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rfc:rfc8300

Internet Engineering Task Force (IETF) P. Quinn, Ed. Request for Comments: 8300 Cisco Category: Standards Track U. Elzur, Ed. ISSN: 2070-1721 Intel

                                                     C. Pignataro, Ed.
                                                                 Cisco
                                                          January 2018
                    Network Service Header (NSH)

Abstract

 This document describes a Network Service Header (NSH) imposed on
 packets or frames to realize Service Function Paths (SFPs).  The NSH
 also provides a mechanism for metadata exchange along the
 instantiated service paths.  The NSH is the Service Function Chaining
 (SFC) encapsulation required to support the SFC architecture (defined
 in RFC 7665).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8300.

Copyright Notice

 Copyright (c) 2018 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
 (https://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.

Quinn, et al. Standards Track [Page 1] RFC 8300 Network Service Header (NSH) January 2018

Table of Contents

 1. Introduction ....................................................3
    1.1. Applicability ..............................................4
    1.2. Requirements Language ......................................4
    1.3. Definition of Terms ........................................4
    1.4. Problem Space ..............................................6
    1.5. NSH-Based Service Chaining .................................6
 2. Network Service Header ..........................................7
    2.1. Network Service Header Format ..............................7
    2.2. NSH Base Header ............................................8
    2.3. Service Path Header .......................................11
    2.4. NSH MD Type 1 .............................................12
    2.5. NSH MD Type 2 .............................................13
         2.5.1. Optional Variable-Length Metadata ..................13
 3. NSH Actions ....................................................15
 4. NSH Transport Encapsulation ....................................16
 5. Fragmentation Considerations ...................................17
 6. Service Path Forwarding with NSH ...............................18
    6.1. SFFs and Overlay Selection ................................18
    6.2. Mapping the NSH to Network Topology .......................21
    6.3. Service Plane Visibility ..................................21
    6.4. Service Graphs ............................................22
 7. Policy Enforcement with NSH ....................................22
    7.1. NSH Metadata and Policy Enforcement .......................22
    7.2. Updating/Augmenting Metadata ..............................24
    7.3. Service Path Identifier and Metadata ......................25
 8. Security Considerations ........................................26
    8.1. NSH Security Considerations from Operators' Environments ..27
    8.2. NSH Security Considerations from the SFC Architecture .....28
         8.2.1. Integrity ..........................................29
         8.2.2. Confidentiality ....................................31
 9. IANA Considerations ............................................32
    9.1. NSH Parameters ............................................32
         9.1.1. NSH Base Header Bits ...............................32
         9.1.2. NSH Version ........................................32
         9.1.3. NSH MD Types .......................................33
         9.1.4. NSH MD Class .......................................33
         9.1.5. NSH IETF-Assigned Optional Variable-Length
                Metadata Types .....................................34
         9.1.6. NSH Next Protocol ..................................35
 10. NSH-Related Codepoints ........................................35
    10.1. NSH Ethertype ............................................35
 11. References ....................................................36
 Acknowledgments ...................................................38
 Contributors ......................................................39
 Authors' Addresses ................................................40

Quinn, et al. Standards Track [Page 2] RFC 8300 Network Service Header (NSH) January 2018

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 WAN, data center, 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 demands an agile service insertion model that
 supports dynamic and elastic service delivery.  Specifically, the
 following functions are necessary:
 1.  The movement of Service Functions and application workloads in
     the network.
 2.  The ability to easily bind service policy to granular
     information, such as per-subscriber state.
 3.  The capability to steer traffic to the requisite Service
     Function(s).
 This document, the Network Service Header (NSH) specification,
 defines a new data-plane protocol, which is an encapsulation for
 SFCs.  The NSH is designed to encapsulate an original packet or frame
 and, in turn, be encapsulated by an outer transport encapsulation
 (which is used to deliver the NSH to NSH-aware network elements), as
 shown in Figure 1:
                   +------------------------------+
                   |    Transport Encapsulation   |
                   +------------------------------+
                   | Network Service Header (NSH) |
                   +------------------------------+
                   |    Original Packet / Frame   |
                   +------------------------------+
            Figure 1: Network Service Header Encapsulation

Quinn, et al. Standards Track [Page 3] RFC 8300 Network Service Header (NSH) January 2018

 The NSH 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).
 [RFC7665] provides an overview of a service chaining architecture
 that clearly defines the roles of the various elements and the scope
 of a SFC encapsulation.  Figure 3 of [RFC7665] depicts the SFC
 architectural components after classification.  The NSH is the SFC
 encapsulation referenced in [RFC7665].

1.1. Applicability

 The NSH is designed to be easy to implement across a range of
 devices, both physical and virtual, including hardware platforms.
 The intended scope of the NSH is for use within a single provider's
 operational domain.  This deployment scope is deliberately
 constrained, as explained also in [RFC7665], and limited to a single
 network administrative domain.  In this context, a "domain" is a set
 of network entities within a single administration.  For example, a
 network administrative domain can include a single data center, or an
 overlay domain using virtual connections and tunnels.  A corollary is
 that a network administrative domain has a well-defined perimeter.
 An NSH-aware control plane is outside the scope of this document.

1.2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

1.3. 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].

Quinn, et al. Standards Track [Page 4] RFC 8300 Network Service Header (NSH) January 2018

 Metadata (MD):  Defined in [RFC7665].  The metadata, or context
    information shared between Classifiers and SFs, and among SFs, is
    carried on the NSH's Context Headers.  It allows summarizing a
    classification result in the packet itself, avoiding subsequent
    re-classifications.  Examples of metadata include classification
    information used for policy enforcement and network context for
    forwarding after service delivery.
 Network Locator:  Data-plane 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 encapsulation) information.
 Network Overlay:  Logical network built on top of an existing network
    (the underlay).  Packets are encapsulated or tunneled to create
    the overlay network topology.
 NSH-aware:  NSH-aware means SFC-encapsulation-aware, where the NSH
    provides the SFC encapsulation.  This specification uses NSH-aware
    as a more specific term from the more generic term "SFC-aware"
    [RFC7665].
 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 the 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].
 Service Plane:  The collection of SFFs and associated SFs creates a
    service-plane overlay in which all SFs and SFC Proxies reside
    [RFC7665].
 SFC Proxy:  Defined in [RFC7665].

Quinn, et al. Standards Track [Page 5] RFC 8300 Network Service Header (NSH) January 2018

1.4. Problem Space

 The NSH addresses several limitations associated with Service
 Function deployments.  [RFC7498] provides a comprehensive review of
 those issues.

