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Versions: 00 01

BESS Working Group                                              J. Drake
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                               A. Farrel
Expires: November 11, 2019                            Old Dog Consulting
                                                            May 10, 2019


    BGP-LS Maps : A Framework for Network Slicing and Enhanced VPNs
                    draft-drake-bess-enhanced-vpn-01

Abstract

   Future networks that support advanced services, such as those enabled
   by 5G mobile networks, envision a set of overlay networks each with
   different performance and scaling properties.  These overlays are
   known as network slices and are realized over a common underlay
   network.

   In order to support network slicing, as well as to offer enhanced VPN
   services in general, it is necessary to define a mechanism by which
   specific resources (links and/or nodes) of an underlay network can be
   used by a specific network slice, VPN, or set of VPNs.  This document
   sets out such a mechanism for use in Segment Routing networks.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://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 November 11, 2019.

Copyright Notice

   Copyright (c) 2019 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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   (https://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
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Approach  . . . . . . . . . . . . . . . . . . . .   3
   4.  Detailed Protocol Operation . . . . . . . . . . . . . . . . .   5
     4.1.  The BGP-LS Map Attribute  . . . . . . . . . . . . . . . .   6
       4.1.1.  The Map TLV . . . . . . . . . . . . . . . . . . . . .   7
       4.1.2.  The DSCP List TLV . . . . . . . . . . . . . . . . . .   9
       4.1.3.  The Color List TLV  . . . . . . . . . . . . . . . . .   9
       4.1.4.  The Root TLV  . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  11
   5.  Comparison With ACTN  . . . . . . . . . . . . . . . . . . . .  12
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  MP2MP Connectivity  . . . . . . . . . . . . . . . . . . .  12
     6.2.  P2MP Unidirectional Connectivity  . . . . . . . . . . . .  13
     6.3.  P2P Unidirectional Connectivity . . . . . . . . . . . . .  14
     6.4.  P2P Bidirectional Connectivity  . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     8.1.  New BGP Path Attribute  . . . . . . . . . . . . . . . . .  16
     8.2.  New BGP-LS Map attribute TLVs Type Registry . . . . . . .  16
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     11.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   Network slicing is an approach to network operations that builds on
   the concept of network abstraction to provide programmability,
   flexibility, and modularity.  Driven largely by needs surfacing from
   5G, the concept of network slicing has gained traction, for example
   in [TS23501] and [TS28530].  Network slicing requires the underlying
   network to support partitioning the network resources to provide the
   client with dedicated (private) networking, computing, and storage
   resources drawn from a shared pool.  The slices may be seen as (and
   operated as) virtual networks.



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   Advanced services drive a need to create virtual networks with
   enhanced characteristics.  The tenant of such a virtual network can
   require a degree of isolation and performance that previously could
   only be satisfied by dedicated networks.  Additionally, the tenant
   may ask for some level of control to their virtual networks, e.g., to
   customize the service forwarding paths in the underlying network.

   The concepts of "enhanced VPNs" and "network slicing" are introduced
   in [I-D.ietf-teas-enhanced-vpn].

   In order to support network slicing, as well as to offer enhanced VPN
   services in general, it is necessary to define a mechanism by which
   specific resources (links and/or nodes) of an underlay network can be
   used by a specific network slice, VPN, or set of VPNs.  This document
   sets out such a mechanism for use in Segment Routing networks
   [RFC8402] and builds on the ideas introduced in
   [I-D.ietf-idr-segment-routing-te-policy].  I.e., it generalizes that
   work to support multipoint-to-multipoint (MP2MP), point-to-multipoint
   (P2MP), and bidirectional point-to-point (P2P) topologies; it
   integrates BGP-based VPN support ([RFC4364], [RFC7432]); it supports
   DSCP as well a Color-based forwarding, and it uses BGP Link-State
   (BGP-LS) [RFC7752] to distribute topology information.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Overview of Approach

   The approach is based on the use of DSCP-based forwarding in the
   underlay network [RFC2474].  For each VPN or sets of VPNs that are to
   use a given underlay network, a central network controller assigns
   resources per {link, DSCP} pair based upon the {source, destination,
   DSCP} traffic matrix.  That is, each VPN or set of VPNs gets a
   subset, either dedicated or shared, of the resources in the underlay
   network.

