Internet DRAFT - draft-dhody-pce-bn-discovery-ospf

draft-dhody-pce-bn-discovery-ospf







PCE Working Group                                               D. Dhody
Internet-Draft                                                  U. Palle
Intended status: Experimental          Huawei Technologies India Pvt Ltd
Expires: March 19, 2015                               September 15, 2014


       OSPF Protocol Extensions for Boundary Node Discovery (BND)
                  draft-dhody-pce-bn-discovery-ospf-09

Abstract

   The Path Computation Element (PCE) may be used for computing multi-
   domain (Area or AS) Multiprotocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) Traffic Engineered (TE) Label Switch Path
   (LSP).

   In this circumstance, it is highly desirable to be able to
   dynamically and automatically discover a set of Boundary Nodes (BN)
   along with their domain information in a simple way.  For that
   purpose, this document defines extensions to the Open Shortest Path
   First (OSPF) routing protocol for the advertisement of Boundary Node
   (BN) Discovery information within an OSPF area or within the entire
   OSPF routing domain.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 19, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Existing Mechanisms . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  OSPF LSA  . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Inter-AS TE Link  . . . . . . . . . . . . . . . . . . . .   6
     4.3.  OSPF Area Topology  . . . . . . . . . . . . . . . . . . .   8
   5.  Other Considerations  . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Static Configurations . . . . . . . . . . . . . . . . . .   8
     5.2.  Importance of Domain Information along with BNs . . . . .   8
     5.3.  Relationship to Domain-Sequence . . . . . . . . . . . . .   9
   6.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Boundary Node (BN) Discovery Information  . . . . . . . .   9
     6.2.  Flooding Scope  . . . . . . . . . . . . . . . . . . . . .   9
   7.  The OSPF BND TLV  . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  BN-ADDRESS Sub-TLV  . . . . . . . . . . . . . . . . . . .  10
     7.2.  BN-DOMAIN Sub-TLV . . . . . . . . . . . . . . . . . . . .  11
   8.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .  12
   9.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  13
   10. Impact on Network . . . . . . . . . . . . . . . . . . . . . .  13
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  OSPF TLV . . . . . . . . . . . . . . . . . . . . . . . .  13
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  14
   13. Manageability Considerations  . . . . . . . . . . . . . . . .  14
   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     15.2.  Informative References . . . . . . . . . . . . . . . . .  15

1.  Introduction

   This document defines extensions to OSPFv2 [RFC2328] and OSPFv3
   [RFC5340] to allow a boundary node in an OSPF routing domain to
   advertise its location, along with domain information.

   Generic capability advertisement mechanisms for OSPF are defined in
   [RFC4970].  These allow a router to advertise its capabilities within



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   an OSPF area or an entire OSPF routing domain.  This document
   leverages this generic capability advertisement mechanism to fully
   satisfy the dynamic BN discovery.

   This document defines a new TLV (named the Boundary Node Discovery
   TLV (BND TLV)) to be carried within the OSPF Router Information LSA
   ([RFC4970]).

   The Boundary Node information advertised is detailed in Section 6.
   Protocol extensions and procedures are defined in Section 7 and
   Section 8.

   A detailed description about the need for auto discovery of Boundary
   Nodes (BN) and thier domains is also provided in this document.

   The OSPF extensions defined in this document allow for Boundary Node
   discovery within an OSPF routing domain.  Boundary Node can be an
   Area Border Router (ABR) or Autonomous System Border Router (ASBR).

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Terminology

   The following terminology is used in this document.

   ABR:  OSPF Area Border Router.  Routers used to connect two IGP
      areas.

   AS:  Autonomous System.

   ASBR:  Autonomous System Border Router.  Router used to connect
      together ASes of the same or different service providers via one
      or more inter-AS links

   BN:  A boundary node is either an ABR in the context of inter-area
      Traffic Engineering or an ASBR in the context of inter-AS Traffic
      Engineering.

   BND:  Boundary Node Discovery

   BRPC:  Backward Recursive Path Computation

   Domain:  Any collection of network elements within a common sphere of
      address management or path computational responsibility.  Examples



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      of domains include Interior Gateway Protocol (IGP) areas and
      Autonomous Systems (ASs).

   H-PCE:  Hierarchical PCE.

   IGP:  Interior Gateway Protocol.  Either of the two routing
      protocols, Open Shortest Path First (OSPF) or Intermediate System
      to Intermediate System (IS-IS).