1.5. NSH-Based Service Chaining

 The NSH creates a dedicated service plane; more specifically, the NSH
 enables:
 1.  Topological Independence: Service forwarding occurs within the
     service plane, so the underlying network topology does not
     require modification.  The NSH provides an identifier used to
     select the network overlay for network forwarding.
 2.  Service Chaining: The NSH enables service chaining per [RFC7665].
     The NSH contains path identification information needed to
     realize a service path.  Furthermore, the NSH provides the
     ability to monitor and troubleshoot a service chain, end-to-end
     via service-specific Operations, Administration, and Maintenance
     (OAM) messages.  The NSH fields can be used by administrators
     (for example, via a traffic analyzer) to verify the path
     specifics (e.g., accounting, ensuring correct chaining, providing
     reports, etc.) of packets being forwarded along a service path.
 3.  The NSH provides a mechanism to carry shared metadata between
     participating entities and Service Functions.  The semantics of
     the shared metadata are communicated via a control plane (which
     is outside the scope of this document) to participating nodes.
     Section 3.3 of [SFC-CONTROL-PLANE] provides an example of this.
     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.  The NSH offers a common and standards-based header for service
     chaining to all network and service nodes.
 5.  Transport Encapsulation Agnostic: The NSH is transport
     encapsulation independent: meaning it can be transported by a
     variety of encapsulation protocols.  An appropriate (for a given
     deployment) encapsulation protocol can be used to carry NSH-
     encapsulated traffic.  This transport encapsulation may form an

Quinn, et al. Standards Track [Page 6] RFC 8300 Network Service Header (NSH) January 2018

     overlay network; and if an existing overlay topology provides the
     required service path connectivity, that existing overlay may be
     used.

2. Network Service Header

 An NSH is imposed on the original packet/frame.  This NSH contains
 service path information and, optionally, metadata that are added to
 a packet or frame and used to create a service plane.  Subsequently,
 an outer transport encapsulation is imposed on the NSH, which is used
 for network forwarding.
 A Service Classifier adds the NSH.  The 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

 The NSH is composed of a 4-byte Base Header, a 4-byte Service Path
 Header, and optional Context Headers, as shown in Figure 2.
    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 2: 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.

Quinn, et al. Standards Track [Page 7] RFC 8300 Network Service Header (NSH) January 2018

2.2. NSH Base Header

 Figure 3 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|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       Figure 3: NSH Base Header
 The field descriptions are as follows:
 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 the NSH.  If a
    packet presumed to carry an NSH header is received at an SFF, and
    the SFF does not understand the version of the protocol as
    indicated in the base header, the packet MUST be discarded, and
    the event SHOULD be logged.  Given the widespread implementation
    of existing hardware that uses the first nibble after an MPLS
    label stack for Equal-Cost Multipath (ECMP) decision processing,
    this document reserves version 01b.  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 OAM packet (see [RFC6291]).
    The actual format and processing of SFC OAM packets is outside the
    scope of this specification (for example, see [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 it 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.

Quinn, et al. Standards Track [Page 8] RFC 8300 Network Service Header (NSH) January 2018

 TTL:  Indicates the maximum SFF hops for an SFP.  This field is used
    for service-plane loop detection.  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 of 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.
    This TTL field is the primary loop-prevention mechanism.  This TTL
    mechanism represents a robust complement to the Service Index (see
    Section 2.3), as the TTL is decremented by each SFF.  The handling
    of an incoming 0 TTL allows for better, although not perfect,
    interoperation with pre-standard implementations that do not
    support this TTL field.
 Length:  The total length, in 4-byte words, of the NSH including the
    Base Header, the Service Path Header, the Fixed-Length Context
    Header, or Variable-Length Context Header(s).  The length MUST be
    0x6 for MD Type 0x1, and it MUST be 0x2 or greater for MD Type
    0x2.  The length of the Network Service Header MUST be an integer
    multiple of 4 bytes; thus, variable-length metadata is always
    padded out to a multiple of 4 bytes.
 Unassigned bits:  All other flag fields, marked U, are unassigned and
    available for future use; see Section 9.1.1.  Unassigned bits MUST
    be set to zero upon origination, and they MUST be ignored and
    preserved unmodified by other NSH supporting elements.  At
    reception, all elements MUST NOT modify their actions based on
    these unknown bits.
 Metadata (MD) Type:  Indicates the format of the NSH beyond the
    mandatory NSH Base Header and the Service Path Header.  MD Type
    defines the format of the metadata being carried.  Please see the
    IANA Considerations in Section 9.1.3.
    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:  This indicates that the format of the header includes a
          Fixed-Length Context Header (see Figure 5 below).

Quinn, et al. Standards Track [Page 9] RFC 8300 Network Service Header (NSH) January 2018

    0x2:  This does not mandate any headers beyond the Base Header and
          Service Path Header, but may contain optional Variable-
          Length Context Header(s).  With MD Type 0x2, a length of 0x2
          implies there are no Context Headers.  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 0xF.
    The format of the Base Header and the Service Path Header is
    invariant and not affected by MD Type.
    The NSH MD Type 1 and MD Type 2 are described in detail in
    Sections 2.4 and 2.5, respectively.  NSH implementations MUST
    support MD Types 0x1 and 0x2 (where the length is 0x2).  NSH
    implementations SHOULD support MD Type 0x2 with length greater
    than 0x2.  Devices that do not support MD Type 0x2 with a length
    greater than 0x2 MUST ignore any optional Context Headers and
    process the packet without them; the Base Header Length field can
    be used to determine the original payload offset if access to the
    original packet/frame is required.  This specification does not
    disallow the MD Type value from changing along an SFP; however,
    the specification of the necessary mechanism to allow the MD Type
    to change along an SFP are outside the scope of this document and
    would need to be defined for that functionality to be available.
    Packets with MD Type values not supported by an implementation
    MUST be silently dropped.
 Next Protocol:  Indicates the protocol type of the encapsulated data.
    The NSH does not alter the inner payload, and the semantics on the
    inner protocol remain unchanged due to NSH SFC.  Please see the
    IANA Considerations in Section 9.1.6.
    This document defines the following Next Protocol values:
    0x1: IPv4
    0x2: IPv6
    0x3: Ethernet
    0x4: NSH
    0x5: MPLS
    0xFE: Experiment 1
    0xFF: Experiment 2

Quinn, et al. Standards Track [Page 10] RFC 8300 Network Service Header (NSH) January 2018

    The functionality of hierarchical NSH using a Next Protocol value
    of 0x4 (NSH) is outside the scope of this specification.  Packets
    with Next Protocol values not supported SHOULD be silently dropped
    by default, although an implementation MAY provide a configuration
    parameter to forward them.  Additionally, an implementation not
    explicitly configured for a specific experiment [RFC3692] SHOULD
    silently drop packets with Next Protocol values 0xFE and 0xFF.

