ippm                                                        F. Brockners
Internet-Draft                                               S. Bhandari
Intended status: Standards Track                            C. Pignataro
Expires: May 3, September 6, 2018                                         Cisco
                                                              H. Gredler
                                                            RtBrick Inc.
                                                                J. Leddy
                                                                 Comcast
                                                               S. Youell
                                                                    JPMC
                                                              T. Mizrahi
                                                                 Marvell
                                                                D. Mozes
                                              Mellanox Technologies Ltd.

                                                             P. Lapukhov
                                                                Facebook
                                                                R. Chang
                                                       Barefoot Networks
                                                              D. Bernier
                                                             Bell Canada
                                                        October 30, 2017
                                                                J. Lemon
                                                                Broadcom
                                                           March 5, 2018

                      Data Fields for In-situ OAM
                      draft-ietf-ippm-ioam-data-01
                      draft-ietf-ippm-ioam-data-02

Abstract

   In-situ Operations, Administration, and Maintenance (IOAM) records
   operational and telemetry information in the packet while the packet
   traverses a path between two points in the network.  This document
   discusses the data fields and associated data types for in-situ OAM.
   In-situ OAM data fields can be embedded into a variety of transports
   such as NSH, Segment Routing, Geneve, native IPv6 (via extension
   header), or IPv4.  In-situ OAM can be used to complement OAM
   mechanisms based on e.g.  ICMP or other types of probe packets.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, September 6, 2018.

Copyright Notice

   Copyright (c) 2017 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Scope, Applicability, and Assumptions . . . . . . . . . . . .   4
   4.  IOAM Data Types and Formats . . . . . . . . . . . . . . . . .   5
     4.1.  IOAM Tracing Options  . . . . . . . . . . . . . . . . . .   6
       4.1.1.  Pre-allocated and Incremental Trace Option Options . . . . .   8
       4.1.2.  IOAM node data fields and associated formats  . . . .  12
       4.1.3.  Examples of IOAM node data  . . . .   8
       4.1.2.  Incremental Trace . . . . . . . . .  17
     4.2.  IOAM Proof of Transit Option  . . . . . . . . . . . . . .  11
       4.1.3.  19
       4.2.1.  IOAM node data fields and associated formats Proof of Transit Type 0  . . . .  14
       4.1.4.  Examples of . . . . . . . .  20
     4.3.  IOAM node data Edge-to-Edge Option  . . . . . . . . . . . . .  19
     4.2.  IOAM Proof of Transit Option . . .  22
   5.  Timestamp Formats . . . . . . . . . . . . . . . . . .  21
     4.3.  IOAM Edge-to-Edge Option . . . .  23
     5.1.  PTP Truncated Timestamp Format  . . . . . . . . . . . . .  23
   5.
     5.2.  NTP 64-bit Timestamp Format . . . . . . . . . . . . . . .  25
     5.3.  POSIX-based Timestamp Format  . . . . . . . . . . . . . .  26
   6.  IOAM Data Export  . . . . . . . . . . . . . . . . . . . . . .  23
   6.  27
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     6.1.  28
     7.1.  Creation of a new In-Situ OAM  Protocol Parameters
           Registry (IOAM) Protocol Parameters IANA registry . . . .  28
     7.2.  IOAM Type Registry  . . . . . . . . . . . . . . . . .  24
     6.2. . .  28
     7.3.  IOAM Trace Type Registry  . . . . . . . . . . . . . . . .  24
     6.3.  29
     7.4.  IOAM Trace Flags Registry . . . . . . . . . . . . . . . .  24
     6.4.  29
     7.5.  IOAM POT Type Registry  . . . . . . . . . . . . . . . . .  25
     6.5.  29
     7.6.  IOAM POT Flags Registry . . . . . . . . . . . . . . . . .  29
     7.7.  IOAM E2E Type Registry  . . . . . . . . . . . . . . . . .  25
   7.  29
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  25
   8.  29
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   9.  30
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   10.  30
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     10.1.  30
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     10.2.  30
     11.2.  Informative References . . . . . . . . . . . . . . . . .  26  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27  32

1.  Introduction

   This document defines data fields for "in-situ" Operations,
   Administration, and Maintenance (IOAM).  In-situ OAM records OAM
   information within the packet while the packet traverses a particular
   network domain.  The term "in-situ" refers to the fact that the OAM
   data is added to the data packets rather than is being sent within
   packets specifically dedicated to OAM.  A discussion of the
   motivation and requirements for in-situ OAM can be found in
   [I-D.brockners-inband-oam-requirements].  IOAM is to complement
   mechanisms such as Ping or Traceroute, or more recent active probing
   mechanisms as described in [I-D.lapukhov-dataplane-probe].  In terms
   of "active" or "passive" OAM, "in-situ" OAM can be considered a
   hybrid OAM type.  While no extra packets are sent, IOAM adds
   information to the packets therefore cannot be considered passive.
   In terms of the classification given in [RFC7799] IOAM could be
   portrayed as Hybrid Type 1.  "In-situ" mechanisms do not require
   extra packets to be sent and hence don't change the packet traffic
   mix within the network.  IOAM mechanisms can be leveraged where
   mechanisms using e.g.  ICMP do not apply or do not offer the desired
   results, such as proving that a certain traffic flow takes a pre-
   defined path, SLA verification for the live data traffic, detailed
   statistics on traffic distribution paths in networks that distribute
   traffic across multiple paths, or scenarios in which probe traffic is
   potentially handled differently from regular data traffic by the
   network devices.

2.  Conventions

   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 [RFC2119].

   Abbreviations used in this document:

   E2E        Edge to Edge

   Geneve:    Generic Network Virtualization Encapsulation
              [I-D.ietf-nvo3-geneve]

   IOAM:      In-situ Operations, Administration, and Maintenance
   MTU:       Maximum Transmit Unit

   NSH:       Network Service Header [I-D.ietf-sfc-nsh]

   OAM:       Operations, Administration, and Maintenance

   POT:       Proof of Transit

   SFC:       Service Function Chain

   SID:       Segment Identifier

   SR:        Segment Routing

   VXLAN-GPE: Virtual eXtensible Local Area Network, Generic Protocol
              Extension [I-D.ietf-nvo3-vxlan-gpe]

3.  Scope, Applicability, and Assumptions

   IOAM deployment assumes a set of constraints, requirements, and
   guiding principles which are described in this section.

   Scope: This document defines the data fields and associated data
   types for in-situ OAM.  The in-situ OAM data field can be transported
   by a variety of transport protocols, including NSH, Segment Routing,
   Geneve, IPv6, or IPv4.  Specification details for these different
   transport protocols are outside the scope of this document.

