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Network Service Header
draft-ietf-sfc-nsh-05

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8300.
Authors Paul Quinn , Uri Elzur
Last updated 2016-05-26
Replaces draft-quinn-sfc-nsh
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draft-ietf-sfc-nsh-05
Service Function Chaining                                  P. Quinn, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                           U. Elzur, Ed.
Expires: November 27, 2016                                         Intel
                                                            May 26, 2016

                         Network Service Header
                       draft-ietf-sfc-nsh-05.txt

Abstract

   This document describes a Network Service Header (NSH) inserted onto
   encapsulated packets or frames to realize service function paths.
   NSH also provides a mechanism for metadata exchange along the
   instantiated service path.  NSH is the SFC encapsulation required to
   support the Service Function Chaining (SFC) Architecture (defined in
   RFC7665).

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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 November 27, 2016.

Copyright Notice

   Copyright (c) 2016 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  . . . . . . . . . . . . . . . . . . . .  2
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Definition of Terms  . . . . . . . . . . . . . . . . . . .  4
     2.2.  Problem Space  . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  NSH-based Service Chaining . . . . . . . . . . . . . . . .  5
   3.  Network Service Header . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Network Service Header Format  . . . . . . . . . . . . . .  7
     3.2.  NSH Base Header  . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Service Path Header  . . . . . . . . . . . . . . . . . . .  9
     3.4.  NSH MD-type 1  . . . . . . . . . . . . . . . . . . . . . . 10
     3.5.  NSH MD-type 2  . . . . . . . . . . . . . . . . . . . . . . 10
       3.5.1.  Optional Variable Length Metadata  . . . . . . . . . . 11
   4.  NSH Actions  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   5.  NSH Encapsulation  . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Fragmentation Considerations . . . . . . . . . . . . . . . . . 16
   7.  Service Path Forwarding with NSH . . . . . . . . . . . . . . . 17
     7.1.  SFFs and Overlay Selection . . . . . . . . . . . . . . . . 17
     7.2.  Mapping NSH to Network Transport . . . . . . . . . . . . . 19
     7.3.  Service Plane Visibility . . . . . . . . . . . . . . . . . 20
     7.4.  Service Graphs . . . . . . . . . . . . . . . . . . . . . . 20
   8.  Policy Enforcement with NSH  . . . . . . . . . . . . . . . . . 21
     8.1.  NSH Metadata and Policy Enforcement  . . . . . . . . . . . 21
     8.2.  Updating/Augmenting Metadata . . . . . . . . . . . . . . . 22
     8.3.  Service Path Identifier and Metadata . . . . . . . . . . . 24
   9.  NSH Encapsulation Examples . . . . . . . . . . . . . . . . . . 26
     9.1.  GRE + NSH  . . . . . . . . . . . . . . . . . . . . . . . . 26
     9.2.  VXLAN-gpe + NSH  . . . . . . . . . . . . . . . . . . . . . 26
     9.3.  Ethernet + NSH . . . . . . . . . . . . . . . . . . . . . . 27
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 28
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 32
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33
     13.1. NSH EtherType  . . . . . . . . . . . . . . . . . . . . . . 33
     13.2. Network Service Header (NSH) Parameters  . . . . . . . . . 33
       13.2.1. NSH Base Header Reserved Bits  . . . . . . . . . . . . 33
       13.2.2. NSH Version  . . . . . . . . . . . . . . . . . . . . . 33
       13.2.3. MD Type Registry . . . . . . . . . . . . . . . . . . . 33
       13.2.4. MD Class Registry  . . . . . . . . . . . . . . . . . . 34
       13.2.5. NSH Base Header Next Protocol  . . . . . . . . . . . . 34
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 36
     14.2. Informative References . . . . . . . . . . . . . . . . . . 36
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38

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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.

   Prior to development of the SFC architecture [RFC7665] and the
   protocol specified in this document, current service function
   deployment models have been 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 dynamic and 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 and steer traffic to the requisite service
   function(s) are necessary.

   NSH defines a new service plane protocol specifically for the
   creation of dynamic service chains and is composed of the following
   elements:

   1.  Service Function Path identification

   2.  Transport independent service function chain

   3.  Per-packet network and service metadata or optional variable
       type-length-value (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.