   It should be noted that resources can be assigned at any of the
   following granularities:

   o  All PEs in a given VPN

   o  A set of PEs in a given VPN




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   o  An individual PE in a given VPN.

   Once the central controller has determined the resource assignments,
   it distributes this information to the PEs that participate in each
   VPN using the usual VPN information dissemination tools, e.g., route
   targets (RT) [RFC4360], route reflectors (RR) [RFC4456], and RT
   constraints [RFC4684].

   One way to distribute this information to those PEs is to give them a
   customized but limited view of the underlay network.  (Note that
   giving each PE a full view of the underlay network does not help the
   PEs to manipulate the resources assigned for use by a particular
   slice or VPN, but providing a customized and limited view of those
   resources as a "virtual network" allows the PE to direct traffic over
   the designated resources as necessary to best deliver the end-to-end
   services.)

   This information is distributed to the PEs by giving them a
   customized and limited view of the underlay network on the basis of a
   network slice, a VPN, or a set of VPNs.  Each PE will have a complete
   view of the underlay network and this customized and limited view
   acts as filter on the underlay network telling the PE which underlay
   network resources it can use to direct the traffic of a given network
   slice, VPN, or set of VPNs to best deliver end-to-end services.

   The resource allocation information is encoded using BGP-LS.  This
   approach is chosen for the following reasons:

   o  It is BGP-based so it integrates easily with the existing BGP-
      based VPN infrastructure ([RFC4364], [RFC4684])

   o  It supports Segment Routing which is necessary to enforce the PEs'
      usage of the resources allocated to the VPN or set of VPNs

   o  It supports inter-AS connectivity which is a perquisite for
      supporting the existing BGP-based VPN infrastructure

   o  It is canonical, in that it can be used to advertise the resources
      of underlay networks that use either IS-IS or OSPF

   It should be noted that this mechanism also follows the scalability
   model of the existing BGP-based VPN infrastructure, which is that the
   per-VPN information is restricted to only those PE routers that are
   supporting that VPN and that the P routers have no per-VPN state.

   Standard VPNs do not receive this resource allocation information and
   continue to use CSPF-based Weighted ECMP (WECMP) in the underlay
   network.  This means that resources used by enhanced VPNs are



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   reserved and are distinct from the resources used by the CSPF-based
   WECMP topology.

   Additional to the programming of the PEs and its computation and
   assignment of resources for use by slices, VPN instances, or groups
   of VPNs, the central controller also instructs the P routers to makes
   actual allocation of resources per-DSCP.

4.  Detailed Protocol Operation

   We define a BGP-LS Map to be a BGP-LS encoded description of a subset
   of the links and nodes in the underlay network.  A BGP-LS Map defines
   the topology for a network slice or a set of one or more VPNs.  The
   topology connects a set of one or more VPNs and which is be used by
   the PEs in those VPNs to send packets.  I.e., it connects the PEs in
   these VPNs and is used by them to send packets to each other.  A
   given map is tagged with the route targets of the VPNs whose PEs are
   to import the map.  A BGP-LS map is pushed southbound to these PEs by
   a network controller and may provide more than one path between a
   given ingress/egress PE pair.

   Note that there will be multiple BGP-LS Maps in a given network
   deployment and that a given underlay network link or node may appear
   in more than one of them.  In order to provide disambiguation AFI
   16388 (BGP-LS) and SAFI 72 (BGP-LS-VPN) are used in BGP-LS UPDATE
   messages and the controller SHOULD allocate a different route
   distinguisher (RD) to each BGP-LS Map.

