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rfc:rfc4973

Network Working Group P. Srisuresh Request for Comments: 4973 Kazeon Systems Category: Experimental P. Joseph

                                                            Consultant
                                                             July 2007
  OSPF-xTE: Experimental Extension to OSPF for Traffic Engineering

Status of This Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 This document defines OSPF-xTE, an experimental traffic engineering
 (TE) extension to the link-state routing protocol OSPF.  OSPF-xTE
 defines new TE Link State Advertisements (LSAs) to disseminate TE
 metrics within an autonomous System (AS), which may consist of
 multiple areas.  When an AS consists of TE and non-TE nodes, OSPF-xTE
 ensures that non-TE nodes in the AS are unaffected by the TE LSAs.
 OSPF-xTE generates a stand-alone TE Link State Database (TE-LSDB),
 distinct from the native OSPF LSDB, for computation of TE circuit
 paths.  OSPF-xTE is versatile and extendible to non-packet networks
 such as Synchronous Optical Network (SONET) / Time Division
 Multiplexing (TDM) and optical networks.

IESG Note

 The content of this RFC was at one time considered by the IETF, and
 therefore it may resemble a current IETF work in progress or a
 published IETF work.  This RFC is not a candidate for any level of
 Internet Standard.  The IETF disclaims any knowledge of the fitness
 of this RFC for any purpose and in particular notes that the decision
 to publish is not based on IETF review for such things as security,
 congestion control, or inappropriate interaction with deployed
 protocols.  The RFC Editor has chosen to publish this document at its
 discretion.  Readers of this RFC should exercise caution in
 evaluating its value for implementation and deployment.  See RFC 3932
 for more information.

Srisuresh & Joseph Experimental [Page 1] RFC 4973 OSPF Traffic Engineering Extension July 2007

 See RFC 3630 for the IETF consensus protocol for OSPF Traffic
 Engineering.  The OSPF WG position at the time of publication is that
 although this proposal has some useful properties, the protocol in
 RFC 3630 is sufficient for the traffic engineering needs that have
 been identified so far, and the cost of migrating to this proposal
 exceeds its benefits.

Table of Contents

 1. Introduction ....................................................3
 2. Principles of Traffic Engineering ...............................3
 3. Terminology .....................................................5
    3.1. Native OSPF Terms ..........................................5
    3.2. OSPF-xTE Terms .............................................6
 4. Motivations behind the Design of OSPF-xTE .......................9
    4.1. Scalable Design ............................................9
    4.2. Operable in Mixed and Peer Networks ........................9
    4.3. Efficient in Flooding Reach ................................9
    4.4. Ability to Reserve TE-Exclusive Links .....................10
    4.5. Extensible Design .........................................11
    4.6. Unified for Packet and Non-Packet Networks ................11
    4.7. Networks Benefiting from the OSPF-xTE Design ..............11
 5. OSPF-xTE Solution Overview .....................................12
    5.1. OSPF-xTE Solution .........................................12
    5.2. Assumptions ...............................................13
 6. Strategy for Transition of Opaque LSAs to OSPF-xTE .............14
 7. OSPF-xTE Router Adjacency -- TE Topology Discovery .............14
    7.1. The OSPF-xTE Router Adjacency .............................14
    7.2. The Hello Protocol ........................................15
    7.3. The Designated Router .....................................15
    7.4. The Backup Designated Router ..............................15
    7.5. Flooding and the Synchronization of Databases .............16
    7.6. The Graph of Adjacencies ..................................16
 8. TE LSAs for Packet Network .....................................18
    8.1. TE-Router LSA (0x81) ......................................18
         8.1.1. Router-TE Flags: TE Capabilities of the Router .....19
         8.1.2. Router-TE TLVs .....................................20
         8.1.3. Link-TE Flags: TE Capabilities of a Link ...........22
         8.1.4. Link-TE TLVs .......................................23
    8.2. TE-Incremental-Link-Update LSA (0x8d) .....................26
    8.3. TE-Circuit-Path LSA (0x8C) ................................28
    8.4. TE-Summary LSAs ...........................................31
         8.4.1. TE-Summary Network LSA (0x83) ......................32
         8.4.2. TE-Summary Router LSA (0x84) .......................33
    8.5. TE-AS-external LSAs (0x85) ................................34
 9. TE LSAs for Non-Packet Network .................................36
    9.1. TE-Router LSA (0x81) ......................................36
         9.1.1. Router-TE flags - TE Capabilities of a Router ......37

Srisuresh & Joseph Experimental [Page 2] RFC 4973 OSPF Traffic Engineering Extension July 2007

         9.1.2. Link-TE Options: TE Capabilities of a TE Link ......38
    9.2. TE-positional-ring-network LSA (0x82) .....................38
    9.3. TE-Router-Proxy LSA (0x8e) ................................40
 10. Abstract Topology Representation with TE Support ..............42
 11. Changes to Data Structures in OSPF-xTE Nodes ..................44
    11.1. Changes to Router Data Structure .........................44
    11.2. Two Sets of Neighbors ....................................44
    11.3. Changes to Interface Data Structure ......................44
 12. IANA Considerations ...........................................45
    12.1. TE LSA Type Values .......................................45
    12.2. TE TLV Tag Values ........................................46
 13. Acknowledgements ..............................................46
 14. Security Considerations .......................................47
 15. Normative References ..........................................48
 16. Informative References ........................................48

1. Introduction

 This document defines OSPF-xTE, an experimental traffic engineering
 (TE) extension to the link-state routing protocol OSPF.  The
 objective of OSPF-xTE is to discover TE network topology and
 disseminate TE metrics within an autonomous system (AS).  A stand-
 alone TE Link State Database (TE-LSDB), different from the native
 OSPF LSDB, is created to facilitate computation of TE circuit paths.
 Devising algorithms to compute TE circuit paths is not an objective
 of this document.
 OSPF-xTE is different from the Opaque-LSA-based approach outlined in
 [OPQLSA-TE].  Section 4 describes the motivations behind the design
 of OSPF-xTE.  Section 6 outlines a transition path for those
 currently using [OPQLSA-TE] for intra-area and wish to extend this
 using OSPF-xTE across the AS.
 Readers interested in TE extensions for packet networks alone may
 skip section 9.0.

2. Principles of Traffic Engineering

 The objective of traffic engineering (TE) is to set up circuit
 path(s) between a pair of nodes or links and to forward traffic of a
 certain forwarding equivalency class (FEC) through the circuit path.
 Only unicast circuit paths are considered in this section; multicast
 variations are outside the scope.
 A traffic engineered circuit path is unidirectional and may be
 identified by the tuple: (FEC, TE circuit parameters, origin
 node/link, destination node/link).

Srisuresh & Joseph Experimental [Page 3] RFC 4973 OSPF Traffic Engineering Extension July 2007

 A forwarding equivalency class (FEC) is a grouping of traffic that is
 forwarded in the same manner by a node.  An FEC may be classified
 based on a number of criteria, as follows:
      a) traffic arriving on a specific interface,
      b) traffic arriving at a certain time of day,
      c) traffic meeting a certain packet based classification
         criteria (ex: based on a match of the fields in the IP and
         transport headers within a packet),
      d) traffic in a certain priority class,
      e) traffic arriving on a specific set of TDM (Synchronous
         Transport Signal (STS)) circuits on an interface, or
      f) traffic arriving on a certain wavelength of an interface.
 Discerning traffic based on the FEC criteria is mandatory for Label
 Edge Routers (LERs).  The intermediate Label-Switched Routers (LSRs)
 are transparent to the traffic content.  LSRs are only responsible
 for maintaining the circuit for its lifetime.  This document will not
 address definition of FEC criteria, the mapping of an FEC to circuit,
 or the associated signaling to set up circuits.  [MPLS-TE] and
 [GMPLS-TE] address the FEC criteria. [RSVP-TE] and [CR-LDP] address
 signaling protocols to set up circuits.
 This document is concerned with the collection of TE metrics for all
 the TE enforceable nodes and links within an autonomous system.  TE
 metrics for a node may include the following.
      a) Ability to perform traffic prioritization,
      b) Ability to provision bandwidth on interfaces,
      c) Support for Constrained Shortest Path First (CSPF)
         algorithms,
      d) Support for certain TE-Circuit switch type, and
      e) Support for a certain type of automatic protection switching.
 TE metrics for a link may include the following.
      a) available bandwidth,
      b) reliability of the link,
      c) color assigned to the link,
      d) cost of bandwidth usage on the link, and
      e) membership in a Shared Risk Link Group (SRLG).
 A number of CSPF (Constraint-based Shortest Path First) algorithms
 may be used to dynamically set up TE circuit paths in a TE network.
 OSPF-xTE mandates that the originating and the terminating entities
 of a TE circuit path be identifiable by IP addresses.

Srisuresh & Joseph Experimental [Page 4] RFC 4973 OSPF Traffic Engineering Extension July 2007

3. Terminology

 Definitions of the majority of the terms used in the context of the
 OSPF protocol may be found in [OSPF-V2].  MPLS and traffic
 engineering terms may be found in [MPLS-ARCH].  RSVP-TE and CR-LDP
 signaling-specific terms may be found in [RSVP-TE] and [CR-LDP],
 respectively.
 The following subsections describe the native OSPF terms and the
 OSPF-xTE terms used within this document.

3.1. Native OSPF Terms

 o  Native node (Non-TE node)
     A native or non-TE node is an OSPF router that is capable of IP
     packet forwarding but does not take part in a TE network.  A
     native OSPF node forwards IP traffic using the shortest-path
     forwarding algorithm and does not run the OSPF-xTE extensions.
 o  Native link (Non-TE link)
     A native (or non-TE) link is a network attachment to a TE or
     non-TE node used for IP packet traversal.
 o  Native OSPF network (Non-TE network)
     A native OSPF network refers to an OSPF network that does not
     support TE.  "Non-TE network", "native-OSPF network", and "non-TE
     topology" are used synonymously throughout the document.
 o  LSP
     LSP stands for "Label-Switched Path".  An LSP is a TE circuit
     path in a packet network.  The terms "LSP" and "TE circuit path"
     are used synonymously in the context of packet networks.
 o  LSA
     LSA stands for OSPF "Link State Advertisement".

