN share
   the same VPN-ID. A VPN-ID is carried in the NLRI to make addresses
   of VRs globally unique. Making these addresses globally unique is
   necessary if one uses BGP for VRs' autodiscovery.

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5.1.1 Encoding of the VPN-ID in the NLRI

   For the virtual router model, the VPN-ID is carried within the route
   distinguisher (RD) field. In order to hold the 7-bytes VPN-ID, the
   first byte of RD type field is used to indicate the existence of the
   VPN-ID format. A value of 0x80 in the first byte of RD's type field
   indicates that the RD field is carrying the VPN-ID format. In this
   case, the type field range 0x8000-0x80ff will be reserved for the
   virtual router case.


5.1.2 VPN-ID Extended Community

   A new extended community is used to carry the VPN-ID format. This
   attribute is transitive across the Autonomous system boundary. The
   type field of the VPN-ID extended community is of regular type to be
   assigned by IANA [BGP-COMM]. The remaining 7 bytes hold the VPN-ID
   value field as per [RFC-2685]. The BGP UPDATE message will carry
   information for a single VPN. It is the VPN-ID Extended Community,
   or more precisely route filtering based on the Extended Community
   that allows one VR to find out about other VRs in the same VPN.




5.2 VPN Topology Information

   A new extended community is used to indicate different VPN topology
   values. This attribute is transitive across the Autonomous system
   boundary. The value of the type field for extended type is assigned
   by IANA. The first two bytes of the value field (of the remaining 6
   bytes) are reserved. The actual topology values are carried within
   the remaining four bytes. The following topology values are defined:

         Value    Topology Type

           1          "Hub"
           2          "Spoke"
           3          "Mesh"

   Arbitrary values can also be used to allow specific topologies to be
   constructed. VPN connectivity between two VRs within the same VPN is
   achieved if and only if at least one of them is a hub (the other is
   a hub or a spoke), or if both VRs are part of a full mesh VPN
   topology.


5.3  Tunnel Discovery



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   Network-based VPNs must be implemented through some form of
   tunneling mechanism, where the packet formats and/or the addressing
   used within the VPN can be unrelated to that used to route the
   tunneled packets across the backbone. There are numerous tunneling
   mechanisms that can be used by a network based VPN (e.g., IP/IP
   [RFC-2003], GRE tunnels [RFC-1701], IPSec [RFC-2401], and MPLS
   tunnels [MPLS-ARCH]). Each of these tunnels allows for opaque
   transport of frames as packet payload across the backbone, with
   forwarding disjoint from the address fields of the encapsulated
   packets. A provider edge router may terminate multiple type of
   tunnels and forward packets between these tunnels and other network
   interfaces in different ways.

   BGP can be used to carry tunnel endpoint addresses between edge
   routers. For scalability purposes, this draft recommends the use of
   tunneling mechanisms with demultiplexing capabilities such as IPSec,
   MPLS, and GRE (with respect to using GRE -the key field, it is no
   different than just MPLS over GRE, however there is no specification
   on how to exchange the key field, while there is a specification and
   implementations on how to exchange the label). Note that IP in IP
   doesn't have demultiplexing capabilities.


   The BGP next hop will carry the service provider tunnel endpoint
   address. As an example, if IPSec is used as tunneling mechanism, the
   IPSec tunnel remote address will be discovered through BGP, and the
   actual tunnel establishment is achieved through IPSec signaling
   protocol.

   When MPLS tunneling is used, the label carried in the NLRI field is
   associated with an address of a VR, where the address is carried in
   the NLRI and is encoded as a VPN-IP address.


6. Virtual Router and [RFC2547-bis] Interworking Scenarios

   Two interwoking scenarios are considered when the network is using
   both virtual routers and [RFC2547-bis]. The first scenario is a CE-
   PE relationship between a PE (implementing [RFC2547-bis]), and a VR
   appearing as a CE to the PE. The connection between the VR, and the
   PE can be either direct connectivity, or through a tunnel (e.g.,
   IPSec).

   The second scenario is when a PE is implementing both architectures.
   In this particular case, a single BGP session configured on the
   service provider network can be used to advertise either [RFC2547-
   bis] VPN information or the virtual router related VPN information.
   From the VR and the [RFC2547-bis] point of view there is complete
   separation from data path and addressing schemes. However the PE's
   interfaces are shared between both architectures.

