Network Resource Partition Identifier (NRP-ID) in SRv6 segment
draft-liu-spring-nrp-id-in-srv6-segment-00

SPRING Working Group                                            Y. Liu
Internet Draft                                            China Mobile
Intended status: Standards Track                                C. Lin
Expires: January 11, 2023                                        H. Li
                                                  New H3C Technologies
                                                               L. Gong
                                                          China Mobile
                                                         July 10, 2022

       Network Resource Partition Identifier (NRP-ID) in SRv6 segment
                draft-liu-spring-nrp-id-in-srv6-segment-00

Abstract

   This document proposes a method to carry the Network Resource
   Partition Identifier (NRP-ID) with the packet in the SRv6 segment.

Status of this Memo

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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Encoding NRP-ID in SRv6 segment................................3
   3. Deployment consideration of NRP-ID In segment..................4
   4. NRP-ID position information advertisement......................5
      4.1. Static configuration mode.................................5
      4.2. Dynamic advertising mode..................................6
   5. Behavior of headend............................................6
   6. Behavior of endpoint...........................................7
   7. Behavior of transit node.......................................8
   8. Example........................................................9
   9. IANA Considerations...........................................10
   10. Security Considerations......................................10
   11. References...................................................11
      11.1. Normative References....................................11
   Authors' Addresses...............................................12

1. Introduction

   Network slicing provides the ability to partition a physical network
   into multiple isolated logical networks of varying sizes,
   structures, and functions so that each slice can be dedicated to
   specific services or customers. [I-D.ietf-teas-ietf-network-slices]
   defines the term "IETF Network Slice" and establishes the general
   principles of network slicing in the IETF context. [I-D.cheng-teas-
   network-slice-usecase] describes several use cases of IETF Network
   Slice.  [I-D.ietf-teas-ns-ip-mpls] proposes a solution to realize
   network slicing in IP/MPLS networks.  Network nodes need to identify
   a packet belonging to a network slice before it can apply the proper
   forwarding treatment, so a slice ID must be carried in each packet.

   Packets belong to a network slice need to be forwarded using the
   specific network resources. [I-D.draft-ietf-teas-ietf-network-

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   slices] defines the network resource mapped to the network slice as
   NRP, that is, the Network Resource Partition, and defines the NRP-ID
   to identify the NRP used in the forwarding process.

   In a network that provides slicing services, the NRP-ID can be
   carried in the packet. In the process of packet forwarding, the
   routers on the forwarding path can extract NRP-ID from the packet,
   determine the NRP to which the packet belongs, and then forward the
   packet using the resources associated with the NRP.

   Segment Routing (SR) allows a headend node to steer a packet flow
   along any path. Per-path states of Intermediate nodes are eliminated
   thanks to source routing.  The headend node steers a flow into an SR
   Policy. The packets steered into an SR Policy carry an ordered list
   of segments associated with that SR Policy.

   When SRv6 network provides network slicing service, it is also
   necessary to consider how to carry NRP-ID with packet. This document
   proposes a method to carry the NRP-ID in the SRv6 network. By
   setting the NRP-ID in the SRv6 segment, the SRv6 endpoint or transit
   node can be aware the NRP to which the packet belongs and carry out
   relevant forwarding processing.

1.1. 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.

2. Encoding NRP-ID in SRv6 segment

   The structure of SRv6 segment is defined in RFC[8986]. An SRv6
   segment consists of three parts, LOC:FUNCT:ARG.

   +------------------------------------------------------------------+
   |     Locator             | Function |           Argument          |
   +------------------------------------------------------------------+
    <--------- LOC ---------><- FUNCT -><----------- ARG-------------->
                       Figure 1: structure of segment

   After the packet enters the SRv6 domain, the ingress node (headend)
   adds SRv6 Encapsulation to packet. In SRv6 TE (traffic engineer)
   mode, the headend node encapsulates an IPv6 header and an SRH header
   at the same time. A group of SRv6 segments is encapsulated in the

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   SRH header to indicate the forwarding path. NRP-ID can be carried in
   segment to identify the NRP to which the packet belongs.

   This document proposes to use the ARG part of the segment to carry
   the NRP-ID.

