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Versions: (draft-quinn-sfc-nsh) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18

Service Function Chaining                                  P. Quinn, Ed.
Internet-Draft                                                     Cisco
Intended status: Standards Track                           U. Elzur, Ed.
Expires: January 17, 2018                                          Intel
                                                       C. Pignataro, Ed.
                                                                   Cisco
                                                           July 16, 2017


                      Network Service Header (NSH)
                         draft-ietf-sfc-nsh-14

Abstract

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

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 January 17, 2018.

Copyright Notice

   Copyright (c) 2017 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



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Definition of Terms . . . . . . . . . . . . . . . . . . .   4
     1.3.  Problem Space . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.  NSH-based Service Chaining  . . . . . . . . . . . . . . .   5
   2.  Network Service Header  . . . . . . . . . . . . . . . . . . .   5
     2.1.  Network Service Header Format . . . . . . . . . . . . . .   6
     2.2.  NSH Base Header . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Service Path Header . . . . . . . . . . . . . . . . . . .   9
     2.4.  NSH MD Type 1 . . . . . . . . . . . . . . . . . . . . . .  10
     2.5.  NSH MD Type 2 . . . . . . . . . . . . . . . . . . . . . .  11
       2.5.1.  Optional Variable Length Metadata . . . . . . . . . .  11
   3.  NSH Actions . . . . . . . . . . . . . . . . . . . . . . . . .  12
   4.  NSH Transport Encapsulation . . . . . . . . . . . . . . . . .  14
   5.  Fragmentation Considerations  . . . . . . . . . . . . . . . .  15
   6.  Service Path Forwarding with NSH  . . . . . . . . . . . . . .  15
     6.1.  SFFs and Overlay Selection  . . . . . . . . . . . . . . .  15
     6.2.  Mapping NSH to Network Transport  . . . . . . . . . . . .  18
     6.3.  Service Plane Visibility  . . . . . . . . . . . . . . . .  19
     6.4.  Service Graphs  . . . . . . . . . . . . . . . . . . . . .  19
   7.  Policy Enforcement with NSH . . . . . . . . . . . . . . . . .  19
     7.1.  NSH Metadata and Policy Enforcement . . . . . . . . . . .  19
     7.2.  Updating/Augmenting Metadata  . . . . . . . . . . . . . .  21
     7.3.  Service Path Identifier and Metadata  . . . . . . . . . .  23
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  24
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  26
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
     11.1.  NSH EtherType  . . . . . . . . . . . . . . . . . . . . .  27
     11.2.  Network Service Header (NSH) Parameters  . . . . . . . .  27
       11.2.1.  NSH Base Header Reserved Bits  . . . . . . . . . . .  27
       11.2.2.  NSH Version  . . . . . . . . . . . . . . . . . . . .  27
       11.2.3.  MD Type Registry . . . . . . . . . . . . . . . . . .  28
       11.2.4.  MD Class Registry  . . . . . . . . . . . . . . . . .  28
       11.2.5.  NSH Base Header Next Protocol  . . . . . . . . . . .  29
       11.2.6.  New IETF assigned MD Type Registry . . . . . . . . .  29
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     12.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31





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1.  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.

   Network Service Header (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.  Indication of location within a Service Function Path.

   3.  Optional, per packet metadata (fixed length or variable).

   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].

1.1.  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].



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1.2.  Definition of Terms

   Byte:  All references to "bytes" in this document refer to 8-bit
      bytes, or octets.

   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 an 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].

1.3.  Problem Space

   NSH addresses several limitations associated with service function
   deployments.  [RFC7498] provides a comprehensive review of those
   issues.







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1.4.  NSH-based Service Chaining

   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
       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.  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.  NSH provides a mechanism to carry shared metadata between
       participating entities and service functions.  The semantics of
       the shared metadata is communicated via a control plane, which is
       outside the scope of this document, to participating nodes.
       [I-D.ietf-sfc-control-plane] provides an example of such in
       Section 3.3.  Examples of metadata include classification
       information used for policy enforcement and network context for
       forwarding post service delivery.  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.

