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Network Working Group                                          R. Browne
Internet Draft                                               A. Chilikin
Intended status: Informational                                     Intel
Expires: August 2019                                          T. Mizrahi
                                        Huawei Network.IO Innovation Lab
                                                       February 25, 2019


                    A Key Performance Indicators (KPI)
               Stamping for the Network Service Header (NSH)
                     draft-browne-sfc-nsh-kpi-stamp-07


Abstract

   This document describes a method of carrying Key Performance
   Indicators (KPIs) using the Network Service Header (NSH). This method
   may be used, for example, to monitor latency and QoS marking to
   identify problems on some links or service functions.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 25, 2019.

Copyright Notice

   Copyright (c) 2019 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



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

Table of Contents


   1. Introduction ................................................ 2
   2. Terminology ................................................. 3
      2.1. Requirement Language ................................... 3
      2.2. Definition of Terms .................................... 3
         2.2.1. Terms Defined in this Document .................... 4
      2.3. Abbreviations .......................................... 4
   3. NSH KPI Stamping: An Overview ............................... 6
      3.1. Prerequisites .......................................... 7
      3.2. Operation ............................................. 10
         3.2.1. Flow Selection ................................... 10
         3.2.2. SCP Interface .................................... 10
      3.3. Performance Considerations ............................ 11
   4. NSH KPI-stamping Encapsulation ............................. 12
      4.1. KPI-stamping Extended Encapsulation ................... 13
         4.1.1. NSH Timestamping Encapsulation (Extended Mode) ... 15
         4.1.2. NSH QoS-stamping Encapsulation (Extended Mode) ... 17
      4.2. KPI-stamping Encapsulation (Detection Mode) ........... 20
   5. Hybrid Models .............................................. 22
      5.1. Targeted VNF Stamp .................................... 23
   6. Fragmentation Considerations ............................... 23
   7. Security Considerations .................................... 24
   8. IANA Considerations ........................................ 25
   9. Contributors ............................................... 25
   10. Acknowledgments ........................................... 25
   11. References ................................................ 25
      11.1. Normative References ................................. 25
      11.2. Informative References ............................... 26

1. Introduction

   Network Service Header (NSH), as defined by [RFC8300], specifies a
   method for steering the traffic among an ordered set of Service
   Functions (SFs) using an extensible service header. This allows for
   flexibility and programmability in the forwarding plane to invoke the
   appropriate SFs for specific flows.



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   NSH promises a compelling vista of operational flexibility. However,
   many service providers are concerned about service and configuration
   visibility. This concern increases when considering that many service
   providers wish to run their networks seamlessly in 'hybrid' mode,
   whereby they wish to mix physical and virtual SFs and run services
   seamlessly between the two domains.

   This document describes generic methods to monitor and debug service
   function chains in terms of latency and QoS marking of the flows
   within a service function chain.  This is refered to detection mode
   and extended mode and explained in section 4.

   The method described in the document is compliant with hybrid
   architectures in which Virtual Network Functions (VNFs) and Physical
   Network Functions (PNFs) are freely mixed in the service function
   chain. This method also provides flexibility to monitor the
   performance and configuration of an entire chain or part thereof as
   desired. This method is extensible to monitoring other KPIs. Please
   refer to [RFC7665] for an architectural context for this document.

   The method described in this document is not an OAM protocol such as
   [Y.1731] or [Y.1564]. As such it does not define new OAM packet types
   or operation. Rather it monitors the service function chain
   performance and configuration for subscriber payloads and indicates
   subscriber QoE rather than out-of-band infrastructure metrics. This
   document differs from to [I-D.ippm.ioam] in the sense that it is
   specifically tied to NSH operation and not generic in nature.

2. Terminology

2.1. Requirement 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 BCP 14
   [RFC2119][RFC8174] when, and only when, they appear in all capitals,
   as shown here.

2.2. Definition of Terms

   This section presents the main terms used in this document. This
   document makes use of the terms defined in [RFC7665] and [RFC8300].






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2.2.1. Terms Defined in this Document

   First Stamping Node (FSN): The first node along a service function
   chain that stamps packets using KPI stamping. The FSN matches each
   packet with a Stamping Controller flow based on a stamping
   classification criterion such as transport 5-tuple coordinates, but
   not limited to.

   Last Stamping Node (LSN): The last node along a service function
   chain that stamps packets using KPI stamping. From forwarding point
   of view the LSN removes the NSH header and forwards the raw IP packet
   to the next hop. From a control plane point of view the LSN reads all
   the metadata and exports it to a system performance statistics agent
   or repository. The LSN should use the NSH Service Index (SI) to
   indicate if a SF was at the end of the chain. The LSN may change the
   Service Path Identifier (SPI) to preconfigured value in order that
   the network underlay forwards the metadata back directly to the KPI
   database (KPIDB) based on this value.