Srisuresh & Joseph Experimental [Page 5] RFC 4973 OSPF Traffic Engineering Extension July 2007

 o  LSDB
     LSDB stands for "Link State Database".  An LSDB contains a
     representation of the topology of a network.  A native LSDB,
     constituted of native OSPF LSAs, represents the topology of a
     native IP network.  The TE-LSDB, on the other hand, is
     constituted of TE LSAs and is a representation of the TE network
     topology.

3.2. OSPF-xTE Terms

 o  TE node
     A TE node is a node in the traffic engineering (TE) network.  A
     TE node has a minimum of one TE link attached to it.  Associated
     with each TE node is a set of supported TE metrics.  A TE node
     may also participate in a native IP network.
     In a SONET/TDM or photonic cross-connect network, a TE node is
     not required to be an OSPF-xTE node.  An external OSPF-xTE node
     may act as proxy for the TE nodes that cannot be routers
     themselves.
 o  TE link
     A TE link is a network attachment point to a TE node and is
     intended for traffic engineering use.  Associated with each TE
     link is a set of supported TE metrics.  A TE link may also
     optionally carry native IP traffic.
     Of the various links attached to a TE node, only the links that
     take part in a traffic-engineered network are called TE links.
 o  TE circuit path
     A TE circuit path is a unidirectional data path that is defined
     by a list of TE nodes connected to each other through TE links.
     A TE circuit path is also often referred simply as a circuit path
     or a circuit.
     For the purposes of OSPF-xTE, the originating and terminating
     entities of a TE circuit path must be identifiable by their IP
     addresses.  As a general rule, all nodes and links party to a
     traffic-engineered network should be uniquely identifiable by an
     IP address.

Srisuresh & Joseph Experimental [Page 6] RFC 4973 OSPF Traffic Engineering Extension July 2007

 o  OSPF-xTE node (OSPF-xTE router)
     An OSPF-xTE node is a TE node that runs the OSPF routing protocol
     and the OSPF-xTE extensions described in this document.  An
     autonomous system (AS) may consist of a combination of native and
     OSPF-xTE nodes.
 o  TE Control network
     The IP network used by the OSPF-xTE nodes for OSPF-xTE
     communication is referred as the TE control network or simply the
     control network.  The control network can be independent of the
     TE data network.
 o  TE network (TE topology)
     A TE network is a network of connected TE nodes and TE links, for
     the purpose of setting up one or more TE circuit paths.  The
     terms "TE network", "TE data network", and "TE topology" are used
     synonymously throughout the document.
 o  Packet-TE network (Packet network)
     A packet-TE network is a TE network in which the nodes switch
     MPLS packets.  An MPLS packet is defined in [MPLS-TE] as a packet
     with an MPLS header, followed by data octets.  The intermediary
     node(s) of a circuit path in a packet-TE network perform MPLS
     label swapping to emulate the circuit.
     Unless specified otherwise, the term "packet network" is used
     throughout the document to refer to a packet-TE network.
 o  Non-packet-TE network (Non-packet network)
     A non-packet-TE network is a TE network in which the nodes switch
     non-packet entities such as STS time slots, Lambda wavelengths,
     or simply interfaces.
     SONET/TDM and fiber cross-connect networks are examples of non-
     packet-TE networks.  Circuit emulation in these networks is
     accomplished by the switch fabric in the intermediary nodes
     (based on TDM time slot, fiber interface, or Lambda).
     Unless specified otherwise, the term non-packet network is used
     throughout the document to refer a non-packet-TE network.

Srisuresh & Joseph Experimental [Page 7] RFC 4973 OSPF Traffic Engineering Extension July 2007

 o  Mixed network
     A mixed network is a network that is constituted of both packet-
     TE and non-TE networks.  Traffic in the network is strictly
     datagram oriented, i.e., IP datagrams or MPLS packets.  Routers
     in a mixed network may be TE or native nodes.
     OSPF-xTE is usable within a packet network or a mixed network.
 o  Peer network
     A peer network is a network that is constituted of packet-TE and
     non-packet-TE networks combined.  In a peer network, a TE node
     could potentially support TE links for the packet as well as
     non-packet data.
     OSPF-xTE is usable within a packet network or a non-packet
     network or a peer network, which is a combination of the two.
 o  CSPF
     CSPF stands for "Constrained Shortest Path First".  Given a TE
     LSDB and a set of constraints that must be satisfied to form a
     circuit path, there may be several CSPF algorithms to obtain a TE
     circuit path that meets the criteria.
 o  TLV
     A TLV stands for a data object in the form: Tag-Length-Value.
     All TLVs are assumed to be of the following format, unless
     specified otherwise.  The Tag and Length are 16 bits wide each.
     The Length includes the 4 octets required for Tag and Length
     specification.  All TLVs described in this document are padded to
     32-bit alignment.  Any padding required for alignment will not be
     a part of the length field, however.  TLVs are used to describe
     traffic engineering characteristics of the TE nodes, TE links,
     and TE circuit paths.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag                |     Length (4 or more)        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Value ....                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            ....                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Srisuresh & Joseph Experimental [Page 8] RFC 4973 OSPF Traffic Engineering Extension July 2007

 o  Router-TE TLVs (Router TLVs)
     TLVs used to describe the TE capabilities of a TE node.
 o  Link-TE TLVs (Link TLVs)
     TLVs used to describe the TE capabilities of a TE link.

4. Motivations behind the Design of OSPF-xTE

 There are several motivations that led to the design of OSPF-xTE.
 OSPF-xTE is scalable, efficient, and usable across a variety of
 network topologies.  These motivations are explained in detail in the
 following subsections.  The last subsection lists real-world network
 scenarios that benefit from the OSPF-xTE.

4.1. Scalable Design

 In OSPF-xTE, an area-level abstraction provides the scaling required
 for the TE topology in a large autonomous system (AS).  An OSPF-xTE
 area border router will advertise summary LSAs for TE and non-TE
 topologies independent of each other.  Readers may refer to section
 10 for a topological view of the AS from the perspective of a OSPF-
 xTE node in an area.
 [OPQLSA-TE], on the other hand, is designed for intra-area and is not
 scalable to AS-wide scope.

4.2. Operable in Mixed and Peer Networks

 OSPF-xTE assumes that an AS may be constituted of coexisting TE and
 non-TE networks.  OSPF-xTE dynamically discovers TE topology and the
 associated TE metrics of the nodes and links that form the TE
 network.  As such, OSPF-xTE generates a stand-alone TE-LSDB that is
 fully representative of the TE network.  Stand-alone TE-LSDB allows
 for speedy TE computations.
 [OPQLSA-TE] is designed for packet networks and is not suitable for
 mixes and peer networks.  TE-LSDB in [OPQLSA-TE] is derived from the
 combination of Opaque LSAs and native LSDB.  Further, the TE-LSDB
 thus derived has no knowledge of the TE capabilities of the routers
 in the network.

4.3. Efficient in Flooding Reach

 OSPF-xTE is able to identify the TE topology in a mixed network and
 to limit the flooding of TE LSAs to only the TE nodes.  Non-TE nodes
 are not bombarded with TE LSAs.

Srisuresh & Joseph Experimental [Page 9] RFC 4973 OSPF Traffic Engineering Extension July 2007

 In a TE network, a subset of the TE metrics may be prone to rapid
 change, while others remain largely unchanged.  Changes in TE metrics
 must be communicated at the earliest throughout the network to ensure
 that the TE-LSDB is up-to-date within the network.  As a general
 rule, a TE network is likely to generate significantly more control
 traffic than a native network.  The excess traffic is almost directly
 proportional to the rate at which TE circuits are set up and torn
 down within the TE network.  The TE database synchronization should
 occur much quicker compared to the aggregate circuit set up and
 tear-down rates.  OSPF-xTE defines TE-Incremental-Link-update LSA
 (section 8.2) to advertise only a subset of the metrics that are
 prone to rapid changes.
 The more frequent and wider the flooding, the larger the number of
 retransmissions and acknowledgements.  The same information (needed
 or not) may reach a router through multiple links.  Even if the
 router did not forward the information past the node, it would still
 have to send acknowledgements across all the various links on which
 the LSAs tried to converge.  It is undesirable to flood non-TE nodes
 with TE information.

4.4. Ability to Reserve TE-Exclusive Links

 OSPF-xTE draws a clear distinction between TE and non-TE links.  A TE
 link may be configured to permit TE traffic alone, and not permit
 best-effort IP traffic on the link.  This permits TE enforceability
 on the TE links.
 When links of a TE topology do not overlap the links of a native IP
 network, OSPF-xTE allows for virtual isolation of the two networks.
 Best-effort IP network and TE network often have different service
 requirements.  Keeping the two networks physically isolated can be
 expensive.  Combining the two networks into a single physically
 connected network will bring economies of scale, while service
 enforceability can be maintained individually for each of the TE and
 non-TE sections of the network.
 [OPQLSA-TE] does not support the ability to isolate best-effort IP
 traffic from TE traffic on a link.  All links are subject to best-
 effort IP traffic.  An OSPF router could potentially select a TE link
 to be its least cost link and inundate the link with best-effort IP
 traffic, thereby rendering the link unusable for TE purposes.

Srisuresh & Joseph Experimental [Page 10] RFC 4973 OSPF Traffic Engineering Extension July 2007

4.5. Extensible Design

 The OSPF-xTE design is based on the tried-and-tested OSPF paradigm,
 and it inherits all the benefits of OSPF, present and future.  TE
 LSAs are extensible, just as the native OSPF on which OSPF-xTE is
 founded are extensible.

4.6. Unified for Packet and Non-Packet Networks

 OSPF-xTE is usable within a packet network or a non-packet network or
 a combination peer network.
 Signaling protocols such as RSVP and LDP work the same across packet
 and non-packet networks.  Signaling protocols merely need the TE
 characteristics of nodes and links so they can signal the nodes to
 formulate TE circuit paths.  In a peer network, the underlying
 control protocol must be capable of providing a unified LSDB for all
 TE nodes (nodes with packet-TE links as well as non-packet-TE links)
 in the network.  OSPF-xTE meets this requirement.