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

   5.  Transport Agnostic: NSH is transport-independent.  An appropriate
       (for a given deployment) network transport protocol can be used
       to transport NSH-encapsulated traffic.  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.

2.  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.
   An outer transport header is imposed, on NSH and the original packet/
   frame, for network forwarding.




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

2.1.  Network Service Header Format

   NSH is composed of a 4-byte Base Header, a 4-byte Service Path Header
   and optional Context Headers, as shown in Figure 1 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Base Header                                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Service Path Header                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                Context Header(s)                              ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Network Service Header

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

   Service Path Header: provides path identification and location within
   a service path.

   Context header: carries metadata (i.e., context data) along a service
   path.

2.2.  NSH Base Header

   Figure 2 depicts the NSH base header:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Ver|O|R|    TTL    |   Length  |R|R|R|R|MD Type| Next Protocol |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 2: NSH Base Header

   Base Header Field Descriptions:

   Version: The version field is used to ensure backward compatibility
   going forward with future NSH specification updates.  It MUST be set
   to 0x0 by the sender, in this first revision of NSH.  Given the



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   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.  Please see [RFC7325] for further
   discussion of MPLS-related forwarding requirements.

   O bit: Setting this bit indicates an Operations, Administration, and
   Maintenance (OAM) packet.  The actual format and processing of SFC
   OAM packets is outside the scope of this specification (see for
   example [I-D.ietf-sfc-oam-framework] for one approach).

   The O bit MUST be set for OAM packets and MUST NOT be set for non-OAM
   packets.  The O bit MUST NOT be modified along the SFP.

   SF/SFF/SFC Proxy/Classifier implementations that do not support SFC
   OAM procedures SHOULD discard packets with O bit set, but MAY support
   a configurable parameter to enable forwarding received SFC OAM
   packets unmodified to the next element in the chain.  Forwarding OAM
   packets unmodified by SFC elements that do not support SFC OAM
   procedures may be acceptable for a subset of OAM functions, but can
   result in unexpected outcomes for others, thus it is recommended to
   analyze the impact of forwarding an OAM packet for all OAM functions
   prior to enabling this behavior.  The configurable parameter MUST be
   disabled by default.


   TTL: Indicates the maximum SFF hops for an SFP.  The initial TTL
   value SHOULD be configurable via the control plane; the configured
   initial value can be specific to one or more SFPs.  If no initial
   value is explicitly provided, the default initial TTL value 63 MUST
   be used.  Each SFF involved in forwarding an NSH packet MUST
   decrement the TTL value by 1 prior to NSH forwarding lookup.
   Decrementing by 1 from an incoming value of 0 shall result in a TTL
   value of 63.  The packet MUST NOT be forwarded if TTL is, after
   decrement, 0.

   All other flag fields are reserved for future use.  Reserved bits
   MUST be set to zero upon origination and MUST be preserved unmodified
   by other NSH supporting elements.  Elements which do not understand
   the meaning of any of these bits MUST NOT modify their actions based
   on those unknown bits.

   Length: The total length, in 4-byte words, of NSH including the Base
   Header, the Service Path Header, the Fixed Length Context Header or
   Variable Length Context Header(s).  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 length of the NSH header MUST be an integer




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   multiple of 4 bytes, thus variable length metadata is always padded
   out to a multiple of 4 bytes.

   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 the IANA Considerations
   Section 11.2.3.

   This document specifies the following four MD Type values:

   0x0 - this is a reserved value.  Implementations SHOULD silently
   discard packets with MD Type 0x0.

   0x1 - which indicates that the format of the header includes a fixed
   length Context Header (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
   Header(s).  The semantics of the variable length Context Header(s)
   are not defined in this document.  The format of the optional
   variable length Context Headers is provided in Section 2.5.1.

   0xF - this value is reserved for experimentation and testing, as per
   [RFC3692].  Implementations not explicitly configured to be part of
   an experiment SHOULD silently discard packets with MD Type 0x15.

