Spring                                                     J. Brzozowski
Internet-Draft                                                  J. Leddy
Intended status: Informational                                   Comcast
Expires: March 4, 2016                                          I. Leung
                                                   Rogers Communications
                                                              S. Previdi
                                                             M. Townsley
                                                               C. Martin
                                                            C.  Filsfils
                                                        R. Maglione, Ed.
                                                           Cisco Systems
                                                          September 2015

                         IPv6 SPRING Use Cases


   Source Packet Routing in Networking (SPRING) architecture leverages
   the source routing paradigm.  A node steers a packet through a
   controlled set of instructions, called segments, by prepending the
   packet with SPRING header.  A segment can represent any instruction,
   topological or service-based.  A segment can have a local semantic to
   the SPRING node or global within the SPRING domain.  SPRING allows to
   enforce a flow through any topological path and service chain while
   maintaining per-flow state only at the ingress node to the SPRING

   The objective of this document is to illustrate some use cases that
   need to be taken into account by the Source Packet Routing in
   Networking (SPRING) architecture.

Status of This Memo

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   This Internet-Draft will expire on March 4, 2016.

Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IPv6 SPRING use cases . . . . . . . . . . . . . . . . . . . .   3
     2.1.  SPRING in the Home Network  . . . . . . . . . . . . . . .   5
     2.2.  SPRING in the Access Network  . . . . . . . . . . . . . .   6
     2.3.  SPRING in the Data Center . . . . . . . . . . . . . . . .   7
       2.3.1.  VM isolation in a Data Center . . . . . . . . . . . .   7
     2.4.  SPRING in the Content Delivery Networks . . . . . . . . .   8
     2.5.  SPRING in the Core networks . . . . . . . . . . . . . . .   9
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  Informative References  . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Source Packet Routing in Networking (SPRING) architecture leverages
   the source routing paradigm.  An ingress node steers a packet through
   a controlled set of instructions, called segments, by prepending the
   packet with SPRING header.  A segment can represent any instruction,
   topological or service-based.  A segment can represent a local
   semantic on the SPRING node, or a global semantic within the SPRING
   domain.  SPRING allows one to enforce a flow through any topological
   path and service chain while maintaining per-flow state only at the
   ingress node to the SPRING domain.

   The SPRING architecture is described in
   [I-D.ietf-spring-segment-routing].  The SPRING control plane is
   agnostic to the dataplane, thus it can be applied to both MPLS and

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   IPv6.  In case of MPLS the (list of) segment identifiers are carried
   in the MPLS label stack, while for the IPv6 dataplane, a new type of
   routing extension header is required.

   The details of the new routing extension header are described in
   [I-D.previdi-6man-segment-routing-header] which also covers the
   security considerations and the aspects related to the deprecation of
   the IPv6 Type 0 Routing Header described in [RFC5095].

2.  IPv6 SPRING use cases

   In today's networks, source routing is typically accomplished by
   encapsulating IP packets in MPLS LSPs that are signaled via RSVP-TE.
   Therefore, there are scenarios where it may be possible to run IPv6
   on top of MPLS, and as such, the MPLS Segment Routing architecture
   described in [I-D.ietf-spring-segment-routing-mpls] could be
   leveraged to provide SPRING capabilities in an IPv6/MPLS environment.

   However, there are other cases and/or specific network segments (such
   as for example the Home Network, the Data Center, etc.) where MPLS
   may not be available or deployable for lack of support on network
   elements or for an operator's design choice.  In such scenarios a
   non-MPLS based solution would be preferred by the network operators
   of such infrastructures.

   In addition there are cases where the operators could have made the
   design choice to disable IPv4, for ease of management and scale
   (return to single-stack) or due to an address constraint, for example
   because they do not possess enough IPv4 addresses resources to number
   all the endpoints and other network elements on which they desire to
   run MPLS.

   In such scenario the support for MPLS operations on an IPv6-only
   network would be required.  However today's IPv6-only networks are
   not fully capable of supporting MPLS.  There is ongoing work in the
   MPLS Working Group, described in [RFC7439] to identify gaps that must
   be addressed in order to allow MPLS-related protocols and
   applications to be used with IPv6-only networks.  This is an another
   example of scenario where an IPv6-only solution could represent a
   valid option to solve the problem and meet operators' requirements.