   LSA:  Link State Advertisement.

   OSPF:  Open Shortest Path First.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   TLV:  Type-Length-Variable data encoding.

3.  Applications

   Backward Recursive Path Computation (BRPC) procedure as defined in
   [RFC5441], requires Path Computation Element (PCE) [RFC4655] to be
   aware of the Boundary Nodes (BN) for the inter-domain path
   computation.  This information would be either statically configured
   at PCE or learned via some mechanism, as listed in Section 4.

   In case of static configuration, as shown in the Figure 1, incase of
   OSPF Area0, configuration of BNs at PCE5 is extensive.  BRPC
   procedure guarantees a best path only if BNs are selected correctly,
   any change in BNs at run time may lead to sub-optimal path.  Also
   Administrator need to configure ABR / ASBR ID in such a way that it
   is reachable from all the domains, BND TLV can take care of this
   automatically.
















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                           +--------------------+
                           |             +-----+|
                           |      Area 2 | PCE2||
                           |             +-----+|
                           |                    |
                           |                    |
                           |     BN4+----+      |
                           +--------+----+------+
                         +----------+----+---------+
                         |          +----+         |
                         |                         |
                         |                         |
                         |                         |
       +---------------+ |                         |+----------------+
       |           BN1 | |                         ||  BN5           |
       |             +-+-++                       +++--+             |
       |             | | ||                       |||  |             |
       |             +-+-++                       +++--+             |
       |               | |                         ||                |
       |           BN2 | |                         ||  BN6           |
       |             +-+-++       Area 0          +++--+             |
       |  Area 1     | | ||                       |||  |   Area 3    |
       |             +-+-++                       +++--+             |
       |               | |                         ||                |
       |           BN3 | |          +-----+        ||  BN7           |
       |+-----+      +-+-++         | PCE5|       +++--+     +-----+ |
       || PCE1|      | | ||         +-----+       |||  |     | PCE3| |
       |+-----+      +-+-++                       +++--+     +-----+ |
       |               | |                         ||                |
       +---------------+ |                         |+----------------+
                         |                         |
                         |                         |
                         |          +----+         |
                         +----------+----+---------+
                           +--------+----+------+
                           |    BN8 +----+      |
                           |                    |
                           |                    |
                           |      Area 4 +-----+|
                           |             | PCE4||
                           |             +-----+|
                           +--------------------+

                       Figure 1: OSPF Area Topology

   The problems with existing mechanism to discover Boundary nodes are
   listed in Section 4.




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   Hierarchal PCE (H-PCE) [RFC6805] mechanim MAY require a parent PCE to
   be aware of child domain's boundary node, child PCE in any case
   should be aware of all its boundary nodes and can use mechnims as
   described in this document.

4.  Existing Mechanisms

4.1.  OSPF LSA

   o  E bit and B bit of Router LSA defined in [RFC2328] can help in
      finding a router acting as ABR/ASBR but there is no way to find
      out the domain information of this ABR/ASBR.  As stated in
      Section 5.2, Selection of correct BN is based on domain and thus
      it is ineffective.

   o  Selection of ABR based on summary LSA or ASBR based on AS-external
      LSA is not a good idea, first it requires PCE to look into the
      OSPF core data structure - Link State Database (LSDB) thus adding
      to coupling, second it MAY require Border Gateway Protocol (BGP)
      routes to be redistributed into OSPF which is also not a good
      network design principle.

4.2.  Inter-AS TE Link

   o  [RFC5392] specifies how to advertise TE properties of inter-AS
      links; through which ASBR and remote AS can be discovered, but ABR
      and their domain information cannot be discovered via above RFC.

   o  AS is made up of multiple Area, there maybe a need to clearly
      identify a BN by combination of both AS number and Area-id.  Refer
      [DOMAIN-SEQ].

   o  AS shown in below figure, just the knowledge of AS 100 and AS 200
      is not sufficient, the BN should have both AS and Area
      information.  The area information cannot be provided by
      [RFC5392].