4.7. Networks Benefiting from the OSPF-xTE Design

 Below are examples of some real-world network scenarios that benefit
 from OSPF-xTE.
 o  IP providers transitioning to provide TE services
     Providers needing to support MPLS-based TE in their IP network
     may choose to transition gradually.  They may add new TE links or
     convert existing links into TE links within an area first and
     progressively advance to offering MPLS in the entire AS.
     Not all routers will support TE extensions at the same time
     during the migration process.  Use of TE-specific LSAs and their
     flooding to OSPF-xTE only nodes will allow the vendor to
     introduce MPLS TE without destabilizing the existing network.
     The native OSPF-LSDB will remain undisturbed while newer TE links
     are added to the network.
 o  Providers offering best-effort-IP & TE services
     Providers choosing to offer both best-effort-IP and TE based
     packet services simultaneously on the same physically connected
     network will benefit from the OSPF-xTE design.  By maintaining
     independent LSDBs for each type of service, TE links are not
     cannibalized in a mixed network.

Srisuresh & Joseph Experimental [Page 11] RFC 4973 OSPF Traffic Engineering Extension July 2007

 o  Large TE networks
     The OSPF-xTE design is advantageous in large TE networks that
     require the AS to be sub-divided into multiple areas.  OSPF-xTE
     permits inter-area exchange of TE information, which ensures that
     all nodes in the AS have up-to-date, AS-wide, TE reachability
     knowledge.  This in turn will make TE circuit setup predictable
     and computationally bounded.
 o  Non-Packet Networks and Peer Networks
     Vendors may also use OSPF-xTE for their non-packet TE networks.
     OSPF-xTE defines the following functions in support of non-packet
     TE networks.
      (a) "Positional-Ring" type network LSAs.
      (b) Router proxying -- allowing a router to advertise on behalf
            of other nodes (that are not packet/OSPF-capable).

5. OSPF-xTE Solution Overview

5.1. OSPF-xTE Solution

 Locally-scoped Opaque LSA (type 9) is used to discovery the TE
 topology within a network.  Section 7.1 describes in detail the use
 of type 9 Opaque LSA for TE topology discovery.  TE LSAs are designed
 for use by the OSPF-xTE nodes.  Section 8.0 describes the TE LSAs in
 detail.  Changes required of the OSPF data structures to support
 OSPF-xTE are described in section 11.0.  A new TE-neighbors data
 structure will be used to advertise TE LSAs along TE topology.
 An OSPF-xTE node will have a native LSDB and a TE-LSDB, while a
 native OSPF node will have just a native LSDB.  Consider the OSPF
 area, constituted of OSPF-xTE and native OSPF routers, shown in
 Figure 1.  Nodes RT1, RT2, RT3, and RT6 are OSPF-xTE routers with TE
 and non-TE link attachments.  Nodes RT4 and RT5 are native OSPF
 routers with no TE links.  When the LSA database is synchronized, all
 nodes will share the same native LSDB.  OSPF-xTE nodes alone will
 have the additional TE-LSDB.

Srisuresh & Joseph Experimental [Page 12] RFC 4973 OSPF Traffic Engineering Extension July 2007

            +---+
            |   |--------------------------------------+
            |RT6|\\                                    |
            +---+  \\                                  |
             ||      \\                                |
             ||        \\                              |
             ||          \\                            |
             ||          +---+                         |
             ||          |   |----------------+        |
             ||          |RT1|\\              |        |
             ||          +---+  \\            |        |
             ||          //|      \\          |        |
             ||        //  |        \\        |        |
             ||      //    |          \\      |        |
            +---+  //      |            \\  +---+      |
            |RT2|//        |              \\|RT3|------+
            |   |----------|----------------|   |
            +---+          |                +---+
                           |                  |
                           |                  |
                           |                  |
                         +---+              +---+
                         |RT5|--------------|RT4|
                         +---+              +---+
       Legend:
            --   Native (non-TE) network link
            |    Native (non-TE) network link
            \\   TE network link
            ||   TE network link
           Figure 1.  A (TE + native) OSPF Network Topology

5.2. Assumptions

 OSPF-xTE is an extension to the native OSPF protocol and does not
 mandate changes to the existing OSPF.  OSPF-xTE design makes the
 following assumptions.
 (1)  An OSPF-xTE node will need to establish router adjacency with at
      least one other OSPF-xTE node in the area in order for the
      router's TE database to be synchronized within the area.
      Failing this, the OSPF router will not be in the TE calculations
      of other TE routers in the area.
      It is the responsibility of the network administrator(s) to
      ensure connectedness of the TE network.  Otherwise, there can be
      disjoint TE topologies within a network.

Srisuresh & Joseph Experimental [Page 13] RFC 4973 OSPF Traffic Engineering Extension July 2007

 (2)  OSPF-xTE nodes must advertise the link state of its TE links.
      TE links are not obligated to support native IP traffic.  Hence,
      an OSPF-xTE node cannot be required to synchronize its link-
      state database with neighbors on all its links.  The only
      requirement is to have the TE LSDB synchronized across all
      OSPF-xTE nodes in the area.
 (3)  A link in a packet network may be designated as a TE link or a
      native-IP link or both.  For example, a link may be used for
      both TE and non-TE traffic, as long as the link is under
      subscribed in bandwidth for TE traffic (for example, 50% of the
      link capacity is set aside for TE traffic).
 (4)  Non-packet TE sub-topologies must have a minimum of one node
      running OSPF-xTE protocol.  For example, a SONET/SDH TDM ring
      must have a minimum of one Gateway Network Element (GNE) running
      OSPF-xTE.  The OSPF-xTE node will advertise on behalf of all the
      TE nodes in the ring.

6. Strategy for Transition of Opaque LSAs to OSPF-xTE

 Below is a strategy to transition implementations currently using
 Opaque LSAs ([OPQLSA-TE]) within an area to adapt OSPF-xTE in a
 gradual fashion across the AS.
 (1)  Use [OPQLSA-TE] within an area.  Derive TE topology within the
      area from the combination of Opaque LSAs and native LSDB.
 (2)  Use TE-Summary LSAs and TE-AS-external LSAs for inter-area
      communication.  Use the TE topology within an area to summarize
      the TE networks in the area and advertise the same to all TE
      nodes in the backbone.  The TE-ABRs (TE area border routers) on
      the backbone area will in turn advertise these summaries within
      their connected areas.

7. OSPF-xTE Router Adjacency – TE Topology Discovery

 OSPF creates adjacencies between neighboring routers for the purpose
 of exchanging routing information.  The following subsections
 describe the use of locally-scoped Opaque LSAs to discover OSPF-xTE
 neighboring routers.  The capability is used as the basis to build a
 TE topology.

7.1. The OSPF-xTE Router Adjacency

 OSPF uses the options field in the Hello packet to advertise optional
 router capabilities [OSPF-V2].  However, all the bits in this field
 have been allocated and there is no way to advertise OSPF-xTE

Srisuresh & Joseph Experimental [Page 14] RFC 4973 OSPF Traffic Engineering Extension July 2007

 capability using the options field at this time.  This document
 proposes using local-scope Opaque LSA (OPAQUE-9 LSA) to advertise
 support for OSPF-xTE and establish OSPF-xTE adjacency.  In order to
 exchange Opaque LSAs, the neighboring routers must have the O-bit
 (Opaque option bit) set in the options field.
 [OSPF-CAP] proposes a format for exchanging router capabilities via
 OPAQUE-9 LSA.  Routers supporting OSPF-xTE will be required to set
 the "OSPF Experimental TE" bit within the "router capabilities"
 field.  Two routers will not become TE neighbors unless they share a
 common network link on which both routers advertise support for
 OSPF-xTE.  Routers that do not support OSPF-xTE may simply ignore the
 advertisement.

7.2. The Hello Protocol

 The Hello protocol is primarily responsible for dynamically
 establishing and maintaining neighbor adjacencies.  In a TE network,
 it is not required for all links and neighbors to establish adjacency
 using this protocol.  OSPF-xTE router adjacency between two routers
 is established using the method described in the previous section.
 For non-broadcast multi-access (NBMA) and broadcast networks, the
 HELLO protocol is responsible for electing the Designated Router and
 the Backup Designated Router.  Routers supporting the TE option shall
 be given a higher precedence for becoming a designated router over
 those that do not support TE.

7.3. The Designated Router

 When a router's non-TE link first becomes functional, it checks to
 see whether there is currently a Designated Router for the network.
 If there is one, it accepts that Designated Router, regardless of its
 router priority, so long as the current designated router is TE
 compliant.  Otherwise, the router itself becomes Designated Router if
 it has the highest Router Priority on the network and is TE
 compliant.
 OSPF-xTE must be implemented on the most robust routers, as they
 become likely candidates to take on the role as Designated Router.

7.4. The Backup Designated Router

 The Backup Designated Router is also elected by the Hello Protocol.
 Each Hello Packet has a field that specifies the Backup Designated
 Router for the network.  Once again, TE-compliance must be weighed in
 conjunction with router priority in electing the Backup Designated
 Router.

