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Versions: (draft-chen-ospf-ttz) 00 01 02 03 04 05 06 RFC 8099

Internet Engineering Task Force                                  H. Chen
Internet-Draft                                                     R. Li
Intended status: Experimental                        Huawei Technologies
Expires: September 11, 2016                                    A. Retana
                                                                 Y. Yang
                                                     Cisco Systems, Inc.
                                                                  V. Liu
                                                            China Mobile
                                                                  M. Toy
                                                                 Comcast
                                                          March 10, 2016


                     OSPF Topology-Transparent Zone
                       draft-ietf-ospf-ttz-03.txt

Abstract

   This document presents a topology-transparent zone in an OSPF area.
   A topology-transparent zone comprises a group of routers and a number
   of links connecting these routers.  Any router outside of the zone is
   not aware of the zone.  The information about the links and routers
   such as a link down inside the zone is not advertised to any router
   outside of the zone.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 11, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   Provisions Relating to IETF Documents
   (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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  5
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Topology-Transparent Zone  . . . . . . . . . . . . . . . . . .  5
     5.1.  Overview of Topology-Transparent Zone  . . . . . . . . . .  5
     5.2.  Some Details on TTZ  . . . . . . . . . . . . . . . . . . .  6
   6.  Extensions to OSPF Protocols . . . . . . . . . . . . . . . . .  7
     6.1.  General Format of TTZ LSA  . . . . . . . . . . . . . . . .  8
     6.2.  TTZ ID TLV . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.3.  TTZ Router TLV . . . . . . . . . . . . . . . . . . . . . .  9
     6.4.  TTZ Options TLV  . . . . . . . . . . . . . . . . . . . . . 10
     6.5.  Link Scope TTZ LSA . . . . . . . . . . . . . . . . . . . . 11
   7.  Constructing LSAs for TTZ  . . . . . . . . . . . . . . . . . . 11
   8.  Establishing Adjacencies . . . . . . . . . . . . . . . . . . . 13
     8.1.  Discover TTZ Neighbors . . . . . . . . . . . . . . . . . . 13
     8.2.  Adjacency between TTZ Edge and TTZ External Router . . . . 14
   9.  Advertisement of LSAs  . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Advertisement of LSAs within TTZ . . . . . . . . . . . . . 15
     9.2.  Advertisement of LSAs through TTZ  . . . . . . . . . . . . 15
   10. Computation of Routing Table . . . . . . . . . . . . . . . . . 15
   11. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Configuring TTZ  . . . . . . . . . . . . . . . . . . . . . 16
     11.2. Smooth Migration to TTZ  . . . . . . . . . . . . . . . . . 16
     11.3. Adding a Router into TTZ . . . . . . . . . . . . . . . . . 18
   12. Prototype Implementation . . . . . . . . . . . . . . . . . . . 18
     12.1. What are Implemented and Tested  . . . . . . . . . . . . . 18
     12.2. Implementation Experience  . . . . . . . . . . . . . . . . 20
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   14. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   15. Contributors and Other Authors . . . . . . . . . . . . . . . . 21
   16. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 22
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     17.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Constants for LSA Advertisement . . . . . . . . . . . 23



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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23


















































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1.  Introduction

   The number of routers in a network becomes larger and larger as the
   network expands.  For scalability and manageability, the network is
   reorganized into more areas when it becomes too big.  However, this
   causes a number of issues.

   At first, reorganizing a network from one area into multiple areas or
   from a number of existing areas into even more areas is a very
   challenging and time consuming task since it involves significant
   network architecture changes.  Considering the one area case,
   originally the network has only one area, which is the backbone.
   This original backbone area will be reorganized into a new backbone
   and a number of non-backbone areas.  In general, each of the non-
   backbone areas is connected to the new backbone area through the Area
   Border Routers (ABRs) between the non-backbone and the backbone area
   (refer to RFC 2328 section 3).

   Secondly, the services carried by the network may be interrupted
   while the network is being reorganized from one area into multiple
   areas or from a number of existing areas into even more areas since
   every OSPF interface with an area change is going down with its old
   area and then up with a new area.

   This document presents a topology-transparent zone (TTZ) in an OSPF
   area and describes extensions to OSPF for supporting the topology-
   transparent zone, which is scalable and resolves the issues above.


2.  Terminology

   TTZ internal link: a link between two TTZ adjacent routers in the
   same TTZ.  A TTZ internal link is called a TTZ link in general.

   TTZ internal router: a router in a TTZ whose adjacent routers are all
   in the same TTZ.

