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SPRING Working Group                                             J. Dong
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                               S. Bryant
Expires: January 31, 2021                         Futurewei Technologies
                                                             T. Miyasaka
                                                        KDDI Corporation
                                                                  Y. Zhu
                                                           China Telecom
                                                                  F. Qin
                                                                   Z. Li
                                                            China Mobile
                                                                 F. Clad
                                                           Cisco Systems
                                                           July 30, 2020


             Introducing Resource Awareness to SR Segments
              draft-ietf-spring-resource-aware-segments-00

Abstract

   This document describes the mechanism to associate network resource
   attributes to Segment Routing Identifiers (SIDs).  Such SIDs are
   referred to as resource-aware SIDs in this document.  The resource-
   aware SIDs retain their original forwarding semantics, but with the
   additional semantics to identify the set of network resources
   available for the packet processing action.  The resource-aware SIDs
   can therefore be used to build SR paths or virtual networks with a
   set of reserved network resources.  The proposed mechanism is
   applicable to both segment routing with MPLS data plane (SR-MPLS) and
   segment routing with IPv6 data plane (SRv6).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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/.




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   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 January 31, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Segments with Resource Awareness  . . . . . . . . . . . . . .   3
     2.1.  SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  SRv6  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Control Plane Considerations  . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Segment Routing (SR) [RFC8402] specifies a mechanism to steer packets
   through an ordered list of segments.  A segment is referred to by its
   Segment Identifier (SID).  With SR, explicit source routing can be
   achieved without introducing per-path state into the network.
   Compared with RSVP-TE [RFC3209], currently SR does not have the
   capability of reserving network resources or identifying a set of
   network resources reserved for individual services or customers.
   Although a centralized controller can have a global view of network



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   state and can provision different services using different SR paths,
   in data packet forwarding it still relies on traditional DiffServ QoS
   mechanism [RFC2474] [RFC2475] to provide coarse-grained traffic
   differentiation in the network.  While such kind of mechanism may be
   sufficient for some types of services, some customers or services may
   require a set of dedicated network resources to be allocated in the
   network to achieve resource isolation from other customers/services
   in the same network.  Also note the number of such customers or
   services can be larger than the number of traffic classes available
   with DiffServ QoS.

   This document extends the SR paradigm without the need of defining
   new SID types by associating SIDs with network resource attributes.
   These resource-aware SIDs retain their original functionality, with
   the additional semantics of identifying the set of network resources
   available for the packet processing action.  On a particular network
   segment, multiple resource-aware SIDs can be allocated, each of which
   represents a subset of network resources allocated to meet the
   requirement of individual customers or services.  The allocation of
   network resources on a network segment can be done via a controller
   or via local configuration, then each set of resource is associated
   with a resource-aware SID.  These resource-aware SIDs can be used to
   build SR paths with a set of reserved network resources, which can be
   used in network scenarios which require to allocate a set of network
   resources for the processing of groups of service traffic.  The
   resource-aware SIDs can also be used to build SR based virtual
   networks with the required network topology and resource attributes.
   The proposed mechanism is applicable to SR with both MPLS data plane
   (SR-MPLS) and IPv6 data plane (SRv6).

2.  Segments with Resource Awareness

   In segment routing architecture [RFC8402], several types of segments
   are defined to represent either topological or service instructions.
   A topological segment can be a node segment or an adjacency segment.
   A service segment may be associated with specific service functions
   for service chaining purposes.  This document introduces additional
   resource semantics to these existing types of SIDs, so that the SIDs
   can be used to identify the topology or service functions, and the
   set of network resources allocated on the network segments for packet
   processing.

   This section describes the mechanisms of using SR SIDs to identify
   the additional resource information of SR paths or virtual networks
   with the two SR data plane instantiations: SR-MPLS and SRv6.  The
   mechanisms to identify the forwarding path or network topology with a
   SID as defined in [RFC8402] are unchanged, and the control plane can
   be based on [RFC4915], [RFC5120] and [I-D.ietf-lsr-flex-algo].



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2.1.  SR-MPLS

   As specified in [RFC8402], an IGP Adjacency Segment (Adj-SID) is an
   IGP-segment attached to a unidirectional adjacency or a set of
   unidirectional adjacencies.  An IGP Prefix segment is an IGP segment
   representing an IGP prefix, and IGP node segment is an IGP-Prefix
   segment that identifies a specific router (e.g., a loopback).  As
   described in [I-D.ietf-spring-segment-routing-central-epe] and
   [I-D.ietf-idr-bgpls-segment-routing-epe], BGP PeerAdj SID is used as
   an instruction to steer over a specific local interface towards a
   specific peer node in a peering Autonomous System (AS).  These types
   of SIDs can be extended to represent both topological elements and
   the resources allocated on a network segment.  The MPLS instantiation
   of Segment Routing is specified in [RFC8660].