   Deployment domain (or scope) of in-situ OAM deployment: IOAM is a
   network domain focused feature, with "network domain" being a set of
   network devices or entities within a single administration.  For
   example, a network domain can include an enterprise campus using
   physical connections between devices or an overlay network using
   virtual connections / tunnels for connectivity between said devices.
   A network domain is defined by its perimeter or edge.  Designers of
   carrier protocols for IOAM must specify mechanisms to ensure that
   IOAM data stays within an IOAM domain.  In addition, the operator of
   such a domain is expected to put provisions in place to ensure that
   IOAM data does not leak beyond the edge of an IOAM domain, e.g. using
   for example packet filtering methods.  The operator should consider
   potential operational impact of IOAM to mechanisms such as ECMP
   processing (e.g.  load-balancing schemes based on packet length could
   be impacted by the increased packet size due to IOAM), path MTU (i.e.
   ensure that the MTU of all links within a domain is sufficiently
   large to support the increased packet size due to IOAM) and ICMP
   message handling (i.e. in case of a native IPv6 transport, IOAM
   support for ICMPv6 Echo Request/Reply could desired which would
   translate into ICMPv6 extensions to enable IOAM data fields to be
   copied from an Echo Request message to an Echo Reply message).

   IOAM control points: IOAM data fields are added to or removed from
   the live user traffic by the devices which form the edge of a domain.
   Devices within an IOAM domain can update and/or add IOAM data-fields.
   Domain edge devices can be hosts or network devices.

   Traffic-sets that IOAM is applied to: IOAM can be deployed on all or
   only on subsets of the live user traffic.  It SHOULD be possible to
   enable IOAM on a selected set of traffic (e.g., per interface, based
   on an access control list or flow specification defining a specific
   set of traffic, etc.)  The selected set of traffic can also be all
   traffic.

   Encapsulation independence: Data formats for IOAM SHOULD be defined
   in a transport-independent manner.  IOAM applies to a variety of
   encapsulating protocols.  A definition of how IOAM data fields are
   carried by different transport protocols is outside the scope of this
   document.

   Layering: If several encapsulation protocols (e.g., in case of
   tunneling) are stacked on top of each other, IOAM data-records could
   be present at every layer.  The behavior follows the ships-in-the-
   night model.

   Combination with active OAM mechanisms: IOAM should be usable for
   active network probing, enabling for example a customized version of
   traceroute.  Decapsulating IOAM nodes may have an ability to send the
   IOAM information retrieved from the packet back to the source address
   of the packet or to the encapsulating node.

   IOAM implementation: The IOAM data-field definitions take the
   specifics of devices with hardware data-plane and software data-plane
   into account.

4.  IOAM Data Types and Formats

   This section defines IOAM data types and data fields and associated
   data types required for IOAM.  The different uses of IOAM require

   To accommodate the
   definition of different types uses of data.  The IOAM, IOAM data fields fall into
   different categories, e.g. edge-to-edge, per node tracing, or for the
   data being carried corresponds to the three main categories
   proof of transit.  In IOAM
   data defined in [I-D.brockners-inband-oam-requirements], which are:
   edge-to-edge, per node, and these categories are referred to as IOAM-
   Types.  A common registry is maintained for selected nodes only.

   Transport options IOAM-Types, see
   Section 7.2 for details.  Corresponding to these IOAM-Types,
   different IOAM data fields are outside the scope of this memo,
   and are discussed in [I-D.brockners-inband-oam-transport]. defined.  IOAM data fields are fixed length data fields.  A bit field determines the set
   of OAM data fields embedded in can be
   encapsulated into a packet.  Depending on the type variety of protocols, such as NSH, Geneve, IPv6,
   etc.  The definition of
   the encapsulation, a counter field indicates how many IOAM data fields are
   included in a particular packet. encapsulated into
   other protocols is outside the scope of this document.

   IOAM is expected to be deployed in a specific domain rather than on
   the overall Internet.  The part of the network which employs IOAM is
   referred to as the "IOAM-domain".  IOAM data is added to a packet
   upon entering the IOAM-domain and is removed from the packet when
   exiting the domain.  Within the IOAM-domain, the IOAM data may be
   updated by network nodes that the packet traverses.  The device which
   adds an IOAM data container to the packet to capture IOAM data is
   called the "IOAM encapsulating node", whereas the device which
   removes the IOAM data container is referred to as the "IOAM
   decapsulating node".  Nodes within the domain which are aware of IOAM
   data and read and/or write or process the IOAM data are called "IOAM
   transit nodes".  IOAM nodes which add or remove the IOAM data
   container can also update the IOAM data fields at the same time.  Or
   in other words, IOAM encapsulation or decapsulating nodes can also
   serve as IOAM transit nodes at the same time.  Note that not every
   node in an IOAM domain needs to be an IOAM transit node.  For
   example, a Segment Routing deployment might require the segment
   routing path to be verified.  In that case, only the SR nodes would
   also be IOAM transit nodes rather than all nodes.

4.1.  IOAM Tracing Options

   "IOAM tracing data" is expected to be collected at every node that a
   packet traverses to ensure visibility into the entire path a packet
   takes within an IOAM domain, i.e., in a typical deployment all nodes
   in an in-situ OAM-domain would participate in IOAM and thus be IOAM
   transit nodes, IOAM encapsulating or IOAM decapsulating nodes.  If
   not all nodes within a domain are IOAM capable, IOAM tracing
   information will only be collected on those nodes which are IOAM
   capable.  Nodes which are not IOAM capable will forward the packet
   without any changes to the IOAM data fields.  The maximum number of
   hops and the minimum path MTU of the IOAM domain is assumed to be
   known.

   To optimize hardware and software implementations tracing is defined
   as two separate options.  Any deployment MAY choose to configure and
   support one or both of the following options.  An implementation of
   the transport protocol that carries these in-situ OAM data MAY choose
   to support only one of the options.  In the event that both options
   are utilized at the same time, the Incremental Trace Option MUST be
   placed before the Pre-allocated Trace Option.  Given that the
   operator knows which equipment is deployed in a particular IOAM, the
   operator will decide by means of configuration which type(s) of trace
   options will be enabled for a particular domain.

   Pre-allocated Trace Option:  This trace option is defined as a
      container of node data fields with pre-allocated space for each
      node to populate its information.  This option is useful for
      software implementations where it is efficient to allocate the
      space once and index into the array to populate the data during
      transit.  The IOAM encapsulating node allocates the option header
      and sets the fields in the option header.  The in situ OAM
      encapsulating node allocates an array which is used to store
      operational data retrieved from every node while the packet
      traverses the domain.  IOAM transit nodes update the content of
      the array.  A pointer which is part of the IOAM trace data points
      to the next empty slot in the array, which is where the next IOAM
      transit node fills in its data.

   Incremental Trace Option:  This trace option is defined as a
      container of node data fields where each node allocates and pushes
      its node data immediately following the option header.  The
      maximum length of the node data list is written into the option
      header.  This type
      of trace recording is useful for some of the hardware
      implementations as this eliminates the need for the transit
      network elements to read the full array in the option and allows
      for arbitrarily long packets as the MTU allows.  The in-
      situ in-situ OAM
      encapsulating node allocates the option header.  The in-
      situ in-situ OAM
      encapsulating node based on operational state and configuration
      sets the fields in the header to that control what node data fields
      should be collected, and how large the node data list can grow.  IOAM
      The in-situ OAM transit nodes push their node data to the node
      data list list, decrease the remaining length available to subsequent
      nodes, and increment adjust the number of node data
      fields lengths and possibly checksums in the header. outer
      headers.

