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Computing Segment for Service Routing in SAN
draft-zhou-intarea-computing-segment-san-01

Document Type Active Internet-Draft (individual)
Authors Fenlin Zhou , Dongyu Yuan , Dong Yang
Last updated 2022-10-23
Replaces draft-computing-segment-for-service-routing
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draft-zhou-intarea-computing-segment-san-01
INTAREA                                                          F. Zhou
Internet-Draft                                                   D. Yuan
Intended status: Standards Track                         ZTE Corporation
Expires: 27 April 2023                                           D. Yang
                                             Beijing Jiaotong University
                                                         24 October 2022

              Computing Segment for Service Routing in SAN
              draft-zhou-intarea-computing-segment-san-01

Abstract

   Since services delivered from cloud need delicate coordination among
   the client, network and cloud, this draft defines a new Segment to
   provide service routing and addressing functions by leveraging SRv6
   Segment programming capabilities.  With Computing Segments proposed,
   the network gains its capability to identify and process SAN header
   in need and a complete service routing procedure can be achieved.

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
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   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 27 April 2023.

Copyright Notice

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

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   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Service Identification in SAN . . . . . . . . . . . . . .   2
     1.2.  Service Routing in SAN  . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Computing Segment . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  When a SAN Header is Carried as an Option in the HBH  . .   6
     4.2.  When a SAN Header is Carried as an Option in the DOH  . .   6
     4.3.  When a SAN Header is Carried as a Type of SRH TLV . . . .   7
   5.  Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

1.1.  Service Identification in SAN

   In order to deliver responsive services to clients, computing
   resources continuously migrate and spread from central sites to edge
   nodes.  As shown in Figure 1, multiple instances located
   distributedly in different resource pools are capable of providing
   services.  Compared with applying traditional IP routing protocols, a
   fine-grained service routing policy is capable of achieving optimal
   and efficient invocation of both computing power and the network.

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                                            +-------------+ +---------+
                                          +-+Load Balancer+-+Service 1|
                                          | +-------------+ +---------+
                                          |
    +------+   +----------+   +---------+ | +-------------+ +---------+
    |Client+---+Ingress PE+---+Egress PE+-+-+Load Balancer+-+Service 2|
    +------+   +----------+   +---------+ | +-------------+ +---------+
                                          |
                                          | +-------------+ |---------+
                                          +-+Load Balancer+-|Service 3|
                                            +-------------+ +---------+
    |<-Client->|<---------Network-------->|<----------Cloud---------->|

                     Figure 1: Computing Power Networks

   In order to implement service routing, the network should be aware of
   specific services and a service awareness network framework is
   introduced in [I-D.huang-service-aware-network-framework].  Within
   the proposed network framework, a service identification is defined
   as a SAN ID(Service ID) in
   [I-D.ma-intarea-identification-header-of-san] to represent a globally
   unique service semantic identification.

   As mentioned in [I-D.ma-intarea-encapsulation-of-san-header], a SAN
   ID is encapsulated in a SAN header which can be carried as an option
   in the IPv6 Hop-by-Hop Options Header, Destination Options Header and
   a type of SRH TLV.  Since services delivered from cloud need delicate
   coordination among the client, network and cloud and thus simply
   encapsulating SAN header among packets delivery can hardly satisfy
   various practical situations:

   *  The Destination Options header is used to carry optional
      information that need be examined by the destination of the path
      which is defined in [RFC8200], SAN header will only be resolved by
      the destination node.  When a multi-layer routing protocol is
      applied in the network domain, a quantity of relay nodes besides
      the destination are required to identify SAN ID and forward the
      received packet accordingly as well.  Thus, simply carring a SAN
      header can not fulfill a multi-layer service routing procedure.

   *  When a SAN header is carried as an option in the IPv6 Hop-by-Hop
      Options Header, it may be processed by each nodes.  Practically,
      not all nodes along the delivery path of the packet are capable of
      identifying and processing a SAN header.  The SAN header may be
      modified and changed and the packet may even be discarded in the
      forwarding process.

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   *  The Segment Routing Header (SRH) and the SRH TLV is defined in
      [RFC8754].  Since the segment list is encoded in order, it must be
      orchestrated in advance which indicates various endpoint
      behaviours in order to successively implement the designated
      service routing.  Previous orchestration should be regarded to be
      severe restrictions.

   To achieve a SAN header being processed in need in the network domain
   and to preserve its identifiability along the path from the client to
   the server, a new Segment to specify and standardize node behaviours
   is urgently required.

1.2.  Service Routing in SAN

   As shown in Figure 2, a service routing table is designed to
   establish a mapping relationship between the SAN ID and the
   conventional IP routing table.

               +-------+   +-------+
               |Service|   |  I P  |
   SAN ID<---->|Routing|<->|Routing|
               | Table |   | Table |
               +-------+   +-------+
   +--------+        +-----------+          +----------+        +-----+
   | Client +--------+Ingress  PE+----------+Egress  PE+--------+ L B |
   +--------+        +-----------+          +----------+        +-----+

                      Figure 2: Service Routing in SAN

   A service routing table can be published from a control and
   management system to the network domain within a centralized control
   plane while it can also be calculated and generated by the Ingress PE
   itself under a distributed control plane.