2.3. Service Path Header

 Figure 4 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 4: NSH Service Path Header
 The meaning of these fields is as follows:
 Service Path Identifier (SPI): Uniquely identifies a Service Function
 Path (SFP).  Participating nodes MUST use this identifier for SFP
 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 the SI as
 appropriate (i.e., taking into account the length of the SFP).  The
 Service Index MUST be decremented by a value of 1 by Service
 Functions or by SFC Proxy nodes after performing required services;
 the new decremented SI value MUST be used in the egress packet's NSH.
 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 the Service Path Identifier for
 SFP selection and for determining the next SFF/SF in the path.  The
 SI is also valuable when troubleshooting or reporting service paths.
 While the TTL provides the primary SFF-based loop prevention for this
 mechanism, SI decrement by SF serves as a limited loop-prevention

Quinn, et al. Standards Track [Page 11] RFC 8300 Network Service Header (NSH) January 2018

 mechanism.  NSH packets, as described above, are discarded when an
 SFF decrements the TTL to 0.  In addition, an SFF that is not the
 terminal SFF for an SFP will discard any NSH packet with an SI of 0,
 as there will be no valid next SF information.

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 5.  The value of 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|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Service Path Identifier              | Service Index |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                 Fixed-Length Context Header                   |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       Figure 5: 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 it does not describe the structure or meaning
 of the included metadata.
 An SFC-aware SF or SFC Proxy needs to receive the data structure and
 semantics first in order to process the data placed in the mandatory
 context field.  The data structure and semantics include both the
 allocation schema and order as well as the meaning of the included
 data.  How an SFC-aware SF or SFC Proxy gets the data structure and
 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).
 [NSH-DC-ALLOCATION] and [NSH-BROADBAND-ALLOCATION] provide specific
 examples of how metadata can be allocated.

Quinn, et al. Standards Track [Page 12] RFC 8300 Network Service Header (NSH) January 2018

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 6).  Therefore, Length = 0x2,
 indicates that only the Base Header and Service Path Header are
 present (and in that order).  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|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Service Path Identifier              | Service Index |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~              Variable-Length Context Headers  (opt.)          ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       Figure 6: 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 7.
    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     |U|    Length   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Variable-Length Metadata                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 7: Variable-Length Context Headers
 Metadata Class (MD Class):  Defines the scope of the Type field to
    provide a hierarchical namespace.  Section 9.1.4 defines how the
    MD Class values can be allocated to standards bodies, vendors, and
    others.

Quinn, et al. Standards Track [Page 13] RFC 8300 Network Service Header (NSH) January 2018

 Type:  Indicates the explicit type of metadata being carried.  The
    definition of the Type is the responsibility of the MD Class
    owner.
 Unassigned bit:  One unassigned bit is available for future use.
    This bit MUST NOT be set, and it MUST be ignored on receipt.
 Length:  Indicates the length of the variable-length metadata, in
    bytes.  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 the Length field up 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
    bytes) and MUST ignore the remaining bytes up to the nearest
    4-byte-word boundary.  The length may be 0 or greater.
    A value of 0 denotes a Context Header without a Variable-Length
    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 the Context Header together with its scoping (see e.g.,
 Section 3.3.3 of [SFC-CONTROL-PLANE]).
 Upon receipt of a packet that belongs 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 an error at least once per
 the SPI for which the 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 and the SFC-aware SF will make use of or modify the specific
 Context Header, then the SFC-aware SF MUST process these Context
 Headers in the order they 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 the first instance and ignore
 subsequent instances.  The SFC-aware SF MAY log or increase a counter
 for this event.

Quinn, et al. Standards Track [Page 14] RFC 8300 Network Service Header (NSH) January 2018

3. NSH Actions

 NSH-aware nodes (which include Service Classifiers, SFFs, SFs, and
 SFC Proxies) may alter the contents of the NSH headers.  These nodes
 have several possible NSH-related actions:
 1.  Insert or remove the NSH: These actions can occur respectively at
     the start and end of a service path.  Packets are classified, and
     if determined to require servicing, an NSH will be imposed.  A
     Service Classifier MUST insert an NSH at the start of an SFP.  An
     imposed NSH MUST contain both a valid Base Header and Service
     Path Header.  At the end of an SFP, an SFF MUST remove the NSH
     before forwarding or delivering the un-encapsulated packet.
     Therefore, it is the last node operating on the service header.
     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 of a different SFP.
     When the logical Classifier performs re-classification that
     results in a change of service path, it MUST replace the existing
     NSH with a new NSH with the Base Header and Service Path Header
     reflecting the new service path information and MUST set the
     initial SI.  The O bit, the TTL field, and unassigned flags MUST
     be copied transparently from the old NSH to a new NSH.  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 the 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 SFP, 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 an NSH-unaware
     Service Function for NSH actions), then the proxy MUST update the
     Service Index and MAY update contexts.  When an SFC Proxy
     receives an NSH-encapsulated packet, it MUST remove the 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-encapsulate it with the correct NSH, and it MUST decrement the
     Service Index by one.

Quinn, et al. Standards Track [Page 15] RFC 8300 Network Service Header (NSH) January 2018

 4.  Service policy selection: Service Functions derive policy (i.e.,
     service actions such as permit or deny) selection and enforcement
     from the NSH.  Metadata shared in the NSH can provide a range of
     service-relevant information such as traffic classification.
 Figure 8 maps each of the four actions above to the components in the
 SFC architecture that can perform it.
 +-----------+-----------------------+-------+---------------+-------+
 |           | Insert, remove, or    |Forward| Update        |Service|
 |           | replace the NSH       |the NSH| the NSH       |policy |
 |           |                       |packets|               |sel.   |
 |Component  +-------+-------+-------+       +-------+-------+       |
 |           |       |       |       |       |Dec.   |Update |       |
 |           |Insert |Remove |Replace|       |Service|Context|       |
 |           |       |       |       |       |Index  |Header |       |
 +-----------+-------+-------+-------+-------+-------+-------+-------+
 |           |  +    |       |   +   |       |       |   +   |       |
 |Classifier |       |       |       |       |       |       |       |
 +-----------+-------+-------+-------+-------+-------+-------+-------+
 |Service    |       |   +   |       |   +   |       |       |       |
 |Function   |       |       |       |       |       |       |       |
 |Forwarder  |       |       |       |       |       |       |       |
 |(SFF)      |       |       |       |       |       |       |       |
 +-----------+-------+-------+-------+-------+-------+-------+-------+
 |Service    |       |       |       |       |   +   |   +   |   +   |
 |Function   |       |       |       |       |       |       |       |
 |(SF)       |       |       |       |       |       |       |       |
 +-----------+-------+-------+-------+-------+-------+-------+-------+
 |           |  +    |   +   |       |       |   +   |   +   |       |
 |SFC Proxy  |       |       |       |       |       |       |       |
 +-----------+-------+-------+-------+-------+-------+-------+-------+
                 Figure 8: NSH Action and Role Mapping

4. NSH Transport Encapsulation

 Once the NSH is added to a packet, an outer transport 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.