   Every node data entry is to hold information for a particular IOAM
   transit node that is traversed by a packet.  The in-situ OAM
   decapsulating node removes the IOAM data and processes and/or exports
   the metadata.  IOAM data uses its own name-space for information such
   as node identifier or interface identifier.  This allows for a
   domain-specific definition and interpretation.  For example: In one
   case an interface-id could point to a physical interface (e.g., to
   understand which physical interface of an aggregated link is used
   when receiving or transmitting a packet) whereas in another case it
   could refer to a logical interface (e.g., in case of tunnels).

   The following IOAM data is defined for IOAM tracing:

   o  Identification of the IOAM node.  An IOAM node identifier can
      match to a device identifier or a particular control point or
      subsystem within a device.

   o  Identification of the interface that a packet was received on,
      i.e. ingress interface.

   o  Identification of the interface that a packet was sent out on,
      i.e. egress interface.

   o  Time of day when the packet was processed by the node.  Different
      definitions of processing time are feasible and expected, though
      it is important that all devices of an in-situ OAM domain follow
      the same definition.

   o  Generic data: Format-free information where syntax and semantic of
      the information is defined by the operator in a specific
      deployment.  For a specific deployment, all IOAM nodes should
      interpret the generic data the same way.  Examples for generic
      IOAM data include geo-location information (location of the node
      at the time the packet was processed), buffer queue fill level or
      cache fill level at the time the packet was processed, or even a
      battery charge level.

   o  A mechanism to detect whether IOAM trace data was added at every
      hop or whether certain hops in the domain weren't in-situ OAM
      transit nodes.

   The "node data list" array in the packet is populated iteratively as
   the packet traverses the network, starting with the last entry of the
   array, i.e., "node data list [n]" is the first entry to be populated,
   "node data list [n-1]" is the second one, etc.

4.1.1.  Pre-allocated and Incremental Trace Option
   In-situ Options

   The in-situ OAM pre-allocated trace option: option and the in-situ OAM
   incremental trace option have similar formats.  Except where noted
   below, the internal formats and fields of the two trace options are
   identical.

   Pre-allocated and incremental trace option header: headers:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        IOAM-Trace-Type       |NodeLen|  Flags        | Octets-left NodeLen | Flags |RemainingLen |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Pre-allocated Trace Option Data

   The trace option data MUST be 4-octet aligned:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
   |                                                               |  |
   |                        node data list [0]                     |  |
   |                                                               |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  D
   |                                                               |  a
   |                        node data list [1]                     |  t
   |                                                               |  a
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                             ...                               ~  S
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  p
   |                                                               |  a
   |                        node data list [n-1]                   |  c
   |                                                               |  e
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
   |                                                               |  |
   |                        node data list [n]                     |  |
   |                                                               |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

   IOAM-Trace-Type:  A 16-bit identifier which specifies which data
      types are used in this node data list.

      The IOAM-Trace-Type value is a bit field.  The following bit
      fields are defined in this document, with details on each field
      described in the Section 4.1.3. 4.1.2.  The order of packing the data
      fields in each node data element follows the bit order of the
      IOAM-Trace-Type field, as follows:

      Bit 0    (Most significant bit) When set indicates presence of
               Hop_Lim and node_id in the node data.

      Bit 1    When set indicates presence of ingress_if_id and
               egress_if_id (short format) in the node data.

      Bit 2    When set indicates presence of timestamp seconds in the
               node data data.

      Bit 3    When set indicates presence of timestamp nanoseconds subseconds in
               the node data.

      Bit 4    When set indicates presence of transit delay in the node
               data.

      Bit 5    When set indicates presence of app_data (short format) in
               the node data.

      Bit 6    When set indicates presence of queue depth in the node
               data.

      Bit 7    When set indicates presence of variable length Opaque
               State Snapshot field.

      Bit 8    When set indicates presence of Hop_Lim and node_id in
               wide format in the node data.

      Bit 9    When set indicates presence of ingress_if_id and
               egress_if_id in wide format in the node data.

      Bit 10   When set indicates presence of app_data wide in the node
               data.

      Bit 11   When set indicates presence of the Checksum Complement
               node data.

      Bit 12-15  Undefined in  Undefined.  An IOAM encapsulating node must set the
               value of each of these bits to 0.  If an IOAM transit
               node receives a packet with one or more of these bits set
               to 1, it must either:

               1.  Add corresponding node data filled with the reserved
                   value 0xFFFFFFFF, after the node data fields for the
                   IOAM-Trace-Type bits defined above, such that the
                   total node data added by this draft. node in units of
                   4-octets is equal to NodeLen, or

               2.  Not add any node data fields to the packet, even for
                   the IOAM-Trace-Type bits defined above.

      Section 4.1.3 4.1.2 describes the IOAM data types and their formats.
      Within an in-situ OAM domain possible combinations of these bits
      making the IOAM-Trace-Type can be restricted by configuration
      knobs.

   NodeLen:  4-bit  5-bit unsigned integer.  This field specifies the length of
      data added by each node in multiples of 4-octets.  For example, if
      3 IOAM-Trace-Type bits are set and none 4-octets, excluding the
      length of them is wide, then the
      NodeLen would be "Opaque State Snapshot" field.

      If IOAM-Trace-Type bit 7 is not set, then NodeLen specifies the
      actual length added by each node.  If IOAM-Trace-Type bit 7 is
      set, then the actual length added by a node would be (NodeLen +
      Opaque Data Length).

      For example, if 3 IOAM-Trace-Type bits are set and none of them
      are wide, then NodeLen would be 3.  If 3 IOAM-Trace-Type bits are
      set and 2 of them are wide, then the NodeLen would be 5.

      An IOAM encapsulating node must set NodeLen.

      A node receiving an IOAM Pre-allocated or Incremental Trace Option
      may rely on the NodeLen value, or it may ignore the NodeLen value
      and calculate the node length from the IOAM-Trace-Type bits.

   Flags  5-bit  4-bit field.  Following flags are defined:

      Bit 0  "Overflow" (O-bit) (most significant bit).  This bit is set
         by the network element if there is not enough number of octets
         left to record node data, no field is added and the overflow
         "O-bit" must be set to "1" in the header.  This is useful for
         transit nodes to ignore further processing of the option.

      Bit 1  "Loopback" (L-bit).  Loopback mode is used to send a copy
         of a packet back towards the source.  Loopback mode assumes
         that a return path from transit nodes and destination nodes
         towards the source exists.  The encapsulating node decides
         (e.g. using a filter) which packets loopback mode is enabled
         for by setting the loopback bit.  The encapsulating node also
         needs to ensure that sufficient space is available in the IOAM
         header for loopback operation.  The loopback bit when set
         indicates to the transit nodes processing this option to create
         a copy of the packet received and send this copy of the packet
         back to the source of the packet while it continues to forward
         the original packet towards the destination.  The source
         address of the original packet is used as destination address
         in the copied packet.  The address of the node performing the
         copy operation is used as the source address.  The L-bit MUST
         be cleared in the copy of the packet that a nodes node sends it back
         towards the source.  On its way back towards the source, the
         packet is processed like a regular packet with IOAM
         information.  Once the return packet reaches the IOAM domain
         boundary IOAM decapsulation occurs as with any other packet
         containing IOAM information.