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                    |
                    |  +-------------+                +----------------+
                    |  |Area 2       |                |Area 4          |
                    |  |         +--+|                |          +--+  |
                    |  |         |  ||                |          |  |  |
                    |  |  +--+   +--+|                |   +--+   +--+  |
                    |  |  |  |       |                |   |  |         |
                    |  |  *--+       |                |   +--+         |
                    |  | /      +--+ |                |          +--+  |
                    |  |/       |  | |                |          |  |  |
                    |  /        +--+ |                |   +--+   +--+  |
                    | /|  +--+       |+--------------+|   |  |         |
                    |/ |  |  |       ++-+          +-++   +--+         |
     +-------------+/  |  +--+       || |          | ||                |
     |             /|  |             ++-+          +-++                |
     |         +--*||  +-------------+|              |+----------------+
     |         |  |||                 |     +--+     |
     |         +--+||                 |     |  |     |
     |    +--+     ||                 |     +--+     |
     |    |  |     ||                 |              |
     |    +--+     ||                 |              |
     |             ||                 |     +--+     |
     |+--+         ||                 |     |  |     |
     ||  |         ||                 |     +--+     |
     |+--+         ||                 |              |
     |             ||                 |     +--+     |
     |    +--+     ||  +------------+ |     |  |     |+----------------+
     |    |  |     ||  |Area 3      +-++    +--+   +-++ Area 5         |
     |    +--+     ||  |            | ||           | ||                |
     |             ||  |            +-++           +-++                |
     |         +--+||  |       +--+ | |  Area 0      ||   +--+         |
     |         |  |||  |       |  | | +--------------+|   |  |         |
     |         +--*||  |       +--+ |                 |   +--+         |
     |             \|  |            |                 |          +--+  |
     |Area 1       |\  |   +--+     |                 |   +--+   |  |  |
     +-------------+|\ |   |  |     |                 |   |  |   +--+  |
                    | \|   +--+  +--+                 |   +--+         |
                    |  \         |  |                 |                |
                    |  |\        +--+                 |          +--+  |
                    |  | \ +--+     |                 |          |  |  |
                    |  |  \|  |     |                 |          +--+  |
                    |  |   *--+     |                 |                |
                    |  |            |                 |                |
                    |  +------------+                 +----------------+
                    |
                    |
         As 100     |  AS 200
                    |



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4.3.  OSPF Area Topology

   o  Consider OSPF topology as shown in Figure 1, One can make a
      generalization that all ABR connects to Area 0, and one doesnt
      need the area information.

   o  But as per [RFC3509], there are alternative interpretaion of ABR,
      which needs to be considered.  If there is a connectivity between
      Area 1 and Area 2 directly that needs to be considered.  In the
      scope of path computation. it is not correct to force all paths to
      go through area 0, irrespective of actual topology.

                         .                .
                              .    Area 0    .
                               +--+      +--+
                             ..|R1|..  ..|R2|..
                            .  +--+  ..  +--+  .
                            .        ..        .
                            .       +--+       .
                            . Area1 |R3| Area2 .
                            .       +--+  +--+ .
                            .        ..   |R4| .
                            .       .  .  +--+ .
                             .......    .......

5.  Other Considerations

5.1.  Static Configurations

   A simple solution would be to configure BNs (ABR and ASBR) at PCE(s)
   along with their domain information.  As this information is fairly
   static this could work in simple situations.  But as PCE are being
   used in bigger and multiple domains, any sort of static
   configurations would put extra effort on the system administrator.
   Selection of correct BNs is the core of any inter-domain path
   computation procedure, this information should be dynamically learned
   and maintained.

5.2.  Importance of Domain Information along with BNs

   There are methods to learn BNs dynamically from IGP, but the
   knowledge of neighboring-domains is not possible to obtain.  Without
   this the correct BN based on the domain-path can not be selected.
   [RFC5441] mentions:

   "Note that PCE(i) only considers the entry BNs of domain(i), i.e.,
   only the BNs that provide connectivity from domain(i-1).  In other




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   words, the set BN-en(k,i) is only made of those BNs that provide
   connectivity from domain (i-1) to domain(i)."

   This selection of correct BNs providing connectivity between correct
   domains cannot be made by the information obtained from IGP.  Without
   the correct selection we would not be following [RFC5441].

5.3.  Relationship to Domain-Sequence

   [DOMAIN-SEQ] provides a standard representation of Domain Sequence in
   all deployment scenarios.  The Domain Information carried in the BN-
   DOMAIN sub-tlv is same as the sub-objects inside the domain sequence.