   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 MD Type = 0x2
   (where the length is of value 0x2).  NSH implementations SHOULD
   support MD Type 0x2 with length > 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 encapsulated data.
   NSH does not alter the inner payload, and the semantics on the inner
   protocol remain unchanged due to NSH service function chaining.
   Please see the IANA Considerations section below, Section 11.2.5.

   This document defines the following Next Protocol values:

   0x0: Reserved
   0x1: IPv4
   0x2: IPv6



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   0x3: Ethernet
   0x4: NSH
   0x5: MPLS
   0xFE: Experiment 1
   0xFF: Experiment 2

   An implementation not explicitly configured for a specific experiment
   [RFC3692] SHOULD NOT attempt to process Next Protocol values 0xFE and
   0xFF.

2.3.  Service Path Header

   Figure 3 shows the format of the Service Path Header:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path Identifier (SPI)        | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Service Path Identifier (SPI): 24 bits
     Service Index (SI): 8 bits

                     Figure 3: NSH Service Path Header

   The meaning of these fields is as follows:

   Service Path Identifier (SPI): identifies a service path.
   Participating nodes MUST use this identifier for Service Function
   Path selection.  The initial classifier MUST set the appropriate SPI
   for a given classification result.

   Service Index (SI): provides location within the SFP.  The initial
   classifier for a given SFP 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).
   Service Index MUST be decremented by a value of 1 by Service
   Functions or by SFC Proxy nodes after performing required services
   and the new decremented SI value MUST be used in the egress NSH
   packet.  The initial Classifier MUST send the packet to the first SFF
   in the identified SFP for forwarding along an SFP.  If re-
   classification occurs, and that re-classification results in a new
   SPI, the (re)classifier is, in effect, the initial classifier for the
   resultant SPI.

   The SI is used in conjunction with Service Path Identifier for
   Service Function Path Selection and for determining the next SFF/SF
   in the path.  The SI is also valuable when troubleshooting/ reporting



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   service paths.  In addition to indicating the location within a
   Service Function Path, SI can be used for service plane loop
   detection.

2.4.  NSH MD Type 1

   When the Base Header specifies MD Type = 0x1, a Fixed Length Context
   Header (16-bytes) MUST be present immediately following the Service
   Path Header, as per Figure 4.  A Fixed Length Context Header that
   carries no metadata MUST be set to zero.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Ver|O|R|    TTL    |   Length  |R|R|R|R|MD Type| Next Protocol |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path Identifier              | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                 Fixed Length Context Header                   |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 4: NSH MD Type=0x1

   This specification does not make any assumptions about the content of
   the 16 byte Context Header that must be present when the MD Type
   field is set to 1, and does not describe the structure or meaning of
   the included metadata.

   An SFC-aware SF MUST receive the data semantics first in order to
   process the data placed in the mandatory context field.  The data
   semantics include both the allocation schema and the meaning of the
   included data.  How an SFC-aware SF gets the data semantics is
   outside the scope of this specification.

   An SF or SFC Proxy that does not know the format or semantics of the
   Context Header for an NSH with MD Type 1 MUST discard any packet with
   such an NSH (i.e., MUST NOT ignore the metadata that it cannot
   process), and MUST log the event at least once per the SPI for which
   the event occurs (subject to thresholding).

   [I-D.guichard-sfc-nsh-dc-allocation] and
   [I-D.napper-sfc-nsh-broadband-allocation] provide specific examples
   of how metadata can be allocated.






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2.5.  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 (see Figure 5).  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 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
      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|R|    TTL    |   Length  |R|R|R|R|MD Type| Next Protocol |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path Identifier              | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~              Variable Length Context Headers  (opt.)          ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 5: NSH MD Type=0x2

2.5.1.  Optional Variable Length Metadata

   The format of the optional variable length Context Headers, is as
   depicted in Figure 6.

