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Versions: (draft-dimitri-ccamp-gmpls-ason-routing-ospf) 00 01 02 03 04 05 06 07 08 09 RFC 5787

Network Working Group                              Dimitri Papadimitriou
Internet Draft                                          (Alcatel-Lucent)
Category: Standards Track
Created: December 7, 2007
Expires: June 7, 2008



                    OSPFv2 Extensions for ASON Routing

              draft-ietf-ccamp-gmpls-ason-routing-ospf-04.txt



Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   The Generalized MPLS (GMPLS) suite of protocols has been defined to
   control different switching technologies as well as different
   applications. These include support for requesting TDM connections
   including SONET/SDH and Optical Transport Networks (OTNs).

   This document provides the extensions of the OSPFv2 Link State
   Routing Protocol to meet the routing requirements for an
   Automatically Switched Optical Network (ASON) as defined by ITU-T.

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Table of Contents

  1. Conventions Used In This Document .............................. 2
  2. Introduction
  3. Reachability
  3.1 Node IPv4 Local Prefix Sub-TLV
  3.2 Node IPv6 Local Prefix Sub-TLV
  4. Link Attribute
  4.1 Local Adaptation
  4.2 Bandwidth Accounting
  5. Routing Information Scope
  5.1.  Terminology and Identification
  5.2 Link Advertisement (Local and Remote TE Router ID Sub-TLV)
  5.3 Reachability Advertisement (Local TE Router ID Sub-TLV)
  6. Routing Information Dissemination
  6.1 Import/Export Rules
  6.2 Discovery and Selection
  6.2.1 Upward Discovery and Selection
  6.2.2 Downward Discovery and Selection
  6.3 Loop Prevention
  6.3.1 Associated Area ID
  6.3.2 Processing
  6.4 Resiliency
  6.5 Neighbor Relationship and Routing Adjacency
  6.6 Reconfiguration
  7. OSPFv2 Extensions
  7.1 Compatibility
  7.2 Scalability
  8. Security Considerations
  9. IANA Considerations
  10. Acknowledgements
  11. References
  11.1 Normative References
  11.2 Informative References
  12. Author's Address
  Appendix 1: ASON Terminology
  Appendix 2: ASON Routing Terminology














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1. 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 RFC 2119 [RFC2119].

   The reader is assumed to be familiar with the terminology and
   requirements developed in [RFC4258] and the evaluation outcomes
   detailed in [RFC4652].

2. Introduction

   There are certain capabilities that are needed to support the ITU-T
   Automatically Switched Optical Network (ASON) control plane
   architecture as defined in [G.8080].

   [RFC4258] details the routing requirements for the GMPLS suite of
   routing protocols to support the capabilities and functionality of
   ASON control planes identified in [G.7715] and in [G.7715.1].

   [RFC4652] evaluates the IETF Link State Routing Protocols against the
   requirements identified in [RFC4258]. Section 7.1 of [RFC4652]
   summarizes the capabilities to be provided by OSPFv2 [RFC2328] in
   support of ASON routing. From the candidate routing protocols
   identified in [RFC4652] (OSPFv2 and IS-IS), this document details the
   OSPFv2 specifics for ASON routing.

   Note that here is no implied relationship between multi-layer
   transport networks and multi-level routing [RFC4652]. This mechanism
   works either for single layer or multi-layer networks.
   Implementations MAY support a hierarchical routing topology (multi-
   level) for multiple transport network layers and/or a hierarchical
   routing topology for a single transport network layer.

   This document details the processing of the generic (technology
   independent) link attributes that are defined in this document and
   in [RFC3630], [RFC4202], and [RFC4203]. As detailed in Section 4.2,
   technology specific traffic engineering attributes (and their
   processing) MAY complement this document.

   ASON (Routing) terminology sections are provided in Appendix 1 and 2.

3. Reachability

   In order to advertise blocks of reachable address prefixes a
   summarization mechanism is introduced that complements the
   techniques described in [OSPF-NODE].

   This extension takes the form of a network mask (a 32-bit number
   indicating the range of IP addresses residing on a single IP

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   network/subnet). The set of local addresses are carried in an OSPFv2
   TE LSA node attribute TLV (a specific sub-TLV is defined per address
   family, e.g., IPv4 and IPv6 used as network-unique identifiers).

