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Versions: (draft-quinn-nsh) 00 01 02 03 04 05 06 07 draft-ietf-sfc-nsh

Network Working Group                                           P. Quinn
Internet-Draft                                               J. Guichard
Intended status: Standards Track                                S. Kumar
Expires: August 28, 2015                                        M. Smith
                                                     Cisco Systems, Inc.
                                                           W. Henderickx
                                                          Alcatel-Lucent
                                                               T. Nadeau
                                                                 Brocade
                                                              P. Agarwal

                                                                R. Manur
                                                                Broadcom
                                                              A. Chauhan
                                                                  Citrix
                                                              J. Halpern
                                                                Ericsson
                                                                S. Majee
                                                                      F5
                                                                U. Elzur
                                                                   Intel
                                                               D. Melman
                                                                 Marvell
                                                                 P. Garg
                                                               Microsoft
                                                            B. McConnell
                                                               Rackspace
                                                               C. Wright
                                                            Red Hat Inc.
                                                               K. Glavin
                                                                Riverbed
                                                                C. Zhang
                                                               L. Fourie
                                                           Huawei US R&D
                                                               R. Parker
                                                       Affirmed Networks
                                                                M. Zarny
                                                           Goldman Sachs
                                                       February 24, 2015


                         Network Service Header
                       draft-quinn-sfc-nsh-07.txt

Abstract

   This draft describes a Network Service Header (NSH) inserted onto
   encapsulated packets or frames to realize service function paths.



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   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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   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 http://datatracker.ietf.org/drafts/current/.

   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 August 28, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.














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Table of Contents

   1.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Definition of Terms  . . . . . . . . . . . . . . . . . . .  5
     2.2.  Problem Space  . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Network Service Header . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Network Service Header Format  . . . . . . . . . . . . . .  9
     3.2.  NSH Base Header  . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Service Path Header  . . . . . . . . . . . . . . . . . . . 11
     3.4.  NSH MD-type 1  . . . . . . . . . . . . . . . . . . . . . . 11
       3.4.1.  Mandatory Context Header Allocation Guidelines . . . . 12
     3.5.  NSH MD-type 2  . . . . . . . . . . . . . . . . . . . . . . 13
       3.5.1.  Optional Variable Length Metadata  . . . . . . . . . . 14
   4.  NSH Actions  . . . . . . . . . . . . . . . . . . . . . . . . . 16
   5.  NSH Encapsulation  . . . . . . . . . . . . . . . . . . . . . . 18
   6.  NSH Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 19
   7.  NSH Proxy Nodes  . . . . . . . . . . . . . . . . . . . . . . . 20
   8.  Fragmentation Considerations . . . . . . . . . . . . . . . . . 21
   9.  Service Path Forwarding with NSH . . . . . . . . . . . . . . . 22
     9.1.  SFFs and Overlay Selection . . . . . . . . . . . . . . . . 22
     9.2.  Mapping NSH to Network Overlay . . . . . . . . . . . . . . 24
     9.3.  Service Plane Visibility . . . . . . . . . . . . . . . . . 25
     9.4.  Service Graphs . . . . . . . . . . . . . . . . . . . . . . 25
   10. Policy Enforcement with NSH  . . . . . . . . . . . . . . . . . 27
     10.1. NSH Metadata and Policy Enforcement  . . . . . . . . . . . 27
     10.2. Updating/Augmenting Metadata . . . . . . . . . . . . . . . 28
     10.3. Service Path ID and Metadata . . . . . . . . . . . . . . . 30
   11. NSH Encapsulation Examples . . . . . . . . . . . . . . . . . . 31
     11.1. GRE + NSH  . . . . . . . . . . . . . . . . . . . . . . . . 31
     11.2. VXLAN-gpe + NSH  . . . . . . . . . . . . . . . . . . . . . 31
     11.3. Ethernet + NSH . . . . . . . . . . . . . . . . . . . . . . 32
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 33
   13. Open Items for WG Discussion . . . . . . . . . . . . . . . . . 34
   14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 35
   15. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 36
   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 37
     16.1. NSH EtherType  . . . . . . . . . . . . . . . . . . . . . . 37
     16.2. Network Service Header (NSH) Parameters  . . . . . . . . . 37
       16.2.1. NSH Base Header Reserved Bits  . . . . . . . . . . . . 37
       16.2.2. MD Type Registry . . . . . . . . . . . . . . . . . . . 37
       16.2.3. TLV Class Registry . . . . . . . . . . . . . . . . . . 38
       16.2.4. NSH Base Header Next Protocol  . . . . . . . . . . . . 38
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 39
     17.2. Informative References . . . . . . . . . . . . . . . . . . 39
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41




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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 the following elements:

   1.  Service path identification

   2.  Transport independent per-packet/frame service metadata.

   3.  Optional variable TLV metadata.

   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
   service 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.