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

                    Figure 6: Variable Context Headers

   Metadata Class (MD Class): defines the scope of the 'Type' field to
   provide a hierarchical namespace.  The IANA Considerations
   Section 11.2.4 defines how the MD Class values can be allocated to
   standards bodies, vendors, and others.

   Type: indicates the explicit type of metadata being carried and is
   the responsibility of the MD Class owner.



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

   Length: indicates the length of the variable metadata, in single byte
   words.  In case the metadata length is not an integer number of
   4-byte words, the sender MUST add pad bytes immediately following the
   last metadata byte to extend the metadata to an integer number of
   4-byte words.  The receiver MUST round up the length field to the
   nearest 4-byte word boundary, to locate and process the next field in
   the packet.  The receiver MUST access only those bytes in the
   metadata indicated by the length field (i.e., actual number of single
   byte words) and MUST ignore the remaining bytes up to the nearest
   4-byte word boundary.  The Length may be 0 or greater.

   A value of 0x0 denotes a Context Header without a Variable Metadata
   field.

   This specification does not make any assumption about Context Headers
   that are mandatory-to-implement or those that are mandatory-to-
   process.  These considerations are deployment-specific.  However, the
   control plane is entitled to instruct SFC-aware SFs with the data
   structure of context header together with their scoping (see
   Section 3.3.3 of [I-D.ietf-sfc-control-plane]).

   Upon receipt of a packet that belong to a given SFP, if a mandatory-
   to-process context header is missing in that packet, the SFC-aware SF
   MUST NOT process the packet and MUST log at least once per the SPI
   for which a mandatory metadata is missing.

   If multiple mandatory-to-process context headers are required for a
   given SFP, the control plane MAY instruct the SFC-aware SF with the
   order to consume these Context Headers.  If no instructions are
   provided, the SFC-aware SF MUST process these Context Headers in the
   order their appear in an NSH packet.

   If multiple instances of the same metadata are included in an NSH
   packet, but the definition of that context header does not allow for
   it, the SFC-aware SF MUST process first instance and ignore
   subsequent instances.

3.  NSH Actions

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



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       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, an SFF, MUST be
       the last node operating on the service header and MUST remove NSH
       before forwarding or delivering the un-encapsulated packet

       Multiple logical classifiers may exist within a given service
       path.  Non-initial classifiers may re-classify data and that re-
       classification MAY result in the selection a different 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
       path 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 NSH: SFs MUST decrement the service index by one.  If an
       SFF receives a packet with an SPI and SI that do not correspond
       to a valid next hop in a valid Service Function Path, that packet
       MUST be dropped by the SFF.

       Classifiers MAY update Context Headers if new/updated context is
       available.

       If an SFC proxy is in use (acting on behalf of a NSH unaware
       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 NSH 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 by
       one.



   4.  Service policy selection: Service Functions derive policy (i.e.,
       service actions such as permit or deny) selection and enforcement
       from NSH.  Metadata shared in NSH can provide a range of service-
       relevant information such as traffic classification.




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   Figure 7 maps each of the four actions above to the components in the
   SFC architecture that can perform it.

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

                   Figure 7: NSH Action and Role Mapping

4.  NSH Transport 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.








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5.  Fragmentation Considerations

   NSH and the associated transport header are "added" to the
   encapsulated packet/frame.  This additional information increases the
   size of the packet.

   As discussed in [I-D.ietf-rtgwg-dt-encap], within an administrative
   domain, an operator can ensure that the underlay MTU is sufficient to
   carry SFC traffic without requiring fragmentation.

   However, there will be cases where the underlay MTU is not large
   enough to carry the NSH traffic.  Since NSH does not provide
   fragmentation support at the service plane, the transport/overlay
   layer MUST provide the requisite fragmentation handling.  Section 6
   of [I-D.ietf-rtgwg-dt-encap] provides guidance for those scenarios.