   The proposed solution is to advertise the local address prefixes of
   a router as new sub-TLVs of the (OSPFv2 TE LSA) Node Attribute top
   level TLV (of Type TBD). This document defines the following sub-
   TLVs:

        - Node IPv4 Local Prefix sub-TLV: Type 3 - Length: variable
        - Node IPv6 Local Prefix sub-TLV: Type 4 - Length: variable

3.1 Node IPv4 Local Prefix Sub-TLV

   The node IPv4 local prefix sub-TLV has a type of 3 and contains one
   or more local IPv4 prefixes. It has the following format:


     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              3                |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Network Mask 1                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         IPv4 Address 1                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                               .                               .
    .                               .                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Network Mask n                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         IPv4 Address n                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length is set to 8 * n where n is the number of local prefixes
   included in the sub-TLV.

   Network mask: A 32-bit number indicating the IPv4 address mask
   for the advertised destination prefix.

   Each <Network mask, IPv4 Address> pair listed as part of this sub-
   TLV represents a reachable destination prefix hosted by the
   advertising Router ID.

   The local addresses that can be learned from TE LSAs i.e. router
   address and TE interface addresses SHOULD not be advertised in the
   node IPv4 local prefix sub-TLV.



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3.2 Node IPv6 Local Prefix Sub-TLV

   The node IPv6 local prefix sub-TLV has a type of 4 and contains one
   or more local IPv6 prefixes. IPv6 Prefix Representation uses RFC
   2740 Section A.4.1. It has the following format:


     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              4                |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | PrefixLength  | PrefixOptions |             (0)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                     IPv6 Address Prefix 1                     |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                               .                               .
    .                               .                               .
    .                               .                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | PrefixLength  | PrefixOptions |             (0)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                     IPv6 Address Prefix n                     |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   PrefixLength: length in bits of the prefix.

   PrefixOptions: 8-bit field describing various capabilities
   associated with the prefix (see [RFC2740] Section A.4.2).

   Address Prefix: encoding of the prefix itself as an even multiple of
   32-bit words, padding with zero bits as necessary.

   The Length is set to Sum[n][4 + #32-bit words/4] where n is the
   number of local prefixes included in the sub-TLV.

   The local addresses that can be learned from TE LSAs i.e. router
   address and TE interface addresses SHOULD not be advertised in the
   node IPv6 local prefix sub-TLV.






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4. Link Attribute

4.1 Local Adaptation

   The Local Adaptation is defined as TE link attribute (i.e. sub-TLV)
   that describes the cross/inter-layer relationships.

   The Interface Switching Capability Descriptor (ISCD) TE Attribute
   [RFC4202] identifies the ability of the TE link to support cross-
   connection to another link within the same layer and the ability to
   use a locally terminated connection that belongs to one layer as a
   data link for another layer (adaptation capability). However, the
   information associated to the ability to terminate connections
   within that layer (referred to as the termination capability) is
   embedded with the adaptation capability.

   For instance, a link between two optical cross-connects will contain
   at least one ISCD attribute describing LSC switching capability.
   Whereas a link between an optical cross-connect and an IP/MPLS LSR
   will contain at least two ISCD attributes: one for the description
   of the LSC termination capability and one for the PSC adaptation
   capability.

   In OSPFv2, the Interface Switching Capability Descriptor is a sub-
   TLV (of type 15) of the top-level Link TLV (of type 2) [RFC4203].

   The adaptation and termination capabilities are advertised using two
   separate ISCD sub-TLVs within the same top-level link TLV.

   Per [RFC4202] and [RFC4203], an interface MAY have more than one
   ISCD sub-TLV. Hence, the corresponding advertisements should not
   result in any compatibility issue.

   Further refinement of the ISCD sub-TLV for multi-layer networks is
   outside the scope of this document.

4.2 Bandwidth Accounting

   GMPLS Routing defines an Interface Switching Capability Descriptor
   (ISCD) that delivers among others the information about the
   (maximum/minimum) bandwidth per priority an LSP can make use of.
   Per [RFC4202] and [RFC4203], one or more ISCD sub-TLVs can be
   associated to an interface. This information combined with the
   Unreserved Bandwidth (sub-TLV defined in [RFC3630], Section 2.5.8)
   provides for the base bandwidth accounting.

   In the ASON context, additional information may be included when the
   representation and information in the other advertised fields are
   not sufficient for a specific technology (e.g., SDH). The definition
   of technology-specific information elements is beyond the scope of

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   this document. Some technologies will not require additional
   information beyond what is already contained in the advertisements.