   Key Performance Indicator Database (KPIDB): denotes the external
   storage of metadata for reporting, trend analysis, etc.

   KPI-stamping: The insertion of latency-related and/or QoS-related
   information into a packet using NSH metadata.

   Flow ID: The Flow ID is a unique 16 bit identifier written into the
   header by the classifier. This allows 65536 flows to be concurrently
   stamped on any given NSH service chain (SPI).

   QoS-stamping: The insertion of QoS-related information into a packet
   using NSH metadata.

   Stamping Controller (SC): The SC is the central logic that decides
   what packets to stamp and how. The SC instructs the classifier on how
   to build the KPI stamp specific parts of the NSH.

   Stamp Control Plane (SCP): the control plane between the FSN and the
   SC.

2.3. Abbreviations

   DEI    Drop Eligible Indicator

   DSCP   Differentiated Services Code Point

   FSN    First Stamping Node



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   KPI    Key Performance Indicator

   KPIDB   Key Performance Indicator Database

   LSN    Last Stamping Node

   MD     Metadata

   NFV    Network Function Virtualization

   NFVI-PoP NFV Infrastructure Point of Presence

   NIC    Network Interface Card

   NSH    Network Service Header

   OAM    Operations, Administration, and Maintenance

   PCP    Priority Code Point

   PNF    Physical Network Function

   PNFN   Physical Network Function Node

   QoE    Quality of Experience

   QoS    Quality of Service

   QS     QoS Stamp

   RSP    Rendered Service Path

   SC     Stamping Controller

   SCL    Service Classifier

   SCP    Stamp Control Plane

   SI     Service Index

   SF     Service Function

   SFC    Service Function Chain

   SFP    Service Function Path

   SSI    Stamp Service Index


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   TC     Traffic Class

   TS     Timestamp

   VLAN   Virtual Local Area Network

   VNF    Virtual Network Function

   vSwitch Virtual Switch



3. NSH KPI Stamping: An Overview

   A typical KPI stamping architecture is presented in Figure 1.

       Stamping
      Controller
         |                                                     KPIDB
         | SCP Interface                                        |
       ,---.             ,---.              ,---.              ,---.
      /     \           /     \            /     \            /     \
     (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
      \ FSN /           \     /            \     /            \ LSN /
       `---'             `---'              `---'              `---'
                Figure 1: Logical roles in NSH KPI Stamping

   The Stamping Controller (SC) will be part of the SFC control plane
   architecture, but it is described separately in this document for
   clarity.

   The SC is responsible for initiating start/stop stamp requests to the
   SCL or First Stamp Node (FSN), and also for distributing NSH stamping
   policy into the service chain via the Stamping Control Plane (SCP)
   interface.

   The FSN will typically be part of the SCL, but again is called out as
   separate logical entity for clarity.

   The FSN is responsible for marking NSH MD fields which tells nodes in
   the service chain how to behave in terms of stamping at SF ingress,
   egress or both, or ignoring the stamp NSH metadata completely.

   The FSN also writes the Reference Time value, a (possibly inaccurate)
   estimate of the current time-of-day, into the header, allowing the


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   {SPI:Flow ID} performance to be compared to previous samples for
   offline analysis.

   The FSN should return an error to the SC if not synchronized to the
   current time-of-day and forward the packet along the service-chain
   unchanged. The code and format of the error is specific to the
   protocol used between the FSN and SC; these considerations are out of
   scope.

   SF1 and SF2 stamp the packets as dictated by the FSN and process the
   payload as per normal.

   Note 1: The exact location of the stamp creation may not be in
           the SF itself, as discussed in Section 3.3.

   Note 2: Special cases exist where some of the SFs are
           NSH-unaware. This is covered in Section 5.

   The Last Stamp Node (LSN) should strip the entire NSH header and
   forward the raw packet to the IP next hop as per [RFC8300]. The LSN
   also exports NSH stamp information to the KPI Database (KPIDB) for
   offline analysis; the LSN may either export the stamping information
   of all packets, or a subset based on packet sampling.

   In fully virtualized environments the LSN is likely to be co-located
   with the SF that decrements the NSH Service Index (SI) to zero.
   Corner cases exist whereby this is not the case and is covered in
   Section 5.



3.1. Prerequisites

   Timestamping presents a set of prerequisites not required to QoS-
   Stamp. In order to guarantee metadata accuracy, all servers hosting
   VNFs should be synchronized from a centralized stable clock. As it is
   assumed that PNFs do not timestamp (as this would involve a software
   change and probable throughput performance impact) there is no need
   for them to synchronize. There are two possible levels of
   synchronization:

   Level A: Low accuracy time-of-day synchronization, based on
            NTP [RFC5905].