   [RFC7665] 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.  NSH is the SFC
   encapsulation referenced in RFC7665 document.

2.1.  Definition of Terms

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   Classification:  Defined in [RFC7665].

   Classifier:  Defined in [RFC7665].

   Metadata:  Defined in [RFC7665].

   Network Locator:  dataplane address, typically IPv4 or IPv6, used to
      send and receive network traffic.

   Network Node/Element:  Device that forwards packets or frames based
      on outer header (i.e. transport) information.

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

   Service Classifier:  Logical entity providing classification
      function.  Since they are logical, classifiers may be co-resident
      with SFC elements such as SFs or SFFs.  Service classifiers
      perform classification and impose NSH.  The initial classifier
      imposes the initial NSH and sends the NSH packet to the first SFF
      in the path.  Non-initial (i.e. subsequent) classification can
      occur as needed and can alter, or create a new service path.

   Service Function (SF):  Defined in [RFC7665].

   Service Function Chain (SFC):  Defined in [RFC7665].

   Service Function Forwarder (SFF):  Defined in [RFC7665].

   Service Function Path (SFP):  Defined in [RFC7665].

   SFC Proxy:  Defined in [RFC7665].

2.2.  Problem Space

   Network Service Header (NSH) addresses several limitations associated
   with service function deployments.  RFC 7498 [RFC7498] provides a
   comprehensive review of those issues.

2.3.  NSH-based Service Chaining

   The NSH creates a dedicated service plane, more specifically, NSH
   enables:

   1.  Topological Independence: Service forwarding occurs within the
       service plane, the underlying network topology does not require
       modification.  NSH provides an identifier used to select the

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       network overlay for network forwarding.

   2.  Service Chaining: NSH enables Service Chaining per [RFC7665].
       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 analyser) to verify (account, ensure
       correct chaining, provide reports, etc.) the path specifics of
       packets being forwarded along a service path.

   3.  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.  Classification and re-classification: sharing the metadata allows
       service functions to share initial and intermediate
       classification results with downstream service functions saving
       re-classification, where enough information was enclosed.

   5.  NSH offers a common and standards-based header for service
       chaining to all network and service nodes.

   6.  Transport Agnostic: NSH is transport independent and is often
       carried via a network transport protocol, over existing
       underlays.  This transport may form an overlay network and if an
       existing overlay topology provides the required service path
       connectivity, that existing overlay may be used.

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3.  Network Service Header

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

   A Service Classifier adds the NSH.  The NSH is removed by the last
   SFF in the service chain or by a SF that consumes the packet.

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 service path.

   Context headers: carry metadata (i.e. context data) along a service
   path.

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.  It MUST be set to 0x0 by the
   sender, in this first revision of NSH.  Given the widespread
   implementation of existing hardware that uses the first nibble after
   an MPLS label stack for ECMP decision processing, this document
   reserves version 01 and this value MUST NOT be used in future
   versions of the protocol.

   O bit: when set to 0x1 indicates that this packet is an Operations,
   Administration and Maintenance (OAM) message.  The receiving 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.  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.  For an MD Type of 0x1 (i.e. no variable
   length metadata is present), the C bit MUST be set to 0x0.

   All other flag fields are reserved for future use.  Reserved bits
   MUST be set to zero when sent and MUST be ignored upon receipt.

   Length: total length, in 4-byte words, of NSH including the Base
   Header, the Service Path Header and the context headers or optional
   variable length metadata.  The Length MUST be of value 0x6 for MD
   Type equal to 0x1 and MUST be of value 0x2 or greater for MD Type
   equal to 0x2.  The NSH header length MUST be an integer number of 4
   bytes.  The length field indicates the "end" of NSH and where the
   original packet/frame begins.

   MD Type: indicates the format of NSH beyond the mandatory Base Header
   and the Service Path Header.  MD Type defines the format of the
   metadata being carried.  Please see IANA Considerations section
   below.

   NSH defines two MD types:

   0x1 - which indicates that the format of the header includes fixed
   length context headers (see Figure 4 below).

   0x2 - which does not mandate any headers beyond the Base Header and
   Service Path Header, but may contain optional variable length context
   information.

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   The format of the base header and the service path header is
   invariant, and not affected by MD Type.

