Network Working Group                                           P. Quinn
Internet-Draft                                               J. Guichard
Intended status: Standards Track                             R. Fernando
Expires: August 16, 2014                                        S. Kumar
                                                                M. Smith
                                                                N. Yadav
                                                     Cisco Systems, Inc.
                                                              P. Agarwal
                                                                R. Manur
                                                              A. Chauhan
                                                            B. McConnell
                                                               C. Wright
                                                            Red Hat Inc.
                                                       February 12, 2014

                         Network Service Header


   This draft describes a Network Service Header (NSH) added to
   encapsulated packets or frames to realize service function paths.
   NSH also provides a mechanism for metadata exchange along the
   instantiated service path.

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1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 August 16, 2014.

Copyright Notice

   Copyright (c) 2014 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.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  2
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Definition of Terms  . . . . . . . . . . . . . . . . . . .  4
     2.2.  Problem Space  . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Network Service Header . . . . . . . . . . . . . . . . . . . .  8
     3.1.  NSH Actions  . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  NSH Encapsulation  . . . . . . . . . . . . . . . . . . . .  9
     3.3.  NSH Usage  . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.4.  NSH Proxy Nodes  . . . . . . . . . . . . . . . . . . . . . 10
   4.  Header Format  . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  NSH Example: GRE . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20

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2.  Introduction

   Service functions are widely deployed and essential in many networks.
   These service functions provide a range of features such as security,
   WAN acceleration, and server load balancing.  Service functions may
   be instantiated at different points in the network infrastructure
   such as the wide area network, data center, campus, and so forth.

   The current service function deployment models are relatively static,
   and bound to topology for insertion and policy selection.
   Furthermore, they do not adapt well to elastic service environments
   enabled by virtualization.

   New data center network and cloud architectures require more flexible
   service function deployment models.  Additionally, the transition to
   virtual platforms requires an agile service insertion model that
   supports elastic service delivery; the movement of service functions
   and application workloads in the network and the ability to easily
   bind service policy to granular information such as per-subscriber
   state are necessary.

   The approach taken by NSH is composed of two elements:

   1.  Fixed size, transport independent per-packet/frame service meta-

   2.  Data plane encapsulation that utilizes the network overlay
       topology used to deliver packets to the requisite services.

   NSH is designed to be easy to implement across a range of devices,
   both physical and virtual, including hardware platforms.

   An NSH aware control plane is outside the scope of this document.

   The SFC Architecture document [SFC-arch] provides an overview of a
   chaining architecture that clearly defines the roles of the various
   elements and the scope of a service function chaining encapsulation.

2.1.  Definition of Terms

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

   SFC Network Forwarder (SFCNF):  SFC network forwarders provide
      network connectivity for service functions forwarders and service
      functions.  SFC network forwarders participate in the network
      overlay used for service function chaining as well as in the SFC

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   Service Function Forwarder (SFF):  A service function forwarder is
      responsible for delivering traffic received from the SFCNF to one
      or more connected service functions, and from service functions to
      the SFCNF.

   Service Function (SF):  A function that is responsible for specific
      treatment of received packets.  A service function can act at the
      network layer or other OSI layers.  A service function can be a
      virtual instance or be embedded in a physical network element.
      One of multiple service functions can be embedded in the same
      network element.  Multiple instances of the service function can
      be enabled in the same administrative domain.

   Service Node (SN):  Physical or virtual element that hosts one or
      more service functions and has one or more network locators
      associated with it for reachability and service delivery.

   Service Function Chain (SFC):  A service Function chain defines an
      ordered set of service functions that must be applied to packets
      and/or frames selected as a result of classification.  The implied
      order may not be a linear progression as the architecture allows
      for nodes that copy to more than one branch.  The term service
      chain is often used as shorthand for service function chain.