Quinn, et al. Standards Track [Page 16] RFC 8300 Network Service Header (NSH) January 2018

 2.  Transit network nodes simply forward the encapsulated packets
     without modification.
 The service header is independent of the transport encapsulation
 used.  Existing transport encapsulations can be used.  The presence
 of an NSH is indicated via a protocol type or another indicator in
 the outer transport encapsulation.

5. Fragmentation Considerations

 The NSH and the associated transport encapsulation header are "added"
 to the encapsulated packet/frame.  This additional information
 increases the size of the packet.
 Within a managed administrative domain, an operator can ensure that
 the underlay MTU is sufficient to carry SFC traffic without requiring
 fragmentation.  Given that the intended scope of the NSH is within a
 single provider's operational domain, that approach is sufficient.
 However, although explicitly outside the scope of this specification,
 there might be cases where the underlay MTU is not large enough to
 carry the NSH traffic.  Since the NSH does not provide fragmentation
 support at the service plane, the transport encapsulation protocol
 ought to provide the requisite fragmentation handling.  For instance,
 Section 9 of [RTG-ENCAP] provides exemplary approaches and guidance
 for those scenarios.
 When the transport encapsulation protocol supports fragmentation, and
 fragmentation procedures needs to be used, such fragmentation is part
 of the transport encapsulation logic.  If, as it is common,
 fragmentation is performed by the endpoints of the transport
 encapsulation, then fragmentation procedures are performed at the
 sending NSH entity as part of the transport encapsulation, and
 reassembly procedures are performed at the receiving NSH entity
 during transport de-encapsulation handling logic.  In no case would
 such fragmentation result in duplication of the NSH header.
 For example, when the NSH is encapsulated in IP, IP-level
 fragmentation coupled with Path MTU Discovery (PMTUD) (e.g.,
 [RFC8201]) is used.  Since PMTUD relies on ICMP messages, an operator
 should ensure ICMP packets are not blocked.  When, on the other hand,
 the underlay does not support fragmentation procedures, an error
 message SHOULD be logged when dropping a packet too big.  Lastly,
 NSH-specific fragmentation and reassembly methods may be defined as
 well, but these methods are outside the scope of this document and
 subject for future work.

Quinn, et al. Standards Track [Page 17] RFC 8300 Network Service Header (NSH) January 2018

6. Service Path Forwarding with NSH

6.1. SFFs and Overlay Selection

 As described above, the 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
 encapsulation.  Furthermore, there is no requirement for, or
 expectation of, an SPI being bound to a predetermined 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.  This combination
 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 SFPs.  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 overlay or
 underlay and, in some cases, can 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 encapsulation occurs on an SFF (as
 discussed above, the first SFF in the path gets an NSH encapsulated
 packet from the Classifier).  The SFF consults the SPI/ID values to
 determine the appropriate overlay transport encapsulation protocol
 (several may be used within a given network) and next hop for the
 requisite SF.  Table 1 depicts an example of a single next-hop SPI/
 SI-to-network overlay network locator mapping.

Quinn, et al. Standards Track [Page 18] RFC 8300 Network Service Header (NSH) January 2018

    +------+------+---------------------+-------------------------+
    | SPI  | SI   | Next Hop(s)         | Transport Encapsulation |
    +------+------+---------------------+-------------------------+
    | 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 an SFC control plane responsibility, as per Tables 2 and
 3.
 Please note: VXLAN-gpe and GRE in the above table refer to
 [VXLAN-GPE] and [RFC2784] [RFC7676], respectively.
                    +------+-----+----------------+
                    | SPI  | SI  | Next Hop(s)    |
                    +------+-----+----------------+
                    | 10   | 3   | SF2            |
                    |      |     |                |
                    | 245  | 12  | SF34           |
                    |      |     |                |
                    | 40   | 9   | SF9            |
                    +------+-----+----------------+
                  Table 2: NSH-to-SF Mapping Example

Quinn, et al. Standards Track [Page 19] RFC 8300 Network Service Header (NSH) January 2018

        +------+-------------------+-------------------------+
        | SF   | Next Hop(s)       | Transport Encapsulation |
        +------+-------------------+-------------------------+
        | 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
 illustrate 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 the state of a Service Function
 (including load, session 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)
                  Table 4: NSH Weighted Service Path
 The information contained in Tables 1-4 may be received from the
 control plane, but the exact mechanism is outside the scope of this
 document.

Quinn, et al. Standards Track [Page 20] RFC 8300 Network Service Header (NSH) January 2018

6.2. Mapping the NSH to Network Topology

 As described above, the mapping of the 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 exists.  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,
 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, IP Flow Information Export (IPFIX),
 etc.).  The information can be used for service scheduling and
 placement decisions, troubleshooting, and compliance verification.

Quinn, et al. Standards Track [Page 21] RFC 8300 Network Service Header (NSH) January 2018

6.4. Service Graphs

 While a given realized SFP is a specific sequence of Service
 Functions, the service, as seen by a user, can actually be a
 collection of SFPs, with the interconnection provided by Classifiers
 (in-service path, non-initial re-classification).  These internal re-
 Classifiers 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, of course, also modify the
 metadata associated with the packet.
 Section 2.1 of [RFC7665] describes Service Graphs in detail.

7. Policy Enforcement with NSH

7.1. NSH Metadata and Policy Enforcement

 As described in Section 2, 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 VPN Routing and
    Forwarding (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 performs very detailed and valuable classification.
 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 2-tuple, or based on a 5-tuple, while a
 Service Function may be able to inspect application information.
 Regardless of granularity, the classification information can be
 represented in the NSH.