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   SFC Network Forwarder (NF):  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
      encapsulation.

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

   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
      elements.





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   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.

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

   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



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       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.

   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
       challenges.

   7.  Transport Dependence: Service functions can and will be deployed
       in networks with a range of transports requiring service
       functions to support and participate in many transports (and
       associated control planes) 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
   areas.



























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3.  Network Service Header

   A Network Service Header (NSH) contains metadata and service path
   information that are 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.

3.1.  Network Service Header Format

   An NSH is composed of a 4-byte base header, a 4-byte service path
   header and 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                                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Service Path Header                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                Context Headers                                ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Network Service Header

   Base header: provides information about the service header and the
   payload protocol.

   Service Path Header: provide path identification and location within
   a path.

   Context headers: carry opaque metadata and variable length encoded
   information.

3.2.  NSH Base Header



      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Ver|O|C|R|R|R|R|R|R|   Length  |    MD Type    | Next Protocol |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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                         Figure 2: NSH Base Header

   Base Header Field Descriptions

   Version: The version field is used to ensure backward compatibility
   going forward with future NSH updates.

   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 (e.g. return status information).

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

   C bit: Indicates that a critical metadata TLV is present (see Section
   3.4.2).  This bit acts as an indication for hardware implementers to
   decide how to handle the presence of a critical TLV without
   necessarily needing to parse all TLVs present.  The C bit MUST be set
   to 1 if one or more critical TLVs are present.

   All other flag fields are reserved.

   Length: total length, in 4-byte words, of the NSH header, including
   optional variable TLVs.

   MD Type: indicates the format of NSH beyond the base header and the
   type of metadata being carried.  This typing is used to describe the
   use for the metadata.  A new registry will be requested from IANA for
   the MD Type.

   NSH defines two MD types:

   0x1 which indicates that the format of the header includes fixed
   length context headers.

   0x2 which does not mandate any headers beyond the base header and
   service path header, and may contain optional variable length context
   information.

   The format of the base header is invariant, and not described by MD
   Type.

   NSH implementations MUST support MD-Type 0x1, and SHOULD support MD-
   Type 0x2.

   Next Protocol: indicates the protocol type of the original packet.  A
   new IANA registry will be created for protocol type.




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   This draft defines the following Next Protocol values:

   0x1 : IPv4
   0x2 : IPv6
   0x3 : Ethernet

3.3.  Service Path Header



      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path ID                      | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Service path ID (SPI): 24 bits
   Service index (SI): 8 bits

                     Figure 3: NSH Service Path Header

   Service Path Identifier (SPI): 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.

   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.

3.4.  NSH MD-type 1

   When the base header specifies MD Type 1, NSH defines four 4-byte
   mandatory context headers, as per Figure 4.  These headers must be
   present and the format is opaque as depicted in Figure 5.













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     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ver|O|C|R|R|R|R|R|R|   Length  |  MD-type=0x1  | Next Protocol |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path ID                      | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                         Figure 4: NSH MD-type=0x1




    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 5: Context Header

3.4.1.  Mandatory Context Header Allocation Guidelines


    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                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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                    Figure 6: Context Data Significance

   Figure 6, above, and the following examples of context header
   allocation are guidelines that illustrate how various forms of
   information can be carried and exchanged via NSH.

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

   The data center[dcalloc] and mobility[moballoc] context header
   allocation drafts provide guidelines for the semantics of NSH fixed
   context headers in each respective environment.

3.5.  NSH MD-type 2

   When the base header specifies MD Type 2, NSH defines variable length
   only context headers.  There may be zero or more of these headers as
   per the length field.


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Ver|O|C|R|R|R|R|R|R|   Length  |  MD-type=0x2  | Next Protocol |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path ID                      | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~           Optional Variable Length Context Headers            ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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                         Figure 7: NSH MD-type=0x2

3.5.1.  Optional Variable Length Metadata

   NSH MD Type 2 MAY contain optional variable length context headers.
   The format of these headers is as described below.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          TLV Class            |      Type     |R|R|R|   Len   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Variable Metadata                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 8: Variable Context Headers

   TLV Class: describes the scope of the "Type" field.  In some cases,
   the TLV Class will identify a specific vendor, in others, the TLV
   Class will identify specific standards body allocated types.