      Bit 2-4 2-3  Reserved: Must be zero.

   Octets-left:

   RemainingLen:  7-bit unsigned integer.  It is  This field specifies the data
      space in multiples of 4-octets remaining for recording the node
      data, before the node data list is considered to have overflowed.
      When RemainingLen reaches 0, nodes are no longer allowed to add
      node data.  This  Given that the sender knows the minimum path MTU, the
      sender MAY set the initial value of RemainingLen according to the
      number of node data bytes allowed before exceeding the MTU.
      Subsequent nodes can carry out a simple comparison between
      RemainingLen and NodeLen, along with the length of the "Opaque
      State Snapshot" if applicable, to determine whether or not data
      can be added by this node.  When node data is added, the node MUST
      decrease RemainingLen by the amount of data added.  In the pre-
      allocated trace option, this is used as an offset in data space to
      record the node data element.

   Node data List [n]:  Variable-length field.  The type of which is
      determined by the IOAM-Trace-Type bit representing the n-th node
      data in the node data list.  The node data list is encoded
      starting from the last node data of the path.  The first element
      of the node data list (node data list [0]) contains the last node
      of the path while the last node data of the node data list (node
      data list[n]) contains the first node data of the path traced.  The  In
      the pre-allocated trace option, the index contained in "Octets-left"
      RemainingLen identifies the offset for current active node data to
      be populated.

4.1.2.  Incremental Trace Option
   In-situ OAM incremental trace option:

   In-situ OAM incremental trace option Header:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        IOAM-Trace-Type        |NodeLen|  Flags  | Max Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  IOAM Incremental Trace Option Data MUST be 4-octet aligned:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                        node data list [0]                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   | node data list [1]                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                             ...                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                        node fields and associated formats

   All the data list [n-1]                   |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   | fields MUST be 4-octet aligned.  If a node data list [n]                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IOAM-trace-type:  A 16-bit identifier which specifies which data
      types are used in this node is
   supposed to update an IOAM data list.

      The IOAM-Trace-Type value field is not capable of populating
   the value of a bit field.  The following bit
      fields are defined in this document, with details on each field
      described set in the Section 4.1.3.  The order of packing IOAM-Trace-Type, the data field value MUST
   be set to 0xFFFFFFFF for 4-octet fields or 0xFFFFFFFFFFFFFFFF for
   8-octet fields, indicating that the value is not populated, except
   when explicitly specified in each node data element follows the bit order field description below.

   Data field and associated data type for each of the
      IOAM-Trace-Type field, data field is
   shown below:

   Hop_Lim and node_id:  4-octet field defined as follows:

      Bit

    0    (Most significant bit) When set indicates presence of 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Hop_Lim and     |              node_id in the node data.

      Bit 1    When                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      Hop_Lim:  1-octet unsigned integer.  It is set indicates presence of ingress_if_id and
               egress_if_id (short format) to the Hop Limit
         value in the packet at the node that records this data.

      Bit 2    When set indicates presence of timestamp seconds in the
               node data.

      Bit 3    When set indicates presence of timestamp nanoseconds in  Hop
         Limit information is used to identify the node data.

      Bit 4    When set indicates presence location of transit delay in the node
               data.

      Bit 5    When set indicates presence of app_data
         in the node data.

      Bit 6    When set indicates presence of queue depth in communication path.  This is copied from the node
               data.

      Bit 7    When set indicates presence of variable length Opaque
               State Snapshot field.

      Bit 8    When set indicates presence of Hop_Lim and node_id wide lower
         layer, e.g., TTL value in the node data.

      Bit 9    When set indicates presence IPv4 header or hop limit field from
         IPv6 header of ingress_if_id and
               egress_if_id in wide format in the node data.

      Bit 10   When set indicates presence of app_data wide in packet when the node
               data.

      Bit 11   When set indicates presence packet is ready for
         transmission.  The semantics of the Checksum Complement
               node data.

      Bit 12-15  Undefined in this draft.

      Section 4.1.3 describes Hop_Lim field depend on the
         lower layer protocol that IOAM data types is encapsulated over, and their formats.

   NodeLen:  4-bit
         therefore its specific semantics are outside the scope of this
         memo.

      node_id:  3-octet unsigned integer.  This  Node identifier field specifies the length of
      data added by each to
         uniquely identify a node in multiples of 4-octets.  For example, if
      3 IOAM-Trace-Type bits are set within in-situ OAM domain.  The
         procedure to allocate, manage and none of them map the node_ids is wide, then beyond
         the
      NodeLen would be 3.  If 3 IOAM-Trace-Type bits are set scope of this document.

   ingress_if_id and egress_if_id:  4-octet field defined as follows:

    0 1 2 of
      them are wide, then the NodeLen would be 5.

   Flags  5-bit field.  Following flags are defined:

      Bit 3 4 5 6 7 8 9 0  "Overflow" (O-bit) (most significant bit).  This bit is set
         by the network element if there is not enough number of octets
         left to record node data, no field is added and the overflow
         "O-bit" must be set to "1" in the header.  This is useful for
         transit nodes to ignore further processing of the option.

      Bit 1  "Loopback" (L-bit).  This bit when set indicates 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ingress_if_id             |         egress_if_id          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      ingress_if_id:  2-octet unsigned integer.  Interface identifier to
         record the
         transit nodes processing this option to send a copy of ingress interface the packet back was received on.

      egress_if_id:  2-octet unsigned integer.  Interface identifier to
         record the source of egress interface the packet while it continues to
         forward is forwarded out of.

   timestamp seconds:  4-octet unsigned integer.  Absolute timestamp in
      seconds that specifies the time at which the original packet towards was received
      by the destination. node.  This field has three possible formats; based on
      either PTP [IEEE1588v2], NTP [RFC5905], or POSIX [POSIX].  The L-bit
         MUST be cleared
      three timestamp formats are specified in Section 5.  In all three
      cases, the copy of the packet before sending it.

      Bit 2-4  Reserved.  Must be zero.

   Maximum Length:  7-bit unsigned integer.  This Timestamp Seconds field specifies contains the
      maximum length 32 most
      significant bits of the node data list timestamp format that is specified in multiples
      Section 5.  If a node is not capable of 4-octets.
      Given that the sender knows the minimum path MTU, populating this field, it
      assigns the sender can
      set the maximum length according to the number of node data bytes
      allowed before exceeding the MTU.  Thus, value 0xFFFFFFFF.  Note that this is a simple comparison
      between "NodeLen" and "Max Length" allows to decide whether or not
      data could be added.