Quinn, et al. Standards Track [Page 22] RFC 8300 Network Service Header (NSH) January 2018

 Once the data is added to the 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.  Figures 9 and 10
 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 9: Metadata and Policy
             +-----+           +-----+            +-----+
             | SFF |---------> | SFF |----------> | SFF |
             +--+--+           +--+--+            +--+--+
                ^                 |                  |
              ,-+-.             ,-+-.              ,-+-.
             /     \           /     \            /     \
            ( Class )         (  SF1  )          (  SF2  )
             \ ify /           \     /            \     /
              `-+-'             `---'              `---'
                |              Permit            Deny AppZ
            +---+---+          employees
            |       |
            +-------+
            External
            system:
            Employee
            AppZ
                Figure 10: 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; instead, they rely on an
 antecedent classification for local policy enforcement.
 Depending on the information carried in the metadata, data privacy
 impact needs to be considered.  For example, if the metadata conveys
 tenant information, that information may need to be authenticated

Quinn, et al. Standards Track [Page 23] RFC 8300 Network Service Header (NSH) January 2018

 and/or encrypted between the originator and the intended recipients
 (which may include intended SFs only); one approach to an optional
 capability to do this is explored in [NSH-ENCRYPT].  The NSH itself
 does not provide privacy functions, rather it relies on the transport
 encapsulation/overlay.  An operator can select the appropriate set of
 transport encapsulation protocols to ensure confidentiality (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), the metadata may be augmented or
 updated:
 1.  Metadata Augmentation: Information may be added to the NSH's
     existing metadata, as depicted in Figure 11.  For example, if the
     initial classification returns the tenant information, a
     secondary classification (perhaps co-resident with deep packet
     inspection (DPI) or server load balancing (SLB)) may augment the
     tenant classification with application information, and impose
     that new information in 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 12 illustrates an example of updating metadata.

Quinn, et al. Standards Track [Page 24] RFC 8300 Network Service Header (NSH) January 2018

             +-----+           +-----+            +-----+
             | SFF |---------> | SFF |----------> | SFF |
             +--+--+           +--+--+            +--+--+
                ^                 |                  |
              ,---.             ,---.              ,---.
             /     \           /     \            /     \
            ( Class )         (  SF1  )          (  SF2  )
             \     /           \     /            \     /
              `-+-'             `---'              `---'
                |              Inspect           Deny
            +---+---+          employees         employee+
            |       |          Class=AppZ        appZ
            +-------+
            External
            system:
            Employee
                   Figure 11: Metadata Augmentation
              +-----+           +-----+            +-----+
              | SFF |---------> | SFF |----------> | SFF |
              +--+--+           +--+--+            +--+--+
                 ^                 |                  |
               ,---.             ,---.              ,---.
              /     \           /     \            /     \
             ( Class )         (  SF1  )          (  SF2  )
              \     /           \     /            \     /
               `---'             `---'              `---'
            5-tuple:            Inspect             Deny
            Tenant A            Tenant A            attack
                                 --> attack
                      Figure 12: Metadata Update

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

Quinn, et al. Standards Track [Page 25] RFC 8300 Network Service Header (NSH) January 2018

 described in Section 6.4.  Figure 13 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"
           Legend:
           SCL = Service Classifier
                    Figure 13: Path ID and Metadata
 Specific algorithms for mapping metadata to an SPI are outside the
 scope of this document.

8. Security Considerations

 NSH security must be considered in the contexts of the SFC
 architecture and operators' environments.  One important
 characteristic of NSH is that it is not an end-to-end protocol.  As
 opposed to a protocol that "starts" on a host and "ends" on a server
 or another host, NSH is typically imposed by a network device on
 ingress to the SFC domain and removed at the egress of the SFC
 domain.  As such, and as with any other network-centric protocols
 (e.g., IP Tunneling, Traffic Engineering, MPLS, or Provider-
 Provisioned Virtual Private Networks), there is an underlying trust
 in the network devices responsible for imposing, removing, and acting
 on NSH information.
 The following sections detail an analysis and present a set of
 requirements and recommendations in those two areas.

Quinn, et al. Standards Track [Page 26] RFC 8300 Network Service Header (NSH) January 2018

8.1. NSH Security Considerations from Operators' Environments

 Trusted Devices
    All Classifiers, SFFs and SFs (hereinafter referred to as "SFC
    devices") within an operator's environment are assumed to have
    been selected, vetted, and actively maintained; therefore, they
    are trusted by that operator.  This assumption differs from the
    oft held view that devices are untrusted, often referred to as the
    "zero-trust model".  Operators SHOULD regularly monitor (i.e.,
    continuously audit) these devices to help ensure compliant
    behavior.  This trust, therefore, extends into NSH operations: SFC
    devices are not, themselves, considered to be attack vectors.
    This assumption, and the resultant conclusion is reasonable since
    this is the very basis of an operator posture; the operator
    depends on this reality to function.  If these devices are not
    trusted, and indeed are compromised, almost the entirety of the
    operator's standard-based IP and MPLS protocol suites are
    vulnerable; therefore, the operation of the entire network is
    compromised.  Although there are well-documented monitoring-based
    methods for detecting compromise (such as included continuous
    monitoring and audit and log review), these may not be sufficient
    to contain damage by a completely compromised element.
    Methods and best practices to secure devices are also widely
    documented and outside the scope of this document.
 Single Domain Boundary
    As per [RFC7665], NSH is designed for use within a single
    administrative domain.  This scoping provides two important
    characteristics:
    i) Clear NSH boundaries
    NSH egress devices MUST strip the NSH headers before they send the
    users' packets or frames out of the NSH domain.
    Means to prevent leaking privacy-related information outside an
    administrative domain are natively supported by the NSH given that
    the last SFF of a service path will systematically remove the NSH
    encapsulation before forwarding a packet exiting the service path.
    The second step in such prevention is to filter the transport
    encapsulation protocol used by NSH at the domain edge.  The
    transport encapsulation protocol MUST be filtered and MUST NOT
    leave the domain edge.