   TTZ external router: a router outside of a TTZ without any TTZ
   internal link.

   TTZ external link: a link between a TTZ edge router and a TTZ
   external router.

   TTZ edge router: a router in a TTZ that has one (or more) adjacent
   routers which belong to the same TTZ, and one (or more) adjacent
   routers which do not belong to the TTZ.

   TTZ router: a router in a TTZ, i.e., a TTZ internal router or a TTZ



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   edge router.


3.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.


4.  Requirements

   Topology-Transparent Zone may be deployed to resolve some critical
   issues in existing networks and future networks.  The requirements
   for TTZ are listed as follows:

   o  Routers outside a TTZ MUST NOT require any changes to operate with
      the TTZ.

   o  A TTZ MUST be enclosed in a single area.

   o  A TTZ MUST hide the topology of the TTZ from any router outside of
      the TTZ.


5.  Topology-Transparent Zone

5.1.  Overview of Topology-Transparent Zone

   A Topology-Transparent Zone is identified by an Identifier (ID), and
   it consists of a group of routers and a number of links connecting
   the routers.  A TTZ MUST be contained within an OSPF area.

   The ID of a TTZ or TTZ ID is a 32-bit number that is unique for
   identifying a TTZ.  The ID SHOULD NOT be 0.

   In addition to having the functions of an OSPF area, an OSPF TTZ
   makes some improvements on an OSPF area, which include:

   o  An OSPF TTZ is virtualized as the TTZ edges connected each other.

   o  An OSPF TTZ receives the link state information about the topology
      outside of the TTZ, stores the information in the TTZ and floods
      the information through the TTZ to the routers outside of the TTZ.







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5.2.  Some Details on TTZ

   The figure below shows an area containing a TTZ: TTZ 600.

                 TTZ 600                       ---- TTZ Internal Link
                   \                           ==== Normal Link
     Area X         \ ^~^~^~^~^~^~^~^~^~^~^~^~
                     (                        )
    ===[R15]========(==[T61]----[T81]---[T63]==)======[R29]===
        ||         (   |    \          /    |   )       ||
        ||         (   |     \        /     |   )       ||
        ||         ( [T75]    \      /      |   )       ||
        ||         (   |    ___\    /       |   )       ||
        ||         (   |   /   [T71]     [T79]  )       ||
        ||         (   | [T73] /    \       |   )       ||
        ||         (   |      /      \      |   )       ||
        ||         (   |     /        \     |   )       ||
        ||         (   |    /          \    |   )       ||
    ===[R17]========(==[T65]---[T77]----[T67]==)======[R31]===
         \\          (//                    \\)       //
          ||         //v~v~v~v~v~v~v~v~v~v~v~\\      ||
          ||        //                        \\     ||
          ||       //                          \\    ||
           \\     //                            \\  //
       ======[R23]==============================[R25]=====
             //                                     \\
            //                                       \\


   All the routers in the figure are in area X. Routers with T (i.e.,
   T61, T63, T65, T67, T71, T73, T75, T77, T79 and T81) are also in TTZ
   600, which contains the TTZ internal links connecting them.  To
   create a TTZ, we need configure it (refer to section 11).

   There are two types of routers in a TTZ: TTZ internal and TTZ edge
   routers.  TTZ 600 has four TTZ edge routers T61, T63, T65 and T67.
   Each of them has at least one adjacent router in TTZ 600 and one
   adjacent router outside of TTZ 600.  For instance, router T61 is a
   TTZ edge router since it has an adjacent router R15 outside of TTZ
   600 and three adjacent routers T75, T71 and T81 in TTZ 600.

   In addition, TTZ 600 comprises six TTZ internal routers T71, T73,
   T75, T77, T79 and T81.  Each of them has all its adjacent routers in
   TTZ 600.  For instance, router T71 is a TTZ internal router since its
   adjacent routers T61, T63, T65, T67 and T73 are all in TTZ 600.  Note
   that none of the TTZ internal routers can be an ABR.

   A TTZ hides the internal topology of the TTZ from the outside.  It



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   does not directly advertise any internal information about the TTZ to
   a router outside of the TTZ.

   For instance, TTZ 600 does not send the information about TTZ
   internal router T71 to any router outside of TTZ 600; it does not
   send the information about the link between TTZ router T61 and T71 to
   any router outside of TTZ 600.

   The figure below illustrates area X from the point of view on a
   router outside of TTZ 600 after TTZ 600 is created.