   Service Function Path (SFP):  The instantiation of a SFC in the
      network.  Packets follow a service function path from a classifier
      through the requisite service functions

   Network Node/Element:  Device that forwards packets or frames based
      on outer header information.  In most cases is not aware of the
      presence of NSH.

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

   Network Service Header:  Data plane header added to frames/packets.
      The header contains information required for service chaining, as
      well as metadata added and consumed by network nodes and service

   Service Classifier:  Function that performs classification and
      imposes an NSH.  Creates a service path.  Non-initial (i.e.
      subsequent) classification can occur as needed and can alter, or
      create a new service path.

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   Service Hop:  NSH aware node, akin to an IP hop but in the service

   Service Path Segment:  A segment of a service path overlay.

   NSH Proxy:  Acts as a gateway: removes and inserts NSH on behalf of a
      service function that is not NSH aware.

2.2.  Problem Space

   Network Service Header (NSH) addresses several limitations associated
   with service function deployments today.

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

   2.  Service Chain Construction: Service function 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 provide not only
       connectivity state, but will also be increasingly utilized for
       the creation of network services.  Such a control/management
       planes could be centralized, or be distributed.

   3.  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.  Furthermore topology-centric information often does
       not convey adequate information to the service functions, forcing
       functions to individually perform more granular classification.

   4.  Per-Service (re)Classification: Classification occurs at each
       service function independent from previously applied service
       functions.  More importantly, the classification functionality
       often differs per service function and service functions may not
       leverage the results from other service functions.

   5.  Common Header Format: Various proprietary methods are used to
       share metadata and create service paths.  An open header provides
       a common format for all network and service devices.

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

   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.

   Please see the Service Function Chaining Problem Statement [SFC-PS]
   for a more detailed analysis of service function deployment problem

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3.  Network Service Header

   A Network Service Header (NSH) contains metadata and service path
   information that is added to a packet or frame and used to create a
   service plane.  The packets and the NSH are then encapsulated in an
   outer header for transport.

   The service header is added by a service classification function - a
   device or application - that determines which packets require
   servicing, and correspondingly which service path to follow to apply
   the appropriate service.

   A NSH is composed of a 64-bit base header, and four 32-bit context
   headers as shown in figure 1 below.

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                                                               |
   |                    Base Header                                |
   |                                                               |
   |                    Context Header                             |
   |                    Context Header                             |
   |                    Context Header                             |
   |                    Context Header                             |

                     Figure 1: Network Service Header

   Base header: provides information about the service header and
   service path identification.

   Context headers: carry opaque metadata.

3.1.  NSH Actions

   Service header aware nodes - service classifiers, SFF, SF and NSH
   proxies, have several possible header related actions:

   1.  Insert or remove service header: These actions can occur at the
       start and end respectively of a service path.  Packets are
       classified, and if determined to require servicing, a service
       header imposed.  The last node in a service chain, an SF, or an

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       associated SFF, removes NSH.  A service classifier MUST insert a
       NSH.  At the end of a service function chain, the last node
       operating on the service header MUST remove it.

       A service function can re-classify data as required and that re-
       classification might result in a new service path.  If a SF
       performs re-classification that results in a change of service
       path, it MUST remove the existing NSH and MUST imposes a new NSH
       with the base header reflecting the new path.

   2.  Select service path: The base header provides service chain
       information and is used by SFFs to determine correct service path
       selection.  SFFs MUST use the base header for selecting the next
       service in the service path.

   3.  Update a service header: NSH aware service functions MUST
       decrement the service index.  A service index = 0 indicates that
       a packet MUST be dropped by the SFF performing NSH based

       Service functions MAY update context headers if new/updated
       context is available.

       If an NSH proxy is in use (acting on behalf of a non-aware
       service function for NSH actions), then the proxy MUST update
       service index and MAY update contexts.

   4.  Service policy selection: Service function instances derive
       policy selection from the service header.  Context shared in the
       service header can provide a range of service-relevant
       information such as traffic classification.  Service functions
       SHOULD use NSH to select local service policy.

