Computing Segment for Service Routing in SAN
draft-zhou-intarea-computing-segment-san-02

INTAREA                                                          F. Zhou
Internet-Draft                                                   D. Yuan
Intended status: Standards Track                         ZTE Corporation
Expires: 22 October 2023                                         D. Yang
                                             Beijing Jiaotong University
                                                           20 April 2023

              Computing Segment for Service Routing in SAN
              draft-zhou-intarea-computing-segment-san-02

Abstract

   Since services provisioning requires 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 a 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
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   This Internet-Draft will expire on 22 October 2023.

Copyright Notice

   Copyright (c) 2023 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
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   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 . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  When the SAN ID is encapsulated in the DOH  . . . . . . .   6
     4.2.  When the SAN ID is encapsulated in the HBH  . . . . . . .   8
     4.3.  When the SAN ID is encapsulated in the SRH TLV  . . . . .  10
   5.  Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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 provisioning requires 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 service routing strategy
      is applied in the network domain, a quantity of relay nodes
      besides the destination are also 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.

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   *  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
      changed accidentally and the packet may even be discarded in the
      forwarding process.

   *  The Segment Routing Header (SRH) and the SRH TLV is defined in
      [RFC8754].  Since the segment list is encoded in order, it
      indicates that the service routing process and successive
      forwarding behaviours must be orchestrated in advance.  However,
      previous orchestration brings visible restrictions to the
      flexibility and adaptability of service routing.

   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.

                                              +-------+
                                              |  I P  |
                       SAN ID <-------------> |Routing|
                                     |        | Table |
                                     |        +-------+
                                     v
                                 +-------+
                                 |Service|
                                 |Routing|
                                 | Table |
                                 +-------+

   +--------+        +-----------+          +----------+        +-----+
   | Client +--------+Ingress  PE+----------+Egress  PE+--------+ L B |
   +--------+        +-----------+          +----------+        +-----+

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                      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 path metrics, computing status 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 identify and resolve
   SAN header in need and to implement a referred forwarding behaviour
   through the complete procedure.

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

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   *  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 service routing table indexed by SAN ID.

   *  Update destination address accordingly.

   *  Push a new IPv6 header with possible SRH containing the list of
      segments of the SRv6 policy.

   *  Forward the packet.

   In the case of SRv6, a new behavior End.C for Computing Segment is
   defined.  Behaviours of End.C are described in the following
   sections.

4.1.  When the SAN ID is encapsulated 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:

   (1) If the traffic is steered into a tunnel, an SRv6 policy for
   instance:

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  S01.  If (IPv6 Hop Limit <= 1) {
  S02.    Send an ICMP Time Exceeded message to the Source Address
          with Code 0 (Hop limit exceeded in transit),
          interrupt packet processing, and discard the packet.
  S03.  }
  S04.  Decrement IPv6 Hop Limit by 1
  S05.  Resolve the SAN ID encapsulated in the DOH
  S06.  Maintain the SAN Header in the DOH
  S07.  Query the service routing table indexed by SAN ID to determine
        an outer gateway and an according SRv6 policy
  S08.  If an SRH is carried in the IPv6 header {
  S09.    If (Segments Left == 0) {
  S10.      Stop processing the SRH, and proceed to process the next
            header in the packet, whose type is identified by
            the Next Header field in the routing header.
  S11.    }
  S12.    max_LE = (Hdr Ext Len / 2) - 1
  S13.    If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
  S14.      Send an ICMP Parameter Problem to the Source Address
            with Code 0 (Erroneous header field encountered)
            and Pointer set to the Segments Left field,
            interrupt packet processing, and discard the packet.
  S15.    }
  S16.    Decrement Segments Left by 1
  S17.    Update IPv6 DA with Segment List[Segments Left]
  S18.  }
  S19.  else {
  S20.      Update IPv6 DA with the queried gateway
  S21.  }
  S22.  Push a new IPv6 header with its own SRH containing the list of
        segments of the SRv6 policy
  S23.  Set the outer IPv6 SA to itself
  S24.  Set the outer IPv6 DA to the first SID of the SRv6 policy
  S25.  Set the outer Payload Length, Traffic Class, Flow Label and
        Next Header fields
  S26.  Submit the packet to the egress IPv6 FIB lookup for transmission
        to the new destination