     Area X                                    ==== Normal Link

    ===[R15]===========[T61]=========[T63]=========[R29]===
        ||             ||  \\      //   ||           ||
        ||             ||   \\    //    ||           ||
        ||             ||    \\  //     ||           ||
        ||             ||     \\//      ||           ||
        ||             ||      //\      ||           ||
        ||             ||     // \\     ||           ||
        ||             ||    //   \\    ||           ||
        ||             ||   //     \\   ||           ||
        ||             ||  //       \\  ||           ||
    ===[R17]===========[T65]=========[T67]=========[R31]===
         \\           //                  \\        //
          ||         //                    \\      ||
          ||        //                      \\     ||
          ||       //                        \\    ||
           \\     //                          \\  //
       ======[R23]============================[R25]=====
             //                                   \\
            //                                     \\


   From a router outside of the TTZ, a TTZ is seen as the TTZ edge
   routers connected each other.  For instance, router R15 sees that
   T61, T63, T65 and T67 are connected each other.

   In addition, a router outside of the TTZ sees TTZ edge routers having
   normal connections to the routers outside of the TTZ.  For example,
   router R15 sees that T61, T63, T65 and T67 have the normal
   connections to R15, R29, R17 and R23, R25 and R31 respectively.


6.  Extensions to OSPF Protocols

   The link state information about a TTZ includes router LSAs, which
   can be contained and advertised in opaque LSAs [RFC5250] within the



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   TTZ.  Some control information regarding a TTZ can also be contained
   and advertised in opaque LSAs within the TTZ.  These opaque LSAs are
   called TTZ opaque LSAs or TTZ LSAs for short.

6.1.  General Format of TTZ LSA

   The following is the general format of a TTZ LSA.  It has an LS Type
   = 10/9 and TTZ-LSA-Type, and contains a number of TLVs.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            LS age             |     Options   | LS Type = 10/9|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |TTZ-LSA-Type(9)|                    Instance ID                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Advertising Router                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      LS Sequence Number                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         LS checksum           |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                              TLVs                             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where TTZ-LSA-Type is 9, the exact number is to be assigned by IANA.

   There are three top-level TLVs defined: TTZ ID TLV, TTZ Router TLV,
   and TTZ Options TLV.  A TTZ LSA of LS Type 10 contains a mandatory
   TTZ ID TLV, which is followed by a number of other top-level TLVs.

   A TTZ LSA having a optional TTZ Router TLV is called a TTZ Router
   LSA.  A TTZ LSA containing a TTZ Options TLV is called a TTZ Control
   LSA.

6.2.  TTZ ID TLV

   A TTZ ID TLV has the following format.  It contains a TTZ ID and some
   flags.










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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     TTZ-ID-TLV-Type (1)       |          TLV-Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            TTZ ID                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Reserved (MUST be zero)                   |E|Z|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      E = 1: Indicating a router is a TTZ Edge router
      Z = 1: Indicating a router has migrated to TTZ


   When a TTZ router originates a TTZ LSA containing a TTZ ID TLV, it
   sets flag E to 1 in the TTZ ID TLV if it is a TTZ edge router, and to
   0 if it is a TTZ internal router.  It sets flag Z to 1 after it has
   migrated to TTZ.

6.3.  TTZ Router TLV

   The format of a TTZ Router TLV is as follows.  It contains the
   contents of a router 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     TTZ-RT-TLV-Type (2)       |          TLV-Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     0   |V|E|B|        0      |            # links            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Link ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Link Data                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     # TOS     |            metric             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                              ...                              ~


   For a router link, the existing eight bit Type field for a router
   link is split into two fields as follows:










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         0   1   2   3   4   5   6   7
       +---+---+---+---+---+---+---+---+
       | I |         Type-1            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       I bit flag:
         1: Router link is a TTZ internal link.
         0: Router link is a TTZ external link.
       Type-1: The kind of the link. The values for Type-1 are the same
               as those for Type defined in RFC 2328 section 12.4.1.


6.4.  TTZ Options TLV

   The format of a TTZ Options TLV is as follows.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     TTZ-OP-TLV-Type (3)       |          TLV-Length           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |T|M|N|R|               Reserved (MUST be zero)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      T = 1: Advertising TTZ Topology Information for Migration
      M = 1: Migrating to TTZ
      N = 1: Advertising Normal Topology Information for Rollback
      R = 1: Rolling back from TTZ


   Flags T, M, N and R are exclusive.  When one of them is set to 1, the
   others MUST be set to 0.

   After a user configures a TTZ router to advertise TTZ topology
   information, the TTZ router originates a TTZ Control LSA having a TTZ
   Options TLV with flag T set to 1.  It also originates its TTZ router
   LSA.  When another TTZ router receives the LSA with T = 1, it
   originates its TTZ router LSA as needed.