   With considerations of both path metrics and service SLA
   requirements, a specific service routing table is introduced,
   including mutiple attributes, SAN ID and outer gateway for instance.
   Afterwards, a corresponding IP routing table should be indexed which
   further determines the next hop or an SRv6 policy.

   In order to describe and standardize the mentioned behaviours, a new
   Computing Segment is proposed.  With Computing Segments, multiple
   nodes in the network domain can be informed to locate and identify
   SAN header in need and to implement a referred forwarding behaviour
   through the complete procedure.

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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.  Terminology

   *  SAN: Service Aware Network

   *  SAN ID: Service Aware Network Identification, an identification
      designed to indicate the fundamental and common service types

   *  SAN header: Encapsulation format of the SAN ID

   *  DOH: Destination Options Header

   *  HBH: Hop-by-Hop Options Header

   *  SRH: Segment Routing Header

   *  SID: Segment Identifier

   *  FIB: Forwarding Information Base

   *  DA: Destination Address

   *  LB: Load Balancer

4.  Computing Segment

   This draft introduces a new SRv6 Segment, namely Computing Segment,
   aiming to describe the behaviour of querying service routing table
   and corresponding packet forwarding.

   Computing Segment is the identifier of packets in which a
   corresponding SAN header should be identified and further being
   forwarded via the matched service routing table entity, indicating
   the following operations:

   *  Identify the SAN ID encapsulated in DOH, HBH or SRH TLV.

   *  Query the forwarding table entry indexed by SAN ID.

   *  Forward the packet to the new destination.

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   In the case of SRv6, a new behavior End.C for Computing Segment is
   defined.  An instance of a Computing SID is associated with a service
   routing table and a source address.

   Behaviours of End.C when a SAN header is carried as an option in the
   HBH, DOH or a type of SRH TLV are described in the following
   sections.

4.1.  When a SAN Header is Carried as an Option in the HBH

   When an IPv6 node (N) receives an IPv6 packet whose destination
   address matches a local IPv6 address instantiated as a SID (S), and S
   is a Computing SID, N does:

    S01.  When an IPv6 packet is processed {
    S02.    Identify the SAN ID encapsulated in the option of the HBH
    S03.      Query the forwarding table entry indexed by SAN ID
    S04.      Set the packet's associated FIB table to the specific FIB
    S05.      Set the IPv6 DA to the next hop
    S06.      Maintain the TLVs in the HBH
    S07.      Resubmit the packet and transmit to the new destination
    S08.  }

       Figure 3: When a SAN Header is Carried as an Option in the HBH

4.2.  When a SAN Header is Carried as an Option in the DOH

   When an IPv6 node (N) receives an IPv6 packet whose destination
   address matches a local IPv6 address instantiated as a SID (S), and S
   is a Computing SID, N does:

    S01.  When an IPv6 packet is processed {
    S02.      Identify the SAN ID encapsulated in the option of the DOH
    S03.      Query the forwarding table entry indexed by SAN ID
    S04.      Set the packet's associated FIB table to the specific FIB
    S05.      Set the IPv6 DA to the next hop
    S06.      Maintain the TLVs in the DOH
    S07.      Resubmit the packet and transmit to the new destination
    S08. }

       Figure 4: When a SAN Header is Carried as an Option in the DOH

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4.3.  When a SAN Header is Carried as a Type of SRH TLV

   When an SRv6-capable node (N) receives an IPv6 packet whose
   destination address matches a local IPv6 address instantiated as an
   SRv6 SID (S), and S is a Computing SID, N does:

S01.  When an SRH is processed {
S02.      If (Segments Left>0) {
S03.              Decrement IPv6 Hop Limit by 1
S04.              Decrement Segments Left by 1
S05.              Update IPv6 DA with Segment List[Segments Left]
S06.              Identify the SAN ID encapsulated in the SRH TLV
S07.              Query the forwarding table entry indexed by SAN ID
S08.              Set the packet's associated FIB table to the specific FIB
S09.              Maintain the TLVs in the SRH
S10.              Resubmit the packet transmit to the new destination
S11.      }
S12.  }

     Figure 5: When a SAN Header is Carried as a Type of SRH TLV

   When a SAN header is carried as a type of SRH TLV, Computing SIDs in
   Segment List are required to be orchestrated in advance which
   previously indicates the the determinism of a multi-segment routing
   policy.  Therefore, Computing Segment does not cooperate well with
   the circumstances when a SAN header is carried as a type of SRH TLV.

5.  Use Case

   When a SAN header is carried as an option in the DOH, a typical
   service addressing procedure is shown in Figure 6.

