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Internet Engineering Task Force (IETF)                     J. Brzozowski
Request for Comments: 8354                                      J. Leddy
Category: Informational                                          Comcast
ISSN: 2070-1721                                              C. Filsfils
                                                        R. Maglione, Ed.
                                                             M. Townsley
                                                           Cisco Systems
                                                              March 2018

    Use Cases for IPv6 Source Packet Routing in Networking (SPRING)


   The Source Packet Routing in Networking (SPRING) architecture
   describes how Segment Routing can be used to steer packets through an
   IPv6 or MPLS network using the source routing paradigm.  This
   document illustrates some use cases for Segment Routing in an
   IPv6-only environment.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2018 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
   to this document.  Code Components extracted from this document must
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  IPv6 SPRING Use Cases . . . . . . . . . . . . . . . . . . . .   3
     2.1.  SPRING in the Small Office  . . . . . . . . . . . . . . .   3
     2.2.  SPRING in the Access Network  . . . . . . . . . . . . . .   4
     2.3.  SPRING in Data Center . . . . . . . . . . . . . . . . . .   5
     2.4.  SPRING in Content Delivery Networks . . . . . . . . . . .   5
     2.5.  SPRING in Core Networks . . . . . . . . . . . . . . . . .   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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1.  Introduction

   Source Packet Routing in Networking (SPRING) architecture leverages
   the source routing paradigm.  An ingress node steers a packet by
   including a controlled set of instructions, called segments, in the
   SPRING header.  The SPRING architecture is described in
   [SEGMENT-ROUTING].  This document illustrates some use cases for
   SPRING / Segment Routing in an IPv6-only environment.

2.  IPv6 SPRING Use Cases

   The use cases described in this section do not constitute an
   exhaustive list of all the possible scenarios: this section only
   includes some of the most common envisioned deployment models for
   Segment Routing over IPv6 (SRv6).

   In addition to the use cases described in this document, all the
   SPRING use cases [RFC7855] are also applicable to the SRv6 data

2.1.  SPRING in the Small Office

   An IPv6-enabled Small Office, Home Office (SOHO) provides ample
   globally routed IP addresses for all devices in the SOHO.  An IPv6
   small office with multiple egress points and associated provider-
   assigned prefixes will, in turn, provide multiple IPv6 addresses to
   hosts.  A small office performing source and destination routing
   [PA-MULTIHOMING] will ensure that packets exit the SOHO at the
   appropriate egress based on the associated delegated prefix for that

   A SPRING-enabled SOHO provides the ability to steer traffic into a
   specific path from end hosts in the SOHO or from a customer edge
   router in the SOHO.  If the selection of the source-routed path is
   enabled at the customer edge router, that router is responsible for
   classifying traffic and steering it into the correct path.  If hosts
   in the SOHO have explicit source selection rules, classification can
   be based on the source address or associated network egress point,
   thus avoiding the need for implicit classification techniques based
   on Deep Packet Inspection (DPI).  If the traffic is steered into a
   specific path by the host itself, it is important to know which
   networks can interpret the SPRING header.  This information can be
   provided as part of the host configuration as a property of the
   configured IP address.

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   The ability to steer traffic to an appropriate egress or utilize a
   specific type of media (e.g., low power, Wi-Fi, wired, femtocell,
   Bluetooth, Multimedia over Coax Alliance (MoCA), HomePlug, etc.)
   within the home itself are obvious cases that may be of interest to
   an application running within a SOHO.

   Steering to a specific egress point may be useful for a number of
   scenarios, including:

   o  regulatory compliance;

   o  performance of a particular service associated with a particular

   o  cost imposed due to data caps or per-byte charges;

   o  distinguishing between personal vs. work traffic in homes with one
      or more teleworkers; and

   o  provision of specific services by one ISP vs. another.