6.  Overview

6.1.  Boundary Node (BN) Discovery Information

   The BN discovery information is composed of:

   o  The BN location: an IPv4 and/or IPv6 address that is used to reach
      the BN.  It is RECOMMENDED to use an address that is always
      reachable from all connected domains;

   o  The set of two or more Domain(s) into which the BN has
      connectivity;

   Changes in BN discovery information may occur as a result of BN
   configuration update or domain status change.

6.2.  Flooding Scope

   The flooding scope for BN information advertised through OSPF can be
   limited to OSPF area(s) the BN belongs to, or can be extended across
   the entire OSPF routing domain.

7.  The OSPF BND TLV

   The OSPF BN Discovery TLV (BND TLV) contains a non-ordered set of
   sub-TLVs.

   The format of the OSPF BND TLV and its sub-TLVs is identical to the
   TLV format used by the Traffic Engineering Extensions to OSPF
   [RFC3630].  That is, the TLV is composed of 2 octets for the type, 2
   octets specifying the TLV length, and a value field.  The Length
   field defines the length of the value portion in octets.

   The OSPF BND TLV has the following format:




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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                            sub-TLVs                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type:     To be assigned by IANA (suggested value 8)
      Length:   Variable
      Value:    This comprises of following sub-TLVs

      Two sub-TLVs are defined:
            Sub-TLV type  Length            Name
                  1      variable     BN-ADDRESS sub-TLV
                  2         4         BN-DOMAIN sub-TLV

   The BN-ADDRESS and BN-DOMAIN sub-TLVs MUST always be present within
   the BND TLV.

   Malformed BND TLVs or sub-TLVs not explicitly described in this
   document MUST cause the LSA to be treated as malformed according to
   the normal procedures of OSPF.

   Any unrecognized sub-TLV MUST be silently ignored.

   The BND TLV is carried within an OSPF Router Information LSA defined
   in [RFC4970].

   The following sub-sections describe the sub-TLVs which are carried
   within the BND TLV.

7.1.  BN-ADDRESS Sub-TLV

   The BN-ADDRESS sub-TLV specifies an IP address that can be used to
   reach the BN.  It is RECOMMENDED to make use of an address that is
   always reachable, provided that the BN is alive and reachable.

   The BN-ADDRESS sub-TLV is mandatory; it MUST be present within the
   BND TLV.  It MAY appear twice, when the BN has both an IPv4 and IPv6
   address.  It MUST NOT appear more than once for the same address
   type.  If it appears more than once for the same address type, only
   the first occurrence is processed and any others MUST be ignored.

   The format of the BN-ADDRESS sub-TLV is as follows:




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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Type = 1           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          address-type         |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                       BN IP Address                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        BN-ADDRESS sub-TLV format

      Type:     1
      Length:   8 (IPv4) or 20 (IPv6)

      Address-type:
                    1   IPv4
                    2   IPv6

   Reserved: SHOULD be set to zero on transmission and MUST be ignored
   on receipt.

   BN IP Address: The IP address to be used to reach the BN.

7.2.  BN-DOMAIN Sub-TLV

   The BN-DOMAIN sub-TLV specifies a BN-Domain (area or AS) where the BN
   has topology connectivity.

   The BN-DOMAIN sub-TLV is mandatory; it MUST be present within the BND
   TLV.

   A BND TLV MUST include two or more BN-DOMAIN sub-TLVs as the BN has
   connectivity into multiple BN-Domains.

   The BN-DOMAIN sub-TLV has the following format:













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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type = 2            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Domain-type          |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Domain ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        BN-DOMAIN sub-TLV format

       Type:     2
       Length:   8

       Two domain-type values are defined:
                     1   OSPF Area ID
                     2   AS Number

   Domain ID: With the domain-type set to 1, this indicates the 32-bit
   Area ID of an area where the BN (ABR) has connectivity.  With domain-
   type set to 2, this indicates an AS number of an AS where the BN
   (ASBR) has connectivity.  When the AS number is coded in two octets,
   the AS Number field MUST have its first two octets set to 0.

8.  Elements of Procedure

   The BND TLV is advertised within OSPFv2 Router Information LSAs
   (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information
   LSAs (function code of 12), which are defined in [RFC4970].  As such,
   elements of procedure are inherited from those defined in [RFC4970].

