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L3VPN WG                                              Hamid Ould-Brahim
Internet Draft                                          Nortel Networks
Expiration Date: January 2004
                                                          Eric C. Rosen
                                                          Cisco Systems

                                                          Yakov Rekhter
                                                       Juniper Networks


                                                              (Editors)

                                                              July 2003




                     Using BGP as an Auto-Discovery
                Mechanism for Provider-provisioned VPNs

                  draft-ietf-l3vpn-bgpvpn-auto-00.txt




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."

   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 Provider Provisioned-Based VPN (PPVPN) scheme, the Provider
   Edge (PE) devices attached to a common VPN must exchange certain
   information as a prerequisite to establish VPN-specific
   connectivity. The purpose of this draft is to define a BGP based

Ould-Brahim, et. al                                           [Page 1] Internet-Draft   draft-ietf-l3vpn-bgpvpn-auto-00.txt       July 2003
   auto-discovery mechanism for both layer-2 VPN architectures and
   layer-3 VPNs ([VPN-VR]). This mechanism is based on the approach
   used by [RFC2547-bis] for distributing VPN routing information
   within the service provider(s). Each VPN scheme uses the mechanism
   to automatically discover the information needed by that particular
   scheme.


1. Introduction


   In any Provider Provisioned-Based VPN (PPVPN) scheme, the Provider
   Edge (PE) devices attached to a common VPN must exchange certain
   information as a prerequisite to establish VPN-specific
   connectivity. The purpose of this draft is to define a BGP based
   auto-discovery mechanism for both layer-2 VPN architectures (i.e.,
   [L2VPN-KOMP], [L2VPN-ROSEN]) and layer-3 VPNs ([VPN-VR]). This
   mechanism is based on the approach used by [RFC2547-bis]
   for distributing VPN routing information within the service
   provider(s). Each VPN scheme uses the mechanism to automatically
   discover the information needed by that particular scheme.

   In [RFC2547-bis] based layer-3 VPNs, VPN-specific routes are
   exchanged, along with the information needed to enable a PE to
   determine which routes belong to which VRFs. 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 BGP-4 multiprotocol extensions are used to carry various
   information about VPNs for both layer-2 and layer-3 VPN
   architectures. VPN-specific information associated with the NLRI is
   encoded either as attributes of the NLRI, or as part of the NLRI
   itself, or both.


2. Provider Provisioned  VPNs Reference Model

   Both the layer-2 and layer-3 vpns 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| +----------+ |
               |              |             |              |

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   +--------+  | +----------+ |             | +----------+ | +--------+
   | 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| | +--------+
               | +----------+ |             | +----------+ |
               +--------------+             +--------------+


                Figure 1: Network based VPN Reference Model


   It is assumed that the PEs 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.


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 layer-2 and layer-3 VPN
   architectures. 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 addressing information 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
   L3VPNs, the  NLRI contains an address prefix  which is within the
   VPN address space, and therefore must be unique within the VPN.



3.1 Carrying Layer-3 VPN Information in BGP-MP

   This is done as follows.  The NLRI is a VPN-IP address or a labeled
   VPN-IP address.


   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.


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3.2 Carrying Layer-2 VPN Information in BGP-MP

   The NLRI carries VPN layer-2 addressing information called VPN-L2
   address. A VPN-L2 address is composed of a quantity beginning with
   an 8 bytes Route Distinguisher (RD) field and a variable length
   quantity encoded according to the layer-2 VPN architecture used.

   Different layer-2 VPN solutions use the same common AFI, but
   different SAFI. The AFI indicates that the NLRI is carrying a VPN-l2
   address, while the SAFI indicates solution-specific semantics and
   syntax of the VPN-l2 address that goes after the RD. The RD must be
   chosen so as it ensures that each NLRI is globally unique  (i.e.,
   the same  NLRI does not appear  in two VPNs).


   BGP Route target extended community is used to constrain route
   distribution between PEs. The BGP Next hop carries the service
   provider tunnel endpoint address.

   This draft doesn't preclude the use of additional extended community
   for encoding specific l2vpn parameters.


4. Interpretation of VPN Information in Layer-3 VPNs

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

   For details, see [RFC2547-bis].

4.2 Interpretation of VPN Information in the [VPN-VR] model

4.2.1 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.



4.2.1 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.


4.2.1.2 VPN-ID Extended Community

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   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.




4.2.2 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.


4.2..3 Tunnel Discovery

   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 [RFC-3031]). 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,

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   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.

5. Interpretation of VPN Information in Layer-2 VPNs

   The interpretation of the VPN information in L2VPNs is to be
   specified as part of each L2VPN solution standardized by PPVPN
   working group.


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
   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

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   virtual router (where the NLRI are carrying a labeled prefixes), and
   a SAFI value of 140 is for non labeled addresses.


7. Scalability Considerations

   In this section, we briefly summarize the main characteristics of
   our model with respect to scalability.

   Recall that the Service Provider network consists of (a) PE routers,
   (b) BGP Route Reflectors, (c) P routers (which are neither PE
   routers nor Route Reflectors), and, in the case of multi-provider
   VPNs, and (d) ASBRs.