   For one IGP link, multiple Adj-SIDs SHOULD be allocated, each of
   which is associated with a network topology the link participates,
   and MAY represent a subset of link resources.  Several approaches can
   be used to partition the link resource, such as [FLEXE], Layer-2
   logical sub-interfaces, dedicated queues, etc.  The detailed
   mechanism of resource partitioning is out of scope of this document.

   Similarly, for one IGP node, multiple prefix-SIDs SHOULD be
   allocated, each of which is associated with a network topology the
   node participates, and MAY represent a subset of the node resource
   (e.g. the processing resources).  For one inter-domain link, multiple
   BGP PeerAdj SIDs SHOULD be allocated, each of which is associated
   with a specific network topology, which spans multiple domains, and
   MAY represent a subset of link resource allocated on the inter-domain
   link.  Note that this per-segment resource allocation complies to the
   SR paradigm, which avoids introducing per-path state into the
   network.

   A group of resource-aware SIDs associated with the same network
   topology can be used to construct the SR paths (either strict or
   loose) to steer traffic within the topology.  Each SID in the SID-
   list of the SR path MAY represent the set of network resources
   reserved on the corresponding network segment.

   In data packet forwarding, the SIDs are used to identify the topology
   the packet belongs to, so that a topology specific next-hop can be
   determined.  In addition, the adj-SIDs MAY also be used to steer
   traffic of different services into different set of link resources.
   The prefix-SIDs MAY be used to steer traffic of different services
   into different set of node resources.  When a prefix-SID is used in
   the SID-list to build an SR loose path, the transit nodes can use the
   prefix-SID to identify the network topology and the associated group
   of resource, and can process the packet using the local resources



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   allocated to the corresponding resource group.  Note in this case, it
   is RECOMMENDED that Penultimate Hop Popping (PHP) [RFC3031] be
   disabled, otherwise the inner service label SHOULD be used to infer
   the set of resources to be used on the egress node of the SR path.

   This mechanism requires to allocate additional prefix-SIDs or adj-
   SIDs for network segments to identify different set of network
   resources.  As the number of resource groups increases, the number of
   SIDs would increase accordingly, while it should be noted that there
   is no per-path state introduced into the network.

2.2.  SRv6

   As specified in [I-D.ietf-spring-srv6-network-programming], an SRv6
   Segment Identifier (SID) is a 128-bit value which consists of a
   locator (LOC) and a function (FUNCT), optionally it may also contain
   additional arguments (ARG) immediately after the FUNCT.  The LOC of
   the SID is routable and leads to the node which instantiates that
   SID, which means the LOC can be parsed by all nodes in the network.
   The FUNCT part of the SID is an opaque identification of a local
   function bound to the SID, which means the FUNCT and ARG parts can
   only be parsed by the node which instantiates that SID.

   Taking the above into consideration, for a network node, multiple
   SRv6 LOCs SHOULD be allocated, each of which is associated with a
   network topology, and MAY represent a subset of the network resources
   associated with a virtual network.  The SRv6 SIDs of a particular
   virtual network SHOULD be allocated from the SID space using the
   resource-aware LOC as the prefix.  These SRv6 SIDs can be used to
   represent virtual network specific local functions.

   A group of SRv6 SIDs associated with the same network topology can be
   used to construct the SR paths (either strict or loose) to steer the
   traffic of particular service within the topology.  Each SID in the
   SID-list of the SR path MAY also represent the set of network
   resources on the corresponding network segment.

   In data packet forwarding, the LOC part of SRv6 SID is used by
   transit nodes to identify the topology the packet belongs to, so that
   a topology specific next-hop can be determined.  The LOC MAY also be
   used to indicate the set of local network resources on the transit
   nodes to be used for the forwarding of the received packet.  The SRv6
   segment endpoint nodes use the SRv6 SID to identify the topology the
   packet belongs to, and the particular local function to perform on
   the received packet.  The local SRv6 SID MAY also be used to identify
   the set of network resource to be used for executing the local
   function.




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   This mechanism requires to allocate additional SRv6 Locators and SIDs
   for network segments to identify different set of network resources.
   As the number of resource groups increases, the number of Locators
   and SIDs would increase accordingly, while it should be noted that
   there is no per-path state introduced into the network.