   Type: the specific type of information being carried, within the
   scope of a given TLV Class.  Value allocation is the responsibility
   of the TLV Class owner.

   The most significant bit of the Type field indicates whether the TLV
   is mandatory for the receiver to understand/process.  This
   effectively allocates Type values 0 to 127 for non-critical options
   and Type values 128 to 255 for critical options.  Figure 7 below
   illustrates the placement of the Critical bit within the Type field.

     +-+-+-+-+-+-+-+-+
     |C|     Type    |
     +-+-+-+-+-+-+-+-+


        Figure 9: Critical Bit Placement Within the TLV Type Field

   Encoding the criticality of the TLV within the Type field is
   consistent with IPv6 option types.

   If a receiver receives an encapsulated packet containing a TLV with
   the Critical bit set in the Type field and it does not understand how
   to process the Type, it MUST drop the packet.  Transit devices MUST
   NOT drop packets based on the setting of this bit.

   Reserved bits: three reserved bit are present for future use.  The



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   reserved bits MUST be zero.

   Length: Length of the variable metadata, in 4-byte words.
















































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4.  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 path, an SFF, removes
       the NSH.  A service classifier MUST insert an 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.  In this case,
       the SF acts as a logical classifier as well.  When the logical
       classifier performs re-classification that results in a change of
       service path, it MUST remove the existing NSH and MUST impose 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
       forwarding.

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

       If an NSH proxy (see Section 7) is in use (acting on behalf of a
       non-NSH-aware service function for NSH actions), then the proxy
       MUST update service index and MAY update contexts.  When an NSH
       proxy receives an NSH-encapsulated packet, it removes the NSH
       before forwarding it to an NSH unaware SF.  When it receives a
       packet back from an NSH unaware SF, it re-encapsulates it with
       the NSH, decrementing the service index.


   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.



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   Figure 10 maps each of the four actions above to the components in
   the SFC architecture that can perform it.

 +----------------+--------------------+-------+---------------+-------+
 |                |  Insert or remove  |Select |   Update a    |Service|
 |                |   service header   |service|service header |Policy |
 |                +------+------+------+ path  +---------------+Select-|
 |                |Insert|Remove|Remove|       | Dec.  |Update |ion    |
 |                |      |      | and  |       |Service|Context|       |
 | Component      |      |      |Insert|       | Index |Header |       |
 +----------------+------+------+------+-------+-------+-------+-------+
 |Service Classif-|  +   |      |      |       |       |   +   |       |
 |ication Function|      |      |      |       |       |       |       |
 + -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
 |Service Function|      |  +   |      |   +   |       |   +   |       |
 |Forwarder(SFF)  |      |      |      |       |       |       |       |
 + -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
 |Service         |      |      |      |       |   +   |   +   |   +   |
 |Function  (SF)  |      |      |      |       |       |       |       |
 + -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
 |NSH Proxy       |  +   |  +   |      |       |   +   |   +   |       |
 +----------------+------+------+------+-------+-------+-------+-------+


                  Figure 10: NSH Action and Role Mapping


























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5.  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
       is.

   The service header is independent of the encapsulation used and is
   encapsulated in existing transports.  The presence of NSH is
   indicated via protocol type or other indicator in the outer
   encapsulation.

   See Section 11 for NSH encapsulation examples.
































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6.  NSH Usage

   The NSH creates a dedicated service plane, that addresses many of the
   limitations highlighted in Section 2.2.  More specifically, NSH
   enables:

   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 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.  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 is carried
       in an overlay, over existing underlays.  If an existing overlay
       topology provides the required service path connectivity, that
       existing overlay may be used.

















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7.  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 the
   original packet/frame via a local attachment circuit to the service
   function.  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
   different attachment circuit.

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

   Typically, an SFF will act as an NSH-proxy when required.

   An NSH proxy MUST perform NSH actions as described in Section 4.



































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8.  Fragmentation Considerations

   Work in progress
















































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9.  Service Path Forwarding with NSH

9.1.  SFFs and Overlay Selection

   As described above, NSH contains a service path identifier (SPI) and
   a service index (SI).  The SPI is, as per its name, an identifier.
   The SPI alone cannot be used to forward packets along a service path.
   Rather the SPI provide a level of indirection between the service
   path/topology and the network transport.  Furthermore, there is no
   requirement, or expectation of an SPI being bound to a pre-determined
   or static network path.