   Node data List [n]:  Variable-length field.  The type of which legitimate
      value that is
      determined by the OAM Type representing the n-th node data valid for 1 second in approximately 136 years; the
      node data list.  The node data list is encoded starting from the
      last node data of
      analyzer should correlate several packets or compare the path.  The first element of timestamp
      value to its own time-of-day in order to detect the node data
      list (node data list [0]) contains error
      indication.

   timestamp subseconds:  4-octet unsigned integer.  Absolute timestamp
      in subseconds that specifies the last node of time at which the path while packet was
      received by the last node data of node.  This field has three possible formats;
      based on either PTP [IEEE1588v2], NTP [RFC5905], or POSIX [POSIX].
      The three timestamp formats are specified in Section 5.  In all
      three cases, the node data list (node data list[n]) Timestamp Subseconds field contains the first node data 32 least
      significant bits of the path traced.

4.1.3.  IOAM node data fields and associated formats

   All the data fields MUST be 4-octet aligned.  The IOAM encapsulating
   node MUST initialize data fields timestamp format that it adds to the packet to zero. is specified in
      Section 5.  If a node which is supposed to update an IOAM data field is not capable of populating this field, it
      assigns the value of 0xFFFFFFFF.  Note that this is a field set in the IOAM-Trace-
   Type, the field legitimate
      value MUST be left unaltered except when explicitly
   specified in the field description below.  In NTP format, valid for approximately 233 picoseconds
      in every second.  If the description of data
   below if zero NTP format is valid value then a non-zero value used the analyzer should
      correlate several packets in order to mean not
   populated is specified.

   Data field and associated data type for each of detect the data field is
   shown below:

   Hop_Lim and node_id: error indication.

   transit delay:  4-octet field defined 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Hop_Lim     |              node_id                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Hop_Lim:  1-octet unsigned integer. integer in the range 0 to 2^31-1.
      It is set to the Hop Limit
         value time in nanoseconds the packet at the node that records this data.  Hop
         Limit information is used to identify the location of the node spent in the communication path. transit
      node.  This is copied from the lower
         layer, e.g., TTL value in IPv4 header or hop limit field from
         IPv6 header can serve as an indication of the packet when queuing delay at the packet is ready for
         transmission.  The semantics of
      node.  If the Hop_Lim field depend on transit delay exceeds 2^31-1 nanoseconds then the
         lower layer protocol that IOAM
      top bit 'O' is encapsulated over, and
         therefore its specific semantics are outside the scope of this
         memo.

      node_id:  3-octet unsigned integer.  Node identifier field to
         uniquely identify a node within in-situ OAM domain.  The
         procedure set to allocate, manage and map the node_ids is beyond
         the scope of this document.

   ingress_if_id indicate overflow and egress_if_id:  4-octet field defined as follows: value set to
      0x80000000.  When this field is part of the data field but a node
      populating the field is not able to fill it, the field position in
      the field must be filled with value 0xFFFFFFFF to mean not
      populated.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ingress_if_id             |         egress_if_id
   |O|                     transit delay                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      ingress_if_id:  2-octet unsigned integer.  Interface identifier to
         record the ingress interface the packet was received on.

      egress_if_id:  2-octet unsigned integer.  Interface identifier to
         record the egress interface the packet is forwarded out of.

   timestamp seconds:

   app_data:  4-octet unsigned integer.  Absolute timestamp in
      seconds that specifies the time at placeholder which the packet was received can be used by the node.  The structure of this field is identical node to the most
      significant 32 bits of the 64 least significant bits of the
      [IEEE1588v2] timestamp.  This truncated field consists of add
      application specific data.  App_data represents a 32-bit
      seconds field.  As "free-format"
      4-octet bit field with its semantics defined in [IEEE1588v2], the timestamp
      specifies the number of seconds elapsed since 1 January 1970
      00:00:00 according to the International Atomic Time (TAI). by a specific
      deployment.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       timestamp seconds                       app_data                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   timestamp nanoseconds:

   queue depth:  4-octet unsigned integer in the range 0 to
      10^9-1.  This timestamp specifies the fractional part of the wall
      clock time at which the packet was received by the node in units
      of nanoseconds. field.  This field is identical to indicates
      the 32 least
      significant bits current length of the [IEEE1588v2] timestamp.  This fields
      allows for delay computation between any two nodes in the network
      when the nodes are time synchronized.  When this field is part egress interface queue of the data field but a node populating interface
      from where the field packet is not able to fill
      it, forwarded out.  The queue depth is
      expressed as the field position in current number of memory buffers used by the field must be filled with value
      0xFFFFFFFF to mean not populated.
      queue (a packet may consume one or more memory buffers, depending
      on its size).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       timestamp nanoseconds                       queue depth                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   transit delay:  4-octet unsigned integer in

   Opaque State Snapshot:  Variable length field.  It allows the range 0 network
      element to 2^31-1.
      It store an arbitrary state in the node data field ,
      without a pre-defined schema.  The schema needs to be made known
      to the analyzer by some out-of-band mechanism.  The specification
      of this mechanism is beyond the time scope of this document.  The
      24-bit "Schema Id" field in nanoseconds the packet spent in field indicates which particular
      schema is used, and should be configured on the transit
      node.  This can serve as an indication of network element by
      the queuing delay at operator.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Length      |                     Schema ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                                                               |
      |                        Opaque data                            |
      ~                                                               ~
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Length:  1-octet unsigned integer.  It is the
      node.  If length in multiples
         of 4-octets of the transit delay exceeds 2^31-1 nanoseconds then Opaque data field that follows Schema Id.

      Schema ID:  3-octet unsigned integer identifying the
      top bit 'O' schema of
         Opaque data.

      Opaque data:  Variable length field.  This field is set to indicate overflow and value set to
      0x80000000. interpreted as
         specified by the schema identified by the Schema ID.

      When this field is part of the data field but a node populating
      the field is not able has no opaque state data to fill it, report, the field position in Length must be
      set to 0 and the field Schema ID must be filled with value 0xFFFFFFFF set to 0xFFFFFF to mean not
      populated. no
      schema.

   Hop_Lim and node_id wide:  8-octet field defined 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |O|                     transit delay
   |   Hop_Lim     |              node_id                          ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   app_data:  4-octet placeholder
   ~                         node_id (contd)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Hop_Lim:  1-octet unsigned integer.  It is set to the Hop Limit
         value in the packet at the node that records this data.  Hop
         Limit information is used to identify the location of the node
         in the communication path.  This is copied from the lower layer
         for e.g.  TTL value in IPv4 header or hop limit field from IPv6
         header of the packet.  The semantics of the Hop_Lim field
         depend on the lower layer protocol that IOAM is encapsulated
         over, and therefore its specific semantics are outside the
         scope of this memo.

      node_id:  7-octet unsigned integer.  Node identifier field to
         uniquely identify a node within in-situ OAM domain.  The
         procedure to allocate, manage and map the node_ids is beyond
         the scope of this document.

   ingress_if_id and egress_if_id wide:  8-octet field defined 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ingress_if_id                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       egress_if_id                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      ingress_if_id:  4-octet unsigned integer.  Interface identifier to
         record the ingress interface the packet was received on.