   NSH implementations MUST support MD-Type = 0x1, and SHOULD support
   MD- Type = 0x2.  There exists, however, a middle ground, wherein a
   device will support MD-Type 0x1 (as per the MUST) metadata, yet be
   deployed in a network with MD-Type 0x2 metadata packets.  In that
   case, the MD-Type 0x1 node, MUST utilize the base header length field
   to determine the original payload offset if it requires access to the
   original packet/frame.

   Next Protocol: indicates the protocol type of the original packet.
   Please see IANA Considerations section below.

   This draft defines the following Next Protocol values:

   0x1 : IPv4
   0x2 : IPv6
   0x3 : Ethernet
   0x4: NSH
   0x5: MPLS
   0x6-0xFD: Unassigned
   0xFE-0xFF: Experimental

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 Identifier (SPI)        | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Service Path Identifier (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 Service Function
   Path selection.

   Service Index (SI): provides location within the SFP.  The first
   classifier (i.e. at the boundary of the NSH domain) in the NSH
   Service Function Path, SHOULD set the SI to 255, however the control
   plane MAY configure the initial value of SI as appropriate (i.e.
   taking into account the length of the service function path).  A

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   Classifier MUST send the packet to the first SFF in the chain.
   Service index MUST be decremented by service functions or proxy nodes
   after performing required services and the new decremented SI value
   MUST be used in the egress NSH packet.  SI SHOULD be used in
   conjunction with Service Path Identifier for Service Function Path
   selection.  Service Index (SI) is also valuable when troubleshooting/
   reporting service paths.  In addition to indicating the location
   within a Service Function Path, SI can be used for service plane loop
   detection.

3.4.  NSH MD-type 1

   When the Base Header specifies MD Type = 0x1, four Context Headers,
   4-byte each, MUST be added immediately following the Service Path
   Header, as per Figure 4.  Context Headers that carry no metadata MUST
   be set to zero.

     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 Identifer               | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Mandatory Context Header                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 4: NSH MD-type=0x1

   [dcalloc] and [broadalloc] provide specific examples of how metadata
   can be allocated.

3.5.  NSH MD-type 2

   When the base header specifies MD Type= 0x2, zero or more Variable
   Length Context Headers MAY be added, immediately following the
   Service Path Header.  Therefore, Length = 0x2, indicates that only
   the Base Header followed by the Service Path Header are present.  The
   optional Variable Length Context Headers MUST be of an integer number

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   of 4-bytes.  The base header length field MUST be used to determine
   the offset to locate the original packet or frame for SFC nodes that
   require access to that information.

        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 Identifier              | Service Index |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~              Variable Length Context Headers  (opt.)          ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 5: NSH MD-type=0x2

3.5.1.  Optional Variable Length Metadata

   The format of the optional variable length context 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Metadata Class       |C|    Type     |R|R|R|   Len   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Variable Metadata                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 6: Variable Context Headers

   Metadata Class (MD Class): describes the scope of the "Type" field.
   In some cases, the MD Class will identify a specific vendor, in
   others, the MD Class will identify specific standards body allocated
   types.  Please see IANA Considerations section below.

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

   Encoding the criticality of the TLV within the Type field is

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   consistent with IPv6 option types: 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 7: Critical Bit Placement Within the TLV Type Field

   If an NSH-aware node receives an encapsulated packet containing a TLV
   with the Critical bit set to 0x1 in the Type field and it does not
   understand how to process the Type, it MUST drop the packet.  Transit
   devices (i.e. network nodes that do not participate in the service
   plane) MUST NOT drop packets based on the setting of this bit.

   Reserved bits: three reserved bit are present for future use.  The
   reserved bits MUST be set to 0x0.

   Length: Length of the variable metadata, in 4-byte words.  A value of
   0x0 or higher can be used.  A value of 0x0 denotes a TLV header
   without a Variable Metadata field.

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4.  NSH Actions

   NSH-aware nodes are the only nodes that MAY alter the content of the
   NSH headers.  NSH-aware nodes include: service classifiers, SFF, SF
   and SFC proxies.  These nodes have several possible header related
   actions:

   1.  Insert or remove NSH: These actions can occur at the start and
       end respectively of a service path.  Packets are classified, and
       if determined to require servicing, NSH will be imposed.  A
       service classifier MUST insert NSH at the start of an SFP.  An
       imposed NSH MUST contain valid Base Header and Service Path
       Header.  At the end of a service function path, a SFF, MUST be
       the last node operating on the service header and MUST remove it.

