Network Working Group                                           P. Quinn
Internet-Draft                                               J. Guichard
Intended status: Informational                                  S. Kumar
Expires: February 27, 2014                           Cisco Systems, Inc.
                                                              P. Agarwal
                                                                R. Manur
                                                              A. Chauhan
                                                              N. Leymann
                                                        Deutsche Telekom
                                                            M. Boucadair
                                                            C. Jacquenet
                                                          France Telecom
                                                                M. Smith
                                                                N. Yadav
                                                        Insieme Networks
                                                               T. Nadeau
                                                                 K. Gray
                                                        Juniper Networks
                                                            B. McConnell
                                                               K. Glavin
                                                         August 26, 2013

               Network Service Chaining Problem Statement


   This document provides an overview of the issues associated with the
   deployment of services functions (such as firewalls, load balancers)
   in large-scale environments.  The term service function chaining is
   used to describe the deployment of such service functions, and the
   ability of a network operator to specify an ordered list of service
   functions that should be applied to a deterministic set of traffic
   flows.  Such service function chains require integration of service
   policy alongside the deployment of applications, while allowing for
   the optimal utilization of network resources.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering

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   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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 February 27, 2014.

Copyright Notice

   Copyright (c) 2013 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
   ( 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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Definition of Terms  . . . . . . . . . . . . . . . . . . .  4
   2.  Problem Areas  . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Service Function Chaining  . . . . . . . . . . . . . . . . . .  9
   4.  Service Function Chaining Use Cases  . . . . . . . . . . . . . 11
     4.1.  Enterprise Data Center Service Chaining  . . . . . . . . . 11
     4.2.  Mobility Service Chaining  . . . . . . . . . . . . . . . . 11
   5.  Related IETF Work  . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17

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1.  Introduction

   Services that are composed of service functions require more flexible
   service function deployment models than those typically available in
   networks today.  Such services may utilize traditional network
   service functions (for example firewalls and server load balancers),
   as well as higher layer applications and features.  Services may be
   delivered within a specific context so that isolated user groups
   attached to a common network may be formed.  Such user groups may
   require unique capabilities with the ability to tailor service
   characteristics on a per-tenant/per-subscriber/per-VPN basis that
   must not affect other user groups

   Current service function deployment models are relatively static in
   that they are bound to fixed network topologies and resources.  At
   present, these deployments are not easily manipulated (i.e.: moved,
   created or destroyed) even when virtualized elements are deployed.
   This poses a problem in highly elastic service environments that
   require relatively rapid creation, destruction or movement of real or
   virtual service functions or network elements.  Additionally, the
   transition to virtual platforms requires an agile service insertion
   model that supports elastic and very granular service delivery, and
   post-facto modification; supports the movement of service functions
   and application workloads in the existing network, all the while
   retaining the network and service policies and the ability to easily
   bind service policy to granular information such as per-subscriber

   This document outlines the problems encountered with existing service
   deployment models for service function chaining (often referred to
   simply as service chaining; in this document the terms will be used
   interchangeably), as well as the problems of service chain creation/
   deletion, policy integration with service chains, and policy
   enforcement within the network infrastructure.

1.1.  Definition of Terms

   Classification:  Locally instantiated policy and customer/network/
      service profile matching of traffic flows for identification of
      appropriate outbound forwarding actions.

   Network Overlay:  Logical network built on top of existing network
      (the underlay).  Packets are encapsulated or tunneled to create
      the overlay network topology.

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   Service Chain:  A service chain defines the required functions and
      associated order (service-function1 --> service-function 2) that
      must be applied to packets and/or frames.  A service chain does
      not specify the network location or specific instance of service
      functions (e.g. firewall1 vs. firewall2).

   Service Function:  A network or application based packet treatment,
      application, compute or storage resource, used singularly or in
      concert with other service functions within a service chain to
      enable a service offered by a network operator.