   After a user configures a TTZ router to migrate to TTZ, the TTZ
   router originates a TTZ Control LSA having a TTZ Options TLV with
   flag M set to 1 and migrates to TTZ.  When another TTZ router
   receives the LSA with M = 1, it also migrates to TTZ.

   After a user configures a TTZ router to advertise normal topology
   information, the TTZ router originates a TTZ Control LSA having a TTZ
   Options TLV with flag N set to 1.  It also advertises its normal LSAs
   such as its normal router LSA and stops advertising its other TTZ
   LSAs.  When another TTZ router receives the LSA with N = 1, it
   advertises its normal LSAs and stops advertising its TTZ LSAs.



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   After a user configures a TTZ router to roll back from TTZ, the TTZ
   router originates a TTZ Control LSA having a TTZ Options TLV with
   flag R set to 1 and rolls back from TTZ.  When another TTZ router
   receives the LSA with R = 1, it also rolls back from TTZ.

   After a TTZ router originates a TTZ control LSA in response to a
   configuration described above to control TTZ, it updates the TTZ
   control LSA accordingly if another configuration to control TTZ is
   issued on it.

6.5.  Link Scope TTZ LSA

   A TTZ LSA of LS Type 9 has the following format.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            LS age             |     Options   | LS Type = 9   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |TTZ-LSA-Type(9)|                   Instance ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Advertising Router                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      LS Sequence Number                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         LS checksum           |           Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                           TTZ ID TLV                          ~
      +---------------------------------------------------------------+
      |                                                               |
      ~                          (Options TLV)                        ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   It contains a mandatory TTZ ID TLV, which may be followed by a
   optional Options TLV.  It is used to discover a TTZ neighbor.


7.  Constructing LSAs for TTZ

   The LSAs for representing a TTZ include TTZ router LSAs and normal
   router LSAs for virtualizing the TTZ.

   A TTZ router LSA generated by a TTZ edge router has a TTZ ID TLV and
   a TTZ Router TLV.  The former includes the ID of the TTZ to which the
   router belongs and flag E set to 1, which indicates the originator of
   the LSA is a TTZ Edge router.  The latter contains the links attached



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   to the router.

   A TTZ router LSA generated by a TTZ internal router has a TTZ ID TLV
   containing the ID of the TTZ to which the router belongs and flag E
   set to 0, which indicates the originator of the LSA is a TTZ internal
   router.  The TTZ internal router generates the TTZ router LSA with
   just the TTZ ID TLV and its normal router LSA.

   After receiving a trigger to migrate to TTZ such as a TTZ LSA with
   flag M = 1, a TTZ edge router originates its normal router LSA for
   virtualizing a TTZ, which comprises three groups of links in general.

   The first group are the router links connecting the TTZ external
   routers.  These router links are normal router links.  There is a
   router link for every adjacency between this TTZ edge router and a
   TTZ external router.

   The second group are the "virtual" router links connecting to the
   other TTZ edge routers.  For each of the other TTZ edge routers,
   there is a corresponding point-to-point router link to it from this
   TTZ edge router.  The cost of the link is the cost of the shortest
   path from this TTZ edge router to the other TTZ edge router within
   the TTZ.

   In addition, the LSA may contain a third group of links, which are
   the stub links for the loopback addresses inside the TTZ to be
   accessed by nodes outside of the TTZ.

   To migrate to a TTZ smoothly, a TTZ edge router virtualizes the TTZ
   in two steps.  At first, the router updates its normal router LSA by
   adding a point-to-point link to each of the other edge routers of the
   TTZ and a stub link for each of the loopback addresses in the TTZ to
   be accessed outside of the TTZ into the LSA.  And then it removes the
   links configured as TTZ links from its updated router LSA after
   sending its updated router LSA and receiving the updated router LSAs
   originated by the other TTZ edge routers for MaxLSAAdvTime or after
   sending its updated router LSA for MaxLSAGenAdvTime (refer to
   Appendix A).

   To roll back from a TTZ smoothly after receiving a trigger to roll
   back from TTZ, a TTZ edge router updates its normal router LSA in the
   above two steps in a reverse way.  At first, it updates its normal
   router LSA by adding the normal links for the links configured as TTZ
   links into the LSA.  And then it removes the point-to-point links to
   the other edge routers of the TTZ for virtualizing the TTZ and the
   stub links for the loopback addresses from its updated router LSA
   after sending its updated router LSA and receiving the updated router
   LSAs originated by the other TTZ edge routers for MaxLSAAdvTime or



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   after sending its updated router LSA for MaxLSAGenAdvTime.