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   +--------+         +-----------+        +----------+         +-----+
   | Client +---------+Ingress  PE+--------+Egress  PE+---------+ L B |
   +--------+         +-----------+        +----------+         +-----+
           +-----------+        +-----------+        +-----------+
           |    SIP    |        |    SIP    |        |    SIP    |
           +-----------+        +-----------+        +-----------+
           |END.C(SID1)|        |END.C(SID2)|        |    DIP    |
           +-----------+        +-----------+        +-----------+
           |    DOH    |        |    DOH    |        |    DOH    |
           +-----------+        +-----------+        +-----------+
           |  PAYLOAD  |        |  PAYLOAD  |        |  PAYLOAD  |
           +-----------+        +-----------+        +-----------+
     DOH:
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Next Header  | Hdr Ext Len   |  Opt  Length  |Opt Data Length|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          SAN Header                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |
     Service Routing Table:          v
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             SAN ID                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         (SRv6 Policy)                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Outer Gateway                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |
     IP ROUTING TABLE:               v
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Outer Gateway                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Next  Hop                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 6: Typical Service Addressing Procedure with Service ID
                          Encapsulated in the DOH

   Suppose the Endpoint behaviour of END.C is configured at Ingress PE
   and Egress PE, namely SID 1 and SID 2 respectively.  SID1 and SID2
   are advertised to the nodes in the network by IGP.  The service
   addressing procedure from the client to the cloud is described below:

   The Computing SID of Ingress PE (SID1) is configured as DA by the
   client.  The packet carrying the SAN header as the option of the DOH
   is forwarded to Ingress PE.

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   When Ingress PE receives the packet, it queries the local routing
   table in accordance with DA and identifys that DA is a Computing SID
   (SID1).  As defined in 4.2, the Ingress PE continues to forward the
   packet carrying the DOH.

   When Egress PE receives the packet, it queries the local routing
   table in accordance with DA and identifys that DA is a Computing SID
   (SID2).  As defined in 4.2, the Egress PE continues to forward the
   packet carrying the DOH.

   When an intra-cloud LB receives the packet, the packet can be
   forwarded in accordance with the Endpoint behaviour defined in 4.2.
   or be processed as a normal IPV6 packet, depending on the practical
   circumstances.

   |<-Client->|<-------------------Network----------------->|<-Cloud->|
   +------+     +----------+                   +---------+     +-----+
   |Client+-----+Ingress PE+-------------------+Egress PE+-----+ L B |
   +------+     +----------+         |         +---------+     +-----+
                             BE:     v      TE:
                         +-----------+  +-----------+
                         |    IIP    |  |    IIP    |
                         +-----------+  +-----------+
                         |    EIP    |  |    SID    |
                         +-----------+  +-----------+
                         |    SIP    |  |    SRH    |
                         +-----------+  +-----------+
                         |END.C(SID2)|  |    SIP    |
                         +-----------+  +-----------+
                         |    DOH    |  |END.C(SID2)|
                         +-----------+  +-----------+
                         |  PAYLOAD  |  |    DOH    |
                         +-----------+  +-----------+
                                        |  PAYLOAD  |
                                        +-----------+

   Figure 7: Outer Headers Encapsulated between Ingress PE and Egress PE

   As shown in Figure 7, between Ingress PE and Egress PE, an outer
   header including SRH should be encapsulated when the traffic follows
   a specific SRv6 TE policy.  Otherwise, a normal IPv6 header should be
   encapsulated under a BE condition.  In the introduced case, the SAN
   header is not perceived by relay devices between Ingress PE and
   Egress PE.

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6.  Security Considerations

   TBA

7.  Acknowledgements

   TBA

8.  IANA Considerations

   This document requires registration of End.C behavior in "SRv6
   Endpoint Behaviors" sub-registry of "Segment Routing Parameters"
   registry.

9.  Normative References

   [I-D.huang-service-aware-network-framework]
              Huang, D. and B. Tan, "Service Aware Network Framework",
              Work in Progress, Internet-Draft, draft-huang-service-
              aware-network-framework-00, 24 May 2022,
              <https://www.ietf.org/archive/id/draft-huang-service-
              aware-network-framework-00.txt>.

   [I-D.ma-intarea-encapsulation-of-san-header]
              Ma, L., Zhao, D., Zhou, F., and D. Yang, "Encapsulation of
              SAN Header", Work in Progress, Internet-Draft, draft-ma-
              intarea-encapsulation-of-san-header-00, 23 October 2022,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ma-intarea-encapsulation-of-san-header/>.

   [I-D.ma-intarea-identification-header-of-san]
              Ma, L., Zhou, F., Li, H., and D. Yang, "Service
              Identification Header of Service Aware Network", Work in
              Progress, Internet-Draft, draft-ma-intarea-identification-
              header-of-san-00, 24 October 2022,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ma-intarea-identification-header-of-san/>.

   [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>.

   [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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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [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>.

Authors' Addresses

   Fenlin Zhou
   ZTE Corporation
   No.50 Software Avenue
   Nanjing
   Jiangsu, 210012
   China
   Email: zhou.fenlin@zte.com.cn

   Dongyu Yuan
   ZTE Corporation
   No.50 Software Avenue
   Nanjing
   Jiangsu, 210012
   China
   Email: yuan.dongyu@zte.com.cn

   Dong Yang
   Beijing Jiaotong University
   No.3 Shangyuancun Haidian District
   Beijing
   100044
   China
   Email: dyang@bjtu.edu.cn

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