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Versions: 00                                                            
IDR                                                              S. Peng
Internet-Draft                                                    Y. Liu
Intended status: Standards Track                         ZTE Corporation
Expires: November 11, 2021                                  May 10, 2021


   BGP Tunnel Encapsulation Attribute Extensions for Network Slicing
          draft-peng-idr-bgp-tea-extensions-network-slicing-00

Abstract

   This document defines extension to BGP Tunnel Encapsulation attribute
   to provide network slicing information needed to create tunnels and
   their corresponding encapsulation headers.

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
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   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, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Gap Analysis of Tunnel Encapsulation Attribute  . . . . . . .   3
     3.1.  Additional Rules to Filter Traffic  . . . . . . . . . . .   3
     3.2.  Additional Tunnel Information for Network Slice . . . . .   4
   4.  BGP Flow Specification Considerations . . . . . . . . . . . .   5
   5.  TEA Extensions  . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Flow Classification Sub-TLV (Type Code TBA1)  . . . . . .   5
       5.1.1.  IP Differentiated Service sub-sub-TLV . . . . . . . .   5
       5.1.2.  IP Source Address Range sub-sub-TLV . . . . . . . . .   6
       5.1.3.  IP Destination Address Range sub-sub-TLV  . . . . . .   7
       5.1.4.  IP Protocol Number Range sub-sub-TLV  . . . . . . . .   7
       5.1.5.  Transport Source Port Range sub-sub-TLV . . . . . . .   7
       5.1.6.  Transport Destination Port Range sub-sub-TLV  . . . .   8
       5.1.7.  Ethernet Frame related sub-sub-TLVs . . . . . . . . .   8
     5.2.  Virtual Network Sub-TLV (Type Code TBA2)  . . . . . . . .   8
     5.3.  SR-BE Encapsulation Sub-TLV . . . . . . . . . . . . . . .  10
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  IP Flex-algo Examples . . . . . . . . . . . . . . . . . .  10
     6.2.  SR Flex-algo Examples . . . . . . . . . . . . . . . . . .  12
     6.3.  Specifying Network Slice Identifier Examples  . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  BGP Tunnel Encapsulation Attribute Sub-TLVs . . . . . . .  14
     7.2.  sub-sub-Types of Flow Classification Sub-TLVs . . . . . .  14
     7.3.  BGP Tunnel Encapsulation Attribute Tunnel Types . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   [I-D.ietf-teas-ietf-network-slices] describes network slicing in the
   context of networks built from IETF technologies.  In order to
   provide network slicing in the operators network for different
   scenarios, some existing control plane technologies are utilized, and
   also some new technologies are developed.  A network slice can be a
   virtual network or a traffic engineering path with guaranteed
   resources.  For example, it could be implemented as an IGP Multi-
   Topology (see [RFC5120], [RFC4915], [RFC5340]), or an IGP Flexible
   Algorithm (see [I-D.ietf-lsr-flex-algo]), or a Slice Aggregate which
   comprises of multiple IETF network slice traffic streams(see
   [I-D.bestbar-teas-ns-packet]), or a simple SR policy(see
   [I-D.ietf-spring-segment-routing-policy]).





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   Once a network slice is created, it is necessary to configure the
   corresponding traffic mapping policy on the entry node of the slice
   to steer the traffic to the that slice.  For example, ACL rules can
   be configured on the entry node of the slice to filter the traffic
   based on 5-tuple fields or other fields (such as Differentiated
   Services) of the packets, then steer the matched traffic to that
   slice; It is also possible to firstly set a Color for the matched
   traffic, then steer the traffic to an SR policy.  However, such
   configuration is inflexible, especially for the case where the slice
   entry node is not the endpoint of overlay service, in this case it is
   not recommended to configure a large number of service-related
   policies on the slice entry node.  From the point of view of
   simplifying operation and maintenance, automatic slice steering is
   necessary.

