OSPF-Based Layer 1 VPN Auto-Discovery

Network Working Group                                         I. Bryskin
Request for Comments: 5252                       ADVA Optical Networking
Category: Standards Track                                      L. Berger
                                                    LabN Consulting, LLC
                                                               July 2008


                 OSPF-Based Layer 1 VPN Auto-Discovery

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.

Abstract

   This document defines an Open Shortest Path First (OSPF) based Layer
   1 Virtual Private Network (L1VPN) auto-discovery mechanism.  This
   mechanism enables provider edge (PE) devices using OSPF to
   dynamically learn about the existence of each other, and attributes
   of configured customer edge (CE) links and their associations with
   L1VPNs.  This document builds on the L1VPN framework and requirements
   and provides a L1VPN basic mode auto-discovery mechanism.

Table of Contents

   1. Introduction ....................................................2
      1.1. Overview ...................................................2
      1.2. Terminology ................................................3
      1.3. Conventions Used in This Document ..........................4
   2. L1VPN LSA and Its TLVs ..........................................4
      2.1. L1VPN LSA ..................................................4
      2.2. L1VPN INFO TLV .............................................6
   3. L1VPN LSA Advertising and Processing ............................7
      3.1. Discussion and Example .....................................7
   4. Backward Compatibility ..........................................8
   5. Security Considerations .........................................9
   6. IANA Considerations .............................................9
   7. Acknowledgments .................................................9
   8. References ......................................................9
      8.1. Normative References .......................................9
      8.2. Informative References ....................................10

1.  Introduction

1.1.  Overview

   The framework for Layer 1 VPNs is described in [RFC4847].  Basic mode
   operation is further defined in [RFC5251].  The L1VPN Basic Mode
   (L1VPN-BM) document [RFC5251] identifies the information that is
   necessary to map customer information (ports identifiers) to provider
   information (identifiers).  It also states that this mapping
   information may be provided via provisioning or via an auto-discovery
   mechanism.  This document provides such an auto-discovery mechanism
   using Open Shortest Path First (OSPF) version 2.  Use of OSPF version
   3 and support for IPv6 are out of scope of this document and will be
   defined separately.

   Figure 1 shows the L1VPN basic service being supported using OSPF-
   based L1VPN auto-discovery.  This figure shows two PE routers
   interconnected over a GMPLS backbone.  Each PE is attached to three
   CE devices belonging to three different L1VPN connections.  In this
   network, OSPF is used to provide the VPN membership, port mapping,
   and related information required to support basic mode operation.

                  PE                        PE
               +---------+             +--------------+
   +--------+  | +------+|             | +----------+ | +--------+
   |  VPN-A |  | |VPN-A ||             | |  VPN-A   | | |  VPN-A |
   |   CE1  |--| |PIT   ||  OSPF LSAs  | |  PIT     | |-|   CE2  |
   +--------+  | |      ||<----------->| |          | | +--------+
               | +------+| Distribution| +----------+ |
               |         |             |              |
   +--------+  | +------+|             | +----------+ | +--------+
   | VPN-B  |  | |VPN-B ||   -------   | |   VPN-B  | | |  VPN-B |
   |  CE1   |--| |PIT   ||--( GMPLS )--| |   PIT    | |-|   CE2  |
   +--------+  | |      ||  (Backbone) | |          | | +--------+
               | +------+|   --------  | +----------+ |
               |         |             |              |
   +--------+  | +-----+ |             | +----------+ | +--------+
   | VPN-C  |  | |VPN-C| |             | |   VPN-C  | | |  VPN-C |
   |  CE1   |--| |PIT  | |             | |   PIT    | |-|   CE2  |
   +--------+  | |     | |             | |          | | +--------+
               | +-----+ |             | +----------+ |
               +---------+             +--------------+

               Figure 1: OSPF Auto-Discovery for L1VPNs

   See [RFC5195] for a parallel L1VPN auto-discovery that uses BGP.  The
   OSPF approach described in this document is particularly useful in
   networks where BGP is not typically used.

   The approach used in this document to provide OSPF-based L1VPN auto-
   discovery uses a new type of Opaque Link State Advertisement (LSA)
   that is referred to as an L1VPN LSA.  The L1VPN LSA carries
   information in TLV (type, length, value) structures.  An L1VPN-
   specific TLV is defined below to propagate VPN membership and port
   information.  This TLV is referred to as the L1VPN Info TLV.  The
   L1VPN LSA may also carry Traffic Engineering (TE) TLVs; see [RFC3630]
   and [RFC4203].

1.2.  Terminology

   The reader of this document should be familiar with the terms used in
   [RFC4847] and [RFC5251].  The reader of this document should also be
   familiar with [RFC2328], [RFC5250], and [RFC3630].  In particular,
   the following terms:

   L1VPN - Layer 1 Virtual Private Network

   CE - Customer (edge) network element directly connected to the
        provider network (terminates one or more links to one or more
        PEs); it is also connected to one or more Cs and/or other CEs

   C - Customer network element that is not connected to the provider
       network but is connected to one or more other Cs and/or CEs

   PE - Provider (edge) network element directly connected to one or
        more customer networks (terminates one or more links to one or
        more CEs associated with the same or different L1VPNs); it is
        also connected to one or more Ps and/or other PEs

   P - Provider (core) network element that is not directly connected to
       any customer networks; P is connected to one or more other Ps
       and/or PEs

   LSA - OSPF link State Advertisement

   LSDB - Link State Database: a data structure supported by an IGP
          speaker

   PIT - Port Information Table

   CPI - Customer Port Identifier

   PPI - Provider Port Identifier

1.3.  Conventions Used in This Document

   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].