3.  Control Plane Considerations

   The mechanism described in this document makes use of a centralized
   controller to collect the information about the network
   (configuration, state, routing databases, etc.) as well as the
   service information (traffic matrix, performance statistics, etc.)
   for the planning of network resources based on service requirement.
   The controller is also responsible for the centralized computation
   and optimization of the SR paths with both the topology and network
   resource constraints.  The resource-aware SIDs can be either
   explicitly provisioned by the controller, or dynamically allocated by
   network nodes then reported to the controller.  The interaction
   between the controller and the network nodes can be based on PCEP
   [RFC5440], Netconf/YANG [RFC6241] [RFC7950] and BGP-LS [RFC7752].  In
   some scenarios, extensions to some of these protocols is needed,
   which are out of the scope of this document and will be specified in
   separate documents.  In some cases, a centralized controller may not
   be used, but this would complicate the operations and planning
   therefore not suggested.

   The distributed control plane is complementary to the centralized
   controller.  A distributed control plane can be used for the
   collection and distribution of the network topology and resource
   information associated with SIDs among network nodes.  Distributed
   route computation for services with topology and resource constraints
   may also be needed.  The distributed control plane may be based on
   [RFC4915], [RFC5120], [I-D.ietf-lsr-flex-algo] or the combination of
   some of them with necessary extensions.  The details are out of the
   scope of this document.

4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

5.  Security Considerations

   The security considerations of segment routing are applicable to this
   document.




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   The Resource-aware SIDs may be used for provisioning of SR paths or
   virtual networks to carry traffic with latency as one of the SLA
   parameters.  By disrupting the latency of such traffic an attack can
   be directly targeted at the customer application, or can be targeted
   at the network operator by causing them to violate their SLA,
   triggering commercial consequences.  Dynamic attacks of this sort are
   not something that networks have traditionally guarded against, and
   networking techniques need to be developed to defend against this
   type of attack.  By rigorously policing ingress traffic and carefully
   provisioning the resources provided to such services, this type of
   attack can be prevented.  However care needs to be taken when
   providing shared resources, and when the network needs to be
   reconfigured as part of ongoing maintenance or in response to a
   failure.

   The details of the underlay network MUST NOT be exposed to third
   parties, to prevent attacks aimed at exploiting a shared resource.

6.  Contributors

   Zhenbin Li
   Email: lizhenbin@huawei.com

   Zhibo Hu
   Email: huzhibo@huawei.com

7.  Acknowledgements

   The authors would like to thank Mach Chen, Stefano Previdi, Charlie
   Perkins, Bruno Decraene, Loa Andersson, Alexander Vainshtein and Joel
   Halpern for the valuable discussion and suggestions to this document.

8.  References

8.1.  Normative References

   [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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   [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>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

8.2.  Informative References

   [FLEXE]    "Flex Ethernet Implementation Agreement", March 2016,
              <http://www.oiforum.com/wp-content/uploads/OIF-FLEXE-
              01.0.pdf>.

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
              S., and J. Dong, "BGP-LS extensions for Segment Routing
              BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
              segment-routing-epe-19 (work in progress), May 2019.

   [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-08 (work in progress), July 2020.

   [I-D.ietf-spring-segment-routing-central-epe]
              Filsfils, C., Previdi, S., Dawra, G., Aries, E., and D.
              Afanasiev, "Segment Routing Centralized BGP Egress Peer
              Engineering", draft-ietf-spring-segment-routing-central-
              epe-10 (work in progress), December 2017.

   [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-08 (work in progress),
              July 2020.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-16 (work in
              progress), June 2020.






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   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <https://www.rfc-editor.org/info/rfc2475>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

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

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [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>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5439]  Yasukawa, S., Farrel, A., and O. Komolafe, "An Analysis of
              Scaling Issues in MPLS-TE Core Networks", RFC 5439,
              DOI 10.17487/RFC5439, February 2009,
              <https://www.rfc-editor.org/info/rfc5439>.






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   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC7810]  Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
              Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
              RFC 7810, DOI 10.17487/RFC7810, May 2016,
              <https://www.rfc-editor.org/info/rfc7810>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [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>.

   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.






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Authors' Addresses

   Jie Dong
   Huawei Technologies

   Email: jie.dong@huawei.com


   Stewart Bryant
   Futurewei Technologies

   Email: stewart.bryant@gmail.com


   Takuya Miyasaka
   KDDI Corporation

   Email: ta-miyasaka@kddi.com


   Yongqing Zhu
   China Telecom

   Email: zhuyq8@chinatelecom.cn


   Fengwei Qin
   China Mobile

   Email: qinfengwei@chinamobile.com


   Zhenqiang Li
   China Mobile

   Email: li_zhenqiang@hotmail.com


   Francois Clad
   Cisco Systems

   Email: fclad@cisco.com









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