   [RFC9012] defines a BGP path attribute known as the "Tunnel
   Encapsulation attribute", which can be used with BGP UPDATEs of
   various Subsequent Address Family Identifiers (SAFIs) to provide
   information needed to create tunnels and their corresponding
   encapsulation headers.  This document describes extensions to Tunnel
   Encapsulation attribute to specify forwarding path within particular
   network slice.

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.  Gap Analysis of Tunnel Encapsulation Attribute

3.1.  Additional Rules to Filter Traffic

   [RFC9012] defines two Sub-TLVs, i.e., Protocol Type Sub-TLV (Type
   Code 2) and Color Sub-TLV (Type Code 4), for aiding tunnel selection.

   For Protocol Type Sub-TLV, the value fileld contains a 2-octet value
   from IANA's "ETHER TYPES" registry, such as IPv4(0x0800),
   IPv6(0x86dd), MPLS(0x8847), to indicate the type of the payload
   packets that are allowed to be encapsulated with the tunnel
   parameters that are being signaled in the parent TLV.  However, for
   network slicing case, it is not enough that the traffic of different
   slices is distinguished based on the coarse-grained ethernet types,
   more fine-grained differentiation is needed, such as Differentiated
   Services field or 5-tuple fields of the IP packet, or Source/
   Destination MAC or VLAN ID/PCP of the Ethernet frame.



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   For Color Sub-TLV, the value field contains a Color Extended
   Community to "color" the corresponding Tunnel TLV.  In more detailed,
   as section "8.  Recursive Next-Hop Resolution" of [RFC9012]
   described, an overlay route (U1) with a Color Extended Community that
   is identified in one of Color sub-TLVs of the underlay route (U2) can
   use tunnel identified in the Tunnel Encapsulation attribute of the
   underlay route (U2).  That is, an overlay route with specific Color
   Extended Community indicates the expected TE purpose during recursive
   next-hop resolution, while an underlay route with specific Color sub-
   TLV of Tunnel Encapsulation attribute indicates the "color" of the
   corresponding Tunnel.  In fact, the corresponding Tunnel itself may
   not have a color attribute, and the color is temporarily set by the
   underlay route.  It is possible that different colors may be set by
   different underlay routes.  Another example that corresponding TE
   path itself has a color attribute is SR policy defined in
   [I-D.ietf-spring-segment-routing-policy].  For network slicing case,
   although a Color Extended Community can be contained in a route
   UPDATE to indicate TE purpose within the specific network slice, that
   means any packets matched that route will have the same forwarding
   behavior.  In some cases these packets may need different treatment.
   It is possible to advertise multiple Color Extended Community for the
   same route, however, ACL rules is necessary at entry nodes of the
   slice to firstly set color for packets and then quest TE purpose,
   that is inflexible.

3.2.  Additional Tunnel Information for Network Slice

   [RFC9012] does not define how to specify the tunnel within a network
   slice.  For example, Tunnel Encapsulation Attribute with IP-in-IP
   Tunnel type will only let the packet be encapsulated in IP-tunnel
   created in physical network.  It is useful to combine the existing
   Tunnel Egress Endpoint Sub-TLV or BGP next-hop with a Network Slice
   Identifier to select tunnel within expected network slice.  Note that
   [RFC9012] defines that some of the tunnel types (for example, VXLAN
   and NVGRE) that can be specified in the Tunnel Encapsulation
   attribute have an encapsulation header containing a virtual network
   identifier of some sort, however they are different from the semantic
   and function of network slice.

   In some network slicing techniques, SID allocation has distinguished
   different network slices, so SR-BE (Best Effort) can be specified
   directly in Tunnel Encapsulation Attribute.  Although, [RFC9012]
   defines Prefix-SID sub-TLV, it is the Prefix-SID that the tunnel's
   egress endpoint uses to represent the prefix appearing in the NLRI
   field of the BGP UPDATE to which the Tunnel Encapsulation attribute
   is attached, it is not the Prefix-SID of the outer SR-BE tunnel.