       Figure 3: When the SAN ID is encapsulated in the DOH: Part 1

   (2) If the traffic is steered in a BE manner:

   The line S07 and lines from S22 to S24 are replaced by the following:

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  S07.    Query the service routing table indexed by SAN ID to determine
          an outer gateway

  S22.    Push a new IPv6 header
  S23.    Set the outer IPv6 SA to itself
  S24.    Set the outer IPv6 DA to the queried outer gateway

       Figure 4: When the SAN ID is encapsulated in the DOH: Part 2

4.2.  When the SAN ID is encapsulated 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:

   (1) If the traffic is steered into a tunnel, an SRv6 policy for
   instance:

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  S01.  If (IPv6 Hop Limit <= 1) {
  S02.    Send an ICMP Time Exceeded message to the Source Address
          with Code 0 (Hop limit exceeded in transit),
          interrupt packet processing, and discard the packet.
  S03.  }
  S04.  Decrement IPv6 Hop Limit by 1
  S05.  Resolve the SAN ID encapsulated in the HBH
  S06.  Maintain the SAN Header in the HBH
  S07.  Query the service routing table indexed by SAN ID to determine
        an outer gateway and an according SRv6 policy
  S08.  If an SRH is carried in the IPv6 header {
  S09.    If (Segments Left == 0) {
  S10.      Stop processing the SRH, and proceed to process the next
            header in the packet, whose type is identified by
            the Next Header field in the routing header.
  S11.    }
  S12.    max_LE = (Hdr Ext Len / 2) - 1
  S13.    If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
  S14.      Send an ICMP Parameter Problem to the Source Address
            with Code 0 (Erroneous header field encountered)
            and Pointer set to the Segments Left field,
            interrupt packet processing, and discard the packet.
  S15.    }
  S16.    Decrement Segments Left by 1
  S17.    Update IPv6 DA with Segment List[Segments Left]
  S18.  }
  S19.  else {
  S20.      Update IPv6 DA with the queried gateway
  S21.  }
  S22.  Push a new IPv6 header with its own SRH containing the list of
        segments of the SRv6 policy
  S23.  Set the outer IPv6 SA to itself
  S24.  Set the outer IPv6 DA to the first SID of the SRv6 policy
  S25.  Set the outer Payload Length, Traffic Class, Flow Label and
        Next Header fields
  S26.  Submit the packet to the egress IPv6 FIB lookup for transmission
        to the new destination

       Figure 5: When the SAN ID is encapsulated in the HBH: Part 1

   (2) If the traffic is steered in a BE manner:

   The line S07 and lines from S22 to S24 are replaced by the following:

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  S07.    Query the service routing table indexed by SAN ID to determine
          an outer gateway

  S22.    Push a new IPv6 header
  S23.    Set the outer IPv6 SA to itself
  S24.    Set the outer IPv6 DA to the queried outer gateway

       Figure 6: When the SAN ID is encapsulated in the HBH: Part 2

4.3.  When the SAN ID is encapsulated in the SRH TLV

   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:

   (1) If the traffic is steered into a tunnel, an SRv6 policy for
   instance:

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S01.  When an SRH is processed {
S02.    If (Segments Left == 0) {
S03.      Stop processing the SRH, and proceed to process the next
          header in the packet, whose type is identified by
         the Next Header field in the routing header.
S04.    }
S05.    If (IPv6 Hop Limit <= 1) {
S06.      Send an ICMP Time Exceeded message to the Source Address
          with Code 0 (Hop limit exceeded in transit),
          interrupt packet processing, and discard the packet.
S07.    }
S08.    max_LE = (Hdr Ext Len / 2) - 1
S09.    If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10.      Send an ICMP Parameter Problem to the Source Address
          with Code 0 (Erroneous header field encountered)
          and Pointer set to the Segments Left field,
          interrupt packet processing, and discard the packet.
S11.    }
S12.    Decrement IPv6 Hop Limit by 1
S13.    Decrement Segments Left by 1
S14.    Update IPv6 DA with Segment List[Segments Left]
S15.    Resolve the SAN ID encapsulated in the HBH, DOH or a type of
        SRH TLV
S16.    Maintain the SAN Header in the HBH, DOH or a type of SRH TLV
S17.    Query the service routing table indexed by SAN ID to determine
        an outer gateway and an according SRv6 policy
S18.    Push a new IPv6 header with its own SRH containing the list of
        segments of the SRv6 policy
S19.    Set the outer IPv6 SA to itself
S20.    Set the outer IPv6 DA to the first SID of the SRv6 policy
S21.    Set the outer Payload Length, Traffic Class, Flow Label and
        Next Header fields
S22.    Submit the packet to the egress IPv6 FIB lookup for transmission
        to the new destination
S23.  }