Srisuresh & Joseph Experimental [Page 15] RFC 4973 OSPF Traffic Engineering Extension July 2007

7.5. Flooding and the Synchronization of Databases

 In OSPF, adjacent routers within an area are required to synchronize
 their databases.  However, a more concise requirement is that all
 routers in an area must converge on the same LSDB.  As stated in item
 2 of section 5.2, a basic assertion of OSPF-xTE is that the links
 used by the OSPF-xTE control network for flooding must not be
 required to match the links used by the data network for real-time
 data forwarding.  For instance, it should not be required to send
 OSPF-xTE messages over a TE link that is configured to reject non-TE
 traffic.  However, the control network must be set up such that a
 minimum of one path exists between any two OSPF or OSPF-xTE routers
 within the network, for flooding purposes.  This revised control
 network connectivity requirement does not jeopardize convergence of
 LSDB within an area.
 In a mixed network, where some of the neighbors are TE compliant and
 others are not, the designated OSPF-xTE router will exchange
 different sets of LSAs with its neighbors.  TE LSAs are exchanged
 only with the TE neighbors.  Native LSAs are exchanged with all
 neighbors (TE and non-TE alike).  Restricting the scope of TE LSA
 flooding to just the OSPF-xTE nodes will not affect the native nodes
 that coexist with the OSPF-xTE nodes.
 The control traffic for a TE network (i.e., TE LSA advertisement) is
 likely to be higher than that of a native OSPF network.  This is
 because the TE metrics may vary with each TE circuit setup and the
 corresponding state change must be advertised at the earliest, not
 exceeding the MinLSInterval of 5 seconds.  To minimize advertising
 repetitive content, OSPF-xTE defines a new TE-incremental-Link-update
 LSA (section 8.2) that would advertise just the TLVs that changed for
 a link.
 The OSPFIGP-TE well-known multicast address 224.0.0.24 has been
 assigned by IANA for the exchange of TE-compliant database
 descriptors during database synchronization.

7.6. The Graph of Adjacencies

 If two routers have multiple networks in common, they may have
 multiple adjacencies between them.  The adjacency may be one of two
 types - native OSPF adjacency and TE adjacency.  OSPF-xTE routers
 will form both types of adjacency.
 Two types of adjacency graphs are possible, depending on whether a
 Designated Router is elected for the network.  On physical point-to-
 point networks, point-to-multipoint networks, and virtual links,
 neighboring routers become adjacent whenever they can communicate

Srisuresh & Joseph Experimental [Page 16] RFC 4973 OSPF Traffic Engineering Extension July 2007

 directly.  The adjacency can be either (a) TE-compliant or (b)
 native.  In contrast, on broadcast and NBMA networks the designated
 router and the backup designated router may maintain two sets of
 adjacency.  The remaining routers will form either TE-compliant or
 native adjacency.
 In the broadcast network in Figure 2, routers RT7 and RT3 are chosen
 as the Designated and Backup Designated Routers, respectively.
 Routers RT3, RT4 and RT7 are TE-compliant, but RT5 and RT6 are not.
 So RT4 will have TE-compliant adjacency with the designated and
 backup routers, while RT5 and RT6 will only have native adjacency
 with the Designated and Backup Designated Routers.
              Network                          Adjacency
       +---+            +---+
       |RT1|------------|RT2|            o-----------------o
       +---+    N1      +---+           RT1               RT2
                                               RT7
                                                o:::::
          +---+   +---+   +---+                /|    :
          |RT7|   |RT3|   |RT4|               / |    :
          +---+   +---+   +---+              /  |    :
            |       |       |               /   |    :
       +-----------------------+        RT5o RT6o    oRT4
          N2    |       |                   *   *    ;
              +---+   +---+                  *  *    ;
              |RT5|   |RT6|                   * *    ;
              +---+   +---+                    **    ;
                                                o;;;;;
                                               RT3
                          Adjacency Legend:
  1. —- Native adjacency (primary)
  • Native adjacency (backup)

::::: TE-compliant adjacency (primary)

                             ;;;;; TE-compliant adjacency (backup)
       Figure 2.  Two Adjacency Graphs with TE-Compliant Routers

Srisuresh & Joseph Experimental [Page 17] RFC 4973 OSPF Traffic Engineering Extension July 2007

8. TE LSAs for Packet Network

 The OSPFv2 protocol currently has a total of 11 LSA types.  LSA types
 1 through 5 are defined in [OSPF-V2].  LSA types 6, 7, and 8 are
 defined in [MOSPF], [NSSA], and [BGP-OSPF], respectively.  LSA types
 9 through 11 are defined in [OPAQUE].
 Each LSA type has a unique flooding scope.  Opaque LSA types 9
 through 11 are general purpose LSAs, with flooding scope set to
 link-local, area-local, and AS-wide (except stub areas) respectively.
 In the following subsections, we define new LSAs for traffic
 engineering (TE) use.  The values for the new TE LSA types are
 assigned with the high bit of the LSA-type octet set to 1.  The new
 TE LSAs are largely modeled after the existing LSAs for content
 format and have a unique flooding scope.
 TE-router LSA is defined to advertise TE characteristics of an OSPF-
 xTE router and all the TE links attached to the router.  TE-
 incremental-Link-Update LSA is defined to advertise incremental
 updates to the metrics of a TE link.  Flooding scope for both these
 LSAs is restricted to an area.
 TE-Summary network and router LSAs are defined to advertise the
 reachability of area-specific TE networks and area border routers
 (along with router TE characteristics) to external areas.  Flooding
 scope of the TE-Summary LSAs is the TE topology in the entire AS less
 the non-backbone area for which the advertising router is an ABR.
 Just as with native OSPF summary LSAs, the TE-Summary LSAs do not
 reveal the topological details of an area to external areas.
 TE-AS-external LSA and TE-Circuit-Path LSA are defined to advertise
 AS external network reachability and pre-engineered TE circuits,
 respectively.  While flooding scope for both these LSAs can be the
 entire AS, flooding scope for the pre-engineered TE circuit LSA may
 optionally be restricted to just the TE topology within an area.

8.1. TE-Router LSA (0x81)

 The TE-router LSA (0x81) is modeled after the router LSA and has the
 same flooding scope as the router LSA.  However, the scope is
 restricted to only the OSPF-xTE nodes within the area.  The TE router
 LSA describes the TE metrics of the router as well as the TE links
 attached to the router.  Below is the format of the TE-router LSA.
 Unless specified explicitly otherwise, the fields carry the same
 meaning as they do in a router LSA.  Only the differences are
 explained below.  Router-TE flags, Router-TE TLVs, Link-TE options,
 and Link-TE TLVs are each described in the following sub-sections.

Srisuresh & Joseph Experimental [Page 18] RFC 4973 OSPF Traffic Engineering Extension July 2007

      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   |     0x81      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Link State ID                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    0    |V|E|B|      0        |       Router-TE flags         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Router-TE flags (contd.)     |       Router-TE TLVs          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     ....                                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     ....      |            # of TE links      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Link ID                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Link Data                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |        0      |    Link-TE flags              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Link-TE flags (contd.)      |  Zero or more Link-TE TLVs    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Link ID                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Link Data                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |

8.1.1. Router-TE Flags: TE Capabilities of the Router

 The following flags are used to describe the TE capabilities of an
 OSPF-xTE router.  The remaining bits of the 32-bit word are reserved
 for future use.
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|L|P| | | |                                             |L|S|C|
     |S|E|S| | | |                                             |S|I|S|
     |R|R|C| | | |                                             |P|G|P|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|

Srisuresh & Joseph Experimental [Page 19] RFC 4973 OSPF Traffic Engineering Extension July 2007

     Bit LSR - When set, the router is considered to have LSR (Label-
               Switched Router) capability.
     Bit LER - When set, the router is considered to have LER
               capability.  All MPLS border routers will be required
               to have LER capability.  Setting both the LER and E
               bits indicates an AS Boundary router with LER
               capability.  Setting both the LER and B bits indicates
               an area border router with LER capability.
     Bit PSC - Indicates the node is packet-switch capable.
     Bit LSP - An MPLS Label switch TLV TE-NODE-TLV-MPLS-SWITCHING
               follows.  This is applicable only when the PSC flag is
               set.
     Bit SIG - An MPLS Signaling-protocol-support TLV TE-NODE-TLV-
               MPLS-SIG-PROTOCOLS follows.
     BIT CSPF - A CSPF algorithm support TLV TE-NODE-TLV-CSPF-ALG
               follows.

8.1.2. Router-TE TLVs

 The following Router-TE TLVs are defined.

8.1.2.1. TE-NODE-TLV-MPLS-SWITCHING

 MPLS switching TLV is applicable only for packet switched nodes.  The
 TLV specifies the MPLS packet switching capabilities of the TE node.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x8001       |     Length = 6                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Label Depth   |  QOS          |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Label Depth is the depth of label stack the node is capable of
 processing on its ingress interfaces.  An octet is used to represent
 label depth.  A default value of 1 is assumed when the TLV is not
 listed.  Label depth is relevant when an LER has to pop multiple
 labels off the MPLS stack.
 QOS is a single-octet field that may be assigned '1' or '0'.  Nodes
 supporting QOS are able to interpret the EXP bits in the MPLS header
 to prioritize multiple classes of traffic through the same LSP.

Srisuresh & Joseph Experimental [Page 20] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.2.2. TE-NODE-TLV-MPLS-SIG-PROTOCOLS

 MPLS signaling protocols TLV lists all the signaling protocol
 supported by the node.  An octet is used to list each signaling
 protocol supported.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x8002       |     Length = 5, 6 or 7        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Protocol-1  |   ...         |      ....                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 RSVP-TE protocol is represented as 1, CR-LDP as 2, and LDP as 3.
 These are the only permitted signaling protocols at this time.