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4.  BGP Flow Specification Considerations

   [RFC8955] defines Flow Specification NLRI and also specifies BGP
   Extended Community encoding formats used to propagate Traffic
   Filtering Actions along with the Flow Specification NLRI.  The
   corresponding flow routes can be installed on the entry nodes of the
   network slice, and that is similar with manually configured policy
   based routes.  However, both of them are inflexible, and some
   implementations may not be easy to route packets in combination with
   flow routes and unicast routes.  Instead, prefix NLRI containing
   Tunnel Encapsulation Attribute is different with Flow Specification
   NLRI, it does not need to introduce flow route state on the entry
   node of the network slice, and all forwarding behaviors are based on
   traditional unicast route with its TEA attributes.

5.  TEA Extensions

5.1.  Flow Classification Sub-TLV (Type Code TBA1)

   The Flow Classification Sub-TLV MAY be included in a given Tunnel
   Encapsulation TLV to indicate the flow classification of the payload
   packets that are allowed to be encapsulated with the tunnel
   parameters that are being signaled in the parent TLV.  It MUST NOT
   appear more than once in its parent TLV.  The Value field of the Flow
   Classification Sub-TLV comprised of multiple sub-sub-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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         sub-sub-TLVs (variable)              //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 1: Flow Classification Sub-TLV Value Field

5.1.1.  IP Differentiated Service sub-sub-TLV

   IP Differentiated Service sub-sub-TLV is used to represent the range
   of Differentiated Service field (such as the TOS field of the IPv4
   header or the TC field of the IPv6 header) that traffic needs to
   match.  It can appear more than once in its parent sub-TLV.

       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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |    DS Begin   |     DS End    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 2: IP Differentiated Service sub-sub-TLV Format



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   Type: TBD (suggest 1)

   Length: 2 octets.

   DS Begin: The begin value of the range of Differentiated Service.

   DS End: The end value of the range of Differentiated Service.  DS
   Begin and DS End field can be same to specify actions for each DS
   value.

5.1.2.  IP Source Address Range sub-sub-TLV

   IP Source Address Range sub-sub-TLV is used to represent the range of
   Source Address field that traffic needs to match.  It can appear more
   than once in its parent sub-TLV.

       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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |V|   Flags     | Prefix Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     IPv4 Prefix or IPv6 Prefix                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 3: IP Source Address Range sub-sub-TLV Format

   Type: TBD (suggest 2)

   Length: variable.

   Flags: Currently only V-flag is defined.  The IP Prefix field
   contains an IPv4 Prefix if V-Flag is clear and an IPv6 Prefix if
   V-Flag is set.  The remaining bits are reserved for future use.  They
   MUST be set to zero on transmission and MUST be ignored on receipt.

   Prefix Length: Number of bits in the Prefix field.  MUST be from the
   range (1 - 32) when V-Flag is clear and (1 - 128) when V-Flag is set.
   The sub-sub-TLV MUST be ignored if the Prefix Length is outside of
   this range.

   IP Prefix: The IP Prefix is encoded in the minimal number of octets
   for the given number of bits.  Trailing bits MUST be set to zero and
   ignored when received.








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5.1.3.  IP Destination Address Range sub-sub-TLV

   IP Destination Address Range sub-sub-TLV is used to represent the
   range of Destination Address field that traffic needs to match.

   It has the same format as IP Source Address Range sub-sub-TLV,
   suggest Type Code 3.

5.1.4.  IP Protocol Number Range sub-sub-TLV

   IP Protocol Number Range sub-sub-TLV is used to represent the range
   of IP Protocol Number field that traffic needs to match.  It can
   appear more than once in its parent sub-TLV.

       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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |Protocol Begin | Protocol End  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 4: IP Protocol Number Range sub-sub-TLV Format

   Type: TBD (suggest 4)

   Length: 2 octets.

   Protocol Begin: The begin value of the range of IP Protocol Number.

   Protocol End: The end value of the range of IP Protocol Number.
   Protocol Begin and Protocol End field can be same to specify actions
   for each Protocol value.

5.1.5.  Transport Source Port Range sub-sub-TLV

   Transport Source Port Range sub-sub-TLV is used to represent the
   range of Source Port field that traffic needs to match.  It can
   appear more than once in its parent sub-TLV.