5. Routing Information Scope

5.1.  Terminology and Identification

   o) Pi is a physical (bearer/data/transport plane) node.

   o) Li is a logical control plane entity that is associated to a
      single data plane (abstract) node. Each Li is identified by a
      unique TE Router_ID. The latter is a control plane identifier,
      defined as the Router_Address top level TLV of the Type 1 TE LSA
      [RFC3630].

      Note: the Router_Address top-level TLV definition, processing and
      usage remain per [RFC3630]. This TLV specifies a stable IP address
      of the advertising router (Ri) that is always reachable if there
      is any IP connectivity to it (e.g. via the Data Communication
      Network). Moreover, each advertising router advertises a unique,
      reachable IP address for each Pi on behalf of which it makes
      advertisements.

   o) Ri is a logical control plane entity that is associated to a
      control plane "router". The latter is the source for topology
      information that it generates and shares with other control plane
      "routers". The Ri is identified by the (advertising) Router_ID
      (32-bit) [RFC2328].

      The Router_ID, which is represented by Ri and which corresponds to
      the RC_ID [RFC4258], does not enter into the identification of the
      logical entities representing the data plane resources such as
      links. The Routing DataBase (RDB) is associated to the Ri.

   Aside from the Li/Pi mappings, these identifiers are not assumed to
   be in a particular entity relationship except that the Ri may have
   multiple Lis in its scope. The relationship between Ri and Li is
   simple at any moment in time: an Li may be advertised by only one Ri
   at any time. However, an Ri may advertise a set of one or more Lis.
   Hence, the OSPFv2 routing protocol must support a single Ri
   advertising on behalf of more than one Li.

5.2 Link Advertisement (Local and Remote TE Router ID Sub-TLV)

   A Router_ID (Ri) advertising on behalf multiple TE Router_IDs (Lis)
   creates a 1:N relationship between the Router_ID and the TE
   Router_ID. As the link local and link remote (unnumbered) ID
   association is not unique per node (per Li unicity), the
   advertisement needs to indicate the remote Lj value and rely on the
   initial discovery process to retrieve the [Li;Lj] relationship. In

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   brief, as unnumbered links have their ID defined on per Li bases,
   the remote Lj needs to be identified to scope the link remote ID to
   the local Li. Therefore, the routing protocol MUST be able to
   disambiguate the advertised TE links so that they can be associated
   with the correct TE Router ID.

   For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
   Link TLV is introduced that defines the local and the remote
   TE_Router_ID.

   The type of this sub-TLV is 17, and length is eight octets. The
   value field of this sub-TLV contains four octets of Local TE Router
   Identifier followed by four octets of Remote TE Router Identifier.
   The value of the Local and the Remote TE Router Identifier SHOULD
   NOT be set to 0.

   The format of this sub-TLV is the following:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              17               |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Local TE Router Identifier                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Remote TE Router Identifier                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This sub-TLV is only required be included as part of the top level
   Link TLV if the Router_ID is advertising on behalf of more than one
   TE_Router_ID. In any other case, this sub-TLV SHOULD be omitted
   except if operator plans to start of with 1 Li and progressively add
   more Li's (under the same Ri) such as to maintain consistency.

   Note: The Link ID sub-TLV that identifies the other end of the link
   (i.e. Router ID of the neighbor for point-to-point links) MUST
   appear exactly once per Link TLV. This sub-TLV MUST be processed as
   defined in [RFC3630].

5.3 Reachability Advertisement (Local TE Router ID Sub-TLV)

   When the Router_ID advertises on behalf of multiple TE Router_IDs
   (Lis), the routing protocol MUST be able to associate the advertised
   reachability information with the correct TE Router ID.

   For this purpose, a new sub-TLV of the (OSPFv2 TE LSA) top level
   Node Attribute TLV is introduced. This TLV associates the local
   prefixes (sub-TLV 3 and 4, see above) to a given TE Router_ID.



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   The type of this sub-TLV is 5, and length is four octets. The value
   field of this sub-TLV contains four octets of Local TE Router
   Identifier [RFC3630].

   The format of this sub-TLV is the following:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              5                |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Local TE Router Identifier                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This sub-TLV is only required to be included be included as part of
   the Node Attribute TLV if the Router_ID is advertising on behalf of
   more than one TE_Router_ID. In any other case, this sub-TLV SHOULD
   be omitted.

