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Versions: 00 01 02 03

BESS Working Group                                              J. Drake
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                               A. Farrel
Expires: November 22, 2020                            Old Dog Consulting
                                                                L. Jalil
                                                                 Verizon
                                                              A. Lingala
                                                                    AT&T
                                                            May 21, 2020


   BGP-LS Filters : A Framework for Network Slicing and Enhanced VPNs
                    draft-drake-bess-enhanced-vpn-03

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 22, 2020.







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Copyright Notice

   Copyright (c) 2020 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
   (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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Approach  . . . . . . . . . . . . . . . . . . . .   3
   4.  Detailed Protocol Operation . . . . . . . . . . . . . . . . .   5
     4.1.  The BGP-LS Filter Attribute . . . . . . . . . . . . . . .   7
       4.1.1.  The Filter TLV  . . . . . . . . . . . . . . . . . . .   8
       4.1.2.  The DSCP List TLV . . . . . . . . . . . . . . . . . .   9
       4.1.3.  The Color List TLV  . . . . . . . . . . . . . . . . .  10
       4.1.4.  The Root TLV  . . . . . . . . . . . . . . . . . . . .  11
     4.2.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  11
   5.  Comparison With ACTN  . . . . . . . . . . . . . . . . . . . .  12
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  MP2MP Connectivity  . . . . . . . . . . . . . . . . . . .  13
     6.2.  P2MP Unidirectional Connectivity  . . . . . . . . . . . .  14
     6.3.  P2P Unidirectional Connectivity . . . . . . . . . . . . .  15
     6.4.  P2P Bidirectional Connectivity  . . . . . . . . . . . . .  16
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  New BGP Path Attribute  . . . . . . . . . . . . . . . . .  17
     9.2.  New BGP-LS Filter attribute TLVs Type Registry  . . . . .  18
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     11.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21








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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.

   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 a network controller that uses the {source,
   destination} traffic matrix and the performance and scaling
   properties of each network slice, VPN, or set of VPNs in conjunction



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   with the topology of the underlay network to assign each network
   slice, VPN, or set of VPNs a set of underlay links and nodes that it
   can use.  That is, each network slice, 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

   o  An individual PE in a given VPN.

   Once the network 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].

   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 Segment Routing which is necessary to enforce the PEs'
      usage of the resources allocated to the network slice, VPN, or set
      of VPNs.  The use of RSVP-TE ([RFC3209]) rather than Segment
      Routing is at the discretion of the network operator as BGP-LS
      supports both and either confines a packet flow to a specific
      path.

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




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   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.

   The PEs in non-enhanced VPNs do not receive this resource allocation
   information and would not confine their usage of the underlay network
   resources.  In order to ensure that the underlay network resources
   allocated to enhanced VPNs are not inadvertently used by the PEs in
   non-enhanced VPNs, the network controller SHOULD ensure that the IGP
   and TE metrics for these resources is higher than the metrics for the
   underlay network resources allocated to non-enhanced VPNs.  In
   certain situations, detailed in Section 4, PEs in enhanced VPNs will
   use the underlay networks resources allocated to non-enhanced VPNs.

   Additional to the programming of the PEs and its computation and
   assignment of resources for use by network slices, VPNs, or sets of
   VPNs, the network controller also instructs the P routers to make the
   actual allocation of these resources by assigning link bandwidth to a
   specific DSCP or adjacency SID.

4.  Detailed Protocol Operation

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

   Note that there will be multiple BGP-LS Filters 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 network controller SHOULD allocate a different route
   distinguisher (RD) to each BGP-LS Filter.

   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 Filters it has imported for that VPN.  It then



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   either adds a segment routing label stack specifying that path to the
   packet or places the packet in an RSVP-TE LSP which uses that path.
   The ingress PE may use any path computation it wishes if that path
   computation confines the path to the topology defined by the relevant
   set of BGP-LS Filters.

   If Segment Routing is used and a nodal SID is placed in the segment
   routing label stack, then when that segment is active the P routers
   will forward the packet using the underlay network resources
   allocated to non-enhanced VPNs.  Similarly, if the RSVP-TE LSP was
   established using a loose source route to the subject node, the path
   to that node was selected using the underlay network resources
   allocated to non-enhanced VPNs.