2.  L1VPN LSA and Its TLVs

   This section defines the L1VPN LSA and its TLVs.

2.1.  L1VPN LSA

   The format of a L1VPN LSA is 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            LS age             |     Options   |  LS Type      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Opaque Type  |               Opaque ID                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Advertising Router                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      LS Sequence Number                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         LS checksum           |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           L1VPN Info TLV                      |
   |                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            TE Link TLV                        |
   |                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   LS age
      As defined in [RFC2328].

   Options
      As defined in [RFC2328].

   LS Type
      This field MUST be set to 11, i.e., an Autonomous System (AS)
      scoped Opaque LSA [RFC5250].

   Opaque Type
      The value of this field MUST be set to 5.

   Opaque ID
      As defined in [RFC5250].

   Advertising Router
      As defined in [RFC2328].

   LS Sequence Number
      As defined in [RFC2328].

   LS checksum
      As defined in [RFC2328].

   Length
      As defined in [RFC2328].

   L1VPN Info TLV
      A single TLV, as defined in Section 3.2, MUST be present.  If more
      than one L1VPN Info TLV is present, only the first TLV is
      processed and the others MUST be ignored on receipt.

   TE Link TLV
      A single TE Link TLV (as defined in [RFC3630] and [RFC4203]) MAY
      be included in a L1VPN LSA.

2.2.  L1VPN INFO TLV

   The following TLV is introduced:

   Name: L1VPN IPv4 Info
   Type: 1
   Length: Variable

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           L1VPN TLV Type      |         L1VPN TLV Length      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 L1VPN Globally Unique Identifier              |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          PE TE Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Link Local Identifier                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   |                 L1VPN Auto-Discovery Information              |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |           Padding             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   L1VPN TLV Type
      The type of the TLV.

   TLV Length
      The length of the TLV in bytes, excluding the 4 bytes of the TLV
      header and, if present, the length of the Padding field.

   L1VPN Globally Unique Identifier
      As defined in [RFC5251].

   PE TE Address
      This field MUST carry an address that has been advertised by the
      LSA originator per [RFC3630] and is either the Router Address TLV
      or Local interface IP address link sub-TLV.  It will typically
      carry the TE Router Address.

   Link Local Identifier
      This field is used to support unnumbered links.  When an
      unnumbered PE TE link is represented, this field MUST contain a
      value advertised by the LSA originator per [RFC4203] in a Link
      Local/Remote Identifiers link sub-TLV.  When a numbered link is
      represented, this field MUST be set to 0.

   L1VPN Auto-discovery information
      As defined in [RFC5251].

   Padding
      A field of variable length and of sufficient size to ensure that
      the TLV is aligned on a 4-byte boundary.  This field is only
      required when the L1VPN Auto-discovery information field is not
      4-byte aligned.  This field MUST be less than 4 bytes long, and
      MUST NOT be present when the size of the L1VPN Auto-discovery
      information field is 4-byte aligned.

3.  L1VPN LSA Advertising and Processing

   PEs advertise local <CPI, PPI> tuples in L1VPN LSAs containing L1VPN
   Info TLVs.  Each PE MUST originate a separate L1VPN LSA with AS
   flooding scope for each local CE-to-PE link.  The LSA MUST be
   originated each time a PE restarts and every time there is a change
   in the PIT entry associated with a local CE-to-PE link.  The LSA MUST
   include a single L1VPN Info TLV and MAY include a single TE Link TLV
   as per [RFC3630] and [RFC4203].  The TE Link TLV carries TE
   attributes of the associated CE-to-PE link.  Note that because CEs
   are outside of the provider TE domain, the attributes of CE-to-PE
   links are not advertised via normal OSPF-TE procedures as described
   in [RFC3630] and [RFC4203].  If more than one L1VPN Info TLVs and/or
   TE Link TLVs are found in the LSA, the subsequent TLVs SHOULD be
   ignored by the receiving PEs.

   L1VPN LSAs are of AS-scope (LS type is set to 11) and therefore are
   flooded to all PEs within the AS according to [RFC5250].  Every time
   a PE receives a new, removed, or modified L1VPN LSA, the PE MUST
   check whether it maintains a PIT associated with the L1VPN specified
   in the L1VPN globally unique identifier field.  If this is the case
   (the appropriate PIT will be found if one or more local CE-to-PE
   links that belong to the L1VPN are configured), the PE SHOULD add,
   remove, or modify the PIT entry associated with each of the
   advertised CE-to-PE links accordingly.  (An implementation MAY choose
   to not remove or modify the PIT according to local policy or
   management directives.)  Thus, in the normal steady-state case, all
   PEs associated with a particular L1VPN will have identical local PITs
   for an L1VPN.