   +------------------------------------------------------------------+
   |     Locator             | Function |           NRP-ID           |
   +------------------------------------------------------------------+
    <--------- LOC ---------><- FUNCT -><----------- ARG-------------->
                      Figure 2: Encoding NRP-ID in segment

3. Deployment consideration of NRP-ID In segment

   In the SRv6 TE mode, multiple segments are encoded in the SRH. The
   last segment in the SRH is usually the service or End SID of the
   tailend node and does not need to carry the NRP-ID.

   Other segments in SRH are usually End or End.X segments, which are
   used to guide intermediate endpoint nodes to forward packets. These
   segments do not need argument and can carry NRP-ID.

   Different segments can carry the same or different NRP-ID, which is
   arranged by the controller or operator by CLI according to the
   actual requirement.

   Segment[0]:
   +------------------------------------------------------------------+
   |     Locator5            | Function |          Argument           |
   +------------------------------------------------------------------+
   Segment[1]
   +------------------------------------------------------------------+
   |     Locator4            | Function |           NRP-ID2           |
   +------------------------------------------------------------------+
   Segment[2]
   +------------------------------------------------------------------+
   |     Locator3            | Function |           NRP-ID2           |
   +------------------------------------------------------------------+
   Segment[3]
   +------------------------------------------------------------------+
   |     Locator2            | Function |           NRP-ID1           |
   +------------------------------------------------------------------+
   Segment[4]
   +------------------------------------------------------------------+
   |     Locator1            | Function |           NRP-ID1           |
   +------------------------------------------------------------------+
                    Figure 3: Encoding NRP-ID in segment list

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4. NRP-ID position information advertisement

   If the network slicing service needs to be supported, when creating
   a locator, the SRv6 node needs to determine the encoding position of
   NRP-ID in the segment according to its own role.

   The locator and encoding positions of NRP-ID need to be advertised
   to the controller and other network nodes. With this information,
   the controller arranges the SRv6 policy, and other network nodes
   need to extract the NRP-ID from address during forwarding.

4.1. Static configuration mode

   In the static configuration mode, configure the locator encoding
   information on the controller and network nodes respectively. For
   the convenience of description, the locator carrying NRP-ID is named
   slice prefix in this document.

   All nodes that support network slicing need to be configured,
   including SRv6 nodes and IPv6 only nodes.

   The aggregation attribute of locator can be used. The following
   figure is an example. The P nodes only provide End/End.x type
   segments, and the positions used to encode NRP-ID are usually the
   same. Therefore, common prefix can be configured to indicate the
   position of NRP-ID.

   If the encoding position of a P node is different from that of most
   nodes, the slice prefix corresponding to the locator of the P node
   can be configured separately to specify its encoding position.

   These slice prefixes will create a local slice prefix table (LSPT)
   on the forwarding plane. When forwarding packets, the network node
   uses the destination address to lookup the LSPT according to the
   longest matching principle, and then extracts the NRP-ID from the
   destination address according to the information of the hit table
   entry.

   Referring to the topology and locators of each node in the Figure 4,
   the following slice prefix can be configured.

   The encoding positions of P1 and P4 nodes are the same, and a slice
   prefix corresponding to common prefix can be configured to identify
   the coding position as the low 16 bits. The encoding position of P3
   is 96bit to 112bit of segment, so a slice prefix corresponding to
   its locator is configured separately to explain its coding position

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   Slice-Prefix1: 2001:1:1::/64 (common prefix)

       NRP-ID Position: [112..127]

   Slice-Prefix2: 2001:1:1:0:130::/80 (locator for P3)

       NRP-ID Position: [96..112] in segment

                           IPv6-only
         +-----+   +----+   +----+   +----+   +----+   +-----+
       --+ PE1 +---+ P1 +---+ P2 +---+ P3 +---+ P4 +---+ PE2 +---
         +-----+   +----+   +----+   +----+   +----+   +-----+
                  SRv6-node          SRv6-node  SRv6-node

   common Prefix: 2001:1:1::/64
   locator
    P1:    2001:1:1:0:110::/80   for End/End.x
    P3:    2001:1:1:0:130::/80   for End/End.x
    P4:    2001:1:1:0:140::/80   for End/End.x
                       Figure 4: example topology for slice prefixes

4.2. Dynamic advertising mode

   To simplify the configuration, slice prefix can be advertised to
   network nodes in the domain through IGP and to controllers through
   BGP-LS. This reduces the configuration of controllers and SRv6
   nodes.

   However, nodes that only support IPv6 need to be configured as
   described in the previous section.

   Relevant protocol extensions will be provided in subsequent
   versions.