   It is assumed that the underlay network is enabled for segment
   routing.  Within a given VPN, when an ingress PE needs to send a
   packet to an egress PE it selects a path to that egress PE from the
   topology defined by the BGP-LS maps it has imported for that VPN and
   it specifies that path using a segment routing label stack.

   To enable this function there is a need for a new attribute that is
   attached to a BGP-LS map update that contains a map ID, the version
   number, a map type (MP2MP, P2MP, or P2P), the total number of
   fragments in the map, and the specific fragment number of the piece
   in hand.  That is, the total number of fragments in the map, and the
   fragment number of the piece currently in hand.  It is assumed that a
   PE may import more than one BGP-LS map, that a given BGP-LS map may
   change over time, and that a given BGP-LS map may span multiple BGP
   updates.  The map ID needs to be unique across the set of VPNs into
   which the BGP-LS map is to be imported.

   A BGP-LS map that is created for a set of VPNs will contain a set of
   network resources sufficient to connect the PEs in each VPN in the




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   set and each of the BGP-LS updates for the map MUST be tagged with
   the RT for each VPN in the set.

   If a PE imports more than one BGP-LS map it may use the union of the
   links and nodes specified in each map when selecting a path.  A PE
   should give precedence to BGP-LS maps of type P2MP and P2P when
   selecting a path.  Routes targets specific to a given VPN/PE pair are
   needed for BGP-LS maps of type P2MP and P2P.

   A given BGP-LS map may change in response to updates to the PE
   membership in a VPN to which the BGP-LS map applies or to updates to
   the underlay network.  When this occurs, the network controller
   should push a new version of the affected BGP-LS maps.  That is, it
   increments the version number of each BGP-LS map.  This implies that
   the network controller needs to be connected to the route reflectors
   associated with the VPNs for which it is providing BGP-LS maps.

   A BGP-LS map cannot be used by a PE until it is completely assembled.
   If the BGP-LS map that is being assembled is a newer version of a
   BGP-LS map that the PE is currently using, the PE should continue to
   use its current version of the BGP-LS map until the newer version is
   completely assembled.

   When selecting a path using one or more BGP-LS maps, an ingress PE
   can use a link or node only if it is active in the underlay network.
   If this precludes connectivity to the egress PE it may use links and
   nodes in the CSPF-based WECMP underlay network topology nominally
   allocated to non-enhanced VPN traffic.

   Additionally, when there is a newly activated PE it will not be
   present in any of the BGP-LS maps used by the other PEs.  Until a new
   BGP-LS map or maps that contain that PE has been distributed, other
   PEs will have to use these links and nodes to reach the newly
   activated PE and it will have to use these links and nodes to reach
   other PEs.

4.1.  The BGP-LS Map Attribute

   [RFC4271] defines the BGP Path attribute.  This document introduces a
   new Optional Transitive Path attribute called the BGP-LS Map
   attribute with value TBD1 to be assigned by IANA.

   The first BGP-LS Map attribute MUST be processed and subsequent
   instances MUST be ignored.

   The common fields of the BGP-LS Map attribute are set as follows:





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   o  Optional bit is set to 1 to indicate that this is an optional
      attribute.

   o  The Transitive bit is set to 1 to indicate that this is a
      transitive attribute.

   o  The Extended Length bit is set according to the length of the BGP-
      LS Map attribute as defined in [RFC4271].

   o  The Attribute Type Code is set to TBD1.

   The content of the BGP-LS Map attribute is a series of Type-Length-
   Value (TLV) constructs.  Each TLV may include sub-TLVs.  All TLVs and
   sub-TLVs have a common format that is:

   o  Type: A single octet indicating the type of the BGP-LS Map
      attribute TLV.  Values are taken from the registry described in
      Section 8.2.

   o  Length: A two octet field indicating the length of the data
      following the Length field counted in octets.

   o  Value: The contents of the TLV.