8.  Establishing Adjacencies

   This section describes the adjacencies in different cases.

8.1.  Discover TTZ Neighbors

   For two routers A and B connected by a P2P link and having a normal
   adjacency, they discover TTZ each other through a TTZ LSA of LS Type
   9 with a TTZ ID TLV.  We call this LSA D-LSA for short.

   If two ends of the link have different TTZ IDs, no TTZ adjacency over
   the link will be "formed".

   If two ends of the link have the same TTZ ID and Z flag value, A and
   B are TTZ neighbors.  The following is a sequence of events related
   to TTZ for this case.

              A                                   B
       Configure TTZ                             Configure TTZ
                           D-LSA (TTZ-ID=100)
                         ----------------------> Same TTZ ID and Z
                                                 A is B's TTZ Neighbor
                            D-LSA (TTZ-ID=100)
       Same TTZ ID and Z <----------------------
       B is A's TTZ Neighbor


   A sends B a D-LSA with TTZ-ID after the TTZ is configured on it.  B
   sends A a D-LSA with TTZ-ID after the TTZ is configured on it.

   When A receives the D-LSA from B and determines they have the same
   TTZ ID and Z flag value, B is A's TTZ neighbor.  A also sends B all
   the TTZ LSAs it has and originates its TTZ router LSA if (Z==0 and
   there is a TTZ LSA with T=1) OR Z==1.

   B is symmetric to A and acts similarly to A.

   If two ends of the link have the same TTZ ID but Z flags are
   different, a TTZ adjacency over the link is "formed" in the following
   steps.  Suppose that A has migrated to TTZ and B has not (i.e., flag
   Z in A's D-LSA is 1 and flag Z in B's D-LSA is 0).

   When A receives the D-LSA from B and determines they have the same
   TTZ ID but its Z=1 and B's Z=0, A sends B all the TTZ LSAs it has and
   triggers B to migrate to TTZ.  A updates and sends B its D-LSA by



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   adding an Options TLV with M=1 after sending B all the TTZ LSAs.

   When B receives the D-LSA from A and determines they have the same
   TTZ ID but its Z=0 and A's Z=1, B sends A all the TTZ LSAs it has and
   starts to migrate to TTZ after receiving A's D-LSA with M=1.  After
   migration to TTZ, B updates and advertises its LSAs as needed.

   After receiving B's D-LSA with Z=1, A updates and sends B its D-LSA
   by removing the Options TLV.  It also updates and advertises its LSAs
   as needed.

   For a number of routers connected through a broadcast link and having
   normal adjacencies among them, they also discover TTZ each other
   through D-LSAs.  The DR for the link "forms" TTZ adjacencies with the
   other routers if all the routers attached to the link have the same
   TTZ ID configured on the connections to the link.  Otherwise, the DR
   does not "form" any TTZ adjacency with any router attached to the
   link.

   For a number of routers connected through a broadcast link and having
   TTZ adjacencies among them, if a mis-configured router is introduced
   on the broadcast link, the DR for the link will not "form" any TTZ
   adjacency with this mis-configured router.

   For routers connected via a link without any adjacency among them,
   they discover TTZ each other through D-LSAs in the same way as
   described above after they form a normal adjacency.

8.2.  Adjacency between TTZ Edge and TTZ External Router

   A TTZ edge router forms an adjacency with any TTZ external router to
   which it is connected.

   When the TTZ edge router synchronizes its link state database with
   the TTZ external router, it sends the TTZ external router the
   information about all the LSAs except for the LSAs belonging to the
   TTZ that are hidden from any router outside of the TTZ.

   At the end of the link state database synchronization, the TTZ edge
   router originates its own router LSA for virtualizing the TTZ and
   sends this LSA to its adjacent routers including the TTZ external
   router.


9.  Advertisement of LSAs

   LSAs can be divided into a couple of classes according to their
   Advertisements.  The first class of LSAs is advertised within a TTZ.



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   The second is advertised through a TTZ.

9.1.  Advertisement of LSAs within TTZ

   Any LSA about a link state in a TTZ is advertised within the TTZ.  It
   is not advertised to any router outside of the TTZ.  For example, a
   router LSA generated for a router in a TTZ is advertised within the
   TTZ.

   Any network LSA generated for a broadcast or NBMA network in a TTZ is
   advertised within the TTZ.

   Any opaque LSA generated for a TTZ internal TE link is advertised
   within the TTZ.