   A PE router, unless it is a Route Reflector should not retain
   VPN-related information unless it has at least one VPN with an
   Import Target identical to one of the VPN-related information Route
   Target attributes.  Inbound filtering should be used to cause such
   information to be discarded.  If a new Import Target is later added
   to one of the PE's VPNs (a "VPN Join" operation), it must then
   acquire the VPN-related information it may previously have
   discarded.

   This can be done using the refresh mechanism described in [BGP-
   RFSH].

   The outbound route filtering mechanism of [BGP-ORF] can also be
   used to advantage to make the filtering more dynamic.

   Similarly, if a particular Import Target is no longer present in
   any of a PE's VPNs (as a result of one or more "VPN Prune"
   operations), the PE may discard all VPN-related information which,
   as a result, no longer have any of the PE's VPN's Import Targets as
   one of their Route Target Attributes.

   Note that VPN Join and Prune operations are non-disruptive, and do
   not require any BGP connections to be brought down, as long as the
   refresh mechanism of [BGP-RFSH] is used.

   As a result of these distribution rules, no one PE ever needs to
   maintain all routes for all VPNs; this is an important scalability
   consideration.

   Route reflectors can be partitioned among VPNs so that each
   partition carries routes for only a subset of the VPNs supported by
   the Service Provider. Thus no single route reflector is required to
   maintain VPN-related information for all VPNs.

   For inter-provider VPNs, if multi-hop EBGP is used, then the ASBRs
   need not maintain and distribute VPN-related information at all.

   P routers do not maintain any VPN-related information.  In order
   to properly forward VPN traffic, the P routers need only maintain

Ould-Brahim, et al.             July 2003                  [Page 7] Internet-Draft   draft-ietf-l3vpn-bgpvpn-auto-00.txt       July 2003
   routes to the PE routers and the ASBRs.

   As a result, no single component within the Service Provider network
   has to maintain all the VPN-related information for all the VPNs.
   So the total capacity of the network to support increasing numbers
   of VPNs is not limited by the capacity of any individual component.

   An important consideration to remember is that one may have any
   number of INDEPENDENT BGP systems carrying VPN-related information.
   This is unlike the case of the Internet, where the Internet BGP
   system must carry all the Internet routes. Thus one significant
   (but perhaps subtle) distinction between the use of BGP for the
   Internet routing and the use of BGP for distributing VPN-related
   information, as described in this document is that the former is not
   amenable to partition, while the latter is.


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

   [RFC-3107] Rekhter Y, Rosen E., "Carrying Label Information in
      BGP4", January 2000, RFC3107

   [L2VPN-ROSEN] Rosen, E., et al., "An Architecture for L2VPNs",
          draft-ietf-ppvpn-l2vpn-00.txt, July 2001,
          work in progress.

   [L2VPN-KOMP] Kompella, K., et al., "Layer-2 VPNs over Tunnels",
       draft-kompella-ppvpn-l2vpn-01.txt, work in progress, June 2001,
       work in progress..

   [L2VPN-VKOMP-LASS] Kompella, V., Lasserre, M., et al., "Transparent
       VLAN Services over MPLS",
       draft-lasserre-vkompella-ppvpn-vpls-00.txt, work in progress,
       November 2001.

   [L2VPN-DTLS] Kompella, K., et. al., "Decoupled Transparent LAN
       Services", draft-kompella-ppvpn-dtls-00.txt,

Ould-Brahim, et al.             July 2003                  [Page 8] Internet-Draft   draft-ietf-l3vpn-bgpvpn-auto-00.txt       July 2003
       October 2001, work in progress.

   [L2VPN-HVPLS] Kandekar, S., et. al., "Hierarchical Virtual Private
       LAN Service", draft-khandekar-ppvpn-hvpls-mpls-00.txt,
       November 2001, work in progress.

   [L2VPN-LPE] Ould-Brahim, H., Chen, M., et al., "VPLS/LPE L2VPNs:
       Virtual Private LAN Services using Logical PE Architecture",
       draft-ouldbrahim-l2vpn-lpe-01.txt, October 2001, work in
       progress.

   [RFC-3031] Rosen, Viswanathan, and Callon, "Multiprotocol Label
      Switching Architecture", RFC3031

   [RFC-3032] Rosen, Rekhter, Tappan, Farinacci, Fedorkow, Li, and
      Conta, "MPLS Label Stack Encoding", RFC3032

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

   [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.

   [TLS-TISSA] "BGP/MPLS Layer-2 VPN", draft-tsenevir-bgpl2vpn-01.txt,
      work in progress, July 2001.

   [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


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   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
   Tahoe Networks
   3052 Orchard Drive
   San Jose, CA 95134 USA
   Email: bryan@tahoenetworks.com

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


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

   Tissa Senevirathne
   Force10 Networks
   1440 McCarthy Blvd,
   Milpitas, CA 95035.

   Phone: 408-965-5103
   Email: tsenevir@hotmail.com





































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