Quinn, et al. Standards Track [Page 27] RFC 8300 Network Service Header (NSH) January 2018

    Depending upon the transport encapsulation protocol used for NSH,
    this can be done either by completely blocking the transport
    encapsulation (e.g., if MPLS is the chosen NSH transport
    encapsulation protocol, it is therefore never allowed to leave the
    domain) or by examining the carried protocol with the transport
    encapsulation (e.g., if VXLAN-gpe is used as the NSH transport
    encapsulation protocol, all domain edges need to filter based on
    the carried protocol in the VXLAN-gpe.)
    The other consequence of this bounding is that ingress packets
    MUST also be filtered to prevent attackers from sending in NSH
    packets with service path identification and metadata of their own
    selection.  The same filters as described above for both the NSH
    at SFC devices and for the transport encapsulation protocol as
    general edge protections MUST be applied on ingress.
    In summary, packets originating outside the SFC-enabled domain
    MUST be dropped if they contain an NSH.  Similarly, packets
    exiting the SFC-enabled domain MUST be dropped if they contain an
    NSH.
    ii) Mitigation of external threats
    As per the trusted SFC device points raised above, given that NSH
    is scoped within an operator's domain, that operator can ensure
    that the environment and its transitive properties comply with
    that operator's required security posture.  Continuous audits for
    assurance are recommended with this reliance on a fully trusted
    environment.  The term "continuous audits" describes a method
    (automated or manual) of checking security-control compliance on a
    regular basis, at some set period of time.

8.2. NSH Security Considerations from the SFC Architecture

 The SFC architecture defines functional roles (e.g., SFF), as well as
 protocol elements (e.g., Metadata).  This section considers each role
 and element in the context of threats posed in the areas of integrity
 and confidentiality.  As with routing, the distributed computation
 model assumes a distributed trust model.
 An important consideration is that NSH contains mandatory-to-mute
 fields, and further, the SFC architecture describes cases where other
 fields in NSH change, all on a possible SFP hop-by-hop basis.  This
 means that any cryptographic solution requires complex key
 distribution and life-cycle operations.

Quinn, et al. Standards Track [Page 28] RFC 8300 Network Service Header (NSH) January 2018

8.2.1. Integrity

 SFC devices
    SFC devices MAY perform various forms of verification on received
    NSH packets such as only accepting NSH packets from expected
    devices, checking that NSH SPI and SI values received from
    expected devices conform to expected values and so on.
    Implementation of these additional checks are a local matter and,
    thus, out of scope of this document.
 NSH Base and Service Path Headers
    Attackers who can modify packets within the operator's network may
    be able to modify the SFP, path position, and/or the metadata
    associated with a packet.
    One specific concern is an attack in which a malicious
    modification of the SPI/SI results in an alteration of the path to
    avoid security devices.  The options discussed in this section
    help thwart that attack, and so does the use of the optional
    "Proof of Transit" method [PROOF-OF-TRANSIT].
    As stated above, SFC devices are trusted; in the case where an SFC
    device is compromised, NSH integrity protection would be subject
    to forging (in many cases) as well.
    NSH itself does not mandate protocol-specific integrity
    protection.  However, if an operator deems protection is required,
    several options are viable:
    1.  SFF/SF NSH verification
        Although, strictly speaking, not integrity protection, some of
        the techniques mentioned above, such as checking expected NSH
        values are received from expected SFC device(s), can provide a
        form of verification without incurring the burden of a full-
        fledged integrity-protection deployment.
    2.  Transport Security
        NSH is always encapsulated by an outer transport encapsulation
        as detailed in Section 4 of this specification, and as
        depicted in Figure 1.  If an operator deems cryptographic
        integrity protection necessary due to their risk analysis,
        then an outer transport encapsulation that provides such
        protection [RFC6071], such as IPsec, MUST be used.

Quinn, et al. Standards Track [Page 29] RFC 8300 Network Service Header (NSH) January 2018

        Although the threat model and recommendations of Section 5 of
        BCP 72 [RFC3552] would normally require cryptographic data
        origin authentication for the header, this document does not
        mandate such mechanisms in order to reflect the operational
        and technical realities of deployment.
        Given that NSH is transport independent, as mentioned above, a
        secure transport, such as IPsec can be used for carry NSH.
        IPsec can be used either alone or in conjunction with other
        transport encapsulation protocols, in turn, encapsulating NSH.
        Operators MUST ensure the selected transport encapsulation
        protocol can be supported by the transport encapsulation/
        underlay of all relevant network segments as well as SFFs,
        SFs, and SFC Proxies in the service path.
        If connectivity between SFC-enabled devices traverses the
        public Internet, then such connectivity MUST be secured at the
        transport encapsulation layer.  IPsec is an example of such a
        transport.
    3.  NSH Variable Header-Based Integrity
        Lastly, NSH MD Type 2 provides, via variable-length headers,
        the ability to append cryptographic integrity protection to
        the NSH packet.  The implementation of such a scheme is
        outside the scope of this document.
 NSH metadata
    As with the Base and Service Path Headers, if an operator deems
    cryptographic integrity protection needed, then an existing,
    standard transport protocol MUST be used since the integrity
    protection applies to entire encapsulated NSH packets.  As
    mentioned above, a risk assessment that deems data-plane traffic
    subject to tampering will apply not only to NSH but to the
    transport information; therefore, the use of a secure transport is
    likely needed already to protect the entire stack.
    If an MD Type 2 variable header integrity scheme is in place, then
    the integrity of the metadata can be ensured via that mechanism as
    well.

Quinn, et al. Standards Track [Page 30] RFC 8300 Network Service Header (NSH) January 2018

8.2.2. Confidentiality

 SFC devices
    SFC devices can "see" (and need to use) NSH information.
 NSH Base and Service Path Headers
    SPI and other base / service path information does not typically
    require confidentiality; however, if an operator does deem
    confidentiality to be required, then, as with integrity, an
    existing transport encapsulation that provides encryption MUST be
    utilized.
 NSH metadata
    An attacker with access to the traffic in an operator's network
    can potentially observe the metadata NSH carries with packets,
    potentially discovering privacy-sensitive information.
    Much of the metadata carried by NSH is not sensitive.  It often
    reflects information that can be derived from the underlying
    packet or frame.  Direct protection of such information is not
    necessary, as the risks are simply those of carrying the
    underlying packet or frame.
    Implementers and operators MUST be aware that metadata can have
    privacy implications, and those implications are sometimes hard to
    predict.  Therefore, attached metadata should be limited to that
    necessary for correct operation of the SFP.  Further, [RFC8165]
    defines metadata considerations that operators can take into
    account when using NSH.
    Protecting NSH metadata information between SFC components can be
    done using transport encapsulation protocols with suitable
    security capabilities, along the lines discussed above.  If a
    security analysis deems these protections necessary, then security
    features in the transport encapsulation protocol (such as IPsec)
    MUST be used.
    One useful element of providing privacy protection for sensitive
    metadata is described under the "SFC Encapsulation" area of the
    Security Considerations of [RFC7665].  Operators can and should
    use indirect identification for metadata deemed to be sensitive
    (such as personally identifying information), significantly
    mitigating the risk of a privacy violation.  In particular,
    subscriber-identifying information should be handled carefully,
    and, in general, SHOULD be obfuscated.