   The formats of the TLVs defined in this document are shown in the
   following sections.  The presence rules and meanings are as follows.

   o  The BGP-LS Map attribute MUST contain a Map TLV.

   o  The BGP-LS Map attribute MAY contain a DSCP List TLV.

   o  The BGP-LS Map attribute MAY contain a Color List TLV.

   o  The BGP-LS Map attribute MAY contain a Root TLV.

4.1.1.  The Map TLV

   The BGP-LS Map attribute MUST contain exactly one Map TLV.  Its
   format is shown in Figure 1.  Note that a given BGP-LS map may span
   multiple UPDATE messages and the Topology, Version Number, and the
   Number of Fragments fields in the BGP-LS Map attribute contained in
   each UPDATE message MUST be set to the same value or the BGP-LS map
   is unusable.








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         +--------------------------------------------+
         |    Type = 1 (1 octet)                      |
         +--------------------------------------------+
         |    Length (2 octets)                       |
         +--------------------------------------------+
         |    Topology (1 Octet)                      |
         +--------------------------------------------+
         |    ID (4 Octets)                           |
         +--------------------------------------------+
         |    Version Number (4 Octets)               |
         +--------------------------------------------+
         |    Number of Fragments (4 Octets)          |
         +--------------------------------------------+
         |    Fragment Number (4 Octets)              |
         +--------------------------------------------+


                       Figure 1: The Map TLV Format

   The fields are as follows:

   o  Type is set to 1 to indicate a Map TLV.

   o  Length is set to 17 octets.

   o  Topology indicates whether this BGP-LS map is MP2MP, P2MP, P2P
      unidirectional, or P2P bidirectional.

   o  The ID of this BGP-LS map.  This ID needs to be unique within the
      set of VPNs into which the BGP-LS map is to be imported.

   o  The Version Number of this BGP-LS map.  I.e., the contents of a
      BGP-LS map with a given ID may change over time and this field
      indicates the latest version of that BGP-LS map.

   o  Number of Fragments indicates the number of BGP UPDATE messages
      defining this BGP-LS map.

   o  Fragment Number indicates ordinal position of this UPDATE message
      within the set of UPDATE messages defining this BGP-LS map.  A
      BGP-LS map is not complete, i.e., usable, until all UPDATE
      messages have been received with Fragment Numbers in the range 1
      <= Fragment Number <= Number of Fragments.  An UPDATE message with
      a Fragment Number outside this range is to be ignored.







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4.1.2.  The DSCP List TLV

   The DSCP List TLV MAY be included in the BGP-LS Map attribute.  If
   included, a packet whose DSCP matches a DSCP in the DSCP list is to
   be forwarded using the BGP-LS map defined by the containing BGP-LS
   Map attribute.  The first DSCP List TLV MUST be processed and
   subsequent instances MUST be ignored.  The format of the DSCP List
   TLV is shown in Figure 2.


         +--------------------------------------------+
         |    Type = 2 (1 octet)                      |
         +--------------------------------------------+
         |    Length (2 octets)                       |
         +--------------------------------------------+
         |    DSCP List (variable)                    |
         +--------------------------------------------+


                    Figure 2: The DSCP List TLV Format

   The fields are as follows:

   o  Type is set to 2 to indicate a DSCP List TLV.

   o  Length indicates the length in octets of the DSCP List.

   o  DSCP List contains a list of DSCPs, each one octet in length and
      encoded in the standard format.

4.1.3.  The Color List TLV

   The Color List TLV MAY be included in the BGP-LS Map attribute.  If a
   BGP UPDATE contains a Color extended community with a color (as
   defined by [RFC5512]) that matches an entry in the Color List, then a
   packet whose destination is covered by one of the routes in that
   UPDATE is to be forwarded using the BGP-LS map defined by the
   containing BGP-LS Map attribute.  The first Color List TLV MUST be
   processed and subsequent instances MUST be ignored.  The format of
   the Color List TLV is shown in Figure 3.