   Information included in the SPRING header, whether imposed by the end
   host itself, a customer edge router, or within the access network of
   the ISP, may be of use at the far ends of the data communication as
   well.  For example, an application running on an end host with
   application support in a data center can utilize the SPRING header as
   a channel to include information that affects its treatment within
   the data center itself, which allows for application-level steering
   and load balancing without relying upon implicit application-
   classification techniques at the edge of the data center.  Further,
   as more and more application traffic is encrypted, the ability to
   extract (and include in the SPRING header) just enough information to
   enable the network and data center to load balance and steer traffic
   appropriately becomes more and more important.

2.2.  SPRING in the Access Network

   Access networks deliver a variety of types of traffic from the
   service provider's network to the home environment and from the home
   towards the service provider's network.

   For bandwidth management or related purposes, the service provider
   may want to associate certain types of traffic to specific physical
   or logical downstream capacity pipes.

   This mapping is not the same thing as classification and scheduling.
   In the cable access network, these pipes are represented at the Data-
   Over-Cable Service Interface Specification [DOCSIS] layer as

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   different service flows, which are better identified as distinct data
   links.  As such, creating this separation allows an operator to
   differentiate between different types of content and perform a
   variety of differing functions on these pipes, such as byte capping,
   regulatory compliance functions, and billing.

   In a cable operator's environment, these downstream pipes could be a
   DOCSIS [DOCSIS] service flow, a service group, or a specific
   Quadrature Amplitude Modulation (QAM) as in Annex B of [ITU.J83].

   Similarly, the operator may want to map traffic from the home sent
   towards the service provider's network to specific upstream capacity
   pipes.  Information carried in a packet's SPRING header could provide
   the target pipe for this specific packet.  The access device would
   not need to know specific details about the packet to perform this
   mapping; instead, the access device would only need to know the
   interpretation of the SPRING header and how to map it to the target

2.3.  SPRING in Data Center

   Some data center operators are transitioning their data center
   infrastructure from IPv4 to native IPv6 only, in order to cope with
   IPv4 address depletion and to achieve larger scale.  In such an
   environment, source routing (as enabled by SRv6) can be used to steer
   traffic across specific paths through the network.  The specific path
   may also include a given function that one or more nodes in the path
   are requested to perform.

   Additionally, one of the fundamental requirements for data center
   architecture is to provide scalable, isolated tenant networks.  In
   such scenarios, Segment Routing can be used to build a construct to
   steer the traffic across that specific path and to identify specific
   nodes, tenants, and functions.

2.4.  SPRING in Content Delivery Networks

   The rise of online video applications and new, video-capable IP
   devices has led to an explosion of video traffic traversing network
   operator infrastructures.  In the drive to reduce the capital and
   operational impact of the massive influx of online video traffic, as
   well as to extend traditional TV services to new devices and screens,
   network operators are increasingly turning to Content Delivery
   Networks (CDNs).

   Several studies showed the benefits of connecting caches in a
   hierarchical structure following the hierarchical nature of the
   Internet.  In a cache hierarchy, one cache establishes peering

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   relationships with its neighbor caches.  There are two types of
   relationships: parent and sibling.  A parent cache is essentially one
   level up in a cache hierarchy.  A sibling cache is on the same level.
   Multiple levels of hierarchy are commonly used in order to build an
   efficient cache architecture.

   In an environment where each single cache system can be uniquely
   identified by its own IPv6 address, a list containing a sequence of
   the caches in a hierarchy can be built.  At each node (cache) in the
   list, the presence of the requested content is checked.  If the
   requested content is found at the cache (a cache hits scenario), the
   sequence ends even if there are more nodes in the list; otherwise,
   the next element in the list (the next node/cache) is examined.

2.5.  SPRING in Core Networks

   While the overall amount of traffic offered to the network continues
   to grow, and considering that multiple types of traffic with
   different characteristics and requirements are quickly converging
   over a single network architecture, the network operators are
   starting to face new challenges.