3.2.  NSH Encapsulation

   Once NSH is added to a packet, an outer encapsulation is used to
   forward the original packet and the associated metadata to the start
   of a service chain.  The encapsulation serves two purposes:

   1.  Creates a topologically independent services plane.  Packets are
       forwarded to the required services without changing the
       underlying network topology.

   2.  Transit network nodes simply forward the encapsulated packets as

   The service header is independent of the encapsulation used and is

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   encapsulated in existing transports.  The presence of NSH is
   indicated via protocol type or other indicator in the outer

   See section 4 for an example using GRE and NSH encapsulation.

3.3.  NSH Usage

   NSH creates a dedicated service plane, that addresses many of the
   limitations highlighted in section 2.2.  More specifically, NSH

   1.  Topological Independence: Service forwarding occurs within the
       service plane, via a network overlay, the underlying network
       topology does not require modification.  Service functions have
       one or more network locators (e.g.  IP address), to receive/send
       data within the service plane, the NSH header contains an
       identifier that is used to uniquely identify a service path and
       the services within that path.

   2.  Service Chaining: NSH contains path identification information
       needed to realize a service path (see section 4 for header
       specifics).  Furthermore, NSH provides the ability to monitor and
       troubleshoot a service chain, end-to-end via service-specific OAM
       messages.  The NSH fields can be used by administrators (via, for
       example a traffic analyzer) to verify (account, ensure correct
       chaining, provide reports, etc.) the path specifics of packets
       being forwarded along a service path.

   3.  Metadata Sharing: NSH provides a mechanism to carry shared
       metadata between network devices and service function, and
       between service functions.  The semantics of the shared metadata
       is communicated via a control plane to participating nodes.
       Examples of metadata include classification information used for
       policy enforcement and network context for forwarding post
       service delivery.

   4.  Transport Agnostic: NSH is transport independent and can be used
       with overlay and underlay forwarding topologies.

3.4.  NSH Proxy Nodes

   In order to support NSH unaware service functions, an NSH proxy is
   used.  The proxy node removes the NSH header and delivers, to the
   service node, the original packet/frame via a local attachment
   circuit.  Examples of a local attachment circuit include, but are not
   limited to: VLANs, IP in IP, GRE, VXLAN.  When complete, the service
   function returns the packet to the NSH-proxy via the same or

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   different attachment circuit.

   NSH is re-imposed on packets returned to the proxy from the non-NSH
   aware service.

   Typically, a SFCNF will act as a NSH-proxy when required.

   An NSH proxy MUST perform NSH actions as described in section 3.1.

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4.  Header Format

   Base Service Header:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |O|C|R|R|R|R|R|R|   Reserved    |     Protocol Type             |
     |                 Service path                  | Service index |

   Flags: 8
   Reserved: 8
   Protocol Type (PT): 16
   Service path (SP): 24
   Service index (SI): 8

                         Figure 2: NSH Base Header

   Base Header Field Descriptions

   O bit: Indicates that this packet is an operations and management
   (OAM) packet.  SFF and SFs nodes MUST examine the payload and take
   appropriate action (i.e. return status information).

   OAM message specifics and handling details are outside the scope of
   this document.

   C bit: Context headers MUST be present.  When C is set, one or more
   contexts are in use (i.e. a value placed in a context is
   significant).  The C bit specifies that their ordering and sizing is
   as per figure 4: network platform (32 bits), network shared (32
   bits), service platform (32 bits), service shared (32 bits).

   A C bit equal to zero indicates that no contexts are in use (although
   they MUST be present to ensure a fixed size header) and that they can
   be ignored.

   If a context header is not in use, the value of that context header
   MUST be zero.

   All other flag fields are reserved.