6.  Service Path Forwarding with NSH

6.1.  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 provides 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 serves as a mechanism for detecting invalid service function path.
   In particular, an SI value of zero indicates that forwarding is
   incorrect and the packet must be discarded

   This indirection -- SPI 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.)  SFs need to be able to return a packet to an appropriate SFF
   (i.e., has the requisite NSH information) when service processing is
   complete.  This can be via the over or underlay and in some case



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   require additional configuration on the SF.  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.  Table 1 below
   depicts an example of a single next-hop SPI/SI to network overlay
   network locator mapping.

         +------+------+---------------------+-------------------+
         | SPI  | SI   | Next hop(s)         | 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              |
         +------+------+---------------------+-------------------+

                     Table 1: 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 Table 2 and Table 3 below.

   Please note: VXLAN-gpe and GRE in the above table refer to
   [I-D.ietf-nvo3-vxlan-gpe] and [RFC2784], respectively.














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                      +------+-----+----------------+
                      | SPI  | SI  | Next hop(s)    |
                      +------+-----+----------------+
                      | 10   | 3   | SF2            |
                      |      |     |                |
                      | 245  | 12  | SF34           |
                      |      |     |                |
                      | 40   | 9   | SF9            |
                      +------+-----+----------------+

                    Table 2: NSH to SF Mapping Example

                +------+-------------------+-------------+
                | SF   | Next hop(s)       | Transport   |
                +------+-------------------+-------------+
                | SF2  | 192.0.2.2         | VXLAN-gpe   |
                |      |                   |             |
                | SF34 | 198.51.100.34     | UDP         |
                |      |                   |             |
                | SF9  | 2001:db8::1       | GRE         |
                +------+-------------------+-------------+

                    Table 3: 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
   Table 4.  The metric depicted in Table 4 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.)


















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                  +------+-----+--------------+---------+
                  | 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)

                    Table 4: NSH Weighted Service Path

6.2.  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 2001:db8::1
       SFFa mapping: SPI=10 --> VXLAN-gpe, dst-ip: 2001:db8::1

   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,



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   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.

6.3.  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
   NSH information (packet capture, IPFIX, etc.)  The information can be
   used for service scheduling and placement decisions, troubleshooting
   and compliance verification.

6.4.  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, if needed, SPI and SI are
   updated (whether this update is a re-write, or the imposition of a
   new NSH with new values is implementation specific) to reflect the
   "result" of the classification.  These classifiers may also of course
   modify the metadata associated with the packet.
   [RFC7665], Section 2.1 describes Service Graphs in detail.

7.  Policy Enforcement with NSH

7.1.  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



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      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.  Figure 8 and Figure 9
   highlight the relationship between metadata and policy:

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

                       Figure 8: Metadata and Policy














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

                  Figure 9: 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.

   Depending on the information carried in the metadata, data privacy
   considerations may need to be considered.  For example, if the
   metadata conveys tenant information, that information may need to be
   authenticated and/or encrypted between the originator and the
   intended recipients (which may include intended SFs only) .  NSH
   itself does not provide privacy functions, rather it relies on the
   transport/overlay layer.  An operator can select the appropriate
   transport to ensure the confidentially (and other security)
   considerations are met.  Metadata privacy and security considerations
   are a matter for the documents that define metadata format.

7.2.  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 10.  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 NSH metadata.  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 traffic as "internet" but a security
       service function determines that the traffic is really "attack".
       Figure 11 illustrates an example of updating metadata.

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

                     Figure 10: Metadata Augmentation

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

                        Figure 11: Metadata Update








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7.3.  Service Path Identifier and Metadata

   Metadata information may influence the service path selection since
   the Service Path Identifier values can represent the result of
   classification.  A given SPI can be defined based on classification
   results (including metadata classification).  The imposition of the
   SPI and SI results in the packet being placed on the newly specified
   SFP at the position indicated by the imposed SPI and SI.

   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 12 illustrates an example of this
   behavior.