   Level B: High accuracy synchronization (typically on the order of
            microseconds), based on [IEEE1588].



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   Each SF SHOULD have a level A synchronization, and MAY have a level B
   synchronization.

   Level A requires each platform (including the Stamp Controller) to
   synchronize its system real-time-clock to an NTP server. This is used
   to mark the metadata in the chain, using the <Reference Time> field
   in the NSH KPI-stamp header (Section 4.2). This timestamp is inserted
   to the NSH by the first SF in the chain. NTP accuracy can vary by
   several milliseconds between locations. This is not an issue as the
   Reference Time is merely being used as a time-of-day reference
   inserted into the KPIDB for performance monitoring and metadata
   retrieval.

   Level B synchronization requires each platform to be synchronized to
   a Primary Reference Time Clock (PRTC) using the Precision Time
   Protocol [IEEE1588]. A platform MAY also use Synchronous Ethernet
   ([G.8261], [G.8262], [G.8264]), allowing more accurate frequency
   synchronization.

   If an SF is not synchronized at the moment of timestamping, it should
   indicate its synchronization status in the NSH. This is described in
   more detail in Section 4.

   By synchronizing the network in this way, the timestamping operation
   is independent of the current Rendered Service Path (RSP). Indeed the
   timestamp metadata can indicate where a chain has been moved due to a
   resource starvation event as indicated in Figure 2, between VNF 3 and
   VNF 4 at time B.



   Delay
    |                                  v
    |                           v
    |                                  x
    |                           x            x = reference time A
    |                    xv                  v = reference time B
    |             xv
    |      xv
    |______|______|______|______|______|_____
          VNF1   VNF2  VNF3   VNF4    VNF5

               Figure 2: Flow performance in a service chain




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   For QoS-stamping it is desired that the SCL or FSN be synchronized in
   order to provide reference time for offline analysis, but this is not
   a hard requirement (they may be in holdover or free-run state, for
   example). Other SFs in the service chain do not need to be
   synchronized for QoS-stamping operation as described below.

   QoS-stamping can be used to check consistency of configuration across
   the entire chain or part thereof. By adding all potential layer 2 and
   layer 3 QoS fields into a QoS sum at SF ingress or egress, this
   allows quick identification of QoS mismatches across multiple L2/L3
   fields which otherwise is a manual, expert-led consuming process.



    |
    |
    |                                  xy
    |                           xy           x = ingress QoS sum
    |                    xv                  v = egress QoS sum
    |             xv                    y = egress QoS sum miss
    |      xv
    |______|______|______|______|______|_____
          SF1    SF2    SF3    SF4    SF5

             Figure 3: Flow QoS Consistency in a service chain



   Referring to Figure 3, x, v, and y are notional sum values of the QoS
   marking configuration of the flow within a given chain. As the
   encapsulation of the flow can change from hop to hop in terms of VLAN
   header(s), MPLS labels, DSCP(s) these values are used to compare
   consistency of configuration from for example payload DSCP through
   overlay and underlay QoS settings in VLAN IEEE 802.1Q bits, MPLS bits
   and infrastructure DSCPs.

   Figure 3 indicates that at SF4 in the chain, the egress QoS marking
   is inconsistent. That is, the ingress QoS settings do not match the
   egress. The method described here will indicate which QoS field(s) is
   inconsistent, and whether this is ingress (whereby the underlay has
   incorrectly marked and queued the packet) or egress (where the SF has
   incorrectly marked and queued the packet.

   Note that the SC must be aware of when a SF remarks QoS fields
   deliberately and thus does not flag an issue for desired behavior.


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3.2. Operation



   KPI-stamping detection mode uses MD type 2 defined in [RFC8300]. This
   involves the SFC classifier stamping the flow at chain ingress, and
   no subsequent stamps being applied, rather each SF upstream can
   compare its local condition with the ingress value and take
   appropriate action. Therefore detection mode is very efficient in
   terms of header size that does not grow after the classification.
   This is further explained in Section 4.1.



3.2.1. Flow Selection

   The SC should maintain a list of flows within each service chain to
   be monitored. This flow table should be in the format 'SPI:FlowID'.
   The SC should map these pairs to unique values presented as Flow IDs
   per service chain within the NSH TLV specified in this document. The
   SC should instruct the FSN to initiate timestamping on flow table
   match. The SC may also tell the classifier the duration of the
   timestamping operation, either by a number of packets in the flow or
   by a time duration.

   In this way the system can monitor the performance of the all en-
   route traffic, or an individual subscriber in a chain, or just a
   specific application or a QoS class that is used in the network.

   The SC should write the list of monitored flows into the KPIDB for
   correlation of performance and configuration data. Thus, when the
   KPIDB receives data from the LSN it understands to which flow the
   data pertains.