      A non-exhaustive list of Service Functions includes: firewalls,
      WAN and application acceleration, Deep Packet Inspection (DPI),
      server load balancers, NAT44 [RFC3022], NAT64 [RFC6146], HOST_ID
      injection, HTTP Header Enrichment functions, TCP optimizer, etc.

      The generic term "L4-L7 services" is often used to describe many
      service functions.

   Service Node:  Physical or virtual element providing one or more
      service functions.

   Network Service:  An externally visible service offered by a network
      operator; a service may consist of a single service function or a
      composite built from several service functions executed in one or
      more pre-determined sequences and delivered by one or more service

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2.  Problem Areas

   The following points describe aspects of existing service deployment
   that are problematic, and are being addressed by the network service
   chaining effort.

   1.   Topological Dependencies: Network service deployments are often
        coupled to the physical network topology creating constraints on
        service delivery and potentially inhibiting the network operator
        from optimally utilizing service resources.  This limits scale,
        capacity, and redundancy across network resources.

        These topologies serve only to "insert" the service function
        (i.e. ensure that traffic traverse a service function); they are
        not required from a native packet delivery perspective.  For
        example, firewalls often require an "in" and "out" layer-2
        segment and adding a new firewall requires changing the topology
        (i.e. adding new L2 segments).

        As more service functions are required - often with strict
        ordering - topology changes are needed before and after each
        service function resulting in complex network changes and device
        configuration.  In such topologies, all traffic, whether a
        service function needs to be applied or not, often passes
        through the same strict order.

        A common example is web servers using a server load balancer as
        the default gateway.  When the web service responds to non-load
        balanced traffic (e.g. administrative or backup operations) all
        traffic from the server must traverse the load balancer forcing
        network administrators to create complex routing schemes or
        create additional interfaces to provide an alternate topology.

   2.   Configuration complexity: A direct consequence of topological
        dependencies is the complexity of the entire configuration,
        specifically in deploying service chains.  Simple actions such
        as changing the order of the service functions in a service
        chain require changes to the topology.  Changes to the topology
        are avoided by the network operator once installed, configured
        and deployed in production environments fearing misconfiguration
        and downtime.  All of this leads to very static service delivery
        models.  Furthermore, the speed at which these topological
        changes can be made is not rapid or dynamic enough as it often
        requires manual intervention, or use of slow provisioning

        The service itself can contribute to complexity: it may require
        an intricate combination of very different capabilities,

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        regardless of the underlying topology.  QoS-based, resilient VPN
        service offerings are a typical example of such complexity.

   3.   Constrained High Availability: An effect of topological
        dependency is constrained service function high availability.
        Worse, when modified, inadvertent non-high availability can

        Since traffic reaches service functions based on network
        topology, alternate, or redundant service functions must be
        placed in the same topology as the primary service.

   4.   Consistent Ordering of Service Functions: Service functions are
        typically independent; service function_1 (SF1)...service
        function_n (SFn) are unrelated and there is no notion at the
        service layer that SF1 occurs before SF2.  However, to an
        administrator many service functions have a strict ordering that
        must be in place, yet the administrator has no consistent way to
        impose and verify the ordering of the functions that used to
        deliver a given service.

   5.   Service Chain Construction: Service chains today are most
        typically built through manual configuration processes.  These
        are slow and error prone.  With the advent of newer service
        deployment models the control / management planes will provide
        not only connectivity state, but will also be increasingly
        utilized for the formation of services.  Such a control /
        management plane could be centrally controlled and managed, or
        be distributed between a subset of end-systems.

   6.   Application of Service Policy: Service functions rely on
        topology information such as VLANs or packet (re) classification
        to determine service policy selection, i.e. the service function
        specific action taken.  Topology information is increasingly
        less viable due to scaling, tenancy and complexity reasons.  The
        topological information is often stale, providing the operator
        with inaccurate placement that can result in suboptimal resource
        utilization.  Per-service function packet classification is
        inefficient and prone to errors, duplicating functionality
        across service functions.  Furthermore packet classification is
        often too coarse lacking the ability to determine class of
        traffic with enough detail.