       Multiple logical classifiers may exist within a given service
       path.  Non-initial classifiers may re-classify data and that re-
       classification MAY result in a new Service Function Path.  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 and Service Path
       Header reflecting the new service path information and set the
       initial SI.  Metadata MAY be preserved in the new NSH.

   2.  Select service path: The Service Path Header provides service
       chain information and is used by SFFs to determine correct
       service path selection.  SFFs MUST use the Service Path Header
       for selecting the next SF or SFF in the service path.

   3.  Update a Service Path Header: NSH-aware service functions (SF)
       MUST decrement the service index.  If an SFF receives a packet
       with SI equal to 0x0, that packet MUST be dropped by the SFF.

       Classifier(s) MAY update Context Headers if new/updated context
       is available.

       If an SFC proxy 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 SFC proxy
       receives an NSH-encapsulated packet, it MUST remove the NSH
       headers before forwarding it to an NSH unaware SF.  When the SFC
       Proxy receives a packet back from an NSH unaware SF, it MUST re-
       encapsulates it with the correct NSH, and MUST decrement the
       Service Index.

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   4.  Service policy selection: Service Function instances derive
       policy (i.e. service actions such as permit or deny) selection
       and enforcement from the service header.  Metadata 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.

   Figure 8 maps each of the four actions above to the components in the
   SFC architecture that can perform it.

 +---------------+------------------+-------+----------------+---------+
 |                |  Insert         |Select |   Update       |Service  |
 |                |  or remove NSH  |Service|    NSH         |policy   |
 |                |                 |Function|               |selection|
 | Component      +--------+--------+Path   +----------------+         |
 |                |        |        |       | Dec.   |Update |         |
 |                | Insert | Remove |       |Service |Context|         |
 |                |        |        |       | Index  |Header |         |
 +----------------+--------+--------+-------+--------+-------+---------+
 |                |   +    |   +    |       |        |   +   |         |
 |Classifier      |        |        |       |        |       |         |
 +--------------- +--------+--------+-------+--------+-------+---------+
 |Service Function|        |   +    |  +    |        |       |         |
 |Forwarder(SFF)  |        |        |       |        |       |         |
 +--------------- +--------+--------+-------+--------+-------+---------+
 |Service         |        |        |       |   +    |   +   |   +     |
 |Function  (SF)  |        |        |       |        |       |         |
 +--------------- +--------+--------+-------+--------+-------+---------+
 |SFC Proxy       |   +    |   +    |       |   +    |       |         |
 +----------------+--------+--------+-------+--------+-------+---------+

                   Figure 8: 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 9 for NSH encapsulation examples.

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6.  Fragmentation Considerations

   NSH and the associated transport header are "added" to the
   encapsulated packet/frame.  This additional information increases the
   size of the packet.  In order the ensure proper forwarding of NSH
   packets, several options for handling fragmentation and re-assembly
   exist:

   1.  Jumbo Frames, when supported, enable the transport of NSH and
       associated transport packets without requiring fragmentation.

   2.  and [RFC1191][RFC1981] describe a technique for dynamically
       discovering the maximum transmission unit (MTU) of an arbitrary
       internet path" and can be utilized to ensure the required packet
       size is used.

   3.  Use the fragmentation provided by the network transport/overlay.
       One example can be found in [RFC6830], section 5.4.

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7.  Service Path Forwarding with NSH

7.1.  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 of a
   logical SF and its order within the service plane, and is used to
   select the appropriate network locator(s) for overlay forwarding.
   The logical SF may be a single SF, or a set of eligible SFs that are
   equivalent.  In the latter case, the SFF provides load distribution
   amongst the collection of SFs as needed.

   SI can also serve as a mechanism for loop detection within a service
   path since each SF in the path decrements the index; an Service Index
   of 0 indicates that a loop occurred and the 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 (as discussed above,
   the first SFF in the path gets a NSH encapsulated packet from the
   Classifier).  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 9 below
   depicts an example of a single next-hop SPI/SI to network overlay
   network locator mapping.

