Independent Submission                                         R. Browne
Request for Comments: 8592                                   A. Chilikin
Category: Informational                                            Intel
ISSN: 2070-1721                                               T. Mizrahi
                                        Huawei Network.IO Innovation Lab
                                                                May 2019

                Key Performance Indicator (KPI) Stamping
                  for the Network Service Header (NSH)


   This document describes methods of carrying Key Performance
   Indicators (KPIs) using the Network Service Header (NSH).  These
   methods 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 document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see 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

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
   ( 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.

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Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
      2.1. Requirements Language ......................................3
      2.2. Definition of Terms ........................................3
           2.2.1. Terms Defined in This Document ......................4
      2.3. Abbreviations ..............................................5
   3. NSH KPI Stamping: An Overview ...................................6
      3.1. Prerequisites ..............................................7
      3.2. Operation ..................................................9
           3.2.1. Flow Selection ......................................9
           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 Stamping .....................................23
   6. Fragmentation Considerations ...................................23
   7. Security Considerations ........................................24
   8. IANA Considerations ............................................24
   9. References .....................................................25
      9.1. Normative References ......................................25
      9.2. Informative References ....................................25
   Acknowledgments ...................................................27
   Contributors ......................................................27
   Authors' Addresses ................................................27

1.  Introduction

   The Network Service Header (NSH), as defined by [RFC8300], specifies
   a method for steering 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.

   The 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.

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   This document describes generic methods to monitor and debug Service
   Function Chains (SFCs) in terms of latency and QoS marking of the
   flows within an SFC.  These are referred to as "detection mode" and
   "extended mode" and are explained in Section 4.

   The methods described in this document are compliant with hybrid
   architectures in which Virtual Network Functions (VNFs) and Physical
   Network Functions (PNFs) are freely mixed in the SFC.  These methods
   also provide flexibility for monitoring the performance and
   configuration of an entire chain or parts thereof as desired.  These
   methods are extensible to monitoring other Key Performance Indicators
   (KPIs).  Please refer to [RFC7665] for an architectural context for
   this document.

   The methods described in this document are not Operations,
   Administration, and Maintenance (OAM) protocols such as [Y.1731].  As
   such, they do not define new OAM packet types or operations.  Rather,
   they monitor the SFC's performance and configuration for subscriber
   payloads and indicate subscriber QoE rather than out-of-band
   infrastructure metrics.  This document differs from [In-Situ-OAM] in
   the sense that it is specifically tied to NSH operations and is not
   generic in nature.

2.  Terminology

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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 also makes use of the terms defined in [RFC7665] and

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2.2.1.  Terms Defined in This Document

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

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

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

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

   Flow ID:  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.

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

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

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

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2.3.  Abbreviations

   DEI         Drop Eligible Indicator

   DSCP        Differentiated Services Code Point

   FSN         First Stamping Node

   KPI         Key Performance Indicator

   KPIDB       Key Performance Indicator Database

   LSN         Last Stamping Node

   MD          Metadata

   NFV         Network Function Virtualization

   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

   RSP         Rendered Service Path

   SC          Stamping Controller

   SCL         Service Classifier

   SCP         Stamping Control Plane

   SF          Service Function

   SFC         Service Function Chain

   SI          Service Index

   SSI         Stamp Service Index

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   TS          Timestamp

   VLAN        Virtual Local Area Network

   VNF         Virtual Network Function

3.  NSH KPI Stamping: An Overview

   A typical KPI-stamping architecture is presented in Figure 1.

         |                                                     KPIDB
         | SCP Interface                                        |
       ,---.             ,---.              ,---.              ,---.
      /     \           /     \            /     \            /     \
     (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
      \ FSN /           \     /            \     /            \ LSN /
       `---'             `---'              `---'              `---'

                Figure 1: Logical Roles in NSH KPI Stamping

   The 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 FSN and also for distributing the NSH-stamping policy into the
   service chain via the SCP interface.

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

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

   The FSN also writes the Reference Time value, a (possibly inaccurate)
   estimate of the current time of day, into the header, allowing the
   "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 are specific to the
   protocol used between the FSN and SC; these considerations are out of

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   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 and may be applied by a hardware device -- for
           example, 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 LSN should strip the entire NSH and forward the raw packet to the
   IP next hop as per [RFC8300].  The LSN also exports NSH-stamping
   information to the KPIDB for offline analysis; the LSN may export the
   stamping information of either (1) all packets or (2) 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 SI to zero.  Corner cases exist
   where this is not the case; see Section 5.

3.1.  Prerequisites

   Timestamping has its own set of prerequisites; however, these
   prerequisites are not required for QoS stamping.  In order to
   guarantee MD 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 a
   probable impact on throughput performance), 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

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

   Each SF SHOULD have Level A synchronization and MAY have Level B

   Level A requires each platform (including the SC) to synchronize its
   system real-time clock to an NTP server.  This is used to mark the MD
   in the chain, using the Reference Time field in the NSH KPI stamp
   header (Section 4.1).  This timestamp is inserted into 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 MD retrieval.