5. Behavior of headend

   If the network slice function is enabled, the SRv6 headend node
   determines the network slice to which the customer traffic belongs
   according to the relevant policies.

   The headend node steers the customer traffic to the SRv6 policy and
   encapsulates the IPv6 header and SRH header for the customer
   traffic. The headend node encapsulates the segment list of the SRv6
   policy in the SRH header.

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   At the same time, set NRP-ID into segment. These NRP-IDs can be the
   same or different values according to actual requirement.

   Generally, the nodes along the route of the message use the same
   NRP-ID to identify the NRP associated with the network slice.
   Therefore, when the headend node encapsulates the segment list in
   the SRH, it writes the same NRP-ID into segments except the last
   segment.

   In some special cases, such as cross domain scenarios, different
   NRP-IDs may be used on the forwarding path. In this case, the
   controller may need to write the NRP-ID into each segment of the
   segment list in advance, and then issue the SRv6 policy to the
   headend node. The headend node only needs to use SRv6 policy to
   encapsulate customer traffic.

       +-----------------------------------------------------------+
       | IPv6 Header                                               |
       .  Source IP Address = IPv6 Address of Ingress              .
       .  Destination IP Address = SegmentList[SL]                 .
       .  Next-Header = SRH (43)                                   .
       .                                                           .
       +-----------------------------------------------------------+
       | SRH as specified in RFC 8754                              |
       .  <Segment0>                                               .
       .  <Segment1|NRP-ID1>                                      .
       .  <Segment2 NRP-ID2>                                      .
       .  <SegmentN|NRP-IDN>                                      .
       .                                                           .
       +-----------------------------------------------------------+
       | Payload                                                   |
       .                                                           .
       +-----------------------------------------------------------+
                       Figure 5: Format of SRv6 TE with slice ID

6. Behavior of endpoint

   When a SRv6 node receives a packet, the destination address of the
   packet is the segment instantiated locally by the SRv6 node. At this
   time, the SRv6 node processes the packet as endpoint node. The
   endpoint node extracts the NRP-ID from the segment and forwards the
   packet with the NRP identified by the NRP-ID.

   When N receives a packet whose IPv6 DA is S and S is a local End
   SID, the pseudo code processed is modified as follows based on
   RFC[8986]:

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   S01 - S11.
   S12.   Decrement IPv6 Hop Limit by 1
   S13.   Decrement Segments Left by 1
   S14.   Update IPv6 DA with Segment List[Segments Left]
   Insert Extract NRP-ID from destination address.

   Modify:
   S15.   Uses the NRP-ID to select a NRP and apply NRP policies to
   forward packet
   S16. }

   When N receives a packet whose IPv6 DA is S and S is a local End.X
   SID, the pseudo code processed is modified as follows based on
   RFC[8986]:

   S01 - S11.
   S12.   Decrement IPv6 Hop Limit by 1
   S13.   Decrement Segments Left by 1
   Insert Extract NRP-ID from destination address.
   S14.   Update IPv6 DA with Segment List[Segments Left]

   Modify:
   S15.   Submit the packet to the IPv6 module for transmission
          to the new destination via a member of J with using the
             resource of NRP
   S16. }

7. Behavior of transit node

   For the transit node, the destination address of the packet is not a
   local segment, and only IPv6 forwarding is performed for the packet.

   The transit node may be a node that supports SRv6 or a node that
   only supports IPv6.

   When processing SRv6 packets, the transit node can use the
   destination address to lookup the local slice prefix table according
   to the longest matching principle. If a prefix is hit, the NRP-ID
   could be extracted according to the configuration information.

   Therefore, the processing pseudo code can be modified as follows:

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   S1.  If ((Slice forwarding is enabled) && (Destination address hits
   network slice prefix)) {
   S2      Extracts NRP-ID from destination address by using the
   position information of hit prefix
   S2.     Uses the NRP-ID to apply NRP policies to forward packet
   S3.  }
   S4.  Else {
   S5.     Forwards the packet without applying any NRP policies
   S6. }

8. Example

   As shown in the following figure, the IP backbone network deploys
   the network slicing service. The network operator has created two
   NRPs, NRP1 and NRP2. NRP1 guarantees 100Mbps bandwidth and NRP2
   guarantees 200m bandwidth. Set the IDs NRP-ID1 and NRP-ID2 for the
   two NRPs respectively.