   Note that if both a DSCP List and a Color List TLV are included in a
   BGP-LS Map attribute, packets matching an entry in either list are to
   be forwarded using the BGP-LS map defined by the containing BGP-LS
   Map attribute.






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         +--------------------------------------------+
         |    Type = 3 (1 octet)                      |
         +--------------------------------------------+
         |    Length (2 octets)                       |
         +--------------------------------------------+
         |    Color List (variable)                   |
         +--------------------------------------------+


                    Figure 3: The Color List TLV Format

   The fields are as follows:

   o  Type is set to 3 to indicate a Color List TLV.

   o  Length indicates the length in octets of the Color List.

   o  Color List contains a list of Colors, each four octets in length.

4.1.4.  The Root TLV

   The Root TLV MUST be included in the BGP-LS Map attribute if its
   topology is of type P2MP or P2P unidirectional.  It defines the root
   node for that topology and if it is not present the BGP-LS map is
   unusable.  The TLV, if present, MUST be ignored if the topology is of
   type MP2MP or P2P bidirectional.

   The Root TLV is structured as shown in Figure 4 and MAY contain any
   of the sub-TLVs defined in section 3.2.1.4 of [RFC7752].


         +--------------------------------------------+
         |    Type = 3 (1 octet)                      |
         +--------------------------------------------+
         |    Length (2 octets)                       |
         +--------------------------------------------+
         |    Sub-TLVs (variable)                     |
         +--------------------------------------------+


                       Figure 4: The Root TLV Format

   The fields are as follows:

   o  Type is set to 3 to indicate a Color List TLV.

   o  Length indicates the length in octets of the Color List.




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   o  There follows a sequence of zero or more sub-TLVs as defined in
      section 3.2.1.4 of [RFC7752].  The presence of sub-TLVs can be
      deduced from the Length field of the Root TLV and from the Length
      fields of each of the sub-TLVs.

4.2.  Error Handling

   Section 6 of [RFC4271] describes the handling of malformed BGP
   attributes, or those that are in error in some way.  [RFC7606]
   revises BGP error handling specifically for the for UPDATE message,
   provides guidelines for the authors of documents defining new
   attributes, and revises the error handling procedures for a number of
   existing attributes.  This document introduces the BGP-LS Map
   attribute and so defines error handling as follows:

   o  When parsing a message, an unknown Attribute Type code or a length
      that suggests that the attribute is longer than the remaining
      message is treated as a malformed message and the "treat-as-
      withdraw" approach used as per [RFC7606].

   o  When parsing a message that contains an BGP-LS Map attribute, the
      following cases constitute errors:

      1.  Optional bit is set to 0 in BGP-LS Map attribute.

      2.  Transitive bit is set to 0 in BGP-LS Map attribute.

      3.  The attribute does not contain a Map TLV or it contains more
          than one Map TLV.

      4.  The TLV length indicates that the TLV extends beyond the end
          of the BGP-LS Map attribute.

      5.  There is an unknown TLV type field found in BGP-LS Map
          attribute.

   o  The errors listed above are treated as follows:

      1., 2., 3., 4.:  The attribute MUST be treated as malformed and
         the "treat-as-withdraw" approach used as per [RFC7606].

      5.:  Unknown TLVs SHOULD be ignored, and message processing SHOULD
         continue.








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5.  Comparison With ACTN

   TBD

6.  Examples

   Figure 5shows a sample underlay topology.  Six PEs (PE1 through PE6)
   are connected across a network of twelve P nodes (P1 through P12).
   Each PE is dual-homed, and the P nodes are variously connected so
   that there are multiple routes between PEs.