   It is important to clarify that today, it is possible to run IPv6 on
   top of an IPv4 MPLS network by using the mechanism called 6PE,
   described in [RFC4798].  However this approach does not fulfill the
   requirement of removing the need of IPv4 addresses in the network, as
   requested in the above use case.

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   In addition it is worth to note that in today's MPLS dual-stack
   networks IPv4 traffic is labeled while IPv6 traffic is usually
   natively routed, not label-switched.  Therefore in order to be able
   to provide Traffic Engineering "like" capabilities for IPv6 traffic
   additional/alternative encapsulation mechanisms would be required.

   In summary there is a class of use cases that motivate an IPv6 data
   plane.  The authors identify some fundamental scenarios that, when
   recognized in conjunction, strongly indicate an IPv6 data plane:

   1.  There is a need or desire to impose source-routing semantics
       within an application or at the edge of a network (for example, a
       CPE or home gateway)

   2.  There is a strict lack of an MPLS dataplane

   3.  There is a need or desire to remove routing state from any node
       other than the source, such that the source is the only node that
       knows and will know the path a packet will take, a priori

   4.  There is a need to connect millions of addressable segment
       endpoints, thus high routing scalability is a requirement.  IPv6
       addresses are inherently summarizable: a very large operator
       could scale by summarizing IPv6 subnets at various internal
       boundaries.  This is very simple and is a basic property of IP
       routing.  MPLS node segments are not summarizable.  To reach the
       same scale, an operator would need to introduce additional
       complexity, such as mechanisms described in

   In any environment with requirements such as those listed above, an
   IPv6 data plane provides a powerful combination of capabilities for a
   network operator to realize benefits in explicit routing, protection
   and restoration, high routing scalability, traffic engineering,
   service chaining, service differentiation and application flexibility
   via programmability.

   This section will describe some scenarios where MPLS may not be
   present and it will highlight how the SPRING architecture could be
   used to address such use cases, particularly, when an MPLS data plane
   is neither present nor desired.

   The use cases described in the 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
   IPv6 Segment Routing.

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   In addition to the use cases described in this document the SPRING
   architecture can be applied to all the use cases described in
   [I-D.ietf-spring-problem-statement] for the SPRING MPLS data plane,
   when an IPv6 data plane is present.  Here there is a summary of those
   use cases:

   1.  Traffic Engineering

   2.  Disjoint paths in dual-plane networks

   3.  Fast Reroute: Protecting node and adjacency segments

   4.  OAM/monitoring

   5.  Egress Peering Engineering

2.1.  SPRING in the Home Network

   An IPv6-enabled home network provides ample globally routed IP
   addresses for all devices in the home.  An IPv6 home network with
   multiple egress points and associated provider-assigned prefixes
   will, in turn, provide multiple IPv6 addresses to hosts.  A homenet
   performing Source and Destination Routing
   ([I-D.lamparter-rtgwg-dst-src-routing]) will ensure that packets exit
   the home at the appropriate egress based on the associated delegated
   prefix for that link.

   A SPRING enabled home provides the possibility for imposition of a
   Segment List by end-hosts in the home, or a customer edge router in
   the home.  If the Segment List is enabled at the customer edge
   router, that router is responsible for classifying traffic and
   inserting the appropriate Segment List.  If hosts in the home have
   explicit source selection rules, classification can be based on
   source address or associated network egress point, avoiding the need
   for DPI-based implicit classification techniques.  If the Segment
   List is inserted by the host itself, it is important to know which
   networks can interpret the SPRING header.  This information can be
   provided as part of host configuration as a property of the
   configured IP address (see [I-D.ietf-mif-mpvd-dhcp-support]).

   The ability to steer traffic to an appropriate egress or utilize a
   specific type of media (e.g., low-power, WIFI, wired, femto-cell,
   bluetooth, MOCA, HomePlug, etc.) within the home itself are obvious
   cases which may be of interest to an application running within a
   home network.

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

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   o  Regulatory

   o  Performance of a particular service associated with a particular

   o  Cost imposed due to data-caps or per-byte charges

   o  Home vs. work traffic in homes with one or more teleworkers, etc.

   o  Specific services provided by one ISP vs. another

   Information included in the Segment List, 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 Segment List as
   a channel to include information that affects its treatment within
   the data center itself, allowing for application-level steering and
   load-balancing without relying upon implicit application
   classification techniques at the data-center edge.  Further, as more
   and more application traffic is encrypted, the ability to extract
   (and include in the Segment List) 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, each of these pipes are represented at
   the DOCSIS layer as different service flows, which are better
   identified as differing 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 egress vectoring, byte capping, regulatory
   compliance functions, and billing.