   The service index provides an indication of location within a service
   path.  The combination of SPI and SI provides the identification and
   location of a logical SF (locator and order).  The logical SF may be
   a single SF, or a set of SFs that are equivalent.  In the latter
   case, the SFF provides load distribution amongst the collection of
   SFs as needed.  SI may also serve as a mechanism for loop detection
   with in a service path since each SF in the path decrements the
   index; an index of 0 indicates that a loop occurred and packet must
   be discarded.

   This indirection -- path ID to overlay -- creates a true service
   plane.  That is the SFF/SF topology is constructed without impacting
   the network topology but more importantly service plane only
   participants (i.e. most SFs) need not be part of the network overlay
   topology and its associated infrastructure (e.g. control plane,
   routing tables, etc.).  As mentioned above, an existing overlay
   topology may be used provided it offers the requisite connectivity.

   The mapping of SPI to transport occurs on an SFF.  The SFF consults
   the SPI/ID values to determine the appropriate overlay transport
   protocol (several may be used within a given network) and next hop
   for the requisite SF.  Figure 10 below depicts an SPI/SI to network
   overlay mapping.


    +-------------------------------------------------------+
    |  SPI |  SI |  NH                 |   Transport        |
    +-------------------------------------------------------+
    |  10  |  3  |  1.1.1.1            |   VXLAN-gpe        |
    |  10  |  2  |  2.2.2.2            |   nvGRE            |
    |  245 |  12 |  192.168.45.3       |   VXLAN-gpe        |
    |  10  |  9  |  10.1.2.3           |   GRE              |
    |  40  |  9  |  10.1.2.3           |   GRE              |
    |  50  |  7  |  01:23:45:67:89:ab  |   Ethernet         |
    |  15  |  1  |  Null (end of path) |   None             |
    +-------------------------------------------------------+



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                    Figure 11: SFF NSH Mapping Example

   Additionally, further indirection is possible: the resolution of the
   required SF function locator may be a localized resolution on an
   SFF,rather than a service function chain control plane
   responsibility, as per figures 11 and 12 below.


    +-------------------+
    | SPI |  SI |  NH   |
    +-------------------+
    | 10  |  3  |  SF2  |
    | 245 |  12 |  SF34 |
    | 40  |  9  |  SF9  |
    +-------------------+


                   Figure 12: NSH to SF Mapping Example



    +-----------------------------------+
    |  SF  |  NH          |  Transport  |
    +-----------------------------------|
    |  SF2 |  10.1.1.1    |  VXLAN-gpe  |
    |  SF34|  192.168.1.1 |  UDP        |
    |  SF9 |  1.1.1.1     |  GRE        |
    +-----------------------------------+


                   Figure 13: SF Locator Mapping Example

   Since the SPI is a representation of the service path, the lookup may
   return more than one possible next-hop within a service path for a
   given SF, essentially a series of weighted (equally or otherwise)
   overlay links to be used (for load distribution, redundancy or
   policy), see Figure 13.  The metric depicted in Figure 13 is an
   example to help illustrated weighing SFs.  In a real network, the
   metric will range from a simple preference (similar to routing next-
   hop), to a true dynamic composite metric based on some service
   function-centric state (including load, sessions sate, capacity,
   etc.)









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     +----------------------------------+
     | SPI | SI |   NH        |  Metric |
     +----------------------------------+
     | 10  |  3 | 10.1.1.1    |  1      |
     |     |    | 10.1.1.2    |  1      |
     |     |    |             |         |
     | 20  | 12 | 192.168.1.1 |  1      |
     |     |    | 10.2.2.2    |  1      |
     |     |    |             |         |
     | 30  |  7 | 10.2.2.3    |  10     |
     |     |    | 10.3.3.3    |  5      |
     +----------------------------------+
     (encap type omitted for formatting)


                   Figure 14: NSH Weighted Service Path

9.2.  Mapping NSH to Network Overlay

   As described above, the mapping of SPI to network topology may result
   in a single overlay path, or it might result in a more complex
   topology.  Furthermore, the SPIx to overlay mapping occurs at each
   SFF independently.  Any combination of topology selection is
   possible.