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   +-------------------------------------------------------+
   |  SPI |  SI |  NH                 |   Transport        |
   +-------------------------------------------------------+
   |  10  | 255 |  192.0.2.1          |   VXLAN-gpe        |
   |  10  | 254 |  198.51.100.10      |   GRE              |
   |  10  | 251 |  198.51.100.15      |   GRE              |
   |  40  | 251 |  198.51.100.15      |   GRE              |
   |  50  | 200 |  01:23:45:67:89:ab  |   Ethernet         |
   |  15  | 212 |  Null (end of path) |   None             |
   +-------------------------------------------------------+

                     Figure 9: SFF NSH Mapping Example

   Additionally, further indirection is possible: the resolution of the
   required SF network locator may be a localized resolution on an SFF,
   rather than a service function chain control plane responsibility, as
   per figures 10 and 11 below.

   Please note: VXLAN-gpe and GRE in the above table refer to
   [VXLAN-gpe] and [RFC2784], respectively.

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

                   Figure 10: NSH to SF Mapping Example

    +----------------------------------------+
    |  SF  |  NH               |  Transport  |
    +----------------------------------------|
    |  SF2 |  192.0.2.2        |  VXLAN-gpe  |
    |  SF34|  198.51.100.34    |  UDP        |
    |  SF9 |  2001:db8::1      |  GRE        |
    +--------------------------+-------------
    =

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                   Figure 11: 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)
   paths to be used (for load distribution, redundancy or policy), see
   Figure 12.  The metric depicted in Figure 12 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 state, capacity, etc.)

    +----------------------------------+
    | SPI | SI |   NH        |  Metric |
    +----------------------------------+
    | 10  |  3 | 203.0.113.1 |  1      |
    |     |    | 203.0.113.2 |  1      |
    |     |    |             |         |
    | 20  | 12 | 192.0.2.1   |  1      |
    |     |    | 203.0.113.4 |  1      |
    |     |    |             |         |
    | 30  |  7 | 192.0.2.10  |  10     |
    |     |    | 198.51.100.1|  5      |
    +----------------------------------+
     (encapsulation type omitted for formatting)

                   Figure 12: NSH Weighted Service Path

7.2.  Mapping NSH to Network Transport

   As described above, the mapping of SPI to network topology may result
   in a single path, or it might result in a more complex topology.
   Furthermore, the SPI to overlay mapping occurs at each SFF
   independently.  Any combination of topology selection is possible.
   Please note, there is no requirement to create a new overlay topology
   if a suitable one already existing.  NSH packets can use any (new or
   existing) overlay provided the requisite connectivity requirements
   are satisfied.

   Examples of mapping for a topology:

   1.  Next SF is located at SFFb with locator 192.0.2.1
       SFFa mapping: SPI=10 --> VXLAN-gpe, dst-ip: 192.0.2.1

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   2.  Next SF is located at SFFc with multiple network locators for
       load distribution purposes:
       SFFb mapping: SPI=10 --> VXLAN-gpe, dst_ip:203.0.113.1,
       203.0.113.2, 203.0.113.3, equal cost

   3.  Next SF is located at SFFd with two paths from SFFc, one for
       redundancy:
       SFFc mapping: SPI=10 --> VXLAN-gpe, dst_ip:192.0.2.10 cost=10,
       203.0.113.10, 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 network
   paths as required.  For example, the overlay path between SFFs may
   utilize traffic engineering, QoS marking, or 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 plane.

7.3.  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.

7.4.  Service Graphs

   While a given realized service function path is a specific sequence
   of service functions, the service as seen by a user can actually be a
   collection of service function paths, with the interconnection
   provided by classifiers (in-service path, non-initial
   reclassification).  These internal reclassifiers examine the packet
   at relevant points in the network, and rewrite the SPI and SI to
   reflect the results of the reclassification.  (These classifiers may
   also of course modify the metadata associated with the packet.)
   RFC7665, section 2.1 describes Service Graphs in detail.

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8.  Policy Enforcement with NSH

8.1.  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/devices: 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 path egress.

      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 carried in the context
      header(s).

      Service Functions: A classifier co-resident with Service Functions
      often perform very detailed and valuable classification.  In some
      cases they may terminate, and be able to inspect encrypted
      traffic.