   The association of source IP to subscriber identity is outside the
   scope of this document and will vary by network application. For
   example, the method of association of a source IP to IMSI will be
   different to how a CPE with NAT function may be chained in an
   enterprise NFV application.

3.2.2. SCP Interface

   A Stamp Control Plane (SCP) interface is required between the SC and
   the FSN or classifier. This interface is used to:

   o    Query the SFC classifier for a list of active chains and flows.



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   o    Communicate which chains and flows to stamp. This can be a
      specific {SPI:Flow ID} combination or include wildcards for
      monitoring subscribers across multiple chains or multiple flows
      within one chain.

   o    Instruct how the stamp should be applied (ingress, egress, both
      or specific).

   o    Indicate when to stop stamping, either after a certain number
      of packets or duration.

   Typically SCP timestamps flows for a certain duration for trend
   analysis, but only stamps one packet of each QoS class in a chain
   periodically (perhaps once per day or after a network change).
   Therefore, timestamping is generally applied to a much larger set of
   packets than QoS-stamping.

   Exact specification of SCP is for further study.

3.3. Performance Considerations

   This document does not mandate a specific stamping implementation
   method, and thus NSH KPI stamping can either be performed by hardware
   mechanisms, or by software.

   If software-based stamping is used, applying and operating on the
   stamps themselves incur an additional small delay in the service
   chain. However, it can be assumed that these additional delays are
   all relative for the flow in question. This is only pertinent for
   timestamping mode, and not for QoS-stamping mode. Thus, whilst the
   absolute timestamps may not be fully accurate for normal non-
   timestamped traffic they can be assumed to be relative.

   It is assumed that the method described in this document would only
   operate on a small percentage of user flows.

   The service provider may choose a flexible policy in the SC to
   timestamp a selection of user-plane every minute for example to
   highlight any performance issues. Alternatively, the LSN may
   selectively export a subset of the KPI-stamps it receives, based on a
   predefined sampling method. Of course the SC can stress test an
   individual flow or chain should a deeper analysis be required. We can
   expect that this type of deep analysis has an impact on the
   performance of the chain itself whilst under investigation. The
   impact will be dependent on vendor implementation and outside the
   scope of this document.



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   For QoS-stamping the method described here is even less intrusive, as
   typically multiple packets in a flow are QoS stamped periodically
   (perhaps once per day) check one packet in a chain per QoS class.



4. NSH KPI-stamping Encapsulation



   KPI stamping uses NSH MD type 0x2 for detection of anomalies and
   extended mode for root cause analysis of KPI violations. These are
   further explained in this section.

   The generic NSH MD type 2 TLV for KPI Stamping is shown below.



     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ver|O|U|    TTL    |   Length  |U|U|U|U|Type=2 | Next Protocol |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path Identifier              | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Metadata Class         |      Type     |U|    Length   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Variable-length KPI Metadata header and TLV(s)          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 4: Generic NSH KPI Encapsulation


   Relevant fields in header that the FSN must implement:

   o    The O bit must not be set.

   o    The MD type must be set to 0x2

   o    The Metadata Class must be set to a value from the experimental
      range 0xfff6 to 0xfffe according to an agreement by all parties to
      the experiment.

   o    Unassigned bits: all fields, marked U, are unassigned and
      available for future use [RFC8300]




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   o    The Type field may have one of the following values; the
      content of "KPI metadata" depends on the type value:

        o Type = 0x01 Det: Detection

        o Type = 0x02 TS: Timestamp Extended

        o Type = 0x03 QoS: QoS-stamp Extended

   The Type field determines the type of KPI-stamping format. The
   supported formats are presented in the following subsections.

4.1. KPI-stamping Extended Encapsulation

   The generic NSH MD type 2 KPI-stamping header extended mode is shown
   in Figure 5. This is the format for performance monitoring of service
   chain issues with respect to QoS configuration and latency.



     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|Type=2 | Next Protocol |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path Identifier              | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Metadata Class        |     Type      |U|    Length   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Variable Length KPI Configuration Header            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Variable Length KPI Value (LSN)              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Variable Length KPI Value (FSN)              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 5: Generic KPI Encapsulation (Extended Mode)



   As mentioned above, two types are defined under the experimental MD
   class to indicate extended KPI MD: a timestamp type and a QoS-stamp
   type.




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   The KPI Encapsulation Configuration Header format is shown below.

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |K|K|T|K|K|K|K|K|   Stamping SI |           Flow ID             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Reference Time                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 6: KPI Encapsulation Configuration Header



   The bits marked as 'K' are reserved for specific KPI type use and
   described in the corresponding subsections below.

   The T bit should be set if Reference Time follows KPI Encapsulation
   Configuration Header.