                             PE3      PE4
                              |\      /|
                              | \    / |
                              |  \  /  |
                              |   \/   |
                              |   /\   |
                              |  /  \  |
                              | /    \ |
                              |/      \|
                             P1--------P2
                            / |\      /| \
                          /   | \    / |   \
                        /     |  \  /  |     \
                      /       |   \/   |       \
                    P3-------P4--------P5-------P6
                     |      / |   /\   | \      |
                     |    /   |  /  \  |   \    |
                     |  /     | /    \ |     \  |
                     |/       |/      \|       \|
                    P7---P8--P9--------P10-P11-P12
                    |\  /|                 |\  /|
                    | \/ |                 | \/ |
                    | /\ |                 | /\ |
                    |/  \|                 |/  \|
                  PE1    PE2             PE5    PE6


                    Figure 5: Underlay Network Topology

6.1.  MP2MP Connectivity

   Figure 6 shows how a Multi-point-to-multipoint (MP2MP) service that
   connects PE1, PE3, and PE6 can be installed over the underlay
   network.  Path have been computed so that, for example, PE1 is
   connected to both PE3 and PE6 via a pair of redundant paths.




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   Similarly, PE3 is connected to PE1 and PE6, and PE6 is connected to
   PE1 and PE3.


                               PE3       PE4
                                | \
                                |  \
                                |   \
                                |    \
                                |     \
                                |      \
                                |       \
                                |        \
                               P1         P2
                              /  \       /|
                            /     \     / |
                          /        \   /  |
                        /           \ /   |
                      P3       P4    X    P5       P6
                       |            / \     \
                       |           /   \      \
                       |          /     \       \
                       |         /       \        \
                      P7   P8--P9---------P10-P11 P12
                      |   /                    \   |
                      |  /                      \  |
                      | /                        \ |
                      |/                          \|
                    PE1    PE2              PE5    PE6


         Figure 6: An MP2MP Service Installed at PE1, PE3, and PE6

6.2.  P2MP Unidirectional Connectivity

   Figure 7 shows the provision of a Point-to-Multipoint (P2MP) rooted
   at PE3 and connected to PE1 and PE6.  As in the previous example, a
   redundant pair of paths is established between PE3 and each of PE1
   and PE6.  Thus, the two paths from PE3 to PE1 are PE3-P1-P4-P7-PE1
   and PE3-P2-P9-P8-PE1.











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                               PE3       PE4
                                | \
                                |  \
                                |   \
                                |    \
                                |     \
                                |      \
                                |       \
                                |        \
                               P1         P2
                                |\       /  \
                                | \     /     \
                                |  \   /        \
                                |   \ /           \
                      P3       P4    X   P5       P6
                              /     / \            |
                            /      /   \           |
                          /       /     \          |
                        /        /       \         |
                      P7---P8--P9         P10-P11 P12
                      |   /                    \   |
                      |  /                      \  |
                      | /                        \ |
                      |/                          \|
                    PE1    PE2            PE5     PE6


         Figure 7: A P2MP Unidirectional Service Installed at PE3

6.3.  P2P Unidirectional Connectivity

   Figure 8 shows a Point-to-Point (P2P) service rooted at PE1 and
   connected to PE3.  This is equivalent to a Segment Routing Traffic
   Engineering (SR TE) Policy [I-D.ietf-idr-segment-routing-te-policy]
   installed at PE1.

   As in the previous examples, a pair of redundant paths are computed.














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                               PE3      PE4
                                |\
                                | \
                                |  \
                                |   \
                                |    \
                                |     \
                                |      \
                                |       \
                               P1        P2
                                |        |
                                |        |
                                |        |
                                |        |
                      P3       P4        P5       P6
                              /          |
                            /            |
                          /              |
                        /                |
                      P7   P8--P9--------P10 P11 P12
                      |   /
                      |  /
                      | /
                      |/
                    PE1    PE2             PE5    PE6


    Figure 8: A P2P Unidirectional Service (SR TE Policy) Installed at
                                    PE1

6.4.  P2P Bidirectional Connectivity

   Figure 9 show a bidirectional P2P service connecting PE1 and PE6.
   This is equivalent to a Segment Routing Traffic Engineering (SR TE)
   Policy [I-D.ietf-idr-segment-routing-te-policy] installed at PE1 and
   PE6.