   In a cable operator's environment, these downstream pipes could be a
   specific QAM, a DOCSIS service flow or a service group.

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   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 how to map
   the SR SID value to the target pipe.

2.3.  SPRING in the Data Center

   A key use case for SPRING is to cause a packet to follow a specific
   path through the network.  One can think of the service function
   performed at each SPRING node to be forwarding.  More complex service
   functions could be applied to the packet by a SPRING node including
   accounting, IDS, load balancing, and fire walling.

   The term "Service Function Chain", as defined in [RFC7498], it is
   used to describe an ordered set of service functions that must be
   applied to packets.

   A service provider may choose to have these service functions
   performed external to the routing infrastructure, specifically on
   either dedicated physical servers or within VMs running on a
   virtualization platform.

   [I-D.ietf-sfc-dc-use-cases] describes use cases that demonstrate the
   applicability of Service Function Chaining (SFC) within a data center
   environment and provides SFC requirements for data center centric use

2.3.1.  VM isolation in a Data Center

   [I-D.baker-openstack-ipv6-model] describes a network model for an
   OpenStack Data center which is designed to dramatically simplify
   scalable network deployment and operations.  This model proposes the
   use of information within the IPv6 header in order to provide tenant
   VM group isolation without relying on layer 2 logical separation.

   The 128-bit PE Ingress ID in the SRH policy list provides a natural
   place to encode origin information of VM to VM traffic within the
   Data Center.  The Segment List provides a method to direct traffic to
   a specific enforcement point based on traffic destination.  Together,
   these allow for a simple tagging and permit/deny comparison performed
   between twin SR-capable nodes (e.g., the Neutron Virtual Router)
   among VMs in a Data Center.

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2.4.  SPRING in the 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
   relationships with its neighbor caches.  There are two types of
   relationship: 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
   efficient caches architecture.

   In an environment, where each single cache system can be uniquely
   identified by its own IPv6 address, a Segment List containing a
   sequence of the caches in a hierarchy can be built.  At each node
   (cache) present in the Segment List a TCP session to port 80 is
   established and if the requested content is found at the cache (cache
   hits scenario) the sequence ends, even if there are more nodes in the

   To achieve the behavior described above, in addition to the Segment
   List, which specifies the path to be followed to explore the
   hierarchic architecture, a way to instruct the node to take a
   specific action is required.  The function to be performed by a
   service node can be carried into a new header called Network Service
   Header (NSH) defined in [I-D.ietf-sfc-nsh].  A Network Service Header
   (NSH) is metadata added to a packet that is used to create a service
   plane.  The service header is added by a service classification
   function that determines which packets require servicing, and
   correspondingly which service path to follow to apply the appropriate

   In the above example the service to be performed by the service node
   was to establish a TCP session to port 80, but in other scenarios
   different functions may be required.  Another example of action to be
   taken by the service node is the capability to perform
   transformations on payload data, like real-time video transcode
   option (for rate and/or resolution).

   The use of SPRING together with the NSH allows building flexible
   service chains where the topological information related to the path

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   to be followed is carried into the Segment List while the "service
   plane related information" (function/action to be performed) is
   encoded in the metadata, carried into the NSH.  The details about
   using SPRING together with NSH will be described in a separate

2.5.  SPRING in the Core networks

   MPLS is a well-known technology widely deployed in many IP core
   networks.  However there are some operators that do not run MPLS
   everywhere in their core network today, thus moving forward they
   would prefer to have an IPv6 native infrastructure for the core

   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 single
   network architecture, the network operators are starting to face new

   Some operators are looking at the possibility to setup an explicit
   path based on the IPv6 source address for specific types of traffic
   in order to efficiently use their network infrastructure.  In 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 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

   The need to setup a source-based path, going through some specific
   middle/intermediate points in the network may be related to different

   o  The operator may want to be able to use some high bandwidth links
      for specific type of traffic (like video) avoiding the need for
      over-dimensioning all the links of the network;

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

   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 setup a source based
      path for specific services in order to be able to reach some

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      servers hosted in some facilities not always reachable through the
      optimal path;

   o  The operator may have the need to be able to provision guaranteed
      disjoint paths (so-called dual-plane network) for diversity

   All these scenarios would require a form of traffic engineering
   capabilities in IP core networks not running MPLS and not willing to
   run it.