   Stamping Service Index (Stamping SI) contains the Service Index used
   for KPI stamping and described in the corresponding subsections
   below.

   The Flow ID is a unique 16 bit identifier written into the header by
   the classifier. This allows 65536 flows to be concurrently stamped on
   any given NSH service chain (SPI). Flow IDs are not written by
   subsequent SFs in the chain. The FSN may export monitored flow IDs to
   the KPIDB for correlation.

   Reference Time is the wall clock of the FSN, and may be used for
   historical comparison of SC performance. If the FSN is not Level A
   synchronized (see Section 3.1) it should inform the SC over the SCP
   interface. The Reference Time is represented in 64-bit NTP format
   [RFC5905] presented 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Seconds                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Fraction                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 7: NTP [RFC5905] 64-bit Timestamp Format





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4.1.1. NSH Timestamping Encapsulation (Extended Mode)

   The NSH timestamping extended encapsulation is shown 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ver|O|C|U|U|U|U|U|U|   Length  |U|U|U|U|Type=2 |   NextProto   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path ID                      | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Metadata Class         |  Type=TS(2) |U|     Len     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |I|E|T|U|U|U|SSI|  Stamping SI  |           Flow ID             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |              Reference Time (T bit is set)                    |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |I|E|U|U|U| SYN |  Stamping SI  |         Unassigned            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |             Ingress Timestamp (I bit is set)(LSN)             |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Egress Timestamp (E bit is set)(LSN)             |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |I|E|U|U|U| SYN |  Stamping SI  |          Unassigned           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                 Ingress Timestamp (I bit is set)  (FSN)       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Egress Timestamp (E bit is set)  (FSN)        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 8: NSH Timestamp Encapsulation (Extended Mode)




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   The FSN KPI-stamp metadata starts with Stamping Configuration Header.
   This header contains the I, E, T bits and Stamp Service Index (SSI).

   The I bit should be set if Ingress stamp is requested.

   The E bit should be set if Egress stamp is requested.

   SSI field must be set to one of the following values:

   o    0x0 KPI-stamp mode, no Service index specified in the Stamp
      Service Index field.

   o    0x1 KPI-stamp Hybrid mode is selected, Stamp Service Index
      contains LSN Service index. This is used when PNFs or NSH-unaware
      SFs are used at the tail of the chain. If SSI=0x1, then the value
      in the type field informs the chain which SF should act as the
      LSN.

   o    0x2 KPI-stamp Specific mode is selected, Stamp Service Index
      contains the targeted Service Index. In this case the Stamp
      Service Index field indicates which SF is to be stamped. Both
      ingress and egress stamps are performed when the SI=SSI on the
      chain. For timestamping mode, the FSN will also apply the
      Reference Time and Ingress Timestamp. This will indicate the delay
      along the entire service chain to the targeted SF. This method may
      also be used as a light implementation to monitor end-to-end
      service chain performance whereby the targeted SF is the LSN. This
      is not applicable to QoSStamping mode.

   Each stamping Node adds stamping metadata which consist of Stamping
   Reporting Header and timestamps.

   The E bit should be set if Egress stamp is reported.

   The I bit should be set if Ingress stamp is reported.

   With respect to timestamping mode, the SYN bits are an indication of
   the synchronization status of the node performing the timestamp and
   must be set to one of the following values:

   o    In Synch: 0x00

   o    In holdover: 0x01

   o    In free run: 0x02

   o    Out of Synch: 0x03


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   If the platform hosting the SF is out of synch or in free run no
   timestamp is applied by the node and the packet is processed
   normally.

   If FSN is out of synch or in free run timestamp request rejected and
   not propagated though the chain. The FSN should inform the SC in such
   an event over the SCP interface. Similarly if KPIDB receives
   timestamps that are out of order (i.e. a time stamp of a 'N+1' SF is
   in the past of a 'N' SF) it should notify SC of this condition over
   the SCP interface.

   The outer service index value is copied into the stamp metadata as
   Stamping SI to help cater for hybrid chains that are a mix of VNFs
   and PNFs or through NSH-unaware SFs. Thus, if a flow transits through
   a PNF or an NSH-unaware node the delta in the inner service index
   between timestamps will indicate this.

   The Ingress Timestamp and Egress Timestamp are represented in 64-bit
   NTP format. The corresponding bits (I and E) reported in the Stamping
   Reporting Header of the node's metadata.

4.1.2. NSH QoS-stamping Encapsulation (Extended Mode)

   Packets have a variable QoS stack. That is for example the same
   payload IP can have a very different stack in the access part of the
   network to the core. This is most apparent in mobile networks where
   for example in an access circuit we would have 2 layers of
   infrastructure IP header (DSCP) - one transport-based and the other
   IPsec-based, in addition to multiple MPLS and VLAN tags. The same
   packet as it leaves the PDN Gateway Gi egress interface may be very
   much simplified in terms of overhead and related QoS fields.