   Figure 7: When the SAN ID is encapsulated in the SRH TLV: Part 1

   (2) If the traffic is steered in a BE manner:

   The lines from S17 to S20 are replaced by the following:

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  S17.    Query the service routing table indexed by SAN ID to determine
          an outer gateway
  S18.    Push a new IPv6 header
  S19.    Set the outer IPv6 SA to itself
  S20.    Set the outer IPv6 DA to the queried outer gateway

     Figure 8: When the SAN ID is encapsulated in the SRH TLV: Part 2

5.  Use Case

   When a SAN header is carried as an option in the DOH, a typical
   service routing procedure is shown in Figure 9.

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   +--------+         +-----------+        +----------+         +-----+
   | Client +---------+Ingress  PE+--------+Egress  PE+---------+ L B |
   +--------+         +-----------+        +----------+         +-----+

   Inner IPv6 Packet:

           +-----------+        +-----------+        +-----------+
           |    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      |      Gateway      |        Interface      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        ID 1       |      Egress 1     |         Policy 1      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        ID 2       |      Egress 2     |         Policy 2      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            ......                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 9: Typical Service Routing 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 in the network domain by IGP.  The client registers
   with the management and operation system to acquire a SAN ID and
   encapsulates it in the packet.  The initial destination is END.C (SID
   1) which may be configured in a static routing manner.  The service
   addressing procedure from the client to the cloud is described below:

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

   *  When Ingress PE receives the packet, it identifys that DA is a
      Computing SID (SID1).  As defined in 4.2, the Ingress PE
      determines the next hop for service routing which is END.C (SID 2)
      and updates DA.  Ingress PE encapsulates an outer IPv6 header and
      continues to forward the packet carrying the DOH.

   *  When Egress PE receives the packet, it identifys that DA is a
      Computing SID (SID2).  As defined in 4.2, the Egress PE determines
      the next hop for service routing which is DIP which represents a
      specific service instance and updates DA.  Egress PE further
      continues to forward the packet carrying the DOH.

   *  When an intra-cloud LB receives the packet, the packet can be
      forwarded in a service routing manner or be processed in a native
      IP way, depending on the practical circumstances.

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

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        Figure 10: Outer Headers Encapsulated between Ingress PE and
                                 Egress PE

   As shown in Figure 10, 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.

6.  Security Considerations

   Security has always been an indispensable and significant
   consideration for design and innovation in the fields of
   communication and services provisioning.  A Computing Segment as
   END.C defined in this draft may be given security semantics and
   according behaviours, including encryption and decryption, etc.
   Security considerations may be studied in the future work.

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., Tan, B., and D. Yang, "Service Aware Network
              Framework", Work in Progress, Internet-Draft, draft-huang-
              service-aware-network-framework-01, 22 November 2022,
              <https://datatracker.ietf.org/doc/html/draft-huang-
              service-aware-network-framework-01>.

   [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/doc/html/draft-ma-intarea-
              encapsulation-of-san-header-00>.

   [I-D.ma-intarea-identification-header-of-san]
              Ma, L., Zhou, F., lihesong, and D. Yang, "Service
              Identification Header of Service Aware Network", Work in
              Progress, Internet-Draft, draft-ma-intarea-identification-

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              header-of-san-00, 23 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ma-intarea-
              identification-header-of-san-00>.

   [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>.

   [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

Zhou, et al.             Expires 22 October 2023               [Page 16]
Internet-Draft    Computing Segment for Service Routing       April 2023

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

Zhou, et al.             Expires 22 October 2023               [Page 17]