   Examples of mapping for a topology:

   1.  Next SF is located at SFFb with locator 10.1.1.1
       SFFa mapping: SPI=10 --> VXLAN-gpe, dst-ip: 10.1.1.1

   2.  Next SF is located at SFFc with multiple locator for load
       distribution purposes:
       SFFb mapping: SPI=10 --> VXLAN-gpe, dst_ip:10.2.2.1, 10.2.2.2,
       10.2.2.3, equal cost

   3.  Next SF is located at SFFd with two path to SFFc, one for
       redundancy:
       SFFc mapping: SPI=10 --> VXLAN-gpe, dst_ip:10.1.1.1 cost=10,
       10.1.1.2, cost=20

   In the above example, each SFF makes an independent decision about
   the network overlay path and policy for that path.  In other words,
   there is no a priori mandate about how to forward packets in the
   network (only the order of services that must be traversed).

   The network operator retains the ability to engineer the overlay
   paths as required.  For example, the overlay path between service
   functions forwarders may utilize traffic engineering, QoS marking, or



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   ECMP, without requiring complex configuration and network protocol
   support to be extended to the service path explicitly.  In other
   words, the network operates as expected, and evolves as required, as
   does the service function plane.

9.3.  Service Plane Visibility

   The SPI and SI serve an important function for visibility into the
   service topology.  An operator can determine what service path a
   packet is "on", and its location within that path simply by viewing
   the NSH information (packet capture, IPFIX, etc.).  The information
   can be used for service scheduling and placement decisions,
   troubleshooting and compliance verification.

9.4.  Service Graphs

   In some cases, a service path is exactly that -- a linear list of
   service functions that must be traversed.  However, increasingly, the
   "path" is actually a true directed graph.  Furthermore, within a
   given service topology several directed graphs may exist with packets
   moving between graphs based on non-initial classification (usually
   performed by a service function).  Note: strictly speaking a path is
   a form of graph; the intent is to distinguish between a directed
   graph and a path.


                 ,---.          ,---.            ,---.
                /     \        /     \          /     \
               (  SF2  )      (  SF7  )        (  SF3  )
         ,------\     +.       \     /          \     /
        ;        |---'  `-.     `---'\           `-+-'
        |        :         :          \            ;
        |         \        |           :          ;
      ,-+-.        `.     ,+--.        :          |
     /     \         '---+     \        \         ;
    (  SF1  )           (  SF6  )        \       /
     \     /             \     +--.       :     /
      `---'               `---'    `-.  ,-+-.  /
                                      `+     +'
                                      (  SF4  )
                                       \     /
                                        `---'


                     Figure 15: Service Graph Example

   The SPI/SI combination provides a simple representation of a directed
   graph, the SPI represents a graph ID; and the SI a node ID.  The



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   service topology formed by SPI/SI support cycles, weighting, and
   alternate topology selection, all within the service plane.  The
   realization of the network topology occurs as described above: SPI/ID
   mapping to an appropriate transport and associated next network hops.

   NSH-aware services receive the entire header, including the SPI/SI.
   An SF can now, based on local policy, alter the SPI, which in turn
   effects both the service graph, and in turn the selection of overlay
   at the SFF.  The figure below depicts the policy associated with the
   graph in Figure 14 above.  Note: this illustrates multiple graphs and
   their representation; it does not depict the use of metadata within a
   single service function graph.




 +---------------------------------------------------------------------+
 |                                                SPI: 21 Bob: SF7     |
 |                  SPI: 20 Bad : SF2 --> SF6 --> SF4                  |
 |SPI: 10 SF1 --> SF2 --> SF6                     SPI: 22 Alice: SF3   |
 |                  SPI: 30 Good: SF4                                  |
 |                             SPI:31 Bob: SF7                         |
 |                             SPI:32 Alice: SF3                       |
 +---------------------------------------------------------------------+


                    Figure 16: Service Graphs Using SPI

   This example above does not show the mapping of the service topology
   to the network overlay topology.  As discussed in the sections above,
   the overlay selection occurs as per network policy.




















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10.  Policy Enforcement with NSH

10.1.  NSH Metadata and Policy Enforcement

   As described in Section 3, NSH provides the ability to carry metadata
   along a service path.  This metadata may be derived from several
   sources, common examples include:

      Network nodes: Information provided by network nodes can indicate
      network-centric information (such as VRF or tenant) that may be
      used by service functions, or conveyed to another network node
      post-service pathing.

      External (to the network) systems: External systems, such as
      orchestration systems, often contain information that is valuable
      for service function policy decisions.  In most cases, this
      information cannot be deduced by network nodes.  For example, a
      cloud orchestration platform placing workloads "knows" what
      application is being instantiated and can communicate this
      information to all NSH nodes via metadata.

      Service functions: Service functions often perform very detailed
      and valuable classification.  In some cases they may terminate,
      and be able to inspect encrypted traffic.  SFs may update, alter
      or impose metadata information.