   Because of this variability we need to build extra meaning into the
   QoS headers - they are not for example all PTP timestamps of a fixed
   length as in the case of timestamping, rather they are variable
   lengths and types. Also they can be changed on the underlay at any
   time without knowledge by the SFC system. Therefore each SF must be
   able to ascertain and record its ingress and egress QoS configuration
   on the fly.

   The suggested QoS type, lengths are as below. The type is 4 bits
   long.







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   QoS Type(QT)Value     Length    Comment

   IVLAN     0x01     4 Bits    Ingress VLAN (PCP + DEI)

   EVLAN     0x02     4 Bits    Egress VLAN

   IQINQ     0x03     8 Bits    Ingress QinQ (2x PCP+DEI)

   EQINQ     0x04     8 Bits    Egress QinQ

   IMPLS     0x05     3 Bits    Ingress Label

   EMPLS     0x06     3 Bits    Egress Label

   IMPLS     0x07     6 Bits    2 Ingress Labels (2x EXP)

   EMPLS     0x08     6 Bits    2 Egress Labels

   IDSCP     0x09     8 Bits    Ingress DSCP

   EDSCP     0x0A     8 Bits    Egress DSCP



For stacked headers such as MPLS and 802.1ad, we extract the QoS
relevant data from the header and insert into one QoS value in order to
be more efficient on packet size. Thus for MPLS, we represent both EXP
fields in one QoS value, and both 802.1p priority and drop precedence in
one QoS value as indicated above.

For stack types not listed here, for example, 3 or more MPLS tags, SF
would insert IMPLS/EMPLS several times with each layer in the stack
indicating EXP Qos for that layer.















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     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|C|U|U|U|U|U|U|   Length  |U|U|U|U|Type=2 | NextProto=0x0 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path ID                      | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Metadata Class        |   Type=QoS(3) |U|     Len     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |U|U|T|U|U|U|SSI|  Stamping SI  |           Flow ID             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |              Reference Time (T bit is set)                    |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |U|U|U|U|U|U|U|U|  Stamping SI  |         Unassigned            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |   QT  |    QoS Value  |U|U|U|E|  QT   | QoS Value     |U|U|U|E|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |U|U|U|U|U|U|U|U|  Stamping SI  |          Unassigned           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |   QT  |   QoS Value   |U|U|U|E|  QT   | QoS Value     |U|U|U|E|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       Figure 9: NSH QoS Configuration Encapsulation (Extended Mode)

   The encapsulation in Figure 10 is very similar to that detailed in
   Section 4.1 with the following exceptions:

   - I and E bits are not required as we wish to examine the full QoS
      stack at ingress and egress at every SF.

   - Syn status bits are not required.

   - The QT (QoS Type) and QoS value are as outlined in the table
      above.

   - The E bit at the tail of each QoS context field indicates if this
      is the last egress QoS-stamp for a given SF. This should coincide
      with SI=0 at the LSN, whereby the packet is truncated and the NSH
      MD sent to the KPIDB and the subscriber raw IP packet forwarded to
      the underlay next hop.


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   Note: It is possible to compress the frame structure to better
   utilize the header, but this would come at the expense of crossing
   byte boundaries. For ease of implementation, and that QoS-stamping is
   applied on an extremely small subset of user plane traffic, we
   believe the above structure is a pragmatic compromise between header
   efficiency and ease of implementation.

4.2. KPI-stamping Encapsulation (Detection Mode)

   The format of the NSH MD type 2 KPI-stamping TLV (detection mode) is
   shown in Figure 11.

   This TLV is used for KPI anomaly detection. Upon detecting a problem
   or an anomaly it will be possible to enable the use of KPI-stamping
   extended encapsulations, which will provide more detailed analysis.



     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|Type=2 | Next Protocol |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Service Path Identifier              | Service Index |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Metadata Class         | Type=Det(1)   |U|    Length   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   KPI Type    |      Stamping SI      |          Flow ID      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Threshold KPI Value                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Ingress KPI-stamp                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        Figure 10: Generic NSH KPI Encapsulation (Detection Mode)


   The following fields are defined in the KPI TSD metadata:









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   o    KPI Type: determines the type of KPI-stamp that is included in
      this metadata field.
      If a receiver along the path does not understand the KPI Type it
      will pass the packet transparently and not drop.
      The supported values of the KPI Type are:
      0x0 Timestamp
      0x1 QoS-stamp

   o    Threshold KPI Value: In the first header the SFC classifier may
      program a KPI threshold value. This is a value that when exceeded,
      requires the SF to insert the current SI value into the SI field.
      The KPI type is the type of KPI stamp inserted into the header as
      per section 9.