   IPv4 protocol does not provide such functionalities today and it is
   not the intent of this document to address the IPv4 scenario, both
   because this may create a lot of backward compatibility issues with
   currently deployed networks and for the security issues that may

   The described use cases could be addressed with the SPRING
   architecture by having the Edge nodes of network to impose a Segment
   List on specific traffic flows, based on certain classification
   criteria that would include source IPv6 address.

3.  Acknowledgements

   The authors would like to thank Brian Field, Robert Raszuk, Wes
   George, Eric Vyncke, John G.  Scudder and Yakov Rekhter for their
   valuable comments and inputs to this document.

4.  IANA Considerations

   This document does not require any action from IANA.

5.  Security Considerations

   There are a number of security concerns with source routing at the IP
   layer [RFC5095].  Security mechanisms applied to Segment Routing over
   IPv6 networks are detailed in section 9 of

6.  Informative References

              Baker, F., Marino, C., Wells, I., Agarwalla, R., Jeuk, S.,
              and G. Salgueiro, "A Model for IPv6 Operation in
              OpenStack", draft-baker-openstack-ipv6-model-02 (work in
              progress), February 2015.

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              Krishnan, S., Korhonen, J., and S. Bhandari, "Support for
              multiple provisioning domains in DHCPv6", draft-ietf-mif-
              mpvd-dhcp-support-01 (work in progress), March 2015.

              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M., and D. Steinberg, "Seamless MPLS Architecture", draft-
              ietf-mpls-seamless-mpls-07 (work in progress), June 2014.

              Surendra, S., Tufail, M., Majee, S., Captari, C., and S.
              Homma, "Service Function Chaining Use Cases In Data
              Centers", draft-ietf-sfc-dc-use-cases-03 (work in
              progress), July 2015.

              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-01 (work in progress), July 2015.

              Previdi, S., Filsfils, C., Decraene, B., Litkowski, S.,
              Horneffer, M., and R. Shakir, "SPRING Problem Statement
              and Requirements", draft-ietf-spring-problem-statement-04
              (work in progress), April 2015.

              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and r. rjs@rob.sh, "Segment Routing Architecture", draft-
              ietf-spring-segment-routing-04 (work in progress), July

              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
              and E. Crabbe, "Segment Routing with MPLS data plane",
              draft-ietf-spring-segment-routing-mpls-01 (work in
              progress), May 2015.

              Lamparter, D., "Destination/Source Routing", draft-
              lamparter-rtgwg-dst-src-routing-01 (work in progress),
              June 2015.

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              Previdi, S., Filsfils, C., Field, B., Leung, I., Vyncke,
              E., and D. Lebrun, "IPv6 Segment Routing Header (SRH)",
              draft-previdi-6man-segment-routing-header-07 (work in
              progress), July 2015.

   [RFC4798]  De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
              "Connecting IPv6 Islands over IPv4 MPLS Using IPv6
              Provider Edge Routers (6PE)", RFC 4798,
              DOI 10.17487/RFC4798, February 2007,

   [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,

   [RFC7439]  George, W., Ed. and C. Pignataro, Ed., "Gap Analysis for
              Operating IPv6-Only MPLS Networks", RFC 7439,
              DOI 10.17487/RFC7439, January 2015,

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,

Authors' Addresses

   John Brzozowski

   Email: john_brzozowski@cable.comcast.com

   John Leddy

   Email: John_Leddy@cable.comcast.com

   Ida Leung
   Rogers Communications
   8200 Dixie Road
   Brampton, ON  L6T 0C1

   Email: Ida.Leung@rci.rogers.com

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   Stefano Previdi
   Cisco Systems
   Via Del Serafico, 200
   Rome  00142

   Email: sprevidi@cisco.com

   Mark Townsley
   Cisco Systems

   Email: townsley@cisco.com

   Christian Martin
   Cisco Systems

   Email: martincj@cisco.com

   Clarence Filsfils
   Cisco Systems

   Email: cfilsfil@cisco.com

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

   Email: robmgl@cisco.com

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