       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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |   Port Begin  |   Port End    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 5: Transport Source Port Range sub-sub-TLV Format

   Type: TBD (suggest 5)




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   Length: 2 octets.

   Port Begin: The begin value of the range of Source Port.

   Port End: The end value of the range of Source Port.  Port Begin and
   Port End field can be same to specify actions for each Port value.

5.1.6.  Transport Destination Port Range sub-sub-TLV

   Transport Destination Port Range sub-sub-TLV is used to represent the
   range of Destination Port field that traffic needs to match.  It can
   appear more than once in its parent sub-TLV.

   It has the same format as Transport Source Port Range sub-sub-TLV,
   suggest Type Code 6.

5.1.7.  Ethernet Frame related sub-sub-TLVs

   To be defined in future versions.

5.2.  Virtual Network Sub-TLV (Type Code TBA2)

   The Virtual Network Sub-TLV MAY be included in a given Tunnel
   Encapsulation TLV to indicate the expected network slice that the
   traffic is steered to.  It MUST NOT appear more than once in its
   parent TLV.  The Value field of the Virtual Network Sub-TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Flags     |   Algorithm   |R R R R|   Multi-Topology ID   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Network Slice ID                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 6: Virtual Network Sub-TLV Value Field

   Flags: The following flags are defined:

       0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |I|A|T|S|       |
     +-+-+-+-+-+-+-+-+

   where:




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   I-Flag: This flag is only valid when S-Flag is set.  If I-Flag is
   set, the entry node of network slice SHOULD insert the value of
   Network Slice ID field into the outer encapsulated tunnel header,
   otherwise no necessary.

   A-Flag: If A-Flag is set, the Algorithm field contains valid value.

   T-Flag: If T-Flag is set, the Multi-Topology ID field contains valid
   value.

   S-Flag: If S-Flag is set, the Network Slice ID field contains valid
   value.

   The remaining bits are reserved for future use.  They MUST be set to
   zero on transmission and MUST be ignored on receipt.

   Algorithm: Represents IGP algorithm, see IANA "IGP Algorithm Types"
   registry, such as 0 (Shortest Path First algorithm based on link
   metric), 1 (Strict Shortest Path First algorithm based on link
   metric) defined in [RFC8402], and 128~255 (Flexible Algorithm)
   defined in [I-D.ietf-lsr-flex-algo].

   Multi-Topology ID: Represents IGP Multi-Topology defined in [RFC5120]
   and [RFC4915].

   Network Slice ID: Represents an IETF network Slice defined in
   [I-D.ietf-teas-ietf-network-slices].

   In most cases, it only need to set one of Algorithm, Multi-Topology
   ID and Network Slice ID.  However, it is possible to set them at the
   same time.  When not set, the value is 0.

   Virtual Network Sub-TLV is used together with other Sub-TLVs to
   encapsulate the tunnel information corresponding to the specified
   tunnel in a specific virtual network.  For example, when the Tunnel
   Type of Tunnel Encapsulation TLV is 7 (representing IP-in-IP), and
   contains Virtual Network Sub-TLV and Tunnel Egress Endpoint Sub-TLV,
   it means that the packets is encapsulated in the IP tunnel in the
   expected virtual network destinated to the Tunnel Egress Endpoint.
   In detailed, the path of IP tunnel could be determined by <Algorithm,
   Endpoint>, or <MT-ID, Endpoint>, or <Slice-ID, Endpoint>.

   In some network slice control plane schemes, Slice-ID is directly
   used to identify FIB table, so it is easy to get FIB entry by <Slice-
   ID, Endpoint>.  In other shcemes, Slice-ID need firstly be mapped to
   an SA-ID, then get FIB entry by <SA-ID, Endpoint>.  It is the local
   matter for the entry node of the network slice to get FIB entry
   according to the specific deployment mode.  In any case, the entry



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   node of the network slice can, but may not if it has not such
   capability, insert Slice-ID to the outer tunnel header.