   o    Stamping SI: Service Identifier of the SF when the Threshold
      above is exceeded.

   o    Flow ID: The flow ID is inserted into the header by the SFC
      classifier in order to correlate flow data in the KPIDB for
      offline analysis.

   o    Ingress KPI-stamp: The last 8 octets are reserved for the KPI-
      stamp. This is the KPI value at the chain ingress at the SFC
      classifier. Depending on the KPI Type, the KPI-stamp either
      includes a timestamp or a QoS-stamp.
      If the KPI Type is Timestamp, then the Ingress KPI-stamp field
      contains a timestamp in 64-bit NTP timestamp format. If the KPI
      Type is QoS-stamp, then the format of the 64-bit Ingress KPI-stamp
      is as follows.

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   QT  |    QoS Value  |              Unassigned               |
    +-+-+-+-+-+-+-+-+-+-+-+-+                                       +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 11: QoS-stamp Format (Detection Mode)


   As an example operation, say we are using KPI type 0x01 (timestamp)
   when a service function (SFn) receives the packet it can compare
   current local timestamp (it first checks that it is synchronized to
   network PRC) with chain ingress timestamp to calculate the latency in
   the chain. If this value exceeds the timestamp threshold, it then
   inserts its SI and returns the NSH to the KPIDB. This effectively



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   tells the system that at SFn the packet violated the KPI threshold.
   Please refer to figure 9 for timestamp format.

   When this occurs the SFC control plane system would then invoke the
   KPI extended mode, which uses a more sophisticated (and intrusive)
   method to isolate KPI violation root cause as described below.

   Note: Whilst detection mode is a valuable tool for latency actions,
   the authors feel that it is not justified to build the logic into the
   KPI system for QoS configuration. As QoS-stamping is done
   infrequently and on a tiny percentage of user plane, it is more
   practical to use extended mode only for service chain QoS
   verification.



5. Hybrid Models

   A hybrid chain may be defined as a chain whereby there is a mix of
   NSH-aware and NSH-unaware SFs.

Example 1. PNF in the middle

        Stamp
     Controller
         |                                                      KPIDB
         | SCP Interface                                        |
       ,---.             ,---.              ,---.              ,---.
      /     \           /     \            /     \            /     \
     (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
      \ FSN /           \     /            \ PNF1/            \ LSN /
       `---'             `---'              `---'              `---'
                Figure 12: Hybrid chain with PNF in middle

   In this example the FSN begins operation and sets the SI to 3, SF1
   decrements this to 2 and passes the packet to an SFC proxy (not
   shown).

   The SFC proxy strips the NSH and passes to the PNF. On receipt back
   from the PNF, the proxy decrements the SI and passes the packet onto
   the LSN with a SI=1.

   After the LSN processes the traffic it knows it is the last node on
   the chain from the SI value and exports the entire NSH and all
   metadata to the KPIDB. The payload is forwarded to the next hop on


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   the underlay minus the NSH. The stamping information packet may be
   given a new SPI to act as a homing tag to transport the stamp data
   back to the KPIDB.

Example 2. PNF at the end

      Stamp
   Controller
         |                                                      KPIDB
         | SCP Interface                                        |
       ,---.             ,---.              ,---.              ,---.
      /     \           /     \            /     \            /     \
     (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  PNFN )
      \ FSN /           \     /            \ LSN /            \     /
       `---'             `---'              `---'              `---'
                  Figure 13: Hybrid Chain with PNF at end

   In this example the FSN begins operation and sets the SI to 3, the
   SSI field set to 0x1, and the type to 1. Thus, when SF2 receives the
   packet with SI=1, it understands that it is expected to take on the
   role of the LSN as it is the last NSH-aware node in the chain.

5.1. Targeted VNF Stamp

   For the majority of flows within the service chain, stamps (ingress,
   egress or both) will be carried out at each hop until the SI
   decrements to zero and the NSH and Stamp MD is exported to the KPIDB.
   There may exist however the need to just test a particular VNF
   (perhaps after a scale out operation, software upgrade or underlay
   change for example). In this case the FSN should mark the NSH as
   follows:

   SSI field is set to 0x2. Type is set to the expected SI at the SF in
   question. When outer SI is equal to the SSI, stamps are applied at SF
   ingress and egress, and the NSH and MD are exported to the KPIDB.



6. Fragmentation Considerations

   The method described in this document does not support fragmentation.
   The SC should return an error should a stamping request from an
   external system exceed MTU limits and require fragmentation.




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   Depending on the length of the payload and the type of KPI-stamp and
   chain length, this will vary for each packet.