      egress_if_id:  4-octet unsigned integer.  Interface identifier to
         record the egress interface the packet is forwarded out of.

   app_data wide:  8-octet placeholder which can be used by the node to
      add application specific data.  App_data  App data represents a "free-format"
      4-octet "free-
      format" 8-octed bit field with its semantics defined by a specific
      deployment.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       app_data                       app data                                ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                       app data (contd)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   queue depth:

   Checksum Complement:  4-octet unsigned integer node data which contains a two-octet
      Checksum Complement field, and a 2-octet reserved field.  This field indicates
      the current length  The
      Checksum Complement is useful when IOAM is transported over
      encapsulations that make use of a UDP transport, such as VXLAN-GPE
      or Geneve.  Without the egress interface queue of Checksum Complement, nodes adding IOAM
      node data must update the interface
      from where UDP Checksum field.  When the packet is forwarded out.  The queue depth Checksum
      Complement is
      expressed as present, an IOAM encapsulating node or IOAM transit
      node adding node data MUST carry out one of the current number following two
      alternatives in order to maintain the correctness of memory buffers used by the
      queue (a packet may consume one or more memory buffers, depending
      on its size).  When this field UDP
      Checksum value:

      1.  Recompute the UDP Checksum field.

      2.  Use the Checksum Complement to make a checksum-neutral update
          in the UDP payload; the Checksum Complement is part assigned a
          value that complements the rest of the data field but a node populating data fields that
          were added by the current node, causing the existing UDP
          Checksum field is not able to fill it, remain correct.

      IOAM decapsulating nodes MUST recompute the field
      position in UDP Checksum field,
      since they do not know whether previous hops modified the UDP
      Checksum field must be filled with value 0xFFFFFFFF to mean
      not populated. or the Checksum Complement field.

      Checksum Complement fields are used in a similar manner in
      [RFC7820] and [RFC7821].

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       queue depth      Checksum Complement      |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Opaque State Snapshot:  Variable length field.  It allows the network
      element to store an arbitrary state

4.1.3.  Examples of IOAM node data

   An entry in the node "node data field ,
      without a pre-defined schema.  The schema list" array can have different formats,
   following the needs to be made known
      to of the analyzer by some out-of-band mechanism.  The specification
      of this mechanism is beyond deployment.  Some deployments might only
   be interested in recording the scope of this document. node identifiers, whereas others might
   be interested in recording node identifier and timestamp.  The
      24-bit "Schema Id" field
   section defines different types that an entry in the field indicates which particular
      schema "node data list" can
   take.

   0xD400:  IOAM-Trace-Type is used, and should be configured on the network element by 0xD400 then the operator.

       0                   1                   2                   3 format of node data is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Length   Hop_Lim     |                     Schema ID              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id             |         egress_if_id          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  timestamp subseconds                         |                        Opaque data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            app_data                           |
      ~                                                               ~
      .                                                               .
      .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Length:  1-octet unsigned integer.  It is the length in octets of
         the Opaque data field that follows Schema Id.  It MUST always
         be a multiple of 4.

      Schema ID:  3-octet unsigned integer identifying the schema of
         Opaque data.

      Opaque data:  Variable length field.  This field

   0xC000:  IOAM-Trace-Type is interpreted as
         specified by the schema identified by 0xC000 then the Schema ID. format is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim and     |              node_id wide:  8-octet field defined as follows:                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id             |         egress_if_id          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x9000:  IOAM-Trace-Type is 0x9000 then the format is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          ~                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                         node_id (contd)
       |                   timestamp subseconds                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Hop_Lim:  1-octet unsigned integer.  It

   0x8400:  IOAM-Trace-Type is set to the Hop Limit
         value in the packet at 0x8400 then the node that records this data.  Hop
         Limit information is used to identify the location of the node
         in the communication path.  This is copied from the lower layer
         for e.g.  TTL value in IPv4 header or hop limit field from IPv6
         header of the packet.  The semantics of the Hop_Lim field
         depend on the lower layer protocol that IOAM is encapsulated
         over, and therefore its specific semantics are outside the
         scope of this memo.

      node_id:  7-octet unsigned integer.  Node identifier field to
         uniquely identify a node within in-situ OAM domain.  The
         procedure to allocate, manage and map the node_ids is beyond
         the scope of this document.

   ingress_if_id and egress_if_id wide:  8-octet field defined as
      follows: When this field is part of the data field but a node
      populating the field is not able to fill it, the field position in
      the field must be filled with value 0xFFFFFFFFFFFFFFFF to mean not
      populated. format is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       ingress_if_id   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       egress_if_id                            app_data                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      ingress_if_id:  4-octet unsigned integer.  Interface identifier to
         record the ingress interface the packet was received on.

      egress_if_id:  4-octet unsigned integer.  Interface identifier to
         record the egress interface the packet

   0x9400:  IOAM-Trace-Type is forwarded out of.

   app_data wide:  8-octet placeholder which can be used by 0x9400 then the node to
      add application specific data.  App data represents a "free-
      format" 8-octed bit field with its semantics defined by a specific
      deployment. format is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       app data                                ~   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                       app data (contd)
       |                    timestamp subseconds                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Checksum Complement:  4-octet node data which contains a two-octet
      Checksum Complement field, and a 2-octet reserved field.  The
      Checksum Complement can be used when IOAM is transported over
      encapsulations that make use of a UDP transport, such as VXLAN-GPE
      or Geneve.  In this case, incorporating the IOAM node data
      requires the UDP Checksum field to be updated.  Rather than to
      recompute the Chekcsum field, a node can use the Checksum
      Complement to make a checksum-neutral update in the UDP payload;
      the Checksum Complement is assigned a value that complements the
      rest of the node data fields that were added by the current node,
      causing the existing UDP Checksum field to remain correct.
      Checksum Complement fields are used in a similar manner in
      [RFC7820] and [RFC7821].

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Checksum Complement
       |           Reserved                            app_data                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.4.  Examples of IOAM node data

   An entry in the "node data list" array can have different formats,
   following the needs of the deployment.  Some deployments might only
   be interested in recording the node identifiers, whereas others might
   be interested in recording node identifier and timestamp.  The
   section defines different types that an entry in "node data list" can
   take.

   0xD400:

   0x3180:  IOAM-Trace-Type is 0xD400 0x3180 then the format of node data is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim                      timestamp seconds                        |              node_id
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    timestamp subseconds                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id   Length      |         egress_if_id                     Schema Id                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  timestamp nanoseconds                                                               |
       |                                                               |
       |                        Opaque data                            |
       ~                                                               ~
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            app_data                         node_id(contd)                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0xC000:  IOAM-Trace-Type

4.2.  IOAM Proof of Transit Option

   IOAM Proof of Transit data is 0xC000 then to support the format is:

        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 path or service function
   chain [RFC7665] verification use cases.  Proof-of-transit uses
   methods like nested hashing or nested encryption of the IOAM data or
   mechanisms such as Shamir's Secret Sharing Schema (SSSS).  While
   details on how the IOAM data for the proof of transit option is
   processed at IOAM encapsulating, decapsulating and transit nodes are
   outside the scope of the document, all of these approaches share the
   need to uniquely identify a packet as well as iteratively operate on
   a set of information that is handed from node to node.
   Correspondingly, two pieces of information are added as IOAM data to
   the packet:

   o  Random: Unique identifier for the packet (e.g., 64-bits allow for
      the unique identification of 2^64 packets).

   o  Cumulative: Information which is handed from node to node and
      updated by every node according to a verification algorithm.