   After migrating to TTZ, every edge router of a TTZ MUST NOT advertise
   any LSA about a link state in the TTZ to any router outside of the
   TTZ.

   For any TTZ LSA originated by a router within the TTZ, every edge
   router of the TTZ MUST NOT advertise it to any router outside of the
   TTZ.

9.2.  Advertisement of LSAs through TTZ

   Any LSA about a link state outside of a TTZ received by an edge
   router of the TTZ is advertised using the TTZ as transit.  For
   example, when an edge router of a TTZ receives an LSA from a router
   outside of the TTZ, it floods it to its neighboring routers both
   inside the TTZ and outside of the TTZ.  This LSA may be any LSA such
   as a router LSA that is advertised within an OSPF area.

   The routers in the TTZ continue to flood the LSA.  When another edge
   router of the TTZ receives the LSA, it floods the LSA to its
   neighboring routers both outside of the TTZ and inside the TTZ.


10.  Computation of Routing Table

   After a router migrates to TTZ, the computation of the routing table
   on the router is the same as that described in RFC 2328 section 16
   with one exception.  The router in a TTZ ignores the router LSAs
   generated by the TTZ edge routers for virtualizing the TTZ.  This can
   be achieved by adding a flag into every link stored in LSDB and
   setting this flag to 1 in every link in these router LSAs, which
   indicates that the link is unusable.  It computes routes within the
   TTZ topology and the topology outside of the TTZ without using any
   unusable links.



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11.  Operations

11.1.  Configuring TTZ

   This section proposes some options for configuring a TTZ.

   1.  Configuring TTZ on Every Link in TTZ

   If every link in a TTZ is configured with a same TTZ ID as a TTZ
   link, the TTZ is determined.  A router with some TTZ links and some
   normal links is a TTZ edge router.  A router with only TTZ links is a
   TTZ internal router.

   2.  Configuring TTZ on Every Router in TTZ

   A same TTZ ID is configured on every router in a TTZ, and on every
   TTZ edge router's links connecting to the routers in the TTZ.

   A router configured with the TTZ ID on some of its links is a TTZ
   edge router.  A router configured with the TTZ ID only is a TTZ
   internal router.  All the links on a TTZ internal router are TTZ
   links.  This option is simpler than the above one.

11.2.  Smooth Migration to TTZ

   For a group of routers and a number of links connecting the routers
   in an area, making them transfer to work as a TTZ without any service
   interruption takes a few of steps or stages.

   At first, a user configures the TTZ feature on every router in the
   TTZ.  In this stage, a router does not originate its TTZ router LSA.
   It will discover its TTZ neighbors.

   Secondly, after configuring the TTZ, a user issues a CLI command on
   one router in the TTZ, which triggers every router in the TTZ to
   generate and advertise TTZ information among the routers in the TTZ.
   When the router receives the command, it originates a TTZ control LSA
   with T=1 (indicating TTZ information generation and advertisement for
   migration).  It also originates its TTZ router LSA, and advertises
   the LSA to its TTZ neighbors.  When another router in the TTZ
   receives the LSA with T=1, it originates its TTZ router LSA.  In this
   stage, every router in the TTZ has dual roles.  One is to function as
   a normal router.  The other is to generate and advertise TTZ
   information.

   Thirdly, a user checks whether a router in the TTZ is ready for
   migration to TTZ.  A router in the TTZ is ready after it has received
   all the necessary information from all the routers in the TTZ.  This



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   information may be displayed on a router through a CLI command.

   And then a user activates the TTZ through using a CLI command such as
   migrate to TTZ on one router in the TTZ.  The router migrates to TTZ,
   generates and advertises a TTZ control LSA with M = 1 (indicating
   Migrating to TTZ) after it receives the command.  After another
   router in the TTZ receives the TTZ control LSA with M = 1, it also
   migrates to TTZ.  Thus, activating the TTZ on one TTZ router
   propagates to every router in the TTZ, which migrates to TTZ.

   For an edge router of the TTZ, migrating to work as a TTZ router
   comprises generating a router LSA to virtualize the TTZ and flooding
   this LSA to all its neighboring routers in two steps as described in
   section 7.

   In normal operations for migration to TTZ and rollback from TTZ, a
   user issues a series of commands according to certain procedures.  In
   an abnormal case, for example two conflicting commands are issued on
   two TTZ routers in a TTZ at the same time, a TTZ router issues an
   error and logs the error when it detects a conflict.