   7.   Transport Dependence: Service functions can and will be deployed
        in networks with a range of transports, including under and
        overlays.  The coupling of service functions to topology
        requires service functions to support many transports or for a
        transport gateway function to be present.

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   8.   Elastic Service Delivery: Given the current state of the art for
        adding/removing service functions largely centers around VLANs
        and routing changes, rapid changes to the service layer can be
        hard to realize due to the risk and complexity of such changes.

   9.   Traffic Selection Criteria: Traffic selection is coarse, that
        is, all traffic on a particular segment traverse service
        functions whether the traffic requires service enforcement or
        not.  This lack of traffic selection is largely due to the
        topological nature of service deployment since the forwarding
        topology dictates how (and what) data traverses service
        function(s).  In some deployments, more granular traffic
        selection is achieved using policy routing or access control
        filtering.  This results in operationally complex configurations
        and is still relatively inflexible.

   10.  Limited End-to-End Service Visibility: Troubleshooting service
        related issues is a complex process that involve network and
        service expertise.  This is especially the case when service
        chains span multiple DCs, or across administrative boundaries
        such as externally consumable service chain components.
        Furthermore, the physical and virtual environments (network and
        service), can be highly divergent in terms of topology and that
        topological variance adds to these challenges.

   11.  Per-Service (re)Classification: Classification occurs at each
        service, independent from previously applied service functions.
        These unrelated classification events consume resources per
        service.  More importantly, the classification functionality
        often differs per service function and service function cannot
        leverage the results from other deployed network or service.

   12.  Symmetric Traffic Flows: Service chains may be unidirectional or
        bidirectional; unidirectional is one where traffic is passed
        through a set of service functions in one forwarding direction
        only.  Bidirectional is one where traffic is passed through a
        set of service functions in both forwarding directions.
        Existing service deployment models provide a static approach to
        realizing forward and reverse service chain association most
        often requiring complex configuration of each network device
        throughout the forwarding path.

   13.  Multi-vendor Service Functions: Deploying service functions from
        multiple vendors often requires per-vendor expertise: insertion
        models differ, there are limited common attributes and inter-
        vendor service functions do not share information.

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3.  Service Function Chaining

   Service chaining provides a framework to address the aforementioned
   problems associated with service deployments:

   1.  Service Overlay: Service chaining utilizes a service specific
       overlay that creates the service topology: the overlay creates a
       path between service nodes.  The service overlay is independent
       of the network topology and allows operators to use whatever
       overlay or underlay they prefer and to locate service functions
       in the network as needed.

       Within the service topology, service functions can be viewed as
       resources for consumption and an arbitrary topology constructed
       to connect those resources in a required order.  Adding new
       service functions to the topology is easily accomplished, and no
       underlying network changes are required.  Furthermore, additional
       service instances, for redundancy or load distribution, can be
       added or removed to the service topology as required.

       Lastly, the service overlay can provide service specific
       information needed for troubleshooting service-related issues.

   2.  Generic Service Control Plane (GSCP): GSCP provides information
       about the available service functions on a network.  The
       information provided by the control plane includes service
       network location (for topology creation), service type (e.g.
       firewall, load balancer, etc.) and, optionally, administrative
       information about the service functions such as load, capacity
       and operating status.  GSCP allows for the formulation of service
       chains and disseminates the service chains to the network.

   3.  Service Classification: Classification is used to select which
       traffic enters a service overlay.  The granularity of the
       classification varies based on device capabilities, customer
       requirements, and service functionality.  Initial classification
       is used to start the service chain.  Subsequent classification
       can be used within a given service chain to alter the sequence of
       service functions applied.  Symmetric classification ensures that
       forward and reverse chains are in place.