5.3.  SR-BE Encapsulation Sub-TLV

   This document introduce a new Tunnel Type, termed as SR-BE.  For SR-
   BE tunnel, the structure of the Value field in the Encapsulation sub-
   TLV (Type Code 1) is shown as the following:

       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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Reserved   |D|   Flags     |               SID...          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              SID                             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 7: SR-BE Encapsulation Sub-TLV Value Field

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

   Flags: Currently only D-flag is defined.  The SID field contains a 32
   bits SR-MPLS SID (index) if D-Flag is clear and a 128 bits SRv6 SID
   if D-Flag is set.  The remaining bits are reserved for future use.
   They MUST be set to zero on transmission and MUST be ignored on
   receipt.

   SID: 32 bits SR-MPLS SID (index) or 128 bits SRv6 SID.

   For SR-MPLS SID (index), the out-label needs to be obtained based on
   the SRGB of the downstream node and then pushed to the label stack.
   For SRv6 SID, the SID is filled in the DA field of outer IPv6 header.

6.  Examples

6.1.  IP Flex-algo Examples

   The following example describes a most simple network slice
   deployment selection, which steers traffic to the corresponding
   tunnel endpoint according to the traffic class.  In the backbone
   network of some operators, network administrators do not want to
   deploy a large number of traffic engineering paths in the network,
   but they also want to automatically select the appropriate path for
   forwarding according to the traffic characteristics.  The network
   administrator chooses to deploy IGP flex-algo in the backbone network
   of pure IPv6 (refering to [I-D.ietf-lsr-ip-flexalgo]), and creates an
   flex-algo plane based on the calculation path of Delay-metric.  It is



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   expected that the traffic with higher traffic class will be forwarded
   along the flex-algo plane, while the ordinary traffic will continue
   to be forwarded along the physical network.

                      ~~~~~~~~~~~~~~~~~~~~~~~~~
                      ~   ....................~
                      ~  .     FA-128       . ~
       ~~~~~~~~~~~    ~ .  +-----P1----+   .  ~    ~~~~~~~~~~~
       ~         ~    ~.  /      |      \ .   ~    ~         ~
       ~ S-----A---------B1-----P2-----B2------------C-----D ~
       ~         ~    ~   \      |      /     ~    ~         ~
       ~~~~~~~~~~~    ~    +-----p3----+      ~    ~~~~~~~~~~~
                      ~                       ~
                      ~~~~~~~~~~~~~~~~~~~~~~~~~
         Metro-1              Backbone                Metro-2

                      Figure 8: Flex-algo in Backbone

   Nodes B1, P1, P2, B2 and their interconnected links join to the flex-
   algo 128 plane.  Suppose that there are two loopback routes on node
   B2, respectively loopback-B2 and loopback-B200, and loopback-B2 is
   associated with algorithm 0, loopback-B200 is associated with
   algorithm 128.  On node B1, the route forwarding path to loopback-B2
   will be the forwarding path calculated by the minimum IGP metric in
   the physical network, and the route forwarding path to loopback-B200
   will be the forwarding path calculated by the minimum delay metric in
   flex-algo 128 plane.

   Node S of Metro-1 needs to send IPv6 packets to node D of Metro-2.
   Suppose that node D has a local route prefix-D, which is flooded in
   Metro-2.  Node C can advertise prefix-D to node B2 through BGP.  When
   the B2 receives prefix-D from outside the backbone domain, it
   continues to advertise the routes to the boundary node B1 through
   BGP.  At this time, B2 does not pay attention to the difference of
   the announced prefixes (i.e. whether it is for prefix-D or other
   prefix-D').  It just configure a simple local policy to add the
   Tunnel Encapsulation Attribute to the BGP UPDATE that continues to be
   advertised, which includes two Tunnel Cncapsulation TLVs:

   The first Tunnel Encapsulation TLV:

      Tunnel Type: IP in IP

      Tunnel Egress Endpoint Sub-TLV: Loopback-B2

      Flow Classification Sub-TLV: IP Differentiated Service is [0,3]

   The second Tunnel Encapsulation TLV:



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      Tunnel Type: IP in IP

      Tunnel Egress Endpoint Sub-TLV: Loopback-B200

      Flow Classification Sub-TLV: IP Differentiated Service is [4,7]

   Node B1 will maintain to the prefix-D route entry, which contains the
   above two Tunnel Encapsulation Attribute options.