8.1.2.3. TE-NODE-TLV-CSPF-ALGORITHMS

 The CSPF algorithms TLV lists all the CSPF algorithm codes supported.
 Support for CSPF algorithms makes the node eligible to compute
 complete or partial circuit paths.  Support for CSPF algorithms can
 also be beneficial in knowing whether or not a node is capable of
 expanding loose routes (in an MPLS signaling request) into a detailed
 circuit path.
 Two octets are used to list each CSPF algorithm code.  The algorithm
 codes may be vendor defined and unique within an Autonomous System.
 If the node supports 'n' CSPF algorithms, the Length would be (4 + 4
 * ((n+1)/2)) octets.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x8003       |     Length = 4(1 + (n+1)/2)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    CSPF-1     |      ....                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    CSPF-n     |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Srisuresh & Joseph Experimental [Page 21] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.2.4. TE-NODE-TLV-NULL

 When a TE-Router or a TE link has multiple TLVs to describe the
 metrics, the NULL TLV is used to terminate the TLV list.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x8888       |     Length = 4                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8.1.3. Link-TE Flags: TE Capabilities of a Link

 The following flags are used to describe the TE capabilities of a
 link.  The remaining bits of the 32-bit word are reserved for future
 use.
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|N|P| | | |D|                                         |S|L|B|C|
     |E|T|K| | | |B|                                         |R|U|W|O|
     | |E|T| | | |S|                                         |L|G| |L|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|
     Bit TE   - Indicates whether TE is permitted on the link.  A link
                can be denied for TE use by setting the flag to 0.
     Bit NTE  - Indicates whether non-TE traffic is permitted on the
                TE link.  This flag is relevant only when the TE flag
                is set.
     Bit PKT  - Indicates whether or not the link is capable of IP
                packet processing.
     Bit DBS  - Indicates whether or not database synchronization is
                permitted on this link.
     Bit SRLG - Shared Risk Link Group TLV TE-LINK-TLV-SRLG follows.
     Bit LUG  - Link Usage Cost Metric TLV TE-LINK-TLV-LUG follows.
     Bit BW   - One or more Link Bandwidth TLVs follow.
     Bit COL  - Link Color TLV TE-LINK-TLV-COLOR follows.

Srisuresh & Joseph Experimental [Page 22] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.4. Link-TE TLVs

8.1.4.1. TE-LINK-TLV-SRLG

 The SRLG describes the list of Shared Risk Link Groups (SRLG) the
 link belongs to.  Two octets are used to list each SRLG.  If the link
 belongs to 'n' SRLGs, the Length would be (4 + 4 * ((n+1)/2)) octets.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0001       |     Length = 4(1 + (n+1)/2)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    SRLG-1     |      ....                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    SRLG-n     |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8.1.4.2 TE-LINK-TLV-BANDWIDTH-MAX

 The Bandwidth TLV specifies the maximum bandwidth of the link, 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0002       |     Length = 8                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Maximum Bandwidth                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bandwidth is expressed in units of 32 bytes/sec (256 bits/sec).  A
 32-bit field for bandwidth would permit specification not exceeding 1
 terabit/sec.
 Maximum Bandwidth is the maximum link capacity expressed in bandwidth
 units.  Portions or all of this bandwidth may be used for TE use.

Srisuresh & Joseph Experimental [Page 23] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.4.3. TE-LINK-TLV-BANDWIDTH-MAX-FOR-TE

 The Bandwidth TLV specifies the maximum bandwidth available for TE
 use, 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0003       |     Length = 8                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Maximum Bandwidth available for TE use           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bandwidth is expressed in units of 32 bytes/sec (256 bits/sec).  A
 32-bit field for bandwidth would permit specification not exceeding 1
 terabit/sec.
 "Maximum Bandwidth available for TE use" is the total reservable
 bandwidth on the link for use by all the TE circuit paths traversing
 the link.  The link is oversubscribed when this field is more than
 the Maximum Bandwidth.  When the field is less than the Maximum
 Bandwidth, the remaining bandwidth on the link may be used for non-TE
 traffic in a mixed network.

8.1.4.4. TE-LINK-TLV-BANDWIDTH-TE

 The Bandwidth TLV specifies the bandwidth reserved for TE 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0004       |     Length = 8                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      TE Bandwidth subscribed                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Bandwidth is expressed in units of 32 bytes/sec (256 bits/sec).  A
 32-bit field for bandwidth would permit specification not exceeding 1
 terabit/sec.
 "TE Bandwidth subscribed" is the bandwidth that is currently
 subscribed from of the link. "TE Bandwidth subscribed" must be less
 than the "Maximum bandwidth available for TE use".  New TE circuit
 paths are able to claim no more than the difference between the two
 bandwidths for reservation.

Srisuresh & Joseph Experimental [Page 24] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.4.5. TE-LINK-TLV-LUG

 The link usage cost TLV specifies bandwidth unit usage cost, TE
 circuit set-up cost, and any time constraints for setup and teardown
 of TE circuits on the link.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0005       |     Length = 28               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Bandwidth unit usage cost                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      TE circuit set-up cost                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      TE circuit set-up time constraint        |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      TE circuit tear-down time constraint     |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Circuit Setup time constraint
     This 64-bit number specifies the time at or after which a TE-
     circuit path may be set up on the link.  The set-up time
     constraint is specified as the number of seconds from the start
     of January 1, 1970 UTC.  A reserved value of 0 implies no circuit
     setup time constraint.
 Circuit Teardown time constraint
     This 64-bit number specifies the time at or before which all TE-
     circuit paths using the link must be torn down.  The teardown
     time constraint is specified as the number of seconds from the
     start of January 1 1970 UTC.  A reserved value of 0 implies no
     circuit teardown time constraint.

Srisuresh & Joseph Experimental [Page 25] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.1.4.6. TE-LINK-TLV-COLOR

 The color TLV is similar to the SRLG TLV, in that an Autonomous
 System may choose to issue colors to a TE link meeting certain
 criteria.  The color TLV can be used to specify one or more colors
 assigned to the link as follows.  Two octets are used to list each
 color.  If the link belongs to 'n' number of colors, the Length would
 be (4 + 4 * ((n+1)/2)) octets.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Tag = 0x0006       |     Length = 4(1 + (n+1)/2)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Color-1    |      ....                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Color-n    |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8.1.4.7. TE-LINK-TLV-NULL

 When a TE link has multiple TLVs to describe its metrics, the NULL
 TLV is used to terminate the TLV list.  The TE-LINK-TLV-NULL is same
 as the TE-NODE-TLV-NULL described in section 8.1.2.4

8.2. TE-Incremental-Link-Update LSA (0x8d)

 A significant difference between a native OSPF network and a TE
 network is that the latter may be subject to frequent real-time
 circuit pinning and is likely to undergo TE-state updates.  Some
 links might undergo changes more frequently than others.  Flooding
 the network with TE-router LSAs at the aggregated speed of all link
 metric changes is simply not desirable.  A smaller in size TE-
 incremental-link-update LSA is designed to advertise only the
 incremental link updates.
 A TE-incremental-link-update LSA will be advertised as frequently as
 the link state is changed (not exceeding once every MinLSInterval
 seconds).  The TE link sequence is largely the advertisement of a
 sub-portion of router LSA.  The sequence number on this will be
 incremented with the TE-router LSA's sequence as the basis.  When an
 updated TE-router LSA is advertised within 30 minutes of the previous
 advertisement, the updated TE-router LSA will assume a sequence
 number that is larger than the most frequently updated of its links.

Srisuresh & Joseph Experimental [Page 26] RFC 4973 OSPF Traffic Engineering Extension July 2007

 Below is the format of the TE-incremental-link-update LSA.
      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   |     0x8d      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Link State ID (same as Link ID)        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Link Data                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |        0      |    Link-TE options            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Link-TE options           | Zero or more Link-TE TLVs     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     # TOS     |                            metric             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      TOS      |        0      |          TOS  metric          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Link State ID
     This would be exactly the same as would have been specified for
     Link ID, for a link within the router LSA.
 Link Data
     This specifies the router ID the link belongs to.  In majority of
     cases, this would be same as the advertising router.  This choice
     for Link Data is primarily to facilitate proxy advertisement for
     incremental link updates.
     Suppose that a proxy router LSA was used to advertise the TE-
     router LSA of a SONET/TDM node, and that the proxy router is now
     required to advertise incremental-link-update for the same
     SONET/TDM node.  Specifying the actual router-ID to which the
     link in the incremental-link-update LSA belongs helps receiving
     nodes in finding the exact match for the LSA in their database.

Srisuresh & Joseph Experimental [Page 27] RFC 4973 OSPF Traffic Engineering Extension July 2007

     The tuple of (LS Type, LSA ID, Advertising router) uniquely
     identifies the LSA and replaces LSAs of the same tuple with an
     older sequence number.  However, there is an exception to this
     rule in the context of TE-link-update LSA.  TE-Link-update LSA
     will initially assume the sequence number of the TE-router LSA it
     belongs to.  Further, when a new TE-router LSA update with a
     larger sequence number is advertised, the newer sequence number
     is assumed by all the link LSAs.

8.3. TE-Circuit-Path LSA (0x8C)

 TE-Circuit-path LSA (next page) may be used to advertise the
 availability of pre-engineered TE circuit path(s) originating from
 any router in the network.  The flooding scope may be area-wide or
 AS-wide.  Fields are as follows.
 Link State ID
 The ID of the far-end router or the far-end link-ID to which the TE
 circuit path(s) is being advertised.
 TE-circuit-path(s) flags
     Bit G - When set, the flooding scope is set to be AS-wide.
             Otherwise, the flooding scope is set to be area-wide.
     Bit E - When set, the advertised Link-State ID is an AS boundary
             router (E is for external).  The advertising router and
             the Link State ID belong to the same area.
     Bit B - When set, the advertised Link State ID is an area border
             router (B is for Border)
     Bit D - When set, this indicates that the duration of circuit
             path validity follows.
     Bit S - When set, this indicates that setup time of the circuit
             path follows.
     Bit T - When set, this indicates that teardown time of the
             circuit path follows.
     CktType - This 4-bit field specifies the circuit type of the
             Forward Equivalency Class (FEC).