6. Routing Information Dissemination

   An ASON RA represents a partition of the data plane and its
   identifier is used within the control plane as the representation of
   this partition. A RA may contain smaller RAs inter-connected by
   links. The limit of the subdivision results in a RA that contains two
   sub-networks interconnected by a single link. ASON RA levels do not
   reflect routing protocol levels (such as OSPF areas). OSPF routing
   areas containing routing areas that recursively define successive
   hierarchical levels of RAs can be represented by separate instances
   of the protocol.

   RCs supporting RAs disseminate downward/upward this hierarchy. The
   vertical routing information dissemination mechanisms described in
   this section do not introduce or imply a new OSPF routing area
   hierarchy. RCs supporting RAs at multiple levels are structured as
   separate OSPF instances with routing information exchanges between
   levels described by import/export rules.

   The implication is that an RC that performs import/export of routing
   information as described in this document does not implement an Area
   Border Router (ABR) functionality.

6.1 Import/Export Rules

   RCs supporting RAs disseminate downward/upward the hierarchy by
   importing/exporting this routing information as Opaque TE LSA
   (Opaque Type 1) of LS Type 10. The information that MAY be exchanged
   between adjacent levels includes the Router_Address, Link and
   Node_Attribute top level TLV.


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   The Opaque TE LSA import/export rules are governed as follows:

   - If the export target interface is associated to the same area as
     the one associated with the import interface, the Opaque LSA MUST
     NOT imported.

   - If a match is found between the Advertising Router ID in the
     header of the received Opaque TE LSA and one of the Router ID
     belonging to the area of the export target interface, the Opaque
     LSA MUST NOT be imported.

   - If these two conditions are not met the Opaque TE LSA MAY be
     imported and MAY be disseminated following the OSPF flooding
     rules. The Advertising Router ID is set to the importing router's
     router ID.

   The imported/exported routing information content MAY be transformed
   e.g. filtered or aggregated, as long as the resulting routing
   information is consistent. In particular, when more than one RC are
   bound to adjacent levels and both are allowed to import/export
   routing information it is expected that these transformation are
   performed in consistent manner. Definition of these policy-based
   mechanisms is outside the scope of this document.

   In practice, and in order to avoid scalability and processing
   overhead, routing information imported/exported downward/upward the
   hierarchy is expected to include reachability information (see
   Section 3) and upon strict policy control link topology information.

6.2 Discovery and Selection

6.2.1 Upward Discovery and Selection

   In order to discover RCs that are capable to disseminate routing
   information upward the routing hierarchy, the following Capability
   Descriptor bit [RFC4970] are defined:

   - U bit: when set, this flag indicates that the RC is capable to
     disseminate routing information upward the adjacent level.

   In case of multiple RC are advertized with their U bit set, the RC
   with the highest Router ID, among the RCs having set the U bit,
   SHOULD be selected as the RC for upward dissemination of routing
   information. The other RCs MUST NOT participate in the upward
   dissemination of routing information as long as the opaque LSA
   information corresponding to the highest Router ID RC does not reach
   MaxAge. This mechanism prevents from having more than one RC
   advertizing routing information upward the routing hierarchy.



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   Note that alternatively if this information cannot be discovered
   automatically, it MUST be manually configured.

   Once an RC has been selected, it remains unmodified even if an RC
   with a highest Router ID is introduced and advertizes its capability
   to disseminate routing information upward the adjacent level (i.e.
   U-bit set). This hysteresis mechanism prevents from disturbing the
   upward routing information dissemination process in case e.g. of
   flapping.

6.2.2 Downward Discovery and Selection

   The same discovery mechanism is used for selecting the RC taking in
   charge dissemination of routing information downward the hierarchy.
   However, an additional restriction MUST be applied such that the RC
   selection process takes into account that an upper level may be
   adjacent to one or more lower (routing area) levels. For this
   purpose a specific TLV indexing the (lower) area ID to which the
   RC's are capable to disseminate routing information is needed.

   OSPF Downstream Associated Area ID TLV format carried in the OSPF
   router information LSA [RFC4970] is defined. This TLV has the
   following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Associated Area ID                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                             ...                             //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Associated Area ID                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type (16 bits): identifies the TLV type

   Length (16 bits): length of the value field in octets

   Value (n x 32 bits): Associated Area ID whose value space is the
   Area ID as defined in [RFC2328].

   Note that this information MUST be present when the D bit is set. To
   discover RCs that are capable to disseminate routing information
   downward the routing hierarchy, the following Capability Descriptor
   bit [RFC4970] is defined, that MUST be advertised together with the
   OSPF Downstream Associated Area ID TLV:

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   - D bit: when set, this flag indicates that the RC is capable to
     disseminate routing information downward the adjacent level(s).