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

   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 RSP.  Indeed, the timestamp MD can
   indicate where a chain has been moved due to a resource starvation
   event as indicated in Figure 2, between VNF3 and VNF4 at time B.

      |                                  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

   For QoS stamping, it is desired that the SCL or FSN be synchronized
   in order to provide a 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 operations, as described below.

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

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   |                                  xy
   |                           xy           x = ingress QoS sum
   |                    xv                  v = egress QoS sum
   |             xv                         y = egress QoS sum mismatch
   |      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, or DSCP(s), these values are used to compare
   the 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 (where 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 cases when an SF re-marks QoS
   fields deliberately and thus does not flag an issue for desired

3.2.  Operation

   KPI-stamping detection mode uses MD Type 2 as defined in [RFC8300].
   This involves the SFC classifier stamping the flow at the chain
   ingress and no subsequent stamps being applied; rather, each upstream
   SF 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 4.2.

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:Flow ID".
   The SC should map these pairs to unique values presented as Flow IDs
   per service chain within the NSH TLV specified in this document (see
   Section 4).  The SC should instruct the FSN to initiate timestamping

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   on flow table match.  The SC may also tell the classifier the
   duration of the timestamping operation, by either the number of
   packets in the flow or a certain time duration.

   In this way, the system can monitor the performance of all en-route
   traffic, an individual subscriber in a chain, or just a specific
   application or 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 a source IP address with a 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
   address with an International Mobile Subscriber Identity (IMSI) will
   be different from how a Customer Premises Equipment (CPE) entity with
   a Network Address Translation (NAT) function may be chained in an
   enterprise NFV application.

3.2.2.  SCP Interface

   An 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.

   o  Communicate which chains and flows to stamp.  This can be a
      specific "SPI:Flow ID" combination or can 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
      ingress and egress, or specific).

   o  Indicate when to stop stamping (after either a certain number of
      packets or a certain time 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.

   The exact specification of SCP is left for further study.

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3.3.  Performance Considerations

   This document does not mandate a specific stamping implementation
   method; thus, NSH KPI stamping can be performed by either hardware
   mechanisms or 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 methods 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 a 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 will have an impact on the
   performance of the chain itself whilst under investigation.  This
   impact will be dependent on vendor implementations and is outside the
   scope of this document.

   For QoS stamping, the methods described here are even less intrusive,
   as typically packets are only QoS stamped periodically (perhaps once
   per day) to check service chain configuration per QoS class.

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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
     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 the header that the FSN must implement are as

   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].

   o  The Type field may have one of the following values; the content
      of the Variable Length KPI Metadata header and TLV(s) field
      depends on the Type value:

      *  Type = 0x01 (Det): Detection

      *  Type = 0x02 (TS): Timestamp Extended

      *  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.

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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
     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 the extended KPI MD: a timestamp type and a
   QoS-stamp type.

   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

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

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

   The SSI (Stamping SI) contains the SI used for KPI stamping and is
   described in the 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], as 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 64-Bit Timestamp Format (RFC 5905)

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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)

   The FSN KPI stamp MD starts with the Stamping Configuration Header.
   This header contains the I, E, and T bits, and the SSI.

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

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

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

   o  0x0: KPI stamp mode.  No SI is specified in the Stamping SI field.

   o  0x1: KPI stamp hybrid mode is selected.  The Stamping SI field
      contains the LSN SI.  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 regarding which SF should act as
      the LSN.

   o  0x2: KPI stamp Specific mode is selected.  The Stamping SI field
      contains the targeted SI.  In this case, the Stamping SI field
      indicates which SF is to be stamped.  Both Ingress stamps and
      Egress stamps are performed when the SI=SSI in 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 QoS-stamping mode.

   Each stamping node adds stamp MD that consists of the Stamping
   Reporting Header and timestamps.

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

   The I bit should be set if the 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

   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

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

   The outer SI value is copied into the stamp MD as the Stamping SI to
   help cater to 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 SI between timestamps
   will indicate this.

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

4.1.2.  NSH QoS-Stamping Encapsulation (Extended Mode)

   Packets have a variable QoS stack.  For example, the same payload IP
   can have a very different stack in the access part of the network
   than the core.  This is most apparent in mobile networks where, for
   example, in an access circuit we would have an infrastructure IP
   header (DSCP) composed of two layers -- one based on transport and
   the other based on IPsec -- in addition to multiple MPLS and VLAN
   tags.  The same packet, as it leaves the Packet Data Network (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 of
   variable lengths and types.  Also, they can be changed on the
   underlay at any time without the knowledge of the SFC system.
   Therefore, each SF must be able to ascertain and record its ingress
   and egress QoS configuration on the fly.

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   The suggested QoS Type (QT) and lengths are listed below.

    QoS Type  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    Two Ingress Labels (2x EXP)

    EMPLS     0x08     6 Bits    Two 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 relevant
   QoS data from the header and insert it into one QoS value in order to
   be more efficient in terms of packet size.  Thus, for MPLS, we
   represent both experimental bits (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, three or more MPLS
   tags), the 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 9 is very similar to the encapsulation
   detailed in Section 4.1.1, with the following exceptions:

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

   o  SYN status bits are not required.

   o  The QT and QoS values are as outlined in the list above.

   o  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, the NSH MD
      is sent to the KPIDB, and the subscriber's raw IP packet is
      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 so that
   QoS stamping is applied on an extremely small subset of user-plane
   traffic, we believe that 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 10.