Srisuresh & Joseph Experimental [Page 28] RFC 4973 OSPF Traffic Engineering Extension July 2007

              0x01 - Origin is Router, Destination is Router.
              0x02 - Origin is Link,   Destination is Link.
              0x04 - Origin is Router, Destination is Link.
              0x08 - Origin is Link,   Destination is Router.
      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   |      0x84     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Link State ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      0    |G|E|B|D|S|T|CktType| Circuit Duration (Optional)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Circuit Duration cont...                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Circuit Duration cont..       | Circuit Setup time (Optional) |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Circuit Setup time cont...                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Circuit Setup time cont..     |Circuit Teardown time(Optional)|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Circuit Teardown time cont...                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Circuit Teardown time cont..  |  No. of TE Circuit Paths      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Circuit-TE ID                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Circuit-TE Data                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |        0      |    Circuit-TE flags           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Circuit-TE flags (contd.)   |  Zero or more Circuit-TE TLVs |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Circuit-TE ID                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Circuit-TE Data                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |

Srisuresh & Joseph Experimental [Page 29] RFC 4973 OSPF Traffic Engineering Extension July 2007

 Circuit Duration (Optional)
     This 64-bit number specifies the seconds from the time of the LSA
     advertisement for which the pre-engineered circuit path will be
     valid.  This field is specified only when the D-bit is set in the
     TE-circuit-path flags.
 Circuit Setup time (Optional)
     This 64-bit number specifies the time at which the TE circuit
     path may be set up.  This field is specified only when the S-bit
     is set in the TE-circuit-path flags.  The set-up time is
     specified as the number of seconds from the start of January 1,
     1970 UTC.
 Circuit Teardown time (Optional)
     This 64-bit number specifies the time at which the TE circuit
     path may be torn down.  This field is specified only when the
     T-bit is set in the TE-circuit-path flags.  The teardown time is
     specified as the number of seconds from the start of January 1
     1970 UTC.
 No. of TE Circuit Paths
     This specifies the number of pre-engineered TE circuit paths
     between the advertising router and the router specified in the
     Link State ID.
 Circuit-TE ID
     This is the ID of the far-end router for a given TE circuit path
     segment.
 Circuit-TE Data
     This is the virtual link identifier on the near-end router for a
     given TE circuit path segment.  This can be a private interface
     or handle the near-end router uses to identify the virtual link.
     The sequence of (Circuit-TE ID, Circuit-TE Data) pairs lists the
     end-point nodes and links in the LSA as a series.
 Circuit-TE flags
     This lists the zero or more TE-link TLVs that all member elements
     of the LSP meet.

Srisuresh & Joseph Experimental [Page 30] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.4. TE-Summary LSAs

 TE-Summary LSAs are Type 0x83 and 0x84 LSAs.  These LSAs are
 originated by area border routers.  A TE-Summary-network LSA (0x83)
 describes the reachability of TE networks in a non-backbone area,
 advertised by the area border router.  A Type 0x84 summary LSA
 describes the reachability of area border routers and AS border
 routers and their TE capabilities.
 One of the benefits of having multiple areas within an AS is that
 frequent TE advertisements within the area do not impact outside the
 area.  Only the TE abstractions befitting the external areas are
 advertised.

Srisuresh & Joseph Experimental [Page 31] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.4.1. TE-Summary Network LSA (0x83)

 A TE-Summary network LSA may be used to advertise reachability of
 TE-networks accessible to areas external to the originating area.
 The content and the flooding scope of a TE-Summary LSA is different
 from that of a native Summary LSA.
 The scope of flooding for a TE-Summary network LSA is AS-wide, with
 the exception of the originating area and the stub areas.  The area
 border router for each non-backbone area is responsible for
 advertising the reachability of backbone networks into the area.
 Unlike a native-summary network LSA, a TE-Summary network LSA does
 not advertise summary costs to reach networks within an area.  This
 is because TE parameters are not necessarily additive or comparable.
 The parameters can be varied in their expression.  For example, a
 TE-Summary network LSA will not summarize a network whose links do
 not fall under an SRLG (Shared-Risk Link Group).  This way, the TE-
 Summary LSA merely advertises the reachability of TE networks within
 an area.  The specific circuit paths can be computed by the ABR.
 Pre-engineered circuit paths are advertised using TE-Circuit-path
 LSAs(refer to Section 8.3).
      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   |    0x83       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Link State ID  (IP Network Number)           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Advertising Router (Area Border Router)            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Network Mask                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Area-ID                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Srisuresh & Joseph Experimental [Page 32] RFC 4973 OSPF Traffic Engineering Extension July 2007

8.4.2. TE-Summary Router LSA (0x84)

  A TE-Summary router LSA may be used to advertise the availability of
  area border routers (ABRs) and AS border routers (ASBRs) that are
  TE-capable.  The TE-Summary router LSAs are originated by the Area
  Border Routers.  The scope of flooding for the TE-Summary router LSA
  is the non-backbone area the advertising ABR belongs to.
      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   |      0x84     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Link State ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router (ABR)                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    0      |E|B|      0        |       No. of Areas            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Area-ID                                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       ...                                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Router-TE flags                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Router-TE TLVs                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     ....                                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Link State ID
     The ID of the area border router or the AS border router whose TE
     capability is being advertised.
 Advertising Router
     The ABR that advertises its TE capabilities (and the OSPF areas
     it belongs to) or the TE capabilities of an ASBR within one of
     the areas for which the ABR is a border router.

Srisuresh & Joseph Experimental [Page 33] RFC 4973 OSPF Traffic Engineering Extension July 2007

 No. of Areas
     Specifies the number of OSPF areas the link state ID belongs to.
 Area-ID
     Specifies the OSPF area(s) the link state ID belongs to.  When
     the link state ID is same as the advertising router ID, the
     Area-ID lists all the areas the ABR belongs to.  In the case the
     link state ID is an ASBR, the Area-ID simply lists the area the
     ASBR belongs to.  The advertising router is assumed to be the ABR
     from the same area the ASBR is located in.
 Summary-router-TE flags
     Bit E - When set, the advertised Link-State ID is an AS boundary
             router (E is for external).  The advertising router and
             the Link State ID belong to the same area.
     Bit B - When set, the advertised Link state ID is an Area border
             router (B is for Border)
 Router-TE flags, Router-TE TLVs
     TE capabilities of the link-state-ID router.
     TE Flags and TE TLVs are as applicable to the ABR/ASBR specified
     in the link state ID.  The semantics is same as specified in the
     Router-TE LSA.

8.5. TE-AS-external LSAs (0x85)

 TE-AS-external LSAs are the Type 0x85 LSAs.  This is modeled after
 AS-external LSA format and flooding scope.  TE-AS-external LSAs are
 originated by AS boundary routers with TE extensions, and describe
 the TE networks and pre-engineered circuit paths external to the AS.
 As with AS-external LSA, the flooding scope of the TE-AS-external LSA
 is AS-wide, with the exception of stub areas.

Srisuresh & Joseph Experimental [Page 34] RFC 4973 OSPF Traffic Engineering Extension July 2007

      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   |      0x85     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Link State ID                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Network Mask                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Forwarding address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      External Route Tag                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  #  of Virtual TE links       |                 0             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Link-TE flags                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Link-TE TLVs                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      TE-Forwarding address                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      External Route TE Tag                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
 Network Mask
      The IP address mask for the advertised TE destination.  For
      example, this can be used to specify access to a specific TE
      node or TE link with an mask of 0xffffffff.  This can also be
      used to specify access to an aggregated set of destinations
      using a different mask.  ex: 0xff000000.
 Link-TE flags, Link-TE TLVs
      The TE attributes of this route.  These fields are optional and
      are provided only when one or more pre-engineered circuits can
      be specified with the advertisement.  Without these fields, the
      LSA will simply state TE reachability info.

Srisuresh & Joseph Experimental [Page 35] RFC 4973 OSPF Traffic Engineering Extension July 2007

 Forwarding address
      Data traffic for the advertised destination will be forwarded to
      this address.  If the Forwarding address is set to 0.0.0.0, data
      traffic will be forwarded instead to the LSA's originator (i.e.,
      the responsible AS boundary router).
 External Route Tag
      A 32-bit field attached to each external route.  This is not
      used by the OSPF protocol itself.  It may be used to communicate
      information between AS boundary routers; the precise nature of
      such information is outside the scope of this specification.

9. TE LSAs for Non-Packet Network

 A non-packet network would use the TE LSAs described in the previous
 section for a packet network with some variations.  These variations
 are described in the following subsections.
 Two new LSAs, TE-Positional-ring-network LSA and TE-Router-Proxy LSA
 are defined for use in non-packet TE networks.
 Readers may refer to [SONET-SDH] for a detailed description of the
 terms used in the context of SONET/SDH TDM networks,

9.1. TE-Router LSA (0x81)

 The following fields are used to describe each router link (i.e.,
 interface).  Each router link is typed (see the below Type field).
 The Type field indicates the kind of link being described.
 Type
      A new link type "Positional-Ring Type" (value 5) is defined.
      This is essentially a connection to a TDM-Ring.  TDM ring
      network is different from LAN/NBMA transit network in that nodes
      on the TDM ring do not necessarily have a terminating path
      between themselves.  Second, the order of links is important in
      determining the circuit path.  Third, the protection switching
      and the number of fibers from a node going into a ring are
      determined by the ring characteristics, for example, 2-fiber vs.
      4-fiber ring and Unidirectional Path Switched Ring (UPSR) vs.
      Bidirectional Line Switched Ring (BLSR).

Srisuresh & Joseph Experimental [Page 36] RFC 4973 OSPF Traffic Engineering Extension July 2007

             Type   Description
             __________________________________________________
             1      Point-to-point connection to another router
             2      Connection to a transit network
             3      Connection to a stub network
             4      Virtual link
             5      Positional-Ring type.
 Link ID
      Identifies the object that this router link connects to.  Value
      depends on the link's Type.  For a positional-ring type, the
      Link ID shall be IP Network/Subnet number just as the case with
      a broadcast transit network.  The following table summarizes the
      updated Link ID values.
             Type   Link ID
             ______________________________________
             1      Neighboring router's Router ID
             2      IP address of Designated Router
             3      IP network/subnet number
             4      Neighboring router's Router ID
             5      IP network/subnet number
 Link Data
      This depends on the link's Type field.  For type-5 links, this
      specifies the router interface's IP address.

9.1.1 Router-TE flags - TE Capabilities of a Router

 Flags specific to non-packet TE nodes are described below.
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |L|L|P|T|L|F|                                           |S|S|S|C|
     |S|E|S|D|S|S|                                           |T|E|I|S|
     |R|R|C|M|C|C|                                           |A|L|G|P|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|
     Bit TDM - Indicates the node is TDM circuit switch capable.
     Bit LSC - Indicates the node is capable of Lambda switching.
     Bit FSC - Indicates the node is capable of fiber-switching (can
         also be a non-fiber link type).