   In case of multiple supporting RCs for the same Associated Area ID,
   the RC with the highest Router ID, among the RCs having set the D
   bit, MUST be selected as the RC for downward dissemination of
   routing information. The other RCs for the same Associated Area ID
   MUST NOT participate in the downward dissemination of routing
   information as long as the opaque LSA information corresponding to
   the highest Router ID RC does not reach MaxAge. This mechanism
   prevents from having more than one RC advertizing routing
   information downward the routing hierarchy.

   Note that alternatively if this information cannot be discovered
   automatically, it MUST be manually configured.

   The OSPF Router information opaque LSA (opaque type of 4, opaque ID
   of 0) and its content in particular, the Router Informational
   Capabilities TLV [RFC4970] and TE Node Capability Descriptor TLV
   [OSPF-TE-CAP] MUST NOT be re-originated.

6.3 Loop Prevention

   When more than one RC are bound to adjacent levels of the hierarchy,
   configured and selected to redistribute upward and downward the
   routing information, a specific mechanism is required to avoid
   looping/re-introduction of routing information back to the upper
   level. This specific case occurs e.g. when the RC advertizing
   routing information downward the hierarchy is not the one
   advertizing routing upward the hierarchy (or vice-versa).

   When these conditions are met, it is necessary to have a mean by
   which an RC receiving an Opaque TE LSA imported/exported downward by
   an RC associated to the same area, omits to import/export back the
   content of this LSA upward into the (same) upper level.

   Note that configuration and operational simplification can be
   obtained when both functionality are configured on a single RC (per
   pair of adjacent level) fulfilling both roles. Figure 1 provides an
   example where such simplification applies.











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              ....................................................
              .                                                  .
              .            RC_5 ------------ RC_6                .
              .             |                 |                  .
              .             |                 |          Area Y  .
              .           *********         *********            .
              ............* RC_1a *.........* RC_2a *.............
                __________* |     *         * |     *
              ............* RC_1b *...   ...* RC 2b *.............
              .           *********  .   .  *********            .
              .             |        .   .    |                  .
              .  Area Z     |        .   .    |          Area X  .
              .            RC_3      .   .   RC_4                .
              .                      .   .                       .
              ........................   .........................


               Figure 1. Hierarchical Environment (Example)

   In this case, the procedure described in this section MAY be
   omitted, as long as these conditions are permanently guaranteed. In
   all other cases, without exception, the procedure described in this
   section MUST be applied.

6.3.1 Associated Area ID

   Thus, we need some way of filtering the downward/upward re-
   originated Opaque TE LSA. Per [RFC2370], the information contained
   in Opaque LSAs may be used directly by OSPF. Henceforth, by adding
   the Area ID associated to the incoming routing information the loop
   prevention problem can be solved. This additional information that
   MAY be carried in opaque LSAs including the Router Address TLV, in
   opaque LSAs including the Link TLV, and in opaque LSAs including the
   Node Attribute TLV, is referred to as the Associated Area ID. The
   Associated Area ID reflects the identifier of the area from which
   the routing information is received. For example, for a multiple
   level hierarchy, this identifier does not reflect the originating
   Area ID, it will reflect the area from which the routing information
   is imported.

   The format of the Associated Area ID TLV is defined 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Associated Area ID                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   Type (16 bits): identifies the TLV type

   Length (16 bits): length of the value field in octets

   Value (32 bits): Associated Area ID whose value space is the Area ID
   as defined in [RFC2328].

6.3.2 Processing

   When fulfilling the rules detailed in Section 6.1 a given Opaque LSA
   is imported/exported downward or upward the routing hierarchy, the
   Associated Area ID TLV is added to the received opaque LSA list of
   TLVs such as to identify the area from which this routing
   information has been received.

   When the RC adjacent to the lower or upper level routing level
   receives this opaque LSA, the following rule is applied (in addition
   the rule governing the import/export of opaque LSAs as detailed in
   Section 6.1).

   - If a match is found between the Associated Area ID of the received
     Opaque TE LSA and the Area ID belonging to the area of the export
     target interface, the Opaque TE LSA MUST NOT be imported.

   - Otherwise, this opaque LSA MAY be imported and disseminated
     downward or upward the routing hierarchy following the OSPF
     flooding rules.

   This mechanism ensures that no race condition occurs when the
   conditions depicted in Figure 2 are met.