   IOAM proof of transit option:

   IOAM proof of transit option header:

    0                   1                   2                   3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id             |         egress_if_id          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x9000:  IOAM-Trace-Type is 0x9000 then the format is:
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |IOAM POT Type  |   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   timestamp nanoseconds IOAM POT flags|           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x8400:  IOAM-Trace-Type is 0x8400 then the format is:

   IOAM proof of transit option data MUST be 4-octet aligned.:

    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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            app_data                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x9400:  IOAM-Trace-Type is 0x9400 then the format is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    timestamp nanoseconds                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            app_data       POT Option data field determined by IOAM-POT-Type       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x3180:  IOAM-Trace-Type

   IOAM POT Type:  8-bit identifier of a particular POT variant that
      specifies the POT data that is 0x3180 then included.  This document defines
      POT Type 0:

      0: POT data is a 16 Octet field as described below.

   IOAM POT flags:  8-bit.  Following flags are defined:

      Bit 0  "Profile-to-use" (P-bit) (most significant bit).  For IOAM
         POT types that use a maximum of two profiles to drive
         computation, indicates which POT-profile is used.  The two
         profiles are numbered 0, 1.

      Bit 1-7  Reserved: Must be set to zero upon transmission and
         ignored upon receipt.

   Reserved:  16-bit Reserved bits are present for future use.  The
      reserved bits Must be set to zero upon transmission and ignored
      upon receipt.

   POT Option data:  Variable-length field.  The type of which is
      determined by the format is: IOAM-POT-Type.

4.2.1.  IOAM Proof of Transit Type 0
   IOAM proof of transit option of IOAM POT Type 0:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |IOAM POT Type=0|P|R R R R R R R|           Reserved            |                      timestamp seconds
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                           Random                              |                    timestamp nanoseconds  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  P
   |   Length      |                     Schema Id                        Random(contd)                          |  O
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  T
   |                         Cumulative                            |  |                                                               |
       |                        Opaque data                            |
       ~                                                               ~
       .                                                               .
       .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |   Hop_Lim     |              node_id
   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                         Cumulative (contd)                    |                         node_id(contd)  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.  IOAM Proof of Transit Option
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

   IOAM Proof POT Type:  8-bit identifier of Transit a particular POT variant that
      specifies the POT data that is included.  This section defines the
      POT data when the IOAM POT Type is set to support the path or service function
   chain [RFC7665] verification use cases.  Proof-of-transit uses
   methods like nested hashing value 0.

   P bit:  1-bit.  "Profile-to-use" (P-bit) (most significant bit).
      Indicates which POT-profile is used to generate the Cumulative.
      Any node participating in POT will have a maximum of 2 profiles
      configured that drive the computation of cumulative.  The two
      profiles are numbered 0, 1.  This bit conveys whether profile 0 or
      profile 1 is used to compute the Cumulative.

   R (7 bits):  7-bit IOAM POT flags for future use.  MUST be set to
      zero upon transmission and ignored upon receipt.

   Reserved:  16-bit Reserved bits are present for future use.  The
      reserved bits Must be set to zero upon transmission and ignored
      upon receipt.

   Random:  64-bit Per packet Random number.

   Cumulative:  64-bit Cumulative that is updated at specific nodes by
      processing per packet Random number field and configured
      parameters.

   Note: Larger or smaller sizes of "Random" and "Cumulative" data are
   feasible and could be required for certain deployments (e.g. in case
   of space constraints in the transport protocol used).  Future
   versions of this document will address different sizes of data for
   "proof of transit".

4.3.  IOAM Edge-to-Edge Option

   The IOAM edge-to-edge option is to carry data that is added by the
   IOAM encapsulating node and interpreted by IOAM decapsulating node.
   The IOAM transit nodes MAY process the data without modifying it.

     IOAM edge-to-edge option:

      IOAM edge-to-edge option header:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         IOAM-E2E-Type         |             Reserved          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      IOAM edge-to-edge option data MUST be 4-octet aligned:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       E2E Option data field determined by IOAM-E2E-Type       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IOAM-E2E-Type:  A 16-bit identifier which specifies which data types
      are used in the E2E option data.  The IOAM-E2E-Type value is a bit
      field.  The order of packing the E2E option data field elements
      follows the bit order of the IOAM-E2E-Type field, as follows:

      Bit 0    (Most significant bit) When set indicates presence of a
               64-bit sequence number added to a specific tube which is
               used to detect packet loss, packet reordering, or nested encryption packet
               duplication for that tube.  Each tube leverages a
               dedicated namespace for its sequence numbers.

      Bit 1    When set indicates presence of a 32-bit sequence number
               added to a specific tube which is used to detect packet
               loss, packet reordering, or packet duplication for that
               tube.  Each tube leverages a dedicated namespace for its
               sequence numbers.

      Bit 2    When set indicates presence of timestamp seconds for the
               transmission of the frame.  This 4-octet field has three
               possible formats; based on either PTP [IEEE1588v2], NTP
               [RFC5905], or POSIX [POSIX].  The three timestamp formats
               are specified in Section 5.  In all three cases, the
               Timestamp Seconds field contains the 32 most significant
               bits of the timestamp format that is specified in
               Section 5.  If a node is not capable of populating this
               field, it assigns the value 0xFFFFFFFF.  Note that this
               is a legitimate value that is valid for 1 second in
               approximately 136 years; the analyzer should correlate
               several packets or compare the timestamp value to its own
               time-of-day in order to detect the error indication.

      Bit 3    When set indicates presence of timestamp subseconds for
               the transmission of the frame.  This 4-octet field has
               three possible formats; based on either PTP [IEEE1588v2],
               NTP [RFC5905], or POSIX [POSIX].  The three timestamp
               formats are specified in Section 5.  In all three cases,
               the Timestamp Subseconds field contains the 32 least
               significant bits of the timestamp format that is
               specified in Section 5.  If a node is not capable of
               populating this field, it assigns the IOAM data or
   mechanisms such as Shamir's Secret Sharing Schema (SSSS).  While
   details on how value 0xFFFFFFFF.
               Note that this is a legitimate value in the IOAM data NTP format,
               valid for approximately 233 picoseconds in every second.
               If the proof of transit option NTP format is
   processed at IOAM encapsulating, decapsulating and transit nodes are
   outside used the scope of analyzer should correlate
               several packets in order to detect the document, all error indication.

      Bit 4-15 Undefined.  An IOAM encapsulating node Must set the value
               of these approaches share the
   need bits to uniquely identify a packet as well as iteratively operate on
   a zero upon transmission and ignore upon
               receipt.