Srisuresh & Joseph Experimental [Page 37] RFC 4973 OSPF Traffic Engineering Extension July 2007

9.1.2 Link-TE Options: TE Capabilities of a TE Link

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|N|P|T|L|F|D|                                         |S|L|B|C|
     |E|T|K|D|S|S|B|                                         |R|U|W|O|
     | |E|T|M|C|C|S|                                         |L|G|A|L|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|
     TDM, LSC, FSC bits - Same as defined for router TE options.

9.2. TE-positional-ring-network LSA (0x82)

 Network LSA is adequate for packet TE networks.  A new TE-
 positional-ring-network LSA is defined to represent type-5 link
 networks, found in non-packet networks such as SONET/SDH TDM rings.
 A type-5 ring is a collection of network elements (NEs) forming a
 closed loop.  Each NE is connected to two adjacent NEs via a duplex
 connection to provide redundancy in the ring.  The sequence in which
 the NEs are placed on the Ring is pertinent.  The NE that provides
 the OSPF-xTE functionality is termed the Gateway Network Element
 (GNE).  The GNE selection criteria is outside the scope of this
 document.  The GNE is also termed the Designated Router for the ring.
 The TE-positional-ring-network LSA (0x82) is modeled after the
 network LSA and has the same flooding scope as the network LSA
 amongst the OSPF-xTE nodes within the area.  Below is the format of
 the TE-Positional-Ring-network LSA.  Unless specified explicitly
 otherwise, the fields carry the same meaning as they do in a network
 LSA.  Only the differences are explained below.
 A TE-positional-ring-network LSA is originated for each Positional-
 Ring type network in the area.  The tuple of (Link State ID, Network
 Mask) below uniquely represents a ring.  The TE option must be set in
 the Options flag while propagating the LSA.

Srisuresh & Joseph Experimental [Page 38] RFC 4973 OSPF Traffic Engineering Extension July 2007

      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  |     0x82      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Link State ID                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Network Mask                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Ring Type    | Capacity Unit |        Reserved               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Ring capacity                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Network Element Node Id                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
 Link State ID
      This is the IP interface address of the network's Gateway
      Network Element, which is also the designated router.
 Advertising Router
      Router ID of the network's Designated Router.
 Ring type
      There are 8 types of SONET/SDH rings defined as follows.
      1 - A Unidirectional Line Switched 2-fiber ring (2-fiber ULSR)
      2 - A Bidirectional Line switched 2-fiber ring (2-fiber BLSR)
      3 - A Unidirectional Path Switched 2-fiber ring (2-fiber UPSR)
      4 - A Bidirectional Path switched 2-fiber ring (2-fiber BPSR)
      5 - A Unidirectional Line Switched 4-fiber ring (4-fiber ULSR)
      6 - A Bidirectional Line switched 4-fiber ring (4-fiber BLSR)
      7 - A Unidirectional Path Switched 4-fiber ring (4-fiber UPSR)
      8 - A Bidirectional Path switched 4-fiber ring (4-fiber BPSR)

Srisuresh & Joseph Experimental [Page 39] RFC 4973 OSPF Traffic Engineering Extension July 2007

 Capacity Unit
      Two units are currently defined, as follows.
      1 - Synchronous Transport Signal (STS), which is the basic
          signal rate for SONET signals.  The rate of an STS signal is
          51.84 Mbps
      2 - Synchronous Transport Multiplexer (STM), which is the basic
          signal rate for SDH signals.  The rate of an STM signal is
          155.52 Mbps
 Ring capacity
      Ring capacity expressed in number of Capacity Units.
 Network Element Node Id
      The Router ID of each of the routers in the positional-ring
      network.  The list must start with the designated router as the
      first element.  The Network Elements (NEs) must be listed in
      strict clockwise order as they appear on the ring, starting with
      the Gateway Network Element (GNE).  The number of NEs in the
      ring can be deduced from the LSA header's length field.

9.3. TE-Router-Proxy LSA (0x8e)

 This is a variation to the TE-router LSA in that the TE-router LSA is
 not advertised by the network element, but rather by a trusted TE-
 router Proxy.  This is typically the scenario in a non-packet TE
 network, where some of the nodes do not have OSPF functionality and
 count on a helper node to do the advertisement for them.  One such
 example would be the SONET/SDH Add-Drop Multiplexer (ADM) nodes in a
 TDM ring.  The nodes may principally depend upon the GNE (Gateway
 Network Element) to do the advertisement for them.  TE-router-Proxy
 LSA shall not be used to advertise area border routers and/or AS
 border routers.

Srisuresh & Joseph Experimental [Page 40] RFC 4973 OSPF Traffic Engineering Extension July 2007

      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   |     0x8e      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Link State ID  (Router ID of the TE Network Element)     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Advertising Router                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     LS sequence number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         LS checksum           |             length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 0             |       Router-TE flags         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Router-TE flags (contd.)     |       Router-TE TLVs          |
     +---------------------------------------------------------------+
     |                     ....                                      |
     +---------------------------------------------------------------+
     |                     ....      |      # of TE links            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Link ID                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Link Data                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |        0      |    Link-TE options            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Link-TE flags               |  Zero or more Link-TE TLVs    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Link ID                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Link Data                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |

Srisuresh & Joseph Experimental [Page 41] RFC 4973 OSPF Traffic Engineering Extension July 2007

10. Abstract Topology Representation with TE Support

 Below, we consider a TE network composed of three OSPF areas, Area-1,
 Area-2 and Area-3, attached together through the backbone area.
 Area-1 an has a single area border router, ABR-A1 and no ASBRs.
 Area-2 has an area border router ABR-A2 and an AS border router
 ASBR-S1.  Area-3 has two area border routers ABR-A2 and ABR-A3 and an
 AS border router ASBR-S2.  The following network also assumes a pre-
 engineered TE circuit path between ABR-A1 and ABR-A2; between ABR-A1
 and ABR-A3; between ABR-A2 and ASBR-S1; and between ABR-A3 and ASBR-
 S2.
 The following figure is an inter-area topology abstraction from the
 perspective of routers in Area-1.  The abstraction illustrates
 reachability of TE networks and nodes within area to the external
 areas in the same AS and to the external ASes.  The abstraction also
 illustrates pre-engineered TE circuit paths advertised by ABRs and
 ASBRs.

Srisuresh & Joseph Experimental [Page 42] RFC 4973 OSPF Traffic Engineering Extension July 2007

                        +-------+
                        |Area-1 |
                        +-------+
 +-------------+            |
 |Reachable TE |       +--------+
 |networks in  |-------| ABR-A1 |
 |backbone area|       +--------+
 +-------------+          | | |
           +--------------+ | +-----------------+
           |                |                   |
 +-----------------+        |            +-----------------+
 |Pre-engineered TE|    +----------+     |Pre-engineered TE|
 |circuit path(s)  |    | Backbone |     |circuit path(s)  |
 |to ABR-A2        |    | Area     |     |to ABR-A3        |
 +-----------------+    +----------+     +-----------------+
           |               |   |                 |
           +----------+    |   +--------------+  |
 +-----------+        |    |                  |  |     +-----------+
 |Reachable  |      +--------+             +--------+  |Reachable  |
 |TE networks|------| ABR-A2 |             | ABR-A3 |--|TE networks|
 |in Area A2 |      +--------+             +--------+  |in Area A3 |
 +-----------+       | | | |                   | |     +-----------+
       +-------------+ | | +-----------------+ | +----------+
       |               | +-----------+       | |            |
 +-----------+ +--------------+      |       | |    +--------------+
 |Reachable  | |Pre-engineered|      |       | |    |Pre-engineered|
 |TE networks| |TE Ckt path(s)|  +------+  +------+ |TE Ckt path(s)|
 |in Area A3 | |to ASBR-S1    |  |Area-2|  |Area-3| |to ASBR-S2    |
 +-----------+ +--------------+  +------+  +------+ +--------------+
                        |            |       |              |
                        |   +--------+       |  +-----------+
 +-------------+        |   |                |  |
 |AS external  |    +---------+          +---------+
 |TE-network   |----| ASBR-S1 |          | ASBR-S2 |
 |reachability |    +---------+          +---------+
 |from ASBR-S1 |        |                    |  |
 +-------------+    +---+            +-------+  +-----------+
                    |                |                     |
        +-----------------+   +-------------+   +-----------------+
        |Pre-engineered TE|   |AS External  |   |Pre-engineered TE|
        |circuit path(s)  |   |TE-Network   |   |circuit path(s)  |
        |reachable from   |   |reachability |   |reachable from   |
        |ASBR-S1          |   |from ASBR-S2 |   |ASBR-S2          |
        +-----------------+   +-------------+   +-----------------+
     Figure 3: Inter-Area Abstraction as viewed by Area-1 TE-routers

Srisuresh & Joseph Experimental [Page 43] RFC 4973 OSPF Traffic Engineering Extension July 2007

11. Changes to Data Structures in OSPF-xTE Nodes

11.1. Changes to Router Data Structure

 An OSPF-xTE router must be able to include the router-TE capabilities
 (as specified in section 8.1) in the router data structure.  OSPF-xTE
 routers providing proxy service to other TE routers must also track
 the router and associated interface data structures for all the TE
 client nodes for which the proxy service is being provided.
 Presumably, the interaction between the Proxy server and the proxy
 clients is out-of-band.

11.2. Two Sets of Neighbors

 Two sets of neighbor data structures are required.  TE-neighbors set
 is used to advertise TE LSAs.  Only the TE nodes will be members of
 the TE-neighbor set.  Native neighbors set will be used to advertise
 native LSAs.  All neighboring nodes supporting non-TE links are part
 of the Native neighbors set.

