IPv6 Segment Routing Use Cases
draft-martin-spring-segment-routing-ipv6-use-cases-00

Spring                                                     J. Brzozowski
Internet-Draft                                                  J. Leddy
Intended status: Informational                                   Comcast
Expires: September 7, 2014                                      I. Leung
                                                   Rogers Communications
                                                              S. Previdi
                                                             M. Townsley
                                                               C. Martin
                                                            C.  Filsfils
                                                             R. Maglione
                                                           Cisco Systems
                                                           March 6, 2014

                     IPv6 Segment Routing Use Cases
         draft-martin-spring-segment-routing-ipv6-use-cases-00

Abstract

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

   The objective of this document is to illustrate some use cases that
   would benefit from an IPv6 Segment Routing data-plane architecture.

Status of This Memo

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   This Internet-Draft will expire on September 7, 2014.

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Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IPv6 Segment Routing use cases  . . . . . . . . . . . . . . .   3
     2.1.  IPv6 Segment Routing in the Home Network  . . . . . . . .   4
     2.2.  IPv6 Segment Routing in the Access Network  . . . . . . .   5
     2.3.  IPv6 Segment Routing in the Data Center . . . . . . . . .   6
     2.4.  IPv6 Segment Routing in the Content Delivery Networks . .   7
     2.5.  IPv6 Segment Routing in the Core networks . . . . . . . .   8
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Segment Routing (SR) leverages the source routing paradigm.  An
   ingress node steers a packet through a controlled set of
   instructions, called segments, by prepending the packet with an SR
   header.  A segment can represent any instruction, topological or
   service-based.  A segment can represent a local semantic on an SR
   node, or a global semantic within an SR domain.  Segment Routing
   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 Segment Routing domain.

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

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   The details of the new routing extension header are not in scope of
   this document and will be published on a separate draft which also
   will cover the security considerations and the aspects related to the
   deprecation of the IPv6 Type 0 Routing Header described in [RFC5095].

2.  IPv6 Segment Routing 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.filsfils-spring-segment-routing-mpls] could be
   leveraged to provide Segment Routing capabilities in an IPv6/MPLS
   environment.

   However, there are other cases and/or specific network environments
   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 required.

   Specifically, there are a class of use cases that motivate an IPv6
   data plane.  We 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
       [I-D.ietf-mpls-seamless-mpls]

   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,

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   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 an IPv6 Segment Routing solution
   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.

   In addition to the use cases described in this document the IPv6
   Segment Routing architecture can be applied to all the use cases
   described in [I-D.filsfils-rtgwg-segment-routing-use-cases] for the
   Segment Routing MPLS data plane, when an IPv6 data plane is present.

2.1.  IPv6 Segment Routing 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.troan-homenet-sadr])
   will ensure that packets exit the home at the appropriate egress
   based on the associated delegated prefix for that link.

   An IPv6 Segment Routing 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.  The semantic of the data included in the
   Segment List is translated into an IPv6 address.  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 (see
   [I-D.lepape-6man-prefix-metadata]), 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 SR extension header.  This information can
   be provided as part of host configuration as a property of the
   configured IP address (see [I-D.bhandari-dhc-class-based-prefix]).

   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.

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

   o  Regulatory

   o  Performance of a particular service associated with a particular
      link

   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.  IPv6 Segment Routing 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 DOCCIS 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.

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

   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 SR 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.  IPv6 Segment Routing in the Data Center

   A key use case for SR is to cause a packet to follow a specific path
   through the network.  One can think of the service performed at each
   SR node to be forwarding.  Forwarding is one such service provided by
   an SR node.  More complex services could be applied to the packet by
   an SR node including accounting, IDS, load balancing, and fire
   walling.  "Service chaining" is the name given to the mechanism where
   these more complicated services are executed in a specific order for
   a target set of packets.  A service provider may choose to have these
   services performed external to the routing infrastructure,
   specifically on either dedicated physical servers or within VMs
   running on a virtualization platform.

   To support service chaining, an SR header could then be used to
   detail the set of forwarding or services to be applied to the packet
   by creating an SR header with the desired sequence of service IDs to
   be applied to the packet.

   Note that a service, operating on a physical server or within a VM,
   might not be directly connected to an SR aware router.  In fact
   multiple non-SR aware routers might exist between the service and the
   nearest SR router.  Encoding the SIDs as ipv6 addresses allows
   benefiting from SID SR header compaction.