   A conflicting command may be detected on a router on which the
   command is issued.  Thus some abnormal cases may be prevented.  When
   a command for migration/rollback is issued on a router, the router
   checks whether it is in a correct sequence of commands for migration/
   rollback through using the information it has.  For migrating a part
   of an area to a TTZ, the correct sequence of commands is as follows
   in general:

   1) configure TTZ on every router in the part of the area to be
      migrated to TTZ;

   2) configure on one router in the TTZ to trigger every router in the
      TTZ to generate and advertise TTZ information for migration; and

   3) configure on one router in the TTZ to trigger every router in the
      TTZ to migrate to TTZ.

   For rolling back from TTZ, it is similar.

   After receiving a command on a router to migrate to TTZ, which is for
   3), the router checks whether 2) is performed through checking if it
   has received/originated TTZ LSAs.  If it has not, it issues an error
   to an operator (generation and advertisement of TTZ information for
   migration to TTZ is not done yet) and rejects the command at this
   time.

   After a router receives a TTZ LSA with M=1 for 3) from another



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   router, it checks whether 2) is performed through checking if it has
   received/originated TTZ LSAs.  If it has not, it issues an error and
   logs the error.  The operation for migration will continue.

   After receiving a command on a router to generate and advertise TTZ
   information, which is for 2), the router checks whether 1) is
   performed through checking if TTZ is configured on it.  If it is not,
   it issues an error to an operator (TTZ is not configured on it yet)
   and rejects the command at this time.

11.3.  Adding a Router into TTZ

   When a non TTZ router (say R1) is connected via a P2P link to a TTZ
   router (say T1) working as TTZ and there is a normal adjacency
   between them over the link, a user can configure TTZ on two ends of
   the link to add R1 into the TTZ to which T1 belongs.  They discover
   TTZ each other with the TTZ as described in section 8.

   When a number of non TTZ routers are connected via a broadcast link
   to a TTZ router (say T1) working as TTZ and there are normal
   adjacencies among them, a user configures TTZ on the connection to
   the link on every router to add the non TTZ routers into the TTZ to
   which T1 belongs.  The DR for the link "forms" TTZ adjacencies with
   the other routers connected to the link if they all have the same TTZ
   ID configured for the link.  This is determined through the discovery
   process described in section 8.

   When a router (say R1) is connected via a P2P link to a TTZ router
   (say T1) and there is not any adjacency between them over the link, a
   user can configure TTZ on two ends of the link to add R1 into the TTZ
   to which T1 belongs.  R1 and T1 will form an adjacency in the same
   way as described in section 8.


12.  Prototype Implementation

12.1.  What are Implemented and Tested

   1.  CLI Commands for TTZ

   The CLIs implemented and tested include:

    o the CLIs of the simpler option for configuring TTZ, and

    o the CLIs for controlling migration to TTZ.

   2.  Extensions to OSPF Protocols for TTZ




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   All the extensions defined in section "Extensions to OSPF Protocols"
   are implemented and tested except for rolling back from TTZ.  The
   testing results illustrate:

    o A TTZ is virtualized to outside as its edge routers connected each
      other.  Any router outside of the TTZ sees the edge routers (as
      normal routers) connecting each other and to some other routers.

    o The link state information about the routers and links inside the
      TTZ is contained within the TTZ.  It is not advertised to any
      router outside of the TTZ.

    o TTZ is transparent.  From a router inside a TTZ, it sees the
      topology (link state) outside of the TTZ.  From a router outside
      of the TTZ, it sees the topology beyond the TTZ.  The link state
      information outside of the TTZ is advertised through the TTZ.

    o TTZ is backward compatible.  Any router outside of a TTZ does not
      need to support or know TTZ.

   3.  Smooth Migration to TTZ

   The procedures and related protocol extensions for smooth migration
   to TTZ are implemented and tested.  The testing results show:

    o A part of an OSPF area is smoothly migrated to a TTZ without any
      routing disruptions.  The routes on every router are stable while
      the part of the area is being migrated to the TTZ.

    o Migration to TTZ is very easy to operate.

   4.  Add a Router to TTZ

   Adding a router into TTZ is implemented and tested.  The testing
   results illustrate:

    o A router can be easily added into a TTZ and becomes a TTZ router.

    o The router added into the TTZ is not seen on any router outside of
      the TTZ, but it is a part of the TTZ.

   5.  Leak TTZ Loopbacks Outside

   Leaking loopback addresses in a TTZ to routers outside of the TTZ is
   implemented and tested.  The testing results illustrate:






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    o The loopback addresses inside the TTZ are advertised to the
      routers outside of the TTZ.

    o The loopback addresses are accessible from a router outside of the
      TTZ.