   Some operators are currently building, or plan to build in the near
   future, an IPv6-only native infrastructure for their core network.
   These operators are also looking at the possibility to set up an
   explicit path based on the IPv6 source address for specific types of
   traffic in order to efficiently use their network infrastructure.  In
   the case of IPv6, some operators are currently assigning or plan to
   assign IPv6 prefix(es) to their IPv6 customers based on regions/
   geography, thus the subscriber's IPv6 prefix could be used to
   identify the region where the customer is located.  In such an
   environment, the IPv6 source address could be used by the edge nodes
   of the network to steer traffic and forward it through a specific
   path other than the optimal path.

   The need to set up a source-based path that goes through some
   specific middle/intermediate points in the network may be related to
   different requirements:

   o  The operator may want to be able to use some high-bandwidth links
      for a specific type of traffic (like video) and thus avoid the
      need for overdimensioning all the links of the network;

   o  The operator may want to be able to set up a specific path for
      delay-sensitive applications;

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   o  The operator may have the need to be able to select one (or
      multiple) specific exit point(s) at peering points when different
      peering points are available;

   o  The operator may have the need to be able to set up a source-based
      path for specific services in order to be able to reach some
      servers hosted in some facilities that are not always reachable
      through the optimal path; or

   o  The operator may need to be able to provision guaranteed disjoint
      paths (a so-called "dual-plane network") for diversity purposes.

   All these scenarios would require a form of traffic engineering
   capabilities in an IPv6-only network environment.

3.  IANA Considerations

   This document has no IANA actions.

4.  Security Considerations

   This document presents use cases to be considered by the SPRING
   architecture and potential IPv6 extensions.  As such, it does not
   introduce any security considerations.  However, there are a number
   of security concerns with source routing at the IP layer [RFC5095].
   It is expected that any solution that addresses these use cases also
   addresses any security concerns.

5.  References

5.1.  Normative References

   [RFC7855]  Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
              Litkowski, S., Horneffer, M., and R. Shakir, "Source
              Packet Routing in Networking (SPRING) Problem Statement
              and Requirements", RFC 7855, DOI 10.17487/RFC7855,
              May 2016, <https://www.rfc-editor.org/info/rfc7855>.

5.2.  Informative References

   [DOCSIS]   CableLabs, "New Generation of DOCSIS Technology", October
              2013, <http://www.cablelabs.com/news/

   [ITU.J83]  ITU-T, "Digital multi-programme systems for television,
              sound and data services or cable distribution", ITU-T
              Recommendation J.83, December 2007,

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              Baker, F., Bowers, C., and J. Linkova, "Enterprise
              Multihoming using Provider-Assigned Addresses without
              Network Prefix Translation: Requirements and Solution",
              Work in Progress, draft-ietf-rtgwg-enterprise-pa-
              multihoming-03, February 2018.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              DOI 10.17487/RFC5095, December 2007,

              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", Work in Progress, draft-ietf-spring-
              segment-routing-15, January 2018.


   The authors would like to thank Brian Field, Robert Raszuk, Wes
   George, Eric Vyncke, Fred Baker, John G. Scudder, Adrian Farrel,
   Alvaro Retana, Bruno Decraene, and Yakov Rekhter for their valuable
   comments and inputs to this document.


   Many people contributed to this document.  The authors of this
   document would like to thank and recognize them and their
   contributions.  These contributors provided invaluable concepts and
   content for this document's creation.

   Ida Leung
   Email: ida@brumund.ca

   Stefano Previdi
   Cisco Systems
   Via Del Serafico, 200
   Rome  00142
   Email: stefano@previdi.net

   Christian Martin
   Arista Networks
   Email: cmartin@arista.com

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Authors' Addresses

   John Brzozowski

   Email: john_brzozowski@cable.comcast.com

   John Leddy

   Email: John_Leddy@cable.comcast.com

   Clarence Filsfils
   Cisco Systems

   Email: cfilsfil@cisco.com

   Roberta Maglione (editor)
   Cisco Systems
   Via Torri Bianche 8
   Vimercate  20871

   Email: robmgl@cisco.com

   Mark Townsley
   Cisco Systems

   Email: townsley@cisco.com

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