   Regardless of the source, metadata reflects the "result" of
   classification.  The granularity of classification may vary.  For
   example, a network switch might only be able to classify based on a
   5-tuple, whereas, a service function may be able to inspect
   application information.  Regardless of granularity, the
   classification information can be represented in NSH.

   Once the data is added to NSH, it is carried along the service path,
   NSH-aware SFs receive the metadata, and can use that metadata for
   local decisions and policy enforcement.  The following two examples
   highlight the relationship between metadata and policy:














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    +-------------------------------------------------+
    |   ,---.             ,---.              ,---.    |
    |  /     \           /     \            /     \   |
    | (  SCL  )-------->(  SF1  )--------->(  SF2  )  |
    |  \     /           \     /            \     /   |
    |   `---'             `---'              `---'    |
    |5-tuple:            Permit             Inspect   |
    |Tenant A            Tenant A           AppY      |
    |AppY                                             |
    +-------------------------------------------------+

                      Figure 17: Metadata and Policy



    +-------------------------------------------------+
    |    ,---.             ,---.              ,---.   |
    |   /     \           /     \            /     \  |
    |  (  SCL  )-------->(  SF1  )--------->(  SF2  ) |
    |   \     /           \     /            \     /  |
    |    `-+-'             `---'              `---'   |
    |      |              Permit            Deny AppZ |
    |  +---+---+          employees                   |
    |  |       |                                      |
    |  +-------+                                      |
    |  external                                       |
    |  system:                                        |
    |  Employee                                       |
    |  App Z                                          |
    +-------------------------------------------------+

                  Figure 18: External Metadata and Policy

   In both of the examples above, the service functions perform policy
   decisions based on the result of the initial classification: the SFs
   did not need to perform re-classification, rather they relied on a
   antecedent classification for local policy enforcement.

10.2.  Updating/Augmenting Metadata

   Post-initial metadata imposition (typically performed during initial
   service path determination), metadata may be augmented or updated:

   1.  Metadata Augmentation: Information may be added to NSH's existing
       metadata, as depicted in Figure 18.  For example, if the initial
       classification returns the tenant information, a secondary
       classification (perhaps a DPI or SLB) may augment the tenant
       classification with application information.  The tenant



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       classification is still valid and present, but additional
       information has been added to it.

   2.  Metadata Update: Subsequent classifiers may update the initial
       classification if it is determined to be incorrect or not
       descriptive enough.  For example, the initial classifier adds
       metadata that describes the trafic as "internet" but a security
       service function determines that the traffic is really "attack".
       Figure 19 illustrates an example of updating metadata.



     +-------------------------------------------------+
    |    ,---.             ,---.              ,---.   |
    |   /     \           /     \            /     \  |
    |  (  SCL  )-------->(  SF1  )--------->(  SF2  ) |
    |   \     /           \     /            \     /  |
    |    `-+-'             `---'              `---'   |
    |      |              Inspect           Deny      |
    |  +---+---+          employees         employee+ |
    |  |       |          Class=AppZ        appZ      |
    |  +-------+                                      |
    |  external                                       |
    |  system:                                        |
    |  Employee                                       |
    |                                                 |
    +-------------------------------------------------+

                     Figure 19: Metadata Augmentation



    +-------------------------------------------------+
    |   ,---.             ,---.              ,---.    |
    |  /     \           /     \            /     \   |
    | (  SCL  )-------->(  SF1  )--------->(  SF2  )  |
    |  \     /           \     /            \     /   |
    |   `---'             `---'              `---'    |
    |5-tuple:            Inspect             Deny     |
    |Tenant A            Tenant A            attack   |
    |                     --> attack                  |
    +-------------------------------------------------+

                        Figure 20: Metadata Update







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10.3.  Service Path ID and Metadata

   Metadata information may influence the service path selection since
   the service path identifier can represent the result of
   classification.  A given SPI can represent all or some of the
   metadata, and be updated based on metadata classification results.
   This relationship provides the ability to create a dynamic services
   plane based on complex classification without requiring each node to
   be capable of such classification, or requiring a coupling to the
   network topology.  This yields service graph functionality as
   described in Section 9.4.  Figure 20 illustrates an example of this
   behavior.