                           RC_5 ------------- RC_6
                            |                 |
                            |                 |          Area Y
                          *********         *********
                ..........* RC_1a *.........* RC_2a *............
                __________* |     *         * |     *
                ..........* RC_1b *.........* RC 2b *............
                          *********         *********
                            |                 |
                            |                 |          Area X
                           RC_3 --- . . . --- RC_4


               Figure 2. Race Condition Prevention (Example)

   Assume that RC_1b is configured for exporting routing information
   upward toward Area Y (upward the routing hierarchy) and that RC_2a
   is configured for exporting routing information toward Area X

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   (downward the routing hierarchy).

   Assumes that routing information advertised by RC_3 would reach
   faster to RC_4 across Area Y through hierarchy.

   If RC_2b is not able to prevent from importing that information,
   RC_4 may receive that information before the same advertisement
   would propagate in Area X (from RC 3) to RC_4. For this purpose RC
   1a inserts the Associated Area X to the imported routing information
   from Area X. Because RC 2b finds a match between the Associated Area
   ID (X) of the received Opaque TE LSA and the ID (X) of area of the
   export target interface, this LSA MUST NOT be imported.

6.4 Resiliency

   OSPF creates adjacencies between neighboring routers for the purpose
   of exchanging routing information. After a neighbor has been
   discovered, bidirectional communication is ensured, and a routing
   adjacency is formed between RCs, loss of communication may result in
   partitioned areas.

   Consider for instance (see Figure 2.) the case where RC_1a and RC 1b
   is configured for exchanging routing information downward and upward
   Area Y, resp., and that RC_2a and RC_2b are not configured for
   exchanging routing any routing information toward Area X. If the
   communication between RC 1a and RC 2a is broken (due e.g. to RC 5 -
   RC 6 communication failure), Area Y could be partitioned.

   In these conditions, it is RECOMMENDED that RC 2a to be re-
   configurable such as to allow for exchanging routing information
   downward to Area X. This reconfiguration MAY be performed manually
   or automatically. In the latter cases, automatic reconfiguration
   uses the mechanism described in Section 6.2 (forcing MaxAge of the
   corresponding opaque LSA information in case the originating RC
   becomes unreachable). Manual reconfiguration MUST be supported.

6.5 Neighbor Relationship and Routing Adjacency

   It is assumed that (point-to-point) IP control channels are
   provisioned/configured between RCs belonging to the same routing
   level. Provisioning/configuration techniques are outside the scope
   of this document.

   Once established, the OSPF Hello Protocol is responsible for
   establishing and maintaining neighbor relationships. This protocol
   also ensures that communication between neighbors is bidirectional.
   Routing adjacency can subsequently be formed between RCs following
   mechanisms defined in [RFC2328].



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6.6 Reconfiguration

   This section details the Area ID reconfiguration steps.

   Reconfiguration of the Area ID occurs when the Area ID is modified
   e.g. from value Z to value X or Y (see Fig.2).

   The process of reconfiguring the Area ID involves:

   - Disable the import/export of routing information from the upper
     and lower level (to prevent any LS information update)

   - Change the Area ID of the local level Area e.g. from Z to X or Y.
     Perform an LSDB checksum on all routers to verify that LSDB are
     consistent.

   - Enable import of upstream and downstream routing information such
     as to re-synchronize local level LSDB from any LS information that
     may have occurred in an upper or a lower routing level.

   - Enable export of routing information downstream such as to re-sync
     the downstream level with the newly reconfigured Area ID (as part
     of the re-advertised Opaque TE LSA).

   - Enable export of routing information upstream such as to re-sync
     the upstream level with the newly reconfigured Area ID (as part of
     the re-advertised Opaque TE LSA).

   Note that the re-sync operation needs only to be ensured with the
   directly adjacent upper and lower routing level.

7. OSPFv2 Extensions

7.1 Compatibility

   Extensions specified in this document are associated to the

   Opaque TE LSA:

   o) Router Address top level TLV (Type 1):
      - Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
        (see Section 6.2)

   o) Link top level TLV (Type 2):
      - Local and Remote TE Router ID sub-TLV: optional sub-TLV for
        scoping link attributes per TE_Router ID
      - Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
        (see Section 6.2)



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   o) Node Attribute top level TLV (Type TBD):
      - Node IPv4 Local Prefix sub-TLV: optional sub-TLV for IPv4
        reachability advertisement
      - Node IPv6 Local Prefix sub-TLV: optional sub-TLV for IPv6
        reachability advertisement
      - Local TE Router ID sub-TLV: optional sub-TLV for scoping
        reachability per TE_Router ID
      - Associated Area ID sub-TLV: optional sub-TLV for loop avoidance
        (see Section 6.3)