   Protocol type: indicates the protocol type of the original packet or
   frame as per [ETYPES]

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   Service Index (SI): provides location within the service path.
   Service index MUST be decremented by service functions or proxy nodes
   after performing required services.  MAY be used in conjunction with
   service path for path selection.  Service Index is also valuable when
   troubleshooting/reporting service paths.  In addition to location
   within a path, SI can be used for loop detection.

   Service Path: identifies a service path.  Participating nodes MUST
   use this identifier for path selection.  An administrator can use the
   service path value for reporting and troubleshooting packets along a
   specific path.

   Context Headers:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                     Context data                              |

                          Figure 3: Context Data

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                  Network Platform Context                     |
   |                  Network Shared Context                       |
   |                  Service Platform Context                     |
   |                  Service Shared Context                       |

                    Figure 4: Context Data Significance

   The following examples of context header allocation are guidelines
   that illustrate how various forms of information can carried and
   exchanged via NSH.

   Network platform context: provides platform-specific metadata shared
   between network nodes.  Examples include (but are not limited to)

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   ingress port information, forwarding context and encapsulation type.

   Network shared context: metadata relevant to any network node such as
   the result of edge classification.  For example, application
   information, identity information or tenancy information can be
   shared using this context header.

   Service platform context: provides service platform specific metadata
   shared between service functions.  This context header is analogous
   to the network platform context, enabling service platforms to
   exchange platform-centric information such as an identifier used for
   load balancing decisions.

   Service shared context: metadata relevant to, and shared, between
   service functions.  As with the shared network context,
   classification information such as application type can be conveyed
   using this context.

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5.  NSH Example: GRE

    IP Packet:
    |L2 header | L3 header, proto=47|GRE header,PT=0x894F|
    NSH, PT=0x800 |original packet |

    L2 Frame:
    |L2 header | L3 header, proto=47|GRE header, PT=0x894F|
    NSH, PT=0x6558 |original frame |

                            Figure 5: GRE + NSH

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6.  Security Considerations

   As with many other protocols, NSH data can be spoofed or otherwise
   modified.  In many deployments, NSH will be used in a controlled
   environment, with trusted devices (e.g. a data center) thus
   mitigating the risk of unauthorized header manipulation.

   NSH is always encapsulated in a transport protocol and therefore,
   when required, existing security protocols that provide authenticity
   (e.g.  RFC 2119 [RFC6071]) can be used.

   Similarly if confidentiality is required, existing encryption
   protocols can be used in conjunction with encapsulated NSH.

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7.  Acknowledgments

   The authors would like to thank Nagaraj Bagepalli, Abhijit Patra,
   Carlos Pignataro, Ron Parker, Peter Bosch, Tom Nadeau, Darrel Lewis,
   Pritesh Kothari and Ken Gray for their detailed review, comments and

   A special thank you goes to David Ward and Tom Edsall for their
   guidance and feedback.

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8.  IANA Considerations

   An IEEE EtherType, 0x894F, has been allocated for NSH.

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9.  References

9.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

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

9.2.  Informative References

   [ETYPES]   The IEEE Registration Authority, "IEEE 802 Numbers", 2012,

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC6071]  Frankel, S. and S. Krishnan, "IP Security (IPsec) and
              Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
              February 2011.

   [SFC-PS]   Quinn, P., Ed. and T. Nadeau, Ed., "Service Function
              Chaining Problem Statement", 2014, <http://

              Quinn, P., Ed. and A. Beliveau, Ed., "Service Function
              Chaining (SFC) Architecture", 2014,

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Authors' Addresses

   Paul Quinn
   Cisco Systems, Inc.


   Jim Guichard
   Cisco Systems, Inc.


   Rex Fernando
   Cisco Systems, Inc.


   Surendra Kumar
   Cisco Systems, Inc.


   Michael Smith
   Cisco Systems, Inc.


   Navindra Yadav
   Cisco Systems, Inc.


   Puneet Agarwal


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   Rajeev Manur


   Abhishek Chauhan


   Brad McConnell


   Chris Wright
   Red Hat Inc.


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