    +----------------------------------------------------+
    |   ,---.             ,---.              ,---.       |
    |  /     \           /     \            /     \      |
    | (  SCL  )-------->(  SF1  )--------->(  SF2  )     |
    |  \     /           \     /            \     /      |
    |   `---'             `---' \              `---'     |
    |5-tuple:            Inspect \            Original   |
    |Tenant A            Tenant A \           next SF    |
    |                     --> DoS  \                     |
    |                                 \                  |
    |                                  ,---.             |
    |                                 /     \            |
    |                                (  SF10 )           |
    |                                 \     /            |
    |                                  `---'             |
    |                                   DoS              |
    |                                "Scrubber"          |
    +----------------------------------------------------+

                      Figure 21: Path ID and Metadata

   Specific algorithms for mapping metadata to an SPI are outside the
   scope of this draft.














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11.  NSH Encapsulation Examples

11.1.  GRE + NSH


    IPv4 Packet:
    +----------+--------------------+--------------------+
    |L2 header | L3 header, proto=47|GRE header,PT=0x894F|
    +----------+--------------------+--------------------+
    --------------+----------------+
    NSH, NP=0x1   |original packet |
    --------------+----------------+


    L2 Frame:
    +----------+--------------------+--------------------+
    |L2 header | L3 header, proto=47|GRE header,PT=0x894F|
    +----------+--------------------+--------------------+
    ---------------+---------------+
    NSH, NP=0x3    |original frame |
    ---------------+---------------+


                           Figure 22: GRE + NSH

11.2.  VXLAN-gpe + NSH

    IPv4 Packet:
    +----------+------------------------+---------------------+
    |L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)|
    +----------+------------------------+---------------------+
    --------------+----------------+
    NSH, NP=0x1   |original packet |
    --------------+----------------+


    L2 Frame:
    +----------+------------------------+---------------------+
    |L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)|
    +----------+------------------------+---------------------+
    ---------------+---------------+
    NSH,NP=0x3     |original frame |
    ---------------+---------------+


                        Figure 23: VXLAN-gpe + NSH





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11.3.  Ethernet + NSH


  IPv4 Packet:
  +-------------------------------+---------------+--------------------+
  |Outer Ethernet, ET=0x894F      | NSH, NP = 0x1 | original IP Packet |
  +-------------------------------+---------------+--------------------+


  L2 Frame:
  +-------------------------------+---------------+----------------+
  |Outer Ethernet, ET=0x894F      | NSH, NP = 0x3 | original frame |
  +-------------------------------+---------------+----------------+



                         Figure 24: Ethernet + NSH


































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12.  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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13.  Open Items for WG Discussion

   1.  MD type 1 metadata semantics specifics

   2.  Bypass bit in NSH.

   3.  Rendered Service Path ID (RSPID).












































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14.  Contributors

   The following people are active contributors to this document and
   have provided review, content and concepts (listed alphabetically by
   surname):

   Andrew Dolganow
   Alcaltel-Lucent
   Email: andrew.dolganow@alcatel-lucent.com

   Rex Fernando
   Cisco Systems
   Email: rex@cisco.com

   Praveen Muley
   Alcaltel-Lucent
   Email: praveen.muley@alcatel-lucent.com

   Navindra Yadav
   Cisco Systems
   Email: nyadav@cisco.com






























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15.  Acknowledgments

   The authors would like to thank Nagaraj Bagepalli, Abhijit Patra, Ron
   Parker, Peter Bosch, Darrel Lewis, Pritesh Kothari, Tal Mizrahi and
   Ken Gray for their detailed review, comments and contributions.

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

   Additionally the authors would like to thank Carlos Pignataro and
   Larry Kreeger for their invaluable ideas and contributions which are
   reflected throughout this draft.







































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16.  IANA Considerations

16.1.  NSH EtherType

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

16.2.  Network Service Header (NSH) Parameters

   IANA is requested to create a new "Network Service Header (NSH)
   Parameters" registry.  The following sub-sections request new
   registries within the "Network Service Header (NSH) Parameters "
   registry.

16.2.1.  NSH Base Header Reserved Bits

   There are ten bits at the beginning of the NSH Base Header.  New bits
   are assigned via Standards Action [RFC5226].

   Bits 0-1 - Version
   Bit 2 - OAM (O bit)
   Bits 2-9 - Reserved

16.2.2.  MD Type Registry

   IANA is requested to set up a registry of "MD Types".  These are
   8-bit values.  MD Type values 0, 1, 2, 254, and 255 are specified in
   this document.  Registry entries are assigned by using the "IETF
   Review" policy defined in RFC 5226 [RFC5226].