               +-----+           +-----+            +-----+
               | SFF |---------> | SFF |------+---> | SFF |
               +--+--+           +--+--+      |     +--+--+
                  |                 |         |        |
                ,---.             ,---.       |      ,---.
               /     \           / SF1 \      |     /     \
              (  SCL  )         (   +   )     |    (  SF2  )
               \     /           \SCL2 /      |     \     /
                `---'             `---'    +-----+   `---'
             5-tuple:            Inspect   | SFF |    Original
             Tenant A            Tenant A  +--+--+    next SF
                                  --> DoS     |
                                              V
                                            ,-+-.
                                           /     \
                                          (  SF10 )
                                           \     /
                                            `---'
                                             DoS
                                          "Scrubber"

                      Figure 12: Path ID and Metadata

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

8.  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.



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   NSH is always encapsulated in a transport protocol and therefore,
   when required, existing security protocols that provide authenticity
   (e.g., [RFC6071]) can be used.  Similarly, if confidentiality is
   required, existing encryption protocols can be used in conjunction
   with encapsulated NSH.

   Further, existing best practices, such as [BCP38] should be deployed
   at the network layer to ensure that traffic entering the service path
   is indeed "valid".  [I-D.ietf-rtgwg-dt-encap] provides additional
   transport encapsulation considerations.

   NSH metadata authenticity and confidentially must be considered as
   well.  In order to protect the metadata, an operator can leverage the
   aforementioned mechanisms provided the transport layer, authenticity
   and/or confidentiality.  An operator MUST carefully select the
   transport/underlay services to ensure end to end security services,
   when those are sought after.  For example, if [RFC6071] is used, the
   operator MUST ensure it can be supported by the transport/underlay of
   all relevant network segments as well as SFF and SFs.  Further, as
   described in Section 8.1, operators can and should use indirect
   identification for personally identifying information, thus
   significantly mitigating the risk of privacy violation.  Means to
   prevent leaking privacy-related information outside an administrative
   domain are natively supported by NSH given that the last SFF of a
   path will systematically remove the NSH header before forwarding a
   packet upstream.

   Lastly, SF security, although out of scope of this document, should
   be considered, particularly if an SF needs to access, authenticate or
   update NSH metadata.

9.  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



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   Huawei
   james.n.guichard@huawei.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
   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



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   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
   Goldman Sachs
   myo.zarny@gs.com


10.  Acknowledgments

   The authors would like to thank Sunil Vallamkonda, 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 Larry Kreeger for his
   invaluable ideas and contributions which are reflected throughout
   this document.



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

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

   The editors also acknowledge a comprehensive review and respective
   suggestions by Med Boucadair.

   Lastly, David Dolson has provides significant review, feedback and
   suggestions throughout the evolution of this document.  His
   contributions are very much appreciated.

11.  IANA Considerations

11.1.  NSH EtherType

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

11.2.  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.

11.2.1.  NSH Base Header Reserved Bits

   There are five reserved bits in the NSH Base Header.  New bits are
   assigned via Standards Action [RFC8126].
   Bit 3 - Reserved
   Bits 16-19 - Reserved

11.2.2.  NSH Version

   IANA is requested to setup a registry of "NSH Version".  New values
   are assigned via Standards Action [RFC8126].

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








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11.2.3.  MD Type Registry

   IANA is requested to set up a registry of "MD Types".  These are
   4-bit values.  MD Type values 0, 1, 2, and 15 are specified in this
   document, see Table 5.  Registry entries are assigned by using the
   "IETF Review" policy defined in RFC 8126 [RFC8126].

               +---------+-----------------+---------------+
               | MD Type | Description     | Reference     |
               +---------+-----------------+---------------+
               | 0       | Reserved        | This document |
               |         |                 |               |
               | 1       | NSH MD Type 1   | This document |
               |         |                 |               |
               | 2       | NSH MD Type 2   | This document |
               |         |                 |               |
               | 3..14   | Unassigned      |               |
               |         |                 |               |
               | 15      | Experimentation | This document |
               +---------+-----------------+---------------+

                          Table 5: MD Type Values

11.2.4.  MD Class Registry

   IANA is requested to set up a registry of "MD Class".  These are 16-
   bit values.  New allocations are to be made according to the
   following policies:

   0x0000 to 0x01ff: IETF Review
   0x0200 to 0xfff5: Expert Review
   0xfff6 to 0xfffe: Experimental
   0xffff: Reserved

   IANA is requested to assign the values as per Table 6::

         +-----------+-----------------------------+------------+
         | MD Class  | Meaning                     | Reference  |
         +-----------+-----------------------------+------------+
         | 0x0000    | IETF Base NSH MD Class      | This.I-D   |
         +-----------+-----------------------------+------------+

                          Table 6: MD Class Value

   Designated Experts evaluating new allocation requests from the
   "Expert Review" range should principally consider whether a new MD
   class is needed compared to adding MD types to an existing class.
   The Designated Experts should also encourage the existence of an



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   associated and publicly visible registry of MD types although this
   registry need not be maintained by IANA.

11.2.5.  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 document (see Table 7.  New values are assigned via "Expert
   Reviews" as per [RFC8126].

             +---------------+--------------+---------------+
             | 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 7: NSH Base Header Next Protocol Values

11.2.6.  New IETF assigned MD Type Registry

   This document requests IANA to create a registry for the type values
   owned by the IETF (i.e., MD Class set to 0x0000) called the "IETF
   Assigned MD Type Registry."

   The type values are assigned via Standards Action [RFC8126].

   No initial values are assigned at the creation of the registry.








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12.  References

12.1.  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>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <http://www.rfc-editor.org/info/rfc8126>.

12.2.  Informative References

   [BCP38]    Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <http://www.rfc-editor.org/info/rfc2827>.

   [I-D.guichard-sfc-nsh-dc-allocation]
              Guichard, J., Smith, M., Surendra, S., Majee, S., Agarwal,
              P., Glavin, K., and Y. Laribi, "Network Service Header
              (NSH) Context Header Allocation (Data Center)", draft-
              guichard-sfc-nsh-dc-allocation-05 (work in progress),
              August 2016.

   [I-D.ietf-nvo3-vxlan-gpe]
              Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
              Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-04 (work
              in progress), April 2017.

   [I-D.ietf-rtgwg-dt-encap]
              Nordmark, E., Tian, A., Gross, J., Hudson, J., Kreeger,
              L., Garg, P., Thaler, P., and T. Herbert, "Encapsulation
              Considerations", draft-ietf-rtgwg-dt-encap-02 (work in
              progress), October 2016.

   [I-D.ietf-sfc-control-plane]
              Boucadair, M., "Service Function Chaining (SFC) Control
              Plane Components & Requirements", draft-ietf-sfc-control-
              plane-08 (work in progress), October 2016.



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   [I-D.ietf-sfc-oam-framework]
              Aldrin, S., Pignataro, C., Kumar, N., Akiya, N., Krishnan,
              R., and A. Ghanwani, "Service Function Chaining Operation,
              Administration and Maintenance Framework", draft-ietf-sfc-
              oam-framework-02 (work in progress), July 2017.

   [I-D.napper-sfc-nsh-broadband-allocation]
              Napper, J., Kumar, S., Muley, P., Henderickx, W., and M.
              Boucadair, "NSH Context Header Allocation -- Broadband",
              draft-napper-sfc-nsh-broadband-allocation-02 (work in
              progress), January 2017.

   [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>.

   [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful", BCP 82, RFC 3692,
              DOI 10.17487/RFC3692, January 2004,
              <http://www.rfc-editor.org/info/rfc3692>.

   [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>.

   [RFC7325]  Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
              and C. Pignataro, "MPLS Forwarding Compliance and
              Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
              August 2014, <http://www.rfc-editor.org/info/rfc7325>.

   [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>.

Authors' Addresses

   Paul Quinn (editor)
   Cisco Systems, Inc.

   Email: paulq@cisco.com








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   Uri Elzur (editor)
   Intel

   Email: uri.elzur@intel.com


   Carlos Pignataro (editor)
   Cisco Systems, Inc.

   Email: cpignata@cisco.com









































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