11.3. Changes to Interface Data Structure

 The following new fields are introduced to the interface data
 structure.
 TePermitted
     If the value of the flag is TRUE, the interface may be advertised
     as a TE-enabled interface.
 NonTePermitted
     If the value of the flag is TRUE, the interface permits non-TE
     traffic on the interface.  Specifically, this is applicable to
     packet networks, where data links may permit both TE and IP
     packets.  For FSC and LSC TE networks, this flag is set to FALSE.
 FloodingPermitted
     If the value of the flag is TRUE, the interface may be used for
     OSPF and OSPF-xTE packet exchange to synchronize the LSDB across
     all adjacent neighbors.  This is TRUE by default to all
     NonTePermitted interfaces that are enabled for OSPF.  However, it
     is possible to set this to FALSE for some of the interfaces.

Srisuresh & Joseph Experimental [Page 44] RFC 4973 OSPF Traffic Engineering Extension July 2007

 TE-TLVs
     Each interface may define any number of TLVS that describe the
     link characteristics.
 The following existing fields in Interface data structure will take
 on additional values to support TE extensions.
 Type
     The OSPF interface type can also be of type "Positional-Ring".
     The Positional-Ring type is different from other types (such as
     broadcast and NBMA) in that the exact location of the nodes on
     the ring is relevant, even though they are all on the same ring.
     SONET ADM ring is a good example of this.  Complete ring
     positional-ring description may be provided by the GNE on a ring
     as a TE-network LSA for the ring.
 List of Neighbors
     The list may be statically defined for an interface without
     requiring the use of Hello protocol.

12. IANA Considerations

 The IANA has assigned multicast address 224.0.0.24 to OSPFIGP-TE for
 the exchange of TE database descriptors.
 TE LSA types and TE TLVs will be maintained by the IANA, using the
 following criteria.

12.1. TE LSA Type Values

 LSA type is an 8-bit field required by each LSA.  TE LSA types will
 have the high bit set to 1.  TE LSAs can range from 0x80 through
 0xFF.  The following values are defined in sections 8.0 and 9.0.  The
 remaining values are available for assignment by the IANA with IETF
 Consensus [RFC2434].

Srisuresh & Joseph Experimental [Page 45] RFC 4973 OSPF Traffic Engineering Extension July 2007

    TE LSA Type                        Value
    _________________________________________
    TE-Router LSA                      0x81
    TE-Positional-ring-network LSA     0x82
    TE-Summary Network LSA             0x83
    TE-Summary router LSA              0x84
    TE-AS-external LSAs                0x85
    TE-Circuit-paths LSA               0x8C
    TE-incremental-link-Update LSA     0x8d
    TE-Router-Proxy LSA                0x8e

12.2. TE TLV Tag Values

 TLV type is a 16-bit field required by each TE TLV.  TLV type shall
 be unique across the router and link TLVs.  A TLV type can range from
 0x0001 through 0xFFFF.  TLV type 0 is reserved and unassigned.  The
 following TLV types are defined in sections 8.0 and 9.0.  The
 remaining values are available for assignment by the IANA with IETF
 Consensus [RFC2434].
 TE TLV Tag                         Reference       Value
                                    Section
 _________________________________________________________
 TE-LINK-TLV-SRLG                 Section 8.1.4.1  0x0001
 TE-LINK-TLV-BANDWIDTH-MAX        Section 8.1.4.2  0x0002
 TE-LINK-TLV-BANDWIDTH-MAX-FOR-TE Section 8.1.4.3  0x0003
 TE-LINK-TLV-BANDWIDTH-TE         Section 8.1.4.4  0x0004
 TE-LINK-TLV-LUG                  Section 8.1.4.5  0x0005
 TE-LINK-TLV-COLOR                Section 8.1.4.6  0x0006
 TE-LINK-TLV-NULL                 Section 8.1.4.7  0x8888
 TE-NODE-TLV-MPLS-SWITCHING       Section 8.1.2.1  0x8001
 TE-NODE-TLV-MPLS-SIG-PROTOCOLS   Section 8.1.2.2  0x8002
 TE-NODE-TLV-CSPF-ALG             Section 8.1.2.3  0x8003
 TE-NODE-TLV-NULL                 Section 8.1.2.4  0x8888

13. Acknowledgements

 The authors wish to specially thank Chitti Babu and his team for
 implementing the protocol specified in a packet network and verifying
 several portions of the specification in a mixed packet network.  The
 authors also wish to thank Vishwas Manral, Riyad Hartani, and Tricci
 So for their valuable comments and feedback on the document.  Lastly,
 the authors wish to thank Alex Zinin and Mike Shand for their
 document (now defunct) titled "Flooding optimizations in link state
 routing protocols".  The document provided inspiration to the authors
 to be sensitive to the high flooding rate, likely in TE networks.

Srisuresh & Joseph Experimental [Page 46] RFC 4973 OSPF Traffic Engineering Extension July 2007

14. Security Considerations

 Security considerations for the base OSPF protocol are covered in
 [OSPF-V2] and [SEC-OSPF].  This memo does not create any new security
 issues for the OSPF protocol.  Security measures applied to the
 native OSPF (refer [SEC-OSPF]) are directly applicable to the TE LSAs
 described in the document.  Discussed below are the security
 considerations in processing TE LSAs.
 Secure communication between OSPF-xTE nodes has a number of
 components.  Authorization, authentication, integrity and
 confidentiality.  Authorization refers to whether a particular OSPF-
 xTE node is authorized to receive or propagate the TE LSAs to its
 neighbors.  Failing the authorization process might indicate a
 resource theft attempt or unauthorized resource advertisement.  In
 either case, the OSPF-xTE nodes should take proper measures to
 audit/log such attempts so as to alert the administrator to take
 necessary action.  OSPF-xTE nodes may refuse to communicate with the
 neighboring nodes that fail to prompt the required credentials.
 Authentication refers to confirming the identity of an originator for
 the datagrams received from the originator.  Lack of strong
 credentials for authentication of OSPF-xTE LSAs can seriously
 jeopardize the TE service rendered by the network.  A consequence of
 not authenticating a neighbor would be that an attacker could spoof
 the identity of a "legitimate" OSPF-xTE node and manipulate the
 state, and the TE database including the topology and metrics
 collected.  This could potentially cause denial-of-service on the TE
 network.  Another consequence of not authenticating is that an
 attacker could pose as OSPF-xTE neighbor and respond in a manner that
 would divert TE data to the attacker.
 Integrity is required to ensure that an OSPF-xTE message has not been
 accidentally or maliciously altered or destroyed.  The result of a
 lack of data integrity enforcement in an untrusted environment could
 be that an imposter will alter the messages sent by a legitimate
 adjacent neighbor and bring the OSPF-xTE on a node and the whole
 network to a halt or cause a denial of service for the TE circuit
 paths effected by the alteration.
 Confidentiality of OSPF-xTE messages ensures that the TE LSAs are
 accessible only to the authorized entities.  When OSPF-xTE is
 deployed in an untrusted environment, lack of confidentiality will
 allow an intruder to perform traffic flow analysis and snoop the TE
 control network to monitor the traffic metrics and the rate at which
 circuit paths are being setup and torn-down.  The intruder could
 cannibalize a lesser secure OSPF-xTE node and destroy or compromise
 the state and TE-LSDB on the node.  Needless to say, the least secure

Srisuresh & Joseph Experimental [Page 47] RFC 4973 OSPF Traffic Engineering Extension July 2007

 OSPF-xTE will become the Achilles heel and make the TE network
 vulnerable to security attacks.

15. Normative References

 [MPLS-ARCH] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
             Label Switching Architecture", RFC 3031, Jaunary 2001.
 [MPLS-TE]   Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
             McManus, "Requirements for Traffic Engineering Over
             MPLS", RFC 2702, September 1999.
 [OSPF-V2]   Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
 [SEC-OSPF]  Murphy, S., Badger, M., and B. Wellington, "OSPF with
             Digital Signatures", RFC 2154, June 1997.
 [OSPF-CAP]  Lindem, A., Ed., Shen, N., Vasseur, J., Aggarwal, R., and
             S.  Schaffer, "Extensions to OSPF for Advertising
             Optional Router Capabilities", RFC 4970, July 2007.
 [RFC2434]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 2434,
             October 1998.

16. Informative References

 [BGP-OSPF]  Ferguson, D., "The OSPF External Attribute LSA",
             unpublished.
 [CR-LDP]    Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu,
             L., Doolan, P., Worster, T., Feldman, N., Fredette, A.,
             Girish, M., Gray, E., Heinanen, J., Kilty, T., and A.
             Malis, "Constraint-Based LSP Setup using LDP", RFC 3212,
             January 2002.
 [GMPLS-TE]  Berger, L., "Generalized Multi-Protocol Label Switching
             (GMPLS) Signaling Functional Description", RFC 3471,
             January 2003.
 [MOSPF]     Moy, J., "Multicast Extensions to OSPF", RFC 1584, March
             1994.
 [NSSA]      Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
             RFC 3101, January 2003.
 [OPAQUE]    Coltun, R., "The OSPF Opaque LSA Option", RFC 2370, July
             1998.

Srisuresh & Joseph Experimental [Page 48] RFC 4973 OSPF Traffic Engineering Extension July 2007

 [OPQLSA-TE] Katz, D., Yeung, D., and K. Kompella, "Traffic
             Engineering Extensions to OSPF", RFC 3630, September
             2003.
 [RSVP-TE]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
             and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
             Tunnels", RFC 3209, December 2001.
 [SONET-SDH] Chow, M.-C., "Understanding SONET/SDH Standards and
             Applications", Holmdel, N.J.: Andan Publisher, 1995.

Authors' Addresses

 Pyda Srisuresh
 Kazeon Systems, Inc.
 1161 San Antonio Rd.
 Mountain View, CA 94043
 U.S.A.
 Phone: (408) 836-4773
 EMail: srisuresh@yahoo.com
 Paul Joseph
 Consultant
 10100 Torre Avenue, # 121
 Cupertino, CA 95014
 U.S.A.
 Phone: (408) 777-8493
 EMail: paul_95014@yahoo.com

Srisuresh & Joseph Experimental [Page 49] RFC 4973 OSPF Traffic Engineering Extension July 2007

Full Copyright Statement

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Srisuresh & Joseph Experimental [Page 50]

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