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                               PE3      PE4




                               P1        P2




                      P3       P4--------P5       P6
                              /            \
                            /                \
                          /                    \
                        /                        \
                      P7   P8--P9--------P10-P11 P12
                      |   /                   \   |
                      |  /                     \  |
                      | /                       \ |
                      |/                         \|
                    PE1    PE2             PE5    PE6


      Figure 9: A P2P Bidirectional Service Installed at PE1 and PE6

7.  Security Considerations

   TBD

8.  IANA Considerations

8.1.  New BGP Path Attribute

   IANA maintains a registry of "Border Gateway Protocol (BGP)
   Parameters" with a subregistry of "BGP Path Attributes".  IANA is
   requested to assign a new Path attribute called "BGP-LS Map
   attribute" (TBD1 in this document) with this document as a reference.

8.2.  New BGP-LS Map attribute TLVs Type Registry

   IANA maintains a registry of "Border Gateway Protocol (BGP)
   Parameters".  IANA is request to create a new subregistry called the
   "BGP-LS Map attribute TLVs" registry.

   Valid values are in the range 0 to 255.

   o  Values 0 and 255 are to be marked "Reserved, not to be allocated".




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   o  Values 1 through 254 are to be assigned according to the "First
      Come First Served" policy [RFC8126]

   This document should be given as a reference for this registry.  The
   new registry should track:

   o  Type

   o  Name

   o  Reference Document or Contact

   o  Registration Date

   The registry should initially be populated as follows:


      Type  | Name                    | Reference     | Date
      ------+-------------------------+---------------+---------------
        1   | Map TLV                 | [This.I-D]    | Date-to-be-set
        2   | DSCP List TLV           | [This.I-D]    | Date-to-be-set
        3   | Color List TLV          | [This.I-D]    | Date-to-be-set
        4   | Root TLV                | [This.I-D]    | Date-to-be-set


9.  Acknowledgements

   The authors are grateful to all those who contributed to the
   discussions that led to this work: Ron Bonica, Stewart Bryant, Jie
   Dong, and Keyur Patel.

10.  Contributors

   The following people contributed text to this document:


               A N Other
               Email: another@foocorp.doc


11.  References

11.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.



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   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC5512]  Mohapatra, P. and E. Rosen, "The BGP Encapsulation
              Subsequent Address Family Identifier (SAFI) and the BGP
              Tunnel Encapsulation Attribute", RFC 5512,
              DOI 10.17487/RFC5512, April 2009,
              <https://www.rfc-editor.org/info/rfc5512>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.






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11.2.  Informative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
              E., and S. Lin, "Advertising Segment Routing Policies in
              BGP", draft-ietf-idr-segment-routing-te-policy-05 (work in
              progress), November 2018.

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-ietf-teas-enhanced-vpn-01 (work in
              progress), February 2019.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <https://www.rfc-editor.org/info/rfc4360>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
              R., Patel, K., and J. Guichard, "Constrained Route
              Distribution for Border Gateway Protocol/MultiProtocol
              Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
              Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
              November 2006, <https://www.rfc-editor.org/info/rfc4684>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [TS23501]  3GPP, "System architecture for the 5G System (5GS) - 3GPP
              TS23.501", 2016,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.

   [TS28530]  3GPP, "Management and orchestration; Concepts, use cases
              and requirements - 3GPP TS28.530", 2016,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.







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Authors' Addresses

   John Drake
   Juniper Networks

   Email: jdrake@juniper.net


   Adrian Farrel
   Old Dog Consulting

   Email: adrian@olddog.co.uk







































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