   In most service provider architectures we would expect a SI << 10,
   and that may include some PNFs in the chain which do not add
   overhead. Thus for typical IMIX packet sizes we expect to able to
   perform timestamping on the vast majority of flows without
   fragmenting. Thus the classifier can have a simple rule to only allow
   KPI-stamping on packet sizes less than 1200 bytes for example.



7. Security Considerations

   The security considerations of NSH in general are discussed in
   [RFC8300].

   The use of in-band timestamping, as defined in this document, can be
   used as a means for network reconnaissance. By passively
   eavesdropping to timestamped traffic, an attacker can gather
   information about network delays and performance bottlenecks.

   The NSH timestamp is intended to be used by various applications to
   monitor the network performance and to detect anomalies. Thus, a man-
   in-the-middle attacker can maliciously modify timestamps in order to
   attack applications that use the timestamp values. For example, an
   attacker could manipulate the SFC classifier operation, such that it
   forwards traffic through 'better' behaving chains. Furthermore, if
   timestamping is performed on a fraction of the traffic, an attacker
   can selectively induce synthetic delay only to timestamped packets,
   causing systematic error in the measurements.

   Similarly, if an attacker can modify QoS stamps, erroneous values may
   be imported into the KPIDB, resulting is further misconfiguration and
   subscriber QoE impairment.

   An attacker that gains access to the SCP can enable time and QoS-
   stamping for all subscriber flows, thereby causing performance
   bottlenecks, fragmentation, or outages.

   As discussed in previous sections, NSH timestamping relies on an
   underlying time synchronization protocol. Thus, by attacking the time
   protocol an attack can potentially compromise the integrity of the
   NSH timestamp. A detailed discussion about the threats against time
   protocols and how to mitigate them is presented in [RFC7384].




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8. IANA Considerations

   This document makes no requests for IANA action,

9. Contributors

   This document originated as draft-browne-sfc-nsh-timestamp-00 and had
   the following co-authors and contributors. We would like to thank and
   recognize them and their contributions.

   Yoram Moses

   Technion

   moses@ee.technion.ac.il



   Brendan Ryan

   Intel Corporation

   brendan.ryan@intel.com



10. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.

   The authors gratefully acknowledge Mohamed Boucadair, Martin
   Vigoureux and Adrian Farrel for their thorough reviews and helpful
   comments.



11. References

11.1. Normative References

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

   [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>.


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   [RFC8174]    B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC
                 2119 Key Words", RFC8174, May 2017.

   [RFC8300]     Quinn, P., Elzur, U., Pignataro, C., "Network Service
                 Header (NSH)", RFC 8300, 2018.

11.2. Informative References

   [IEEE1588]    IEEE TC 9 Instrumentation and Measurement Society,
                 "1588 IEEE Standard for a Precision Clock
                 Synchronization Protocol for Networked Measurement and
                 Control Systems Version 2", IEEE Standard, 2008.

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

   [RFC5905]     Mills, D., Martin, J., Burbank, J., Kasch, W.,
                 "Network Time Protocol Version 4: Protocol and
                 Algorithms Specification", RFC 5905, June 2010.

   [RFC7384]     Mizrahi, T., "Security Requirements of Time Protocols
                 in Packet Switched Networks", RFC 7384, October 2014.

   [TS]          Mizrahi, T., Fabini, J., and A. Morton, "Guidelines
                 for Defining Packet Timestamps", draft-ietf-ntp-
                 packet-timestamps (work in progress), 2018.

   [Y.1731]     ITU-T Recommendation G.8013/Y.1731, "OAM Functions and
                 Mechanisms for Ethernet-based Networks", August 2015.

   [Y.1564]     ITU-T Recommendation Y.1564, "Ethernet service
                 activation test methodology", March 2011.

   [G.8261]     ITU-T Recommendation G.8261/Y.1361, "Timing and
                 synchronization aspects in packet networks", August
                 2013.

   [G.8262]     ITU-T Recommendation G.8262/Y.1362, "Timing
                 characteristics of a synchronous Ethernet equipment
                 slave clock", January 2015.

   [G.8264]     ITU-T Recommendation G.8264/Y.1364, "Distribution of
                 timing information through packet networks", May 2014.

   [I-D.ippm.ioam]



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                 Brockners, Bhandari et al. "Data Fields for In-situ OAM"
                 draft-ietf-ippm-ioam-data-03 (work in progress), June
                 2018



Authors' Addresses

   Rory Browne
   Intel
   Dromore House
   Shannon
   Co.Clare
   Ireland

   Email: rory.browne@intel.com



   Andrey Chilikin
   Intel
   Dromore House
   Shannon
   Co.Clare
   Ireland

   Email: andrey.chilikin@intel.com



   Tal Mizrahi
   Huawei Network.IO Innovation Lab
   Israel

   Email: tal.mizrahi.phd@gmail.com













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