   Opaque RI LSA:

   o) Routing information dissemination
      - U bit in Capability Descriptor TLV [RFC4970]
      - D bit in Capability Descriptor TLV [RFC4970]
      - Downstream Associated Area ID TLV in the OSPF Routing
        Information LSA [RFC4970]

7.2 Scalability

   o) Routing information exchange upward/downward the hierarchy
   between adjacent areas SHOULD by default be limited to reachability.
   In addition, several transformations such as prefix aggregation are
   recommended when allowing decreasing the amount of information
   imported/exported by a given RC without impacting consistency.

   o) Routing information exchange upward/downward the hierarchy when
   involving TE attributes MUST be under strict policy control. Pacing
   and min/max thresholds for triggered updates are strongly
   recommended.

   o) The number of routing levels MUST be maintained under strict
   policy control.

8. Security Considerations

   This section to be updated in a future revision.

9. IANA Considerations

   This section to be updated in a future revision.

10. Acknowledgements

   The authors would like to thank Dean Cheng, Acee Lindem, Pandian
   Vijay, Alan Davey, Adrian Farrel, and Deborah Brungard for their
   useful comments and suggestions.

   Question 14 of Study Group 15 of the ITU-T provided useful and
   constructive input.

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11. References

11.1 Normative References

   [OSPF-NODE]   R.Aggarwal, and K.Kompella, "Advertising a Router's
                 Local Addresses in OSPF TE Extensions",
                 draft-ietf-ospf-te-node-addr, work in progress.

   [RFC2026]     S.Bradner, "The Internet Standards Process --
                 Revision 3", BCP 9, RFC 2026, October 1996.

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

   [RFC2370]     R.Coltun, "The OSPF Opaque LSA Option", RFC 2370, July
                 1998.

   [RFC2740]     R.Coltun et al. "OSPF for IPv6", RFC 2740, December
                 1999.

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

   [RFC3477]     K.Kompella et al. "Signalling Unnumbered Links in
                 Resource ReSerVation Protocol - Traffic Engineering
                 (RSVP-TE)", RFC 3477, January 2003.

   [RFC3630]     D.Katz et al. "Traffic Engineering (TE) Extensions to
                 OSPF Version 2", RFC 3630, September 2003.

   [RFC4202]     Kompella, K. (Editor) et al., "Routing Extensions in
                 Support of Generalized MPLS", RFC 4202, October 2005.

   [RFC4203]     Kompella, K. (Editor) et al., "OSPF Extensions in
                 Support of Generalized Multi-Protocol Label Switching
                 (GMPLS)", RFC 4203, October 2005.

   [RFC4606]     E.Mannie, and D.Papadimitriou, (Editors) et al.,
                 "Generalized Multi-Protocol Label Switching Extensions
                 for SONET and SDH Control", RFC 4606, August 2006.

   [RFC4970]     A.Lindem et al. "Extensions to OSPF for Advertising
                 Optional Router Capabilities", RFC 4970, July 2007.

11.2 Informative References

   [OSPF-TE-CAP] J.P. Vasseur et al., "Routing extensions for discovery
                 of Traffic Engineering Node Capabilities",
                 draft-ietf-ccamp-te-node-cap, work in progress.



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   [RFC4258]     D.Brungard et al. "Requirements for Generalized MPLS
                 (GMPLS) Routing for Automatically Switched Optical
                 Network (ASON)", RFC 4258, November 2005.

   [RFC4652]     D.Papadimitriou (Ed.) et al. "Evaluation of existing
                 Routing Protocols against ASON Routing Requirements",
                 RFC 4652, October 2006.

   For information on the availability of ITU Documents, please see
   http://www.itu.int

   [G.7715]      ITU-T Rec. G.7715/Y.1306, "Architecture and
                 Requirements for the Automatically Switched Optical
                 Network (ASON)", June 2002.

   [G.7715.1]    ITU-T Draft Rec. G.7715.1/Y.1706.1, "ASON Routing
                 Architecture and Requirements for Link State
                 Protocols", November 2003.

   [G.8080]      ITU-T Rec. G.8080/Y.1304, "Architecture for the
                 Automatically Switched Optical Network (ASON)",
                 November 2001 (and Revision, January 2003).