3.1.  Discussion and Example

   The L1VPN auto-discovery mechanism described in this document does
   not prevent a PE from applying any local policy with respect to PIT
   management.  An example of such a local policy would be the ability
   to configure permanent (static) PIT entries.  Another example would
   be the ability to ignore information carried in L1VPN LSAs advertised
   by a specific TE.

   The reason why it is required that the value specified in the PE TE
   Address field of the L1VPN Info TLV matches a valid PE TE Router ID
   or numbered TE Link ID is to ensure that CEs attached to this PE can
   be resolved to the PE as it is known to the Traffic Engineering
   Database (TED) and hence TE paths toward the CEs across the provider
   domain can be computed.

   Let us consider the example presented in Figure 2.

                            CE11               CE13
                              |                 |
                      CE22---PE1--------P------PE2
                              |         |
                             CE15      PE3
                                        |
                                       CE24

                    Figure 2: Single Area Configuration

   Let us assume that PE1 is connected to CE11 and CE15 in L1VPN1 and to
   CE22 in L1VPN2; PE2 is connected to CE13 in L1VPN1; PE3 is connected
   to CE24 in L1VPN2.  In this configuration PE1 manages two PITs: PIT1
   for L1VPN1 and PIT2 for L1VPN2; PE2 manages only PIT1; and PE3
   manages only PIT2.  PE1 originates three L1VPN LSAs, each containing
   a L1VPN Info TLV advertising links PE1-CE11, PE1-CE22, and PE1-CE15,
   respectively.  PE2 originates a single L1VPN LSA for link PE2-CE13,
   and PE3 originates a single L1VPN LSA for link PE3-CE24.  In steady
   state, the PIT1 on PE1 and PE3 will contain information on links
   PE1-CE11, PE1-CE15, and PE2-CE13; PIT2 on PE1 and PE2 will contain
   entries for links PE1-CE22 and PE3-CE24.  Thus, all PEs will learn
   about all remote PE-to-CE links for all L1VPNs supported by PEs.

   Note that P in this configuration does not have links connecting it
   to any L1VPNs.  It neither originates L1VPN LSAs nor maintains any
   PITs.  However, it does participate in the flooding of all of the
   L1VPN LSAs and hence maintains the LSAs in its LSDB.  This is a cause
   for scalability concerns and could prove to be problematic in large
   networks.

4.  Backward Compatibility

   Neither the TLV nor the LSA introduced in this document present any
   interoperability issues.  Per [RFC5250], OSPF speakers that do not
   support the L1VPN auto-discovery application (Ps for example) just
   participate in the L1VPN LSAs flooding process but should ignore the
   LSAs contents.

5.  Security Considerations

   The approach presented in this document describes how PEs dynamically
   learn L1VPN-specific information.  Mechanisms to deliver the VPN
   membership information to CEs are explicitly out of scope of this
   document.  Therefore, the security issues raised in this document are
   limited to within the OSPF domain.

   This defined approach reuses mechanisms defined in [RFC2328] and
   [RFC5250].  Therefore, the same security approaches and
   considerations apply to this approach.  OSPF provides several
   security mechanisms that can be applied.  Specifically, OSPF supports
   multiple types of authentication, limits the frequency of LSA
   origination and acceptance, and provides techniques to avoid and
   limit impact database overflow.  In cases where end-to-end
   authentication is desired, OSPF's neighbor-to-neighbor authentication
   approach can be augmented with an experimental extension to OSPF; see
   [RFC2154], which supports the signing and authentication of LSAs.

6.  IANA Considerations

   This document requests the assignment of an OSPF Opaque LSA type.
   IANA has made the assignment in the form:

       Value   Opaque Type                              Reference
      -------  -----------                              ---------
       5       L1VPN LSA                                [RFC5252]

7.  Acknowledgments

   We would like to thank Adrian Farrel and Anton Smirnov for their
   useful comments.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630, September
              2003.

   [RFC4203]  Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, October 2005.

   [RFC5250]  Berger, L., Bryskin, I., and A. Zinin, "The OSPF Opaque
              LSA Option", RFC 5250, July 2008.

   [RFC5251]  Fedyk, D., Ed., Rekhter, Y., Ed., Papadimitriou, D.,
              Rabbat, R., and L. Berger, "Layer 1 VPN Basic Mode", RFC
              5251, July 2008.

8.2.  Informative References

   [RFC2154]  Murphy, S., Badger, M., and B. Wellington, "OSPF with
              Digital Signatures", RFC 2154, June 1997.

   [RFC4847]  Takeda, T., Ed., "Framework and Requirements for Layer 1
              Virtual Private Networks", RFC 4847, April 2007.

   [RFC5195]  Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
              Auto-Discovery for Layer-1 VPNs", RFC 5195, June 2008.

Authors' Addresses

   Igor Bryskin
   ADVA Optical Networking Inc
   7926 Jones Branch Drive
   Suite 615
   McLean, VA  22102
   EMail: ibryskin@advaoptical.com

   Lou Berger
   LabN Consulting, LLC
   EMail: lberger@labn.net

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