   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
     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 KPIDB MD:

   o  KPI Type: This field determines the type of KPI stamp that is
      included in this MD.  If a receiver along the path does not
      understand the KPI type, it will pass the packet on transparently
      and will not drop it.  The supported values of KPI Type are:

      *  0x0: Timestamp

      *  0x1: QoS stamp

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   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 Figure 10.

   o  Stamping SI: This is the Service Identifier of the SF when the
      above threshold value 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 includes
      either 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
     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, let's say we are using KPI type 0x01
   (Timestamp).  When an SF (say SFn) receives the packet, it can
   compare the current local timestamp (it first checks that it is
   synchronized to the network's PRC) with the 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 tells the system that at SFn the packet
   violated the KPI threshold.  Please refer to Figure 8 for the
   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 the root cause of the KPI violation, as described

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   Note: Whilst detection mode is a valuable tool for latency actions,
   the authors feel that building the logic into the KPI system for QoS
   configuration is not justified.  As QoS stamping is done infrequently
   and on a tiny percentage of the 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.

   Figure 12 shows an example of a hybrid chain with a PNF in the

         |                                                      KPIDB
         | SCP Interface                                        |
       ,---.             ,---.              ,---.              ,---.
      /     \           /     \            /     \            /     \
     (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
      \ FSN /           \     /            \ PNF1/            \ LSN /
       `---'             `---'              `---'              `---'

                Figure 12: Hybrid Chain with PNF in Middle

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

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

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

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   Figure 13 shows an example of a hybrid chain with a PNF at the end.

        |                                                      KPIDB
        | SCP Interface                                        |
      ,---.             ,---.              ,---.              ,---.
     /     \           /     \            /     \            /     \
    (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  PNFN )
     \ FSN /           \     /            \ LSN /            \     /
      `---'             `---'              `---'              `---'

                  Figure 13: Hybrid Chain with PNF at End

   In this example, the FSN begins its operation and sets the SI to 3.
   The SSI field is set to 0x1, and the type is set 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 Stamping

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

   o  The SSI field is set to 0x2.

   o  Type is set to the expected SI at the SF in question.

   o  When the outer SI is equal to the SSI, stamps are applied at the
      SF ingress and egress, and the NSH and MD are exported to the

6.  Fragmentation Considerations

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

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

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   In most service provider architectures, we would expect SI << 10,
   which may include some PNFs in the chain that do not add overhead.
   Thus, for typical Internet Mix (IMIX) packet sizes [RFC6985], we
   expect to be able to perform timestamping on the vast majority of
   flows without fragmentation.  Thus, the classifier can apply a simple
   rule that only allows KPI stamping on packet sizes less than 1200
   bytes, for example.

7.  Security Considerations

   The security considerations for the NSH in general are discussed in

   In-band timestamping, as defined in this document, can be used as a
   means for network reconnaissance.  By passively eavesdropping on
   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 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-behaved" chains.  Furthermore, if
   timestamping is performed on a fraction of the traffic, an attacker
   can selectively induce synthetic delay only to timestamped packets
   and can systematically trigger measurement errors.

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

   An attacker that gains access to the SCP can enable timestamping 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 attacker 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

8.  IANA Considerations

   This document has no IANA actions.

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9.  References

9.1.  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,

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              RFC 2119 Key Words", BCP 14, RFC 8174,
              DOI 10.17487/RFC8174, May 2017,

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,

9.2.  Informative References

              IEEE, "IEEE Standard for a Precision Clock Synchronization
              Protocol for Networked Measurement and Control Systems",
              IEEE Standard 1588,

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,

   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
              Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
              October 2014, <>.

   [RFC6985]  Morton, A., "IMIX Genome: Specification of Variable Packet
              Sizes for Additional Testing", RFC 6985,
              DOI 10.17487/RFC6985, July 2013,

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   [Y.1731]   ITU-T Recommendation G.8013/Y.1731, "Operations,
              administration and maintenance (OAM) functions and
              mechanisms for Ethernet-based networks", August 2015,

   [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", November 2018,

   [G.8264]   ITU-T Recommendation G.8264/Y.1364, "Distribution of
              timing information through packet networks", August 2017,

              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., Chang, R., Bernier, D., and J. Lemon, "Data Fields for
              In-situ OAM", Work in Progress,
              draft-ietf-ippm-ioam-data-05, March 2019.

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


   This document originated as draft-browne-sfc-nsh-timestamp-00; the
   following people were coauthors of that draft.  We would like to
   thank them and recognize them for their contributions.

   Yoram Moses

   Brendan Ryan
   Intel Corporation

Authors' Addresses

   Rory Browne
   Dromore House
   Co. Clare


   Andrey Chilikin
   Dromore House
   Co. Clare


   Tal Mizrahi
   Huawei Network.IO Innovation Lab


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