Quinn, et al. Standards Track [Page 31] RFC 8300 Network Service Header (NSH) January 2018

    For those situations where obfuscation is either inapplicable or
    judged to be insufficient, an operator can also encrypt the
    metadata.  An approach to an optional capability to do this was
    explored in [NSH-ENCRYPT].  For other situations where greater
    assurance is desired, optional mechanisms such as
    [PROOF-OF-TRANSIT] can be used.

9. IANA Considerations

9.1. NSH Parameters

 IANA has created a new "Network Service Header (NSH) Parameters"
 registry.  The following subsections detail new registries within the
 "Network Service Header (NSH) Parameters" registry.

9.1.1. NSH Base Header Bits

 There are five unassigned bits (U bits) in the NSH Base Header, and
 one assigned bit (O bit).  New bits are assigned via Standards Action
 [RFC8126].
 Bit 2 - O (OAM) bit
 Bit 3 - Unassigned
 Bits 16-19 - Unassigned

9.1.2. NSH Version

 IANA has set up the "NSH Version" registry.  New values are assigned
 via Standards Action [RFC8126].
     +-------------+---------------------------------+-----------+
     | Version     | Description                     | Reference |
     +-------------+---------------------------------+-----------+
     | Version 00b | Protocol as defined by RFC 8300 | RFC 8300  |
     | Version 01b | Reserved                        | RFC 8300  |
     | Version 10b | Unassigned                      |           |
     | Version 11b | Unassigned                      |           |
     +-------------+---------------------------------+-----------+
                         Table 5: NSH Version

Quinn, et al. Standards Track [Page 32] RFC 8300 Network Service Header (NSH) January 2018

9.1.3. NSH MD Types

 IANA has set up the "NSH MD Types" registry, which contains 4-bit
 values.  MD Type values 0x0, 0x1, 0x2, and 0xF are specified in this
 document; see Table 6.  Registry entries are assigned via the "IETF
 Review" policy defined in RFC 8126 [RFC8126].
              +-----------+-----------------+-----------+
              | MD Type   | Description     | Reference |
              +-----------+-----------------+-----------+
              | 0x0       | Reserved        | RFC 8300  |
              |           |                 |           |
              | 0x1       | NSH MD Type 1   | RFC 8300  |
              |           |                 |           |
              | 0x2       | NSH MD Type 2   | RFC 8300  |
              |           |                 |           |
              | 0x3 - 0xE | Unassigned      |           |
              |           |                 |           |
              | 0xF       | Experimentation | RFC 8300  |
              +-----------+-----------------+-----------+
                        Table 6: MD Type Values

9.1.4. NSH MD Class

 IANA has set up the "NSH MD Class" registry, which contains 16-bit
 values.  New allocations are to be made according to the following
 policies:
 0x0000 to 0x01ff: IETF Review
 0x0200 to 0xfff5: Expert Review
 IANA has assigned the values as follows:
      +------------------+------------------------+------------+
      | Value            | Meaning                | Reference  |
      +------------------+------------------------+------------+
      | 0x0000           | IETF Base NSH MD Class | RFC 8300   |
      |                  |                        |            |
      | 0xfff6 to 0xfffe | Experimental           | RFC 8300   |
      |                  |                        |            |
      | 0xffff           | Reserved               | RFC 8300   |
      +------------------+------------------------+------------+
                         Table 7: NSH MD Class
 A registry for Types for the MD Class of 0x0000 is defined in
 Section 9.1.5.

Quinn, et al. Standards Track [Page 33] RFC 8300 Network Service Header (NSH) January 2018

 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
 associated and publicly visible registry of MD Types although this
 registry need not be maintained by IANA.
 When evaluating a request for an allocation, the Expert should verify
 that the allocation plan includes considerations to handle privacy
 and security issues associated with the anticipated individual MD
 Types allocated within this class.  These plans should consider, when
 appropriate, alternatives such as indirection, encryption, and
 limited-deployment scenarios.  Information that can't be directly
 derived from viewing the packet contents should be examined for
 privacy and security implications.

9.1.5. NSH IETF-Assigned Optional Variable-Length Metadata Types

 The Type values within the IETF Base NSH MD Class, i.e., when the MD
 Class is set to 0x0000 (see Section 9.1.4), are the Types owned by
 the IETF.  Per this document, IANA has created a registry for the
 Type values for the IETF Base NSH MD Class called the "NSH IETF-
 Assigned Optional Variable-Length Metadata Types" registry, as
 specified in Section 2.5.1.
 The type values are assigned via Standards Action [RFC8126].
 No initial values are assigned at the creation of the registry.

Quinn, et al. Standards Track [Page 34] RFC 8300 Network Service Header (NSH) January 2018

9.1.6. NSH Next Protocol

 IANA has set up the "NSH Next Protocol" registry, which contains
 8-bit values.  Next Protocol values 0, 1, 2, 3, 4, and 5 are defined
 in this document (see Table 8).  New values are assigned via "Expert
 Review" as per [RFC8126].
             +---------------+--------------+-----------+
             | Next Protocol | Description  | Reference |
             +---------------+--------------+-----------+
             | 0x00          | Unassigned   |           |
             |               |              |           |
             | 0x01          | IPv4         | RFC 8300  |
             |               |              |           |
             | 0x02          | IPv6         | RFC 8300  |
             |               |              |           |
             | 0x03          | Ethernet     | RFC 8300  |
             |               |              |           |
             | 0x04          | NSH          | RFC 8300  |
             |               |              |           |
             | 0x05          | MPLS         | RFC 8300  |
             |               |              |           |
             | 0x06 - 0xFD   | Unassigned   |           |
             |               |              |           |
             | 0xFE          | Experiment 1 | RFC 8300  |
             |               |              |           |
             | 0xFF          | Experiment 2 | RFC 8300  |
             +---------------+--------------+-----------+
             Table 8: NSH Base Header Next Protocol Values
 Expert Review requests MUST include a single codepoint per request.
 Designated Experts evaluating new allocation requests from this
 registry should consider the potential scarcity of codepoints for an
 8-bit value, and check both for duplications and availability of
 documentation.  If the actual assignment of the Next Protocol field
 allocation reaches half of the range (that is, when there are 128
 unassigned values), IANA needs to alert the IESG.  At that point, a
 new more strict allocation policy SHOULD be considered.