   Assuming the two data packets, P1 and P2, sent from node S to node D.
   Suppose that the traffic class in IPv6 header of P1 is 0 and that in
   IPv6 header of P2 is 7.

   When the above packets reache the node B1 of the backbone network, it
   will match the route entry prefix-D and encapsulate the outer IPv6
   tunnel for the packets according to the Tunnel Encapsulation
   Attribute options.  Since the traffic class of P1 is 0, the DA of the
   encapsulated outer IPv6 header is loopback-B2; while the traffic
   class of P2 is 7, the DA of the encapsulated outer IPv6 header is
   loopback-B200.

   The above two packets will be forwarded to the destination node B2
   along the physical topology and flex-algo 128 plane respectively.

6.2.  SR Flex-algo Examples

   The network administrator can also deploy IGP flex-algo in the
   backbone network of SRv6 (refering to [I-D.ietf-lsr-flex-algo]).

   In Figure 8, suppose that there are two SRv6 Locators on node B2,
   respectively LOC-B2 and LOC-B200, and LOC-B2 is associated with
   algorithm 0, LOC-B200 is associated with algorithm 128.  On node B1,
   the route forwarding path to LOC-B2 will be the forwarding path
   calculated by the minimum IGP metric in the physical network, and the
   route forwarding path to LOC-B200 will be the forwarding path
   calculated by the minimum delay metric in flex-algo 128 plane.

   Suppose SID-b2 is allocated in LOC-B2 and SID-B200 is allocated in
   LOC-B200.  These two SIDS may be END SID with USD flavor or END.DT6
   SID used to carry global IPv6 packets.

   Similar with the above example, B2 sends to B1 about BGP UPDATE with
   Tunnel Encapsulation Attribute, which includes two Tunnel
   Cncapsulation TLVs:

   The first Tunnel Encapsulation TLV:

      Tunnel Type: SR-BE



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      SR-BE Encapsulation Sub-TLV: D-Flag is set, SID is SID-B2

      Flow Classification Sub-TLV: IP Differentiated Service is [0,3]

   The second Tunnel Encapsulation TLV:

      Tunnel Type: SR-BE

      SR-BE Encapsulation Sub-TLV: D-Flag is set, SID is SID-B200

      Flow Classification Sub-TLV: IP Differentiated Service is [4,7]

   For the above packet P1, the DA of the encapsulated outer IPv6 header
   is SID-B2; For the above packet P2, the DA of the encapsulated outer
   IPv6 header is SID-B200.  Thus they will be forwarded to the
   destination node B2 along the physical topology and flex-algo 128
   plane respectively.

6.3.  Specifying Network Slice Identifier Examples

   This example describes steering to a specific network slice according
   to the traffic level, which requires the entry node to combine the
   specific Network Slice Identifier with the BGP next-hop of BGP UPDATE
   or the Tunnel Egress Endpoint Sub-TLV to determine the tunnel
   encapsulation to be adopted.  In this way, the tunnel selection of
   the entry node is more flexible, and the constructure of BGP UPDATE
   is more concise.

   Similar with the above example, B2 sends to B1 about BGP UPDATE with
   Tunnel Encapsulation Attribute, which includes two Tunnel
   Cncapsulation TLVs:

   The first Tunnel Encapsulation TLV:

      Tunnel Type: Any-Encapsulation

      Virtual Network Sub-TLV: Algorithm 0, MT-ID 0, Slice-ID 0

      Flow Classification Sub-TLV: IP Differentiated Service is [0,3]

   The second Tunnel Encapsulation TLV:

      Tunnel Type: Any-Encapsulation

      Virtual Network Sub-TLV: Algorithm 128, MT-ID 0, Slice-ID 0

      Flow Classification Sub-TLV: IP Differentiated Service is [4,7]