   In OSPFv2, the flooding scope is controlled by the opaque LSA type(as
   defined in [RFC5250]) and in OSPFv3, by the S1/S2 bits (as defined in
   [RFC5340]).  If the flooding scope is area local, then the BND TLV
   MUST be carried within an OSPFv2 type 10 router information LSA or an
   OSPFV3 Router Information LSA with the S1 bit set and the S2 bit
   clear.  If the flooding scope is the entire IGP domain, then the BND
   TLV MUST be carried within an OSPFv2 type 11 Router Information LSA
   or OSPFv3 Router Information LSA with the S1 bit clear and the S2 bit
   set.

   When the BN function is deactivated, the OSPF speaker MUST originate
   a new Router Information LSA that no longer includes the
   corresponding BND TLV, provided there are other TLVs in the LSA.  If
   there are no other TLVs in the LSA, it MUST either send an empty
   Router Information LSA or purge it by prematurely aging it.




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   The BN address (i.e., the address indicated within the BN-ADDRESS
   sub-TLV) SHOULD be reachable via some prefixes advertised by OSPF.

   The BND TLV information regarding a specific BN is only considered
   current and useable when the router advertising this information is
   itself reachable via OSPF calculated paths in the same area of the
   LSA in which the BND TLV appears.

   A change in the state of a BN (activate, deactivate, domain change)
   MUST result in a corresponding change in the BND TLV information
   advertised by an OSPF router (inserted, removed, updated)in its LSA.
   The way BNs determine the information they advertise, and how that
   information is made available to OSPF, is out of the scope of this
   document.  Some information may be configured and other information
   may be automatically determined by the OSPF.

   A change in information in the BND TLV MUST NOT trigger any SPF
   computation at a receiving router.

9.  Backward Compatibility

   The BND TLV defined in this document does not introduce any
   interoperability issues.

   A router not supporting the BND TLV will just silently ignore the TLV
   as specified in [RFC4970].

10.  Impact on Network

   The routers acting as BNs will originate Opaque LSA with BND Tlv; As
   there are only few BNs exist in the network, the performance impact
   in flooding is very less.

11.  IANA Considerations

11.1.  OSPF TLV

   IANA has defined a registry for TLVs carried in the Router
   Information LSA defined in [RFC4970].  A number of IANA
   considerations have been highlighted in previous sections of this
   document.  IANA is requested to make the following allocations.

   Value      TLV Name                      Reference
   -----     --------                       ----------
   To be        BND                        (this document)
   assigned
   by IANA




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12.  Security Considerations

   This document defines OSPF extensions for BN discovery within an
   administrative domain.  Hence the security of the BN discovery relies
   on the security of OSPF.

   Mechanisms defined to ensure authenticity and integrity of OSPF LSAs
   [RFC2154], and their TLVs, can be used to secure the BN Discovery
   information as well.

   OSPF provides no encryption mechanism for protecting the privacy of
   LSAs and, in particular, the privacy of the BN discovery information.

13.  Manageability Considerations

   TBD

14.  Acknowledgments

   We would like to thank Quintin Zhao, Daniel King, Adrian Ferral,
   Suresh babu, Pradeep Shastry, Saravana Kumar, Srinivasan and
   Venugopal Reddy for their useful comments and suggestions.

15.  References

15.1.  Normative References

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

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

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

   [RFC4970]  Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
              Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, July 2007.

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

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.







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15.2.  Informative References

   [RFC3509]  Zinin, A., Lindem, A., and D. Yeung, "Alternative
              Implementations of OSPF Area Border Routers", RFC 3509,
              April 2003.

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

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, January 2009.

   [RFC5441]  Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
              Backward-Recursive PCE-Based Computation (BRPC) Procedure
              to Compute Shortest Constrained Inter-Domain Traffic
              Engineering Label Switched Paths", RFC 5441, April 2009.

   [RFC6805]  King, D. and A. Farrel, "The Application of the Path
              Computation Element Architecture to the Determination of a
              Sequence of Domains in MPLS and GMPLS", RFC 6805, November
              2012.

   [DOMAIN-SEQ]
              Dhody, D., Palle, U., and R. Casellas, "Standard
              Representation Of Domain Sequence (draft-ietf-pce-pcep-
              domain-sequence-05)", July 2014.

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies India Pvt Ltd
   Leela Palace
   Bangalore, Karnataka  560008
   India

   EMail: dhruv.ietf@gmail.com










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   Udayasree Palle
   Huawei Technologies India Pvt Ltd
   Leela Palace
   Bangalore, Karnataka  560008
   India

   EMail: udayasree.palle@huawei.com












































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