   4.  Dataplane Metadata: Dataplane metadata provides the ability to
       exchange information between the network and service functions,
       service functions and service functions and service functions and
       the network.  Metadata can include the result of antecedent
       classification, information from external sources or forwarding
       related data.  For example, service functions utilize metadata,
       as required, for localized policy decision.  A common approach to

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       service metadata creates a common foundation for interoperability
       between service functions, regardless of vendor.

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4.  Service Function Chaining Use Cases

   The following sections provide high level overviews of several common
   service chaining deployments.

4.1.  Enterprise Data Center Service Chaining


4.2.  Mobility Service Chaining


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5.  Related IETF Work

   The following subsections discuss related IETF work and are provided
   for reference.  This section is not exhaustive, rather it provides an
   overview of the various initiatives and how they relate to network
   service chaining.

   1.  L3VPN[L3VPN]: The L3VPN working group is responsible for
       defining, specifying and extending BGP/MPLS IP VPNs solutions.
       Although BGP/MPLS IP VPNs can be used as transport for service
       chaining deployments, the service chaining WG focuses on the
       service specific protocols, not the general case of VPNs.
       Furthermore, BGP/MPLS IP VPNs do not address the requirements for
       service chaining.

   2.  LISP[LISP]: LISP provides locator and ID separation.  LISP can be
       used as an L3 overlay to transport service chaining data but does
       not address the specific service chaining problems highlighted in
       this document.

   3.  NVO3[NVO3]: The NVO3 working group is chartered with creation of
       problem statement and requirements documents for multi-tenant
       network overlays.  NVO3 WG does not address service chaining

   4.  ALTO[ALTO]: The Application Layer Traffic Optimization Working
       Group is chartered to provide topological information at a higher
       abstraction layer, which can be based upon network policy, and
       with application-relevant service functions located in it.  The
       mechanism for ALTO obtaining the topology can vary and policy can
       apply to what is provided or abstracted.  This work could be
       leveraged and extended to address the need for services

   5.  I2RS[I2RS]: The Interface to the Routing System Working Group is
       chartered to investigate the rapid programming of a device's
       routing system, as well as the service of a generalized, multi-
       layered network topology.  This work could be leveraged and
       extended to address some of the needs for service chaining in the
       topology and device programming areas.

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6.  Summary

   This document highlights problems associated with network service
   deployment today and identifies several key areas that will be
   addressed by the service chaining working group.  Furthermore, this
   document identifies four components that are the basis for serice
   chaining.  These components will form the areas of focus for the
   working group.

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7.  Security Considerations

   Security considerations are not addressed in this problem statement
   only document.  Given the scope of service chaining, and the
   implications on data and control planes, security considerations are
   clearly important and will be addressed in the specific protocol and
   deployment documents created by the service chaining working group.

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8.  Acknowledgments

   The authors would like to thank David Ward, Rex Fernando and Jim
   French for their contributions.

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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2.  Informative References

   [ALTO]     "Application-Layer Traffic Optimization (alto)",

   [I2RS]     "Interface to the Routing System (i2rs)",

   [L3VPN]    "Layer 3 Virtual Private Networks (l3vpn)",

   [LISP]     "Locator/ID Separation Protocol (lisp)",

   [NVO3]     "Network Virtualization Overlays (nvo3)",

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

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Authors' Addresses

   Paul Quinn
   Cisco Systems, Inc.


   Jim Guichard
   Cisco Systems, Inc.


   Surendra Kumar
   Cisco Systems, Inc.


   Puneet Agarwal


   Rajeev Manur


   Abhishek Chauhan


   Nic Leymann
   Deutsche Telekom


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   Mohamed Boucadair
   France Telecom


   Christian Jacquenet
   France Telecom


   Michael Smith
   Insieme Networks


   Navindra Yadav
   Insieme Networks


   Thomas Nadeau
   Juniper Networks


   Ken Gray
   Juniper Networks


   Brad McConnell


   Kevin Glavin


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