   The IP backbone network provides customers with two network slices.
   Network slice1 is mapped to NRP1 and network slice2 is mapped to
   NRP2. SRv6 is used to carry traffic and network slicing services.

   Along with the forwarding path <PE1-P1-P2-PE2>, dedicated queues
   with guaranteed bandwidth for NRP1 and NRP2 are configured at
   corresponding interfaces of each router. Taking the interface P1-P2
   of router P1 as an example, Queue 1 is configured with NRP-ID1 and
   guaranteed bandwidth of 100Mbps, and Queue 2 is configured with NRP-
   ID2 and 200Mbps. When P1 transmits a packet through interface P1-P2,
   the NRP-ID carried in the destination address is checked.

   If NRP-ID1 is encapsulated in the destination address, P1 uses queue
   1 to transmit the packet. If NRP-ID2 is encapsulated in the
   destination address, P1 uses queue 2 to transmit the packet.

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               .................................
               :        IP Backbone            :
      CPE      PE1       P1        P2        PE2   ......
      |----|   |---| NRP1|---| NRP1|---| NRP1|---|  : DC :
      |    o---|o-o|-----|o-o|-----|o-o|-----|o-o|--o    :
      |    o---|o-o|-----|o-o|-----|o-o|-----|o-o|--o    :
      |----|   |---| NRP2|---| NRP2|---| NRP2|---|  :....:
               :                               :
               :...............................:

                    +-------------+     +-------------+
                    |DA=          |     |DA=          |
                    |P1.End|NRP-ID|     |P2.VPNSID    |
                    +-------------+     +-------------+
                    |SRH          |     |SRH          |
                    |PE2.VPNSID   |     |PE2.VPNSID   |
                    |P3.End|NRP-ID|     |P3.End|NRP-ID|
                    |P1.End|NRP-ID|     |P1.End|NRP-ID|
      +-------+ <-> +-------------+<...>+-------------+ <-> +-------+
      |Payload|     | Payload     |     |  Payload    |     |Payload|
      +-------+     +-------------+     +-------------+     +-------+

      |----|         Interface: P1-P2
      |    |  ----------------------------------
      |    |  >>>>>>Queue 1: NRP-ID1, 100Mbps>>>>>>
      | P1 |  >>>>>>Queue 2: NRP-ID2, 200Mbps>>>>>>
      |    |  >>>>>>         ...          >>>>>>
      |    |  ----------------------------------
      |----|
                       Figure 6: example topology

9. IANA Considerations

   This document has no IANA actions.

10. Security Considerations

   The security requirements and mechanisms described in [RFC8402] and
   [RFC8754] also apply to this document.

   This document does not introduce any new security consideration.

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11. References

11.1. Normative References

   [I-D.cheng-teas-network-slice-usecase] Cheng, W., Jiang, W., Chen,
             R., Gong, L., and S. Peng, "IETF Network Slice use cases",
             draft-cheng-teas-network-slice-usecase-01 (expired),
             August 2021.

   [I-D.ietf-teas-ietf-network-slices] Farrel, A., Gray, E., Drake, J.,
             Rokui, R., Homma, S., Makhijani, K., Contreras, L., and J.
             Tantsura, "Framework for IETF Network Slices", draft-ietf-
             teas-ietf-network-slices-12 (work in progress), June 2022.

   [I-D.ietf-teas-ns-ip-mpls] Saad, T., Beeram, Dong, J., Wen, B.,
             Ceccarelli, D., Halpern, J., Peng, S., Chen, R., Liu, X.,
             Contreras, L. M., Rokui, R., and L. Jalil, "Realizing
             Network Slices in IP/MPLSNetworks", Work in Progress,
             Internet-Draft, draft-ietf-teas-ns-ip-mpls-00, June 2022,
             <https://www.ietf.org/archive/id/draft-ietf-teas-ns-ip-
             mpls-00.txt>.

   [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>.

   [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>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy,
             J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing
             Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
             <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
             D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
             (SRv6) Network Programming", RFC 8986, DOI
             0.17487/RFC8986, February 2021, <https://www.rfc-
             editor.org/info/rfc8986>.

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Authors' Addresses

   Yisong Liu
   China Mobile
   China
   Email: liuyisong@chinamobile.com

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Hao Li
   New H3C Technologies
   China
   Email: lihao@h3c.com

   Liyan Gong
   China Mobile
   China
   Email: gongliyan@chinamobile.com

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