   Regardless of the source, metadata reflects the "result" of
   classification.  The granularity of classification may vary.  For
   example, a network switch, acting as a classifier, 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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    +-------+        +-------+        +-------+
    |  SFF  )------->(  SFF  |------->|  SFF  |
    +---^---+        +---|---+        +---|---+
      ,-|-.            ,-|-.            ,-|-.
     /     \          /     \          /     \
    ( Class )           SF1  )        (  SF2  )
     \ ify /          \     /          \     /
      `---'            `---'            `---'
     5-tuple:        Permit             Inspect
     Tenant A        Tenant A           AppY
     AppY

                      Figure 13: Metadata and Policy

       +-----+           +-----+            +-----+
       | SFF |---------> | SFF |----------> | SFF |
       +--+--+           +--+--+            +--+--+
          ^                 |                  |
        ,-+-.             ,-+-.              ,-+-.
       /     \           /     \            /     \
      ( Class )         (  SF1  )          (  SF2  )
       \ ify /           \     /            \     /
        `-+-'             `---'              `---'
          |              Permit            Deny AppZ
      +---+---+          employees
      |       |
      +-------+
      external
      system:
      Employee
      AppZ

                  Figure 14: 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 rely on a
   antecedent classification for local policy enforcement.

8.2.  Updating/Augmenting Metadata

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

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   1.  Metadata Augmentation: Information may be added to NSH's existing
       metadata, as depicted in Figure 17.  For example, if the initial
       classification returns the tenant information, a secondary
       classification (perhaps co-resident with DPI or SLB) may augment
       the tenant classification with application information, and
       impose that new information in the NSH metadata.  The tenant
       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 traffic as "internet" but a security
       service function determines that the traffic is really "attack".
       Figure 18 illustrates an example of updating metadata.

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

                     Figure 15: Metadata Augmentation

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

                        Figure 16: Metadata Update

8.3.  Service Path Identifier 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 service
   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 7.4.  Figure 19 illustrates an example of this
   behavior.

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

                      Figure 17: Path ID and Metadata

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

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9.  NSH Encapsulation Examples

9.1.  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 18: GRE + NSH

9.2.  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 19: VXLAN-gpe + NSH

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9.3.  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 20: Ethernet + NSH

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10.  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.

   Further security considerations are discussed in [nsh-sec].

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11.  Contributors

   This WG document originated as draft-quinn-sfc-nsh and had the
   following co-authors and contributors.  The editors of this document
   would like to thank and recognize them and their contributions.
   These co-authors and contributors provided invaluable concepts and
   content for this document's creation.

   Surendra Kumar
   Cisco Systems
   smkumar@cisco.com

   Michael Smith
   Cisco Systems
   michsmit@cisco.com

   Jim Guichard
   Cisco Systems
   jguichar@cisco.com

   Rex Fernando
   Cisco Systems
   Email: rex@cisco.com

   Navindra Yadav
   Cisco Systems
   Email: nyadav@cisco.com

   Wim Henderickx
   Alcatel-Lucent
   wim.henderickx@alcatel-lucent.com

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

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

   Tom Nadeau
   Brocade
   tnadeau@lucidvision.com

   Puneet Agarwal
   puneet@acm.org

   Rajeev Manur

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   Broadcom
   rmanur@broadcom.com

   Abhishek Chauhan
   Citrix
   Abhishek.Chauhan@citrix.com

   Joel Halpern
   Ericsson
   joel.halpern@ericsson.com

   Sumandra Majee
   F5
   S.Majee@f5.com

   David Melman
   Marvell
   davidme@marvell.com

   Pankaj Garg
   Microsoft
   pankajg@microsoft.com

   Brad McConnell
   Rackspace
   bmcconne@rackspace.com

   Chris Wright
   Red Hat Inc.
   chrisw@redhat.com

   Kevin Glavin
   Riverbed
   kevin.glavin@riverbed.com

   Hong (Cathy) Zhang
   Huawei US R&D
   cathy.h.zhang@huawei.com

   Louis Fourie
   Huawei US R&D
   louis.fourie@huawei.com

   Ron Parker
   Affirmed Networks
   ron_parker@affirmednetworks.com

   Myo Zarny

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   Goldman Sachs
   myo.zarny@gs.com

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12.  Acknowledgments

   The authors would like to thank Nagaraj Bagepalli, Abhijit Patra,
   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 document.

   Loa Andersson provided a thorough review and valuable comments, we
   thank him for that.