12.2.  Implementation Experience

   The implementation of TTZ is relatively easy compared to other
   features of OSPF.  Re-using the existing OSPF code along with
   additional simple logic does the work.  A couple of engineers started
   to work on implementing the TTZ from the middle of June, 2014 and
   finished coding it just before IETF 90.  After some testing and bug
   fixes, it works as expected.

   In our implementation, the link state information in a TTZ opaque LSA
   is stored in the same link state database as the link state
   information in a normal LSA.  For each TTZ link in the TTZ opaque
   LSA, there is an additional flag, which is used to differentiate
   between a TTZ link and a Normal link.

   Before migration to TTZ, every router in the TTZ computes its routing
   table using the normal links.  After migration to TTZ, every router
   in the TTZ computes its routing table using the TTZ links and normal
   links.  In the case where both the TTZ link and the normal link
   exist, the TTZ link is used.


13.  Security Considerations

   The mechanism described in this document does not raise any new
   security issues for the OSPF protocols since a TTZ is enclosed in a
   single area.


14.  IANA Considerations

   Under Registry Name: Opaque Link-State Advertisements (LSA) Option
   Types [RFC5250], IANA is requested to assign a new Opaque type
   registry value for Topology-Transparent Zone (TTZ) LSA as follows:

     +====================+===============+=======================+
     |  Registry Value    |  Opaque Type  |    reference          |
     +====================+===============+=======================+
     |      IANA TBD      |    TTZ LSA    |    This document      |
     |    (9 Suggested)   |               |                       |
     +--------------------+---------------+-----------------------+




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   IANA is requested to assign Types for new TLVs in the new TTZ LSA as
   follows:

      Type          Name                      Allowed in
       1        TTZ ID TLV              TTZ LSA of LS Type 10 and 9
       2        TTZ Router TLV          TTZ LSA of LS Type 10
       3        TTZ Options TLV         TTZ LSA of LS Type 10 and 9


15.  Contributors and Other Authors

   1.  Other Authors

        Gregory Cauchie
        FRANCE
        Email: greg.cauchie@gmail.com



        Anil Kumar S N
        Huawei Technologies
        Banglore
        India
        Email: anil.sn@huawei.com



        Ning So
        Tata Communications
        2613 Fairbourne Cir.
        Plano, TX  75082
        USA
        Email: ningso01@gmail.com



        Lei Liu
        Fujitsu
        USA
        Email: lliu@us.fujitsu.com


   2.  Contributors

        Veerendranatha Reddy Vallem
        Huawei Technologies
        Banglore
        India



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        Email: veerendranatharv@huawei.com



        William McCall
        Rightside Co.
        Kirkland, WA
        USA
        will.mccall@rightside.co



16.  Acknowledgement

   The authors would like to thank Acee Lindem, Abhay Roy, Dean Cheng,
   Russ White, Tony Przygienda, Wenhu Lu, Lin Han, Kiran Makhijani,
   Padmadevi Pillay Esnault and Yang Yu for their valuable comments on
   this draft.


17.  References

17.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/
              RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
              July 2008, <http://www.rfc-editor.org/info/rfc5250>.

17.2.  Informative References

   [RFC5441]  Vasseur, JP., Ed., 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,
              DOI 10.17487/RFC5441, April 2009,
              <http://www.rfc-editor.org/info/rfc5441>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,



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              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.


Appendix A.  Constants for LSA Advertisement

   MaxLSAAdvTime: The maximum time for an LSA to be advertised to all
   the routers in an area.  The value of MaxLSAAdvTime is set to 0.1
   second.

   MaxLSAGenAdvTime: The maximum time for all TTZ router LSAs to be
   generated by all TTZ edge routers and advertised to all the routers
   in an area after a first TTZ router LSA is generated.  The value of
   MaxLSAGenAdvTime is set to 0.3 second.


Authors' Addresses

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: huaimo.chen@huawei.com


   Renwei Li
   Huawei Technologies
   2330 Central expressway
   Santa Clara, CA
   USA

   Email: renwei.li@huawei.com


   Alvaro Retana
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Raleigh, NC  27709
   USA

   Email: aretana@cisco.com









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   Yi Yang
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Raleigh, NC  27709
   USA

   Email: yiya@cisco.com


   Vic Liu
   China Mobile
   No.32 Xuanwumen West Street, Xicheng District
   Beijing,   100053
   China

   Email: liuzhiheng@chinamobile.com


   Mehmet Toy
   Comcast
   1800 Bishops Gate Blvd.
   Mount Laurel, NJ  08054
   USA

   Email: mehmet_toy@cable.comcast.com


























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