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   Node B1 will maintain to the prefix-D route entry, which contains the
   tunnel encapsulation attribute information and specifically contains
   the above two Tunnel Encapsulation options.  Because the Tunnel Type
   is Any-Encapsulation, B1 node needs to select the corresponding
   tunnel according to the actual deployment modes in the backbone
   network.  For example, if the backbone network is an SR-MPLS network,
   it needs to find the prefix-SID allocated by the node B2 for the
   corresponding algorithm in the link-state database, and then obtain
   the corresponding MPLS SR-BE tunnel; If the backbone network is SRv6
   network, it needs to find the END SID assigned by the node B2 for the
   corresponding algorithm in the link state database, and then obtain
   the corresponding IPv6 SR-BE tunnel.

7.  IANA Considerations

7.1.  BGP Tunnel Encapsulation Attribute Sub-TLVs

   This document request the following entries to the "BGP Tunnel
   Encapsulation Attribute Sub-TLVs" registry:

         +=======+=========================+================+
         | Value | Description             |    Reference   |
         +=======+=========================+================+
         | TBA1  | Flow Classification     | This Document  |
         +-------+-------------------------+----------------+
         | TBA2  | Virtual Network         | This Document  |
         +-------+-------------------------+----------------+

7.2.  sub-sub-Types of Flow Classification Sub-TLVs

   This document request new registry named as "sub-sub-Types of Flow
   Classification Sub-TLVs" under the "Border Gateway Protocol (BGP)
   Tunnel Encapsulation" grouping.

   The initial types for this new registry are indicated as the
   following:















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         +=======+==================================+================+
         | Value | Description                      |    Reference   |
         +=======+==================================+================+
         |   1   | IP Differentiated Service        | This Document  |
         +-------+----------------------------------+----------------+
         |   2   | IP Source Address Range          | This Document  |
         +-------+----------------------------------+----------------+
         |   3   | IP Destination Address Range     | This Document  |
         +-------+----------------------------------+----------------+
         |   4   | IP Protocol Number Range         | This Document  |
         +-------+----------------------------------+----------------+
         |   5   | Transport Source Port Range      | This Document  |
         +-------+----------------------------------+----------------+
         |   6   | Transport Destination Port Range | This Document  |
         +-------+----------------------------------+----------------+

7.3.  BGP Tunnel Encapsulation Attribute Tunnel Types

   This document request the following entries to the "BGP Tunnel
   Encapsulation Attribute Tunnel Types" registry:

         +=======+=========================+================+
         | Value | Description             |    Reference   |
         +=======+=========================+================+
         | TBA3  | SR-BE                   | This Document  |
         +-------+-------------------------+----------------+

8.  Security Considerations

   This document inherits the security consideration from [RFC9012].

9.  Acknowledgements

   TBD

10.  Normative References

   [I-D.bestbar-teas-ns-packet]
              Saad, T., Beeram, V. P., Wen, B., Ceccarelli, D., Halpern,
              J., Peng, S., Chen, R., Liu, X., and L. M. Contreras,
              "Realizing Network Slices in IP/MPLS Networks", draft-
              bestbar-teas-ns-packet-02 (work in progress), February
              2021.

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-15 (work in progress), April 2021.



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   [I-D.ietf-lsr-ip-flexalgo]
              Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica,
              R., and P. Psenak, "IGP Flexible Algorithms (Flex-
              Algorithm) In IP Networks", draft-ietf-lsr-ip-flexalgo-02
              (work in progress), April 2021.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-11 (work in progress),
              April 2021.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L. M., and J. Tantsura,
              "Framework for IETF Network Slices", draft-ietf-teas-ietf-
              network-slices-00 (work in progress), April 2021.

   [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>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [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>.

   [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>.





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   [RFC8955]  Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              RFC 8955, DOI 10.17487/RFC8955, December 2020,
              <https://www.rfc-editor.org/info/rfc8955>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

Authors' Addresses

   Shaofu Peng
   ZTE Corporation

   Email: peng.shaofu@zte.com.cn


   Yao Liu
   ZTE Corporation

   Email: liu.yao71@zte.com.cn





























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