10. NSH-Related Codepoints

10.1. NSH Ethertype

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

Quinn, et al. Standards Track [Page 35] RFC 8300 Network Service Header (NSH) January 2018

11. References

11.1. 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,
            <https://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,
            <https://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,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2. Informative References

 [NSH-BROADBAND-ALLOCATION]
            Napper, J., Kumar, S., Muley, P., Henderickx, W., and M.
            Boucadair, "NSH Context Header Allocation -- Broadband",
            Work in Progress, draft-napper-sfc-nsh-broadband-
            allocation-04, November 2017.
 [NSH-DC-ALLOCATION]
            Guichard, J., Smith, M., Kumar, S., Majee, S., Agarwal,
            P., Glavin, K., Laribi, Y., and T. Mizrahi, "Network
            Service Header (NSH) MD Type 1: Context Header Allocation
            (Data Center)", Work in Progress,
            draft-guichard-sfc-nsh-dc-allocation-07, August 2017.
 [NSH-ENCRYPT]
            Reddy, T., Patil, P., Fluhrer, S., and P. Quinn,
            "Authenticated and encrypted NSH service chains", Work in
            Progress, draft-reddy-sfc-nsh-encrypt-00, April 2015.

Quinn, et al. Standards Track [Page 36] RFC 8300 Network Service Header (NSH) January 2018

 [PROOF-OF-TRANSIT]
            Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
            Leddy, J., Youell, S., Mozes, D., and T. Mizrahi, "Proof
            of Transit", Work in Progress, draft-brockners-proof-
            of-transit-04, October 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,
            <https://www.rfc-editor.org/info/rfc2784>.
 [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
            Text on Security Considerations", BCP 72, RFC 3552,
            DOI 10.17487/RFC3552, July 2003,
            <https://www.rfc-editor.org/info/rfc3552>.
 [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
            Considered Useful", BCP 82, RFC 3692,
            DOI 10.17487/RFC3692, January 2004,
            <https://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,
            <https://www.rfc-editor.org/info/rfc6071>.
 [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
            D., and S. Mansfield, "Guidelines for the Use of the "OAM"
            Acronym in the IETF", BCP 161, RFC 6291,
            DOI 10.17487/RFC6291, June 2011,
            <https://www.rfc-editor.org/info/rfc6291>.
 [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, <https://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,
            <https://www.rfc-editor.org/info/rfc7498>.
 [RFC7676]  Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
            for Generic Routing Encapsulation (GRE)", RFC 7676,
            DOI 10.17487/RFC7676, October 2015,
            <https://www.rfc-editor.org/info/rfc7676>.

Quinn, et al. Standards Track [Page 37] RFC 8300 Network Service Header (NSH) January 2018

 [RFC8165]  Hardie, T., "Design Considerations for Metadata
            Insertion", RFC 8165, DOI 10.17487/RFC8165, May 2017,
            <https://www.rfc-editor.org/info/rfc8165>.
 [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
            "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
            DOI 10.17487/RFC8201, July 2017,
            <https://www.rfc-editor.org/info/rfc8201>.
 [RTG-ENCAP]
            Nordmark, E., Tian, A., Gross, J., Hudson, J., Kreeger,
            L., Garg, P., Thaler, P., and T. Herbert, "Encapsulation
            Considerations", Work in Progress,
            draft-ietf-rtgwg-dt-encap-02, October 2016.
 [SFC-CONTROL-PLANE]
            Boucadair, M., "Service Function Chaining (SFC) Control
            Plane Components & Requirements", Work in Progress,
            draft-ietf-sfc-control-plane-08, October 2016.
 [SFC-OAM-FRAMEWORK]
            Aldrin, S., Pignataro, C., Kumar, N., Akiya, N., Krishnan,
            R., and A. Ghanwani, "Service Function Chaining (SFC)
            Operation, Administration and Maintenance (OAM)
            Framework", Work in Progress,
            draft-ietf-sfc-oam-framework-03, September 2017.
 [VXLAN-GPE]
            Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
            Extension for VXLAN", Work in Progress,
            draft-ietf-nvo3-vxlan-gpe-05, October 2017.

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

Quinn, et al. Standards Track [Page 38] RFC 8300 Network Service Header (NSH) January 2018

 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 comprehensive reviews and respective
 useful suggestions by Med Boucadair, Adrian Farrel, Juergen
 Schoenwaelder, Acee Lindem, and Kathleen Moriarty.
 Lastly, David Dolson has provided significant review, feedback, and
 suggestions throughout the evolution of this document.  His
 contributions are very much appreciated.

Contributors

 This WG document originated as draft-quinn-sfc-nsh; the following are
 its coauthors and contributors along with their respective
 affiliations at the time of WG adoption.  The editors of this
 document would like to thank and recognize them and their
 contributions.  These coauthors and contributors provided invaluable
 concepts and content for this document's creation.
 o  Jim Guichard, Cisco Systems, Inc.
 o  Surendra Kumar, Cisco Systems, Inc.
 o  Michael Smith, Cisco Systems, Inc.
 o  Wim Henderickx, Alcatel-Lucent
 o  Tom Nadeau, Brocade
 o  Puneet Agarwal
 o  Rajeev Manur, Broadcom
 o  Abhishek Chauhan, Citrix
 o  Joel Halpern, Ericsson
 o  Sumandra Majee, F5
 o  David Melman, Marvell
 o  Pankaj Garg, Microsoft
 o  Brad McConnell, Rackspace
 o  Chris Wright, Red Hat, Inc.
 o  Kevin Glavin, Riverbed
 o  Hong (Cathy) Zhang, Huawei US R&D
 o  Louis Fourie, Huawei US R&D
 o  Ron Parker, Affirmed Networks
 o  Myo Zarny, Goldman Sachs
 o  Andrew Dolganow, Alcatel-Lucent
 o  Rex Fernando, Cisco Systems, Inc.
 o  Praveen Muley, Alcatel-Lucent
 o  Navindra Yadav, Cisco Systems, Inc.

Quinn, et al. Standards Track [Page 39] RFC 8300 Network Service Header (NSH) January 2018

Authors' Addresses

 Paul Quinn (editor)
 Cisco Systems, Inc.
 Email: paulq@cisco.com
 Uri Elzur (editor)
 Intel
 Email: uri.elzur@intel.com
 Carlos Pignataro (editor)
 Cisco Systems, Inc.
 Email: cpignata@cisco.com

Quinn, et al. Standards Track [Page 40]

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