                +---------+--------------+---------------+
                | MD Type | Description  | Reference     |
                +---------+--------------+---------------+
                | 0       | Reserved     | This document |
                |         |              |               |
                | 1       | NSH          | This document |
                |         |              |               |
                | 2       | NSH          | This document |
                |         |              |               |
                | 3..253  | Unassigned   |               |
                |         |              |               |
                | 254     | Experiment 1 | This document |
                |         |              |               |
                | 255     | Experiment 2 | This document |
                +---------+--------------+---------------+

                                  Table 1





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16.2.3.  TLV Class Registry

   IANA is requested to set up a registry of "TLV Types".  These are 16-
   bit values.  Registry entries are assigned by using the "IETF Review"
   policy defined in RFC 5226 [RFC5226].

16.2.4.  NSH Base Header Next Protocol

   IANA is requested to set up a registry of "Next Protocol".  These are
   8-bit values.  Next Protocol values 0, 1, 2 and 3 are defined in this
   draft.  New values are assigned via Standards Action [RFC5226].

              +---------------+-------------+---------------+
              | Next Protocol | Description | Reference     |
              +---------------+-------------+---------------+
              | 0             | Reserved    | This document |
              |               |             |               |
              | 1             | IPv4        | This document |
              |               |             |               |
              | 2             | IPv6        | This document |
              |               |             |               |
              | 3             | Ethernet    | This document |
              |               |             |               |
              | 4..253        | Unassigned  |               |
              +---------------+-------------+---------------+

                                  Table 2
























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17.  References

17.1.  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.

17.2.  Informative References

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [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://
              datatracker.ietf.org/doc/
              draft-ietf-sfc-problem-statement/>.

   [SFC-arch]
              Quinn, P., Ed. and J. Halpern, Ed., "Service Function
              Chaining (SFC) Architecture", 2014,
              <http://datatracker.ietf.org/doc/draft-quinn-sfc-arch>.

   [VXLAN-gpe]
              Quinn, P., Agarwal, P., Kreeger, L., Lewis, D., Maino, F.,
              Yong, L., Xu, X., Elzur, U., and P. Garg, "Generic
              Protocol Extension for VXLAN",
              <https://datatracker.ietf.org/doc/draft-quinn-vxlan-gpe/>.

   [dcalloc]  Guichard, J., Smith, M., and S. Kumar, "Network Service
              Header (NSH) Context Header Allocation (Data Center)",
              2014, <https://datatracker.ietf.org/doc/
              draft-guichard-sfc-nsh-dc-allocation/>.

   [moballoc]
              Napper, J. and S. Kumar, "NSH Context Header Allocation --
              Mobility", 2014, <https://datatracker.ietf.org/doc/



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              draft-napper-sfc-nsh-mobility-allocation/>.


















































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Authors' Addresses

   Paul Quinn
   Cisco Systems, Inc.

   Email: paulq@cisco.com


   Jim Guichard
   Cisco Systems, Inc.

   Email: jguichar@cisco.com


   Surendra Kumar
   Cisco Systems, Inc.

   Email: smkumar@cisco.com


   Michael Smith
   Cisco Systems, Inc.

   Email: michsmit@cisco.com


   Wim Henderickx
   Alcatel-Lucent

   Email: wim.henderickx@alcatel-lucent.com


   Tom Nadeau
   Brocade

   Email: tnadeau@lucidvision.com


   Puneet Agarwal

   Email: puneet@acm.org


   Rajeev Manur
   Broadcom

   Email: rmanur@broadcom.com




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   Abhishek Chauhan
   Citrix

   Email: Abhishek.Chauhan@citrix.com


   Joel Halpern
   Ericsson

   Email: joel.halpern@ericsson.com


   Sumandra Majee
   F5

   Email: S.Majee@F5.com


   Uri Elzur
   Intel

   Email: uri.elzur@intel.com


   David Melman
   Marvell

   Email: davidme@marvell.com


   Pankaj Garg
   Microsoft

   Email: Garg.Pankaj@microsoft.com


   Brad McConnell
   Rackspace

   Email: bmcconne@rackspace.com


   Chris Wright
   Red Hat Inc.

   Email: chrisw@redhat.com





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   Kevin Glavin
   Riverbed

   Email: kevin.glavin@riverbed.com


   Hong (Cathy) Zhang
   Huawei US R&D

   Email: cathy.h.zhang@huawei.com


   Louis Fourie
   Huawei US R&D

   Email: louis.fourie@huawei.com


   Ron Parker
   Affirmed Networks

   Email: ron_parker@affirmednetworks.com


   Myo Zarny
   Goldman Sachs

   Email: myo.zarny@gs.com























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