   When a DC offers infrastructure as a service to multiple tenants,
   maintaining tenant traffic separation is a key requirement.  This can
   be supported without requiring the DC to run a flat layer 2 network
   segmented with VLANs or to build an overlay like solution (e.g.
   VXLAN).  Instead, multi-tenant separation can be performed using an
   SR header where the outer IPv6 DA is the remote hypervisor IP and the
   SR header contains an identifier of the virtual interface on that
   hypervisor that logically connects to the target remote VM.

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2.4.  IPv6 Segment Routing 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
   list.

   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.quinn-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 service.

   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 Segment Routing together with the NSH allows building
   flexible service chains where the topological information related to

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   the path 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 Segment Routing together with NSH will be described in a
   separate document.

2.5.  IPv6 Segment Routing 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
   network.

   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
   challenges.

   Many 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
   path.

   The need to setup a source-based path, going 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 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.

   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
   raise.

   The described use cases could be addressed with the SR architecture
   applied to the ipv6 data-plane and 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 for his 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].  The new IPv6-based routing header will be defined
   in way that blind attacks are never possible, i.e., attackers will be
   unable to send source routed packets that get successfully processed,
   without being part of the negations for setting up the source routes
   or being able to eavesdrop legitimate source routed packets.  In some
   networks this base level security may be complemented with other
   mechanisms, such as packet filtering, cryptographic security, etc.

6.  Informative References

   [I-D.bhandari-dhc-class-based-prefix]
              Systems, C., Halwasia, G., Gundavelli, S., Deng, H.,
              Thiebaut, L., Korhonen, J., and I. Farrer, "DHCPv6 class
              based prefix", draft-bhandari-dhc-class-based-prefix-05
              (work in progress), July 2013.

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   [I-D.filsfils-rtgwg-segment-routing-use-cases]
              Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
              Crabbe, "Segment Routing Use Cases", draft-filsfils-rtgwg-
              segment-routing-use-cases-02 (work in progress), October
              2013.

   [I-D.filsfils-rtgwg-segment-routing]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing Architecture", draft-filsfils-rtgwg-
              segment-routing-01 (work in progress), October 2013.

   [I-D.filsfils-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing with MPLS data plane", draft-filsfils-
              spring-segment-routing-mpls-00 (work in progress), October
              2013.

   [I-D.ietf-mpls-seamless-mpls]
              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M., and D. Steinberg, "Seamless MPLS Architecture", draft-
              ietf-mpls-seamless-mpls-06 (work in progress), February
              2014.

   [I-D.lepape-6man-prefix-metadata]
              Pape, M., Systems, C., and I. Farrer, "IPv6 Prefix Meta-
              data and Usage", draft-lepape-6man-prefix-metadata-00
              (work in progress), July 2013.

   [I-D.quinn-sfc-nsh]
              Quinn, P., Guichard, J., Fernando, R., Surendra, S.,
              Smith, M., Yadav, N., Agarwal, P., Manur, R., Chauhan, A.,
              Elzur, U., McConnell, B., and C. Wright, "Network Service
              Header", draft-quinn-sfc-nsh-02 (work in progress),
              February 2014.

   [I-D.troan-homenet-sadr]
              Troan, O. and L. Colitti, "IPv6 Multihoming with Source
              Address Dependent Routing (SADR)", draft-troan-homenet-
              sadr-01 (work in progress), September 2013.

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

Authors' Addresses

   John Brzozowski
   Comcast

   Email: john_brzozowski@cable.comcast.com

   John Leddy
   Comcast

   Email: John_Leddy@cable.comcast.com

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

   Email: Ida.Leung@rci.rogers.com

   Stefano Previdi
   Cisco Systems
   Via Del Serafico, 200
   Rome  00142
   Italy

   Email: sprevidi@cisco.com

   Mark Townsley
   Cisco Systems

   Email: townsley@cisco.com

   Christian Martin
   Cisco Systems

   Email: martincj@cisco.com

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   Clarence Filsfils
   Cisco Systems
   Brussels
   BE

   Email: cfilsfil@cisco.com

   Roberta Maglione
   Cisco Systems
   181 Bay Street
   Toronto  M5J 2T3
   Canada

   Email: robmgl@cisco.com

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