   Because the BGP-LS UPDATE messages specifying a BGP-LS Filter may
   arrive in any order and the BGP-LS UPDATE messages of multiple BGP-LS
   Filters may be interleaved, there is a need for a new attribute that
   is attached to a BGP-LS UPDATE.  This attribute contains a Filter ID,
   a Filter version number, a Filter type (MP2MP, P2MP, or P2P), the
   total number of fragments in the filter, and the specific fragment
   number of the piece in hand.  I.e., it is assumed that a PE may
   import more than one BGP-LS Filter, that a given BGP-LS Filter may
   change over time, and that a given BGP-LS Filter may span multiple
   BGP-LS UPDATE messages.  The Filter ID needs to be unique across the
   set of VPNs into which the BGP-LS Filter is to be imported.

   A BGP-LS Filter 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
   set and each of the BGP-LS UPDATE messages for the filter MUST be
   tagged with the RT for each VPN in the set.

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

   A given BGP-LS Filter may change in response to updates to the PE
   membership in a VPN to which the BGP-LS Filter applies or to updates
   to the underlay network.  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.  When this occurs, the
   network controller should push a new version of the affected BGP-LS
   Filters.  That is, it increments the version number of each BGP-LS
   Filter.  Note that a network controller does not need to compute new
   BGP-LS Filters in response to an individual link or node failure in
   the underlay network if connectivity still exists among the PEs in




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   the network slice, VPN or set or VPNs with the existing BGP-LS
   Filters.

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

   When selecting a path using one or more BGP-LS Filters, 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 the
   underlay network resources allocated to non-enhanced VPNs to reach
   the egress PE.

   Additionally, when there is a newly activated PE it will not be
   present in any of the BGP-LS Filters used by the other PEs.  Until a
   new BGP-LS Filter or Filters that contain that PE has been
   distributed, other PEs will use the underlay network resources
   allocated to non-enhanced VPNs to reach the newly activated PE and it
   use these resources to reach other PEs.

4.1.  The BGP-LS Filter Attribute

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

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

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

   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 Filter attribute as defined in [RFC4271].

   o  The Attribute Type Code is set to TBD1.

   The content of the BGP-LS Filter 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:




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   o  Type: A single octet indicating the type of the BGP-LS Filter
      attribute TLV.  Values are taken from the registry described in
      Section 9.2.

   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 Filter attribute MUST contain a Filter TLV.

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

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

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

4.1.1.  The Filter TLV

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


         +--------------------------------------------+
         |    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 Filter TLV Format



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   The fields are as follows:

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

   o  Length is set to 17 octets.

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

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

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

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

   o  Fragment Number indicates ordinal position of this UPDATE message
      within the set of UPDATE messages defining this BGP-LS Filter.  A
      BGP-LS Filter 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.

4.1.2.  The DSCP List TLV

   The DSCP List TLV MAY be included in the BGP-LS Filter attribute.  If
   included, a packet whose DSCP matches a DSCP in the DSCP list is to
   be forwarded using the BGP-LS Filter defined by the containing BGP-LS
   Filter 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:



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   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 Filter 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 Filter defined by the
   containing BGP-LS Filter 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 Filter attribute, packets matching an entry in either list are
   to be forwarded using the BGP-LS Filter defined by the containing
   BGP-LS Filter attribute.  If neither list is included then all
   packets for that network slice, VPN, or set of VPNs can be forwarded
   using the BGP-LS Filter defined by the containing BGP-LS Filter
   attribute.


         +--------------------------------------------+
         |    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.






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4.1.4.  The Root TLV

   The Root TLV MUST be included in the BGP-LS Filter 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 Filter 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.

   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 Filter
   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].



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

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

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

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

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

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

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.

















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














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                               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.  Manageability Considerations

   Per VPN OAM and telemetry will be required in order to monitor and
   verify the performance of network slices.  This is particularly
   important when the performance of a network slice has been committed
   to a customer through a Service Level Agreement.

   TBD

9.  IANA Considerations

9.1.  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 Filter
   attribute" (TBD1 in this document) with this document as a reference.





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9.2.  New BGP-LS Filter 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 Filter 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".

   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   | Filter 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


10.  Acknowledgements

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

11.  References

11.1.  Normative References







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   [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>.

   [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., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-08 (work in progress), November 2019.

   [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+)
              Services", draft-ietf-teas-enhanced-vpn-05 (work in
              progress), February 2020.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [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>.







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

Authors' Addresses

   John Drake
   Juniper Networks

   Email: jdrake@juniper.net


   Adrian Farrel
   Old Dog Consulting

   Email: adrian@olddog.co.uk


   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com


   Avinash Lingala
   AT&T

   Email: ar977m@att.com






















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