   Lastly, Reinaldo Penno deserves a particular thank you for his
   architecture and implementation work that helped guide the protocol
   concepts and design.

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13.  IANA Considerations

13.1.  NSH EtherType

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

13.2.  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.

13.2.1.  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)
   Bit 3 - Critical TLV (C bit)
   Bits 4-9 - Reserved

13.2.2.  NSH Version

   IANA is requested to setup a registry of "NSH Version".  New values
   are assigned via Standards Action [RFC5226].

   Version 00: This protocol version.  This document.
   Version 01: Reserved.  This document.
   Version 10: Unassigned.
   Version 11: Unassigned.

13.2.3.  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].

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

13.2.4.  MD Class Registry

   IANA is requested to set up a registry of "MD Class".  These are 16-
   bit values.  Registry entries are assigned by using the "IETF Review"
   policy defined in RFC 5226 [RFC5226].  TLV Classes defined by this
   document are listed below.  New values are assigned via Standards
   Action [RFC5226].
   0x0000 to 0x01ff: IETF Consensus
   0x0200 to 0x7fff: Expert Review
   0xfff6 to 0xfffe: Experimental
   0xffff: Reserved

13.2.5.  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, 3, 4 and 5 are defined
   in this draft.  New values are assigned via Standards Action
   [RFC5226].

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             +---------------+--------------+---------------+
             | Next Protocol | Description  | Reference     |
             +---------------+--------------+---------------+
             | 0             | Reserved     | This document |
             |               |              |               |
             | 1             | IPv4         | This document |
             |               |              |               |
             | 2             | IPv6         | This document |
             |               |              |               |
             | 3             | Ethernet     | This document |
             |               |              |               |
             | 4             | NSH          | This document |
             |               |              |               |
             | 5             | MPLS         | This document |
             |               |              |               |
             | 6..253        | Unassigned   |               |
             |               |              |               |
             | 254           | Experiment 1 | This document |
             |               |              |               |
             | 255           | Experiment 2 | This document |
             +---------------+--------------+---------------+

                                  Table 2

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14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498, DOI 10.17487/
              RFC7498, April 2015,
              <http://www.rfc-editor.org/info/rfc7498>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/
              RFC7665, October 2015,
              <http://www.rfc-editor.org/info/rfc7665>.

14.2.  Informative References

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <http://www.rfc-editor.org/info/rfc1191>.

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, DOI 10.17487/RFC1981,
              August 1996, <http://www.rfc-editor.org/info/rfc1981>.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <http://www.rfc-editor.org/info/rfc2784>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6071]  Frankel, S. and S. Krishnan, "IP Security (IPsec) and
              Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
              DOI 10.17487/RFC6071, February 2011,
              <http://www.rfc-editor.org/info/rfc6071>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <http://www.rfc-editor.org/info/rfc6830>.

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   [VXLAN-gpe]
              Quinn, P., Manur, R., Agarwal, P., Kreeger, L., Lewis, D.,
              Maino, F., Smith, M., Yong, L., Xu, X., Elzur, U., Garg,
              P., and D. Melman, "Generic Protocol Extension for VXLAN",
              <https://datatracker.ietf.org/doc/
              draft-ietf-nvo3-vxlan-gpe/>.

   [broadalloc]
              Napper, J., Kumar, S., Muley, P., and W. Hendericks, "NSH
              Context Header Allocation -- Mobility", 2016, <https://
              datatracker.ietf.org/doc/
              draft-napper-sfc-nsh-broadband-allocation/>.

   [dcalloc]  Guichard, J., Smith, M., and et al., "Network Service
              Header (NSH) Context Header Allocation (Data Center)",
              2016, <https://datatracker.ietf.org/doc/
              draft-guichard-sfc-nsh-dc-allocation/>.

   [nsh-sec]  Reddy, T., Migault, D., Pignataro, C., Quinn, P., and C.
              Inacio, "NSH Security and Privacy requirements", 2016, <ht
              tps://datatracker.ietf.org/doc/
              draft-reddy-sfc-nsh-security-req/>.

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Authors' Addresses

   Paul Quinn (editor)
   Cisco Systems, Inc.

   Email: paulq@cisco.com

   Uri Elzur (editor)
   Intel

   Email: uri.elzur@intel.com

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