12. Author's Address

   Dimitri Papadimitriou (Alcatel)
   Francis Wellensplein 1,
   B-2018 Antwerpen, Belgium
   Phone: +32 3 2408491
   EMail: dimitri.papadimitriou@alcatel-lucent.be





















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Appendix 1: ASON Terminology

   This document makes use of the following terms:

   Administrative domain: (see Recommendation G.805) for the purposes of
   [G7715.1] an administrative domain represents the extent of resources
   which belong to a single player such as a network operator, a service
   provider, or an end-user. Administrative domains of different players
   do not overlap amongst themselves.

   Control plane: performs the call control and connection control
   functions. Through signaling, the control plane sets up and releases
   connections, and may restore a connection in case of a failure.

   (Control) Domain: represents a collection of (control) entities that
   are grouped for a particular purpose. The control plane is subdivided
   into domains matching administrative domains. Within an
   administrative domain, further subdivisions of the control plane are
   recursively applied. A routing control domain is an abstract entity
   that hides the details of the RC distribution.

   External NNI (E-NNI): interfaces are located between protocol
   controllers between control domains.

   Internal NNI (I-NNI): interfaces are located between protocol
   controllers within control domains.

   Link: (see Recommendation G.805) a "topological component" which
   describes a fixed relationship between a "subnetwork" or "access
   group" and another "subnetwork" or "access group". Links are not
   limited to being provided by a single server trail.

   Management plane: performs management functions for the Transport
   Plane, the control plane and the system as a whole. It also provides
   coordination between all the planes. The following management
   functional areas are performed in the management plane: performance,
   fault, configuration, accounting and security management

   Management domain: (see Recommendation G.805) a management domain
   defines a collection of managed objects which are grouped to meet
   organizational requirements according to geography, technology,
   policy or other structure, and for a number of functional areas such
   as configuration, security, (FCAPS), for the purpose of providing
   control in a consistent manner. Management domains can be disjoint,
   contained or overlapping. As such the resources within an
   administrative domain can be distributed into several possible
   overlapping management domains. The same resource can therefore
   belong to several management domains simultaneously, but a management
   domain shall not cross the border of an administrative domain.


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   Subnetwork Point (SNP): The SNP is a control plane abstraction that
   represents an actual or potential transport plane resource. SNPs (in
   different subnetwork partitions) may represent the same transport
   resource. A one-to-one correspondence should not be assumed.

   Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together
   for the purposes of routing.

   Termination Connection Point (TCP): A TCP represents the output of a
   Trail Termination function or the input to a Trail Termination Sink
   function.

   Transport plane: provides bi-directional or unidirectional transfer
   of user information, from one location to another. It can also
   provide transfer of some control and network management information.
   The Transport Plane is layered; it is equivalent to the Transport
   Network defined in G.805 Recommendation.

   User Network Interface (UNI): interfaces are located between protocol
   controllers between a user and a control domain. Note: there is no
   routing function associated with a UNI reference point.






























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Appendix 2: ASON Routing Terminology

   This document makes use of the following terms:

   Routing Area (RA): a RA represents a partition of the data plane and
   its identifier is used within the control plane as the representation
   of this partition. Per [G.8080] a RA is defined by a set of sub-
   networks, the links that interconnect them, and the interfaces
   representing the ends of the links exiting that RA. A RA may contain
   smaller RAs inter-connected by links. The limit of subdivision
   results in a RA that contains two sub-networks interconnected by a
   single link.

   Routing Database (RDB): repository for the local topology, network
   topology, reachability, and other routing information that is updated
   as part of the routing information exchange and may additionally
   contain information that is configured. The RDB may contain routing
   information for more than one Routing Area (RA).

   Routing Components: ASON routing architecture functions. These
   functions can be classified as protocol independent (Link Resource
   Manager or LRM, Routing Controller or RC) and protocol specific
   (Protocol Controller or PC).

   Routing Controller (RC): handles (abstract) information needed for
   routing and the routing information exchange with peering RCs by
   operating on the RDB. The RC has access to a view of the RDB. The RC
   is protocol independent.

   Note: Since the RDB may contain routing information pertaining to
   multiple RAs (and possibly to multiple layer networks), the RCs
   accessing the RDB may share the routing information.

   Link Resource Manager (LRM): supplies all the relevant component and
   TE link information to the RC. It informs the RC about any state
   changes of the link resources it controls.

   Protocol Controller (PC): handles protocol specific message exchanges
   according to the reference point over which the information is
   exchanged (e.g. E-NNI, I-NNI), and internal exchanges with the RC.
   The PC function is protocol dependent.










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