   A PE implementing only [RFC2547-bis] will not import routes from a
   BGP UPDATE message containing the VPN-ID extended community. On the

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   other hand, a PE implementing the virtual router architecture will
   not import routes from a BGP UPDATE message containing the route
   target extended community attribute.

   The granularity at which the information is either [RFC2547-bis]
   related or VR-related is per BGP UPDATE message. Different SAFI
   numbers are used to indicate that the message carried in BGP
   multiprotocol extension attributes is to be handled by the VR or
   [RFC2547-bis] architectures. SAFI number of 128 is used for [RFC2547-
   bis] related format. A value of 129 for the SAFI number is for the
   virtual router (where the NLRI are carrying a labeled prefixes), and
   a SAFI value of 140 is for non labeled addresses.


7. Use of BGP Capability Advertisement

   A BGP speaker that uses VPN information as described in this
   document with multiprotocol extensions should use the Capability
   Advertisement procedures to determine whether the speaker could use
   Multiprotocol Extensions with a particular peer. The Capability Code
   field is set to 1 (which indicates Multiprotocol Extensions
   capabilities).


8. Security Considerations

   This draft does not introduce any new security considerations to
   either [VPN-VR] or [RFC2547-bis].





9. References


   [BGP-COMM] Ramachandra, Tappan, et al., "BGP Extended Communities
      Attribute", June 2001, work in progress

   [BGP-MP] Bates, Chandra, Katz, and Rekhter, "Multiprotocol
      Extensions for BGP4", February 1998, RFC 2283

   [BGP-MPLS] Rekhter Y, Rosen E., "Carrying Label Information in
      BGP4", January 2000, work in progress

   [MPLS-ARCH] Rosen, Viswanathan, and Callon, "Multiprotocol Label
      Switching Architecture", August 1999, work in progress

   [MPLS-ENCAPS] Rosen, Rekhter, Tappan, Farinacci, Fedorkow, Li, and
      Conta, "MPLS Label Stack Encoding", October 1999,work in progress

   [RFC-1701] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic
      Routing Encapsulation (GRE)", RFC 1701, October 1994.

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   [RFC-2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
      October 1996.

   [RFC-2026] Bradner, S., "The Internet Standards Process -- Revision
      3", RFC2026, October 1996.

   [RFC-2401] Kent S., Atkinson R., "Security Architecture for the
      Internet Protocol", RFC2401, November 1998.

   [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
      Requirement Levels", RFC 2119, March 1997.

   [RFC2547-bis] Rosen E., et al, "BGP/MPLS VPNs", work in progress.

   [RFC-2685] Fox B., et al, "Virtual Private Networks Identifier", RFC
      2685, September 1999.

   [VPN-VR] Ould-Brahim H., et al., "Network based IP VPN Architecture
       using Virtual Routers", work in progress.





10. Acknowledgments


   to be supplied.


11. Author's Addresses


   Hamid Ould-Brahim
   Nortel Networks
   P O Box 3511 Station C
   Ottawa, ON K1Y 4H7, Canada
   Email: hbrahim@nortelnetworks.com
   Phone: +1 613 765 3418


   Bryan Gleeson
   Nortel Networks
   2305 Mission College Blvd
   Santa Clara CA 95054
   Phone: +1 (505) 565 2625
   Email: bgleeson@shastanets.com


   Peter Ashwood-Smith
   Nortel Networks
   P.O. Box 3511 Station C,

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                 draft-ietf-ppvpn-bgpvpn-auto-01.txt        April 2002


   Ottawa, ON K1Y 4H7, Canada
   Phone: +1 613 763 4534
   Email: petera@nortelnetworks.com


   Eric C. Rosen
   Cisco Systems, Inc.
   250 Apollo drive
   Chelmsford, MA, 01824
   E-mail: erosen@cisco.com


   Yakov Rekhter
   Juniper Networks
   1194 N. Mathilda Avenue
   Sunnyvale, CA 94089
   Email: yakov@juniper.net


   Luyuan Fang
   AT&T

   200 Laurel Avenue
   Middletown, NJ 07748
   Email: Luyuanfang@att.com
   Phone: +1 (732) 420 1920


   Jeremy De Clercq
   Alcatel
   Francis Wellesplein 1
   B-2018 Antwerpen, Belgium
   Phone: +32 3 240 47 52
   Email: jeremy.de_clercq@alcatel.be


   Riad Hartani
   Caspian Networks
   170 Baytech Drive
   San Jose, CA 95143
   Phone: 408 382 5216
   Email: riad@caspiannetworks.com











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