   Reserved:  16-bits Reserved bits are present for future use.  The
      reserved bits Must be set of information that is handed from node to node.
   Correspondingly, two pieces zero upon transmission and ignored
      upon receipt.

   E2E Option data:  Variable-length field.  The type of information are added as which is
      determined by the IOAM-E2E-Type.

5.  Timestamp Formats

   The IOAM data to
   the packet:

   o  Random: Unique identifier for fields include a timestamp field which is represented
   in one of three possible timestamp formats.  It is assumed that the packet (e.g., 64-bits allow
   management plane is responsible for
      the unique identification of 2^64 packets).

   o  Cumulative: Information determining which timestamp
   format is used.

5.1.  PTP Truncated Timestamp Format

   The Precision Time Protocol (PTP) [IEEE1588v2] uses an 80-bit
   timestamp format.  The truncated timestamp format is handed from node to node and
      updated by every node according to a verification algorithm.

   IOAM proof of transit option:

   IOAM proof 64-bit field,
   which is the 64 least significant bits of transit option header:

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |IOAM POT Type|P|
   +-+-+-+-+-+-+-+-+

   IOAM proof the 80-bit PTP timestamp.
   The PTP truncated format is specified in Section 4.3 of transit option data MUST be 4-octet aligned:
   [I-D.ietf-ntp-packet-timestamps], and the details are presented below
   for the sake of completeness.

        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
   |                           Random                              |  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  P
       |                        Random(contd)                            Seconds                            |  O
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  T
   |                         Cumulative
       |                          Nanoseconds                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
   |                         Cumulative (contd)                    |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

   IOAM POT Type:  7-bit identifier

            Figure 1: PTP [IEEE1588] Truncated Timestamp Format

   Timestamp field format:

      Seconds: specifies the integer portion of a particular POT variant that
      dictates the POT data that number of seconds
      since the epoch.

      + Size: 32 bits.

      + Units: seconds.

      Nanoseconds: specifies the fractional portion of the number of
      seconds since the epoch.

      + Size: 32 bits.

      + Units: nanoseconds.  The value of this field is included. in the range 0
      to (10^9)-1.

   Epoch:

      The PTP [IEEE1588v2] epoch is 1 January 1970 00:00:00 TAI, which
      is 31 December 1969 23:59:51.999918 UTC.

   Resolution:

      The resolution is 1 nanosecond.

   Wraparound:

      This document defines POT
      Type 0:

      0: POT data time format wraps around every 2^32 seconds, which is a 16 Octet field as described below.

   Profile roughly
      136 years.  The next wraparound will occur in the year 2106.

   Synchronization Aspects:

      It is assumed that nodes that run this protocol are synchronized
      among themselves.  Nodes may be synchronized to use (P):  1-bit.  Indicates which POT-profile a global reference
      time.  Note that if PTP [IEEE1588v2] is used for synchronization,
      the timestamp may be derived from the PTP-synchronized clock,
      allowing the timestamp to be measured with respect to
      generate the Cumulative.  Any node participating clock of
      an PTP Grandmaster clock.

      The PTP truncated timestamp format is not affected by leap
      seconds.

5.2.  NTP 64-bit Timestamp Format

   The Network Time Protocol (NTP) [RFC5905] timestamp format is 64 bits
   long.  This format is specified in POT will have
      a maximum Section 4.2.1 of 2 profiles configured that drive
   [I-D.ietf-ntp-packet-timestamps], and the computation of
      cumulative.  The two profiles details are numbered 0, 1.  This bit conveys
      whether profile presented below
   for the sake of completeness.

        0 or profile                   1 is used to compute the Cumulative.

   Random:  64-bit Per packet Random number.

   Cumulative:                   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 2: NTP [RFC5905] 64-bit Cumulative that is updated at specific nodes by
      processing per packet Random number Timestamp Format

   Timestamp field and configured
      parameters.

   Note: Larger or smaller sizes of "Random" and "Cumulative" data are
   feasible and could be required for certain deployments (e.g.  in case format:

      Seconds: specifies the integer portion of space constraints in the transport protocol used).  Future
   versions number of this document will address different sizes seconds
      since the epoch.

      + Size: 32 bits.

      + Units: seconds.

      Fraction: specifies the fractional portion of data for
   "proof the number of transit".

4.3.  IOAM Edge-to-Edge Option

   The IOAM edge-to-edge option
      seconds since the epoch.

      + Size: 32 bits.

      + Units: the unit is 2^(-32) seconds, which is roughly equal to carry data that
      233 picoseconds.

   Epoch:

      The epoch is added by the
   IOAM encapsulating node and interpreted by IOAM decapsulating node. 1 January 1900 at 00:00 UTC.

   Resolution:

      The resolution is 2^(-32) seconds.

   Wraparound:

      This time format wraps around every 2^32 seconds, which is roughly
      136 years.  The IOAM transit nodes MAY process next wraparound will occur in the data without modifying it.

   Currently only sequence numbers year 2036.

   Synchronization Aspects:

      Nodes that use this timestamp format will typically be
      synchronized to UTC using NTP [RFC5905].  Thus, the IOAM edge-to-edge option.  In
   order timestamp may
      be derived from the NTP-synchronized clock, allowing the timestamp
      to detect packet loss, packet reordering, or packet duplication
   in an in-situ OAM-domain, sequence numbers can be added measured with respect to packets the clock of an NTP server.

      The NTP timestamp format is affected by leap seconds; it
      represents the number of seconds since the epoch minus the number
      of leap seconds that have occurred since the epoch.  The value of
      a particular tube (see [I-D.hildebrand-spud-prototype]).  Each tube
   leverages timestamp during or slightly after a dedicated namespace for its sequence numbers.

     IOAM edge-to-edge option:

      IOAM edge-to-edge option header:

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      | IOAM-E2E-Type |
      +-+-+-+-+-+-+-+-+

      IOAM edge-to-edge option data MUST leap second may be 4-octet aligned:
      temporarily inaccurate.

5.3.  POSIX-based Timestamp Format

   This timestamp format is based on the POSIX time format [POSIX].  The
   detailed specification of the timestamp format used in this document
   is presented 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       E2E Option data field determined by IOAM-E2E-Type                            Seconds                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Microseconds                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IOAM-E2E-Type:  8-bit identifier

                  Figure 3: POSIX-based Timestamp Format

   Timestamp field format:

      Seconds: specifies the integer portion of a particular the number of seconds
      since the epoch.

      + Size: 32 bits.

      + Units: seconds.

      Microseconds: specifies the fractional portion of the number of
      seconds since the epoch.

      + Size: 32 bits.

      + Units: the unit is microseconds.  The value of this field is in situ OAM E2E
      variant.

         0: E2E option data
      the range 0 to (10^6)-1.

   Epoch:

      The epoch is a 64-bit sequence number added 1 January 1970 00:00:00 TAI, which is 31 December
      1969 23:59:51.999918 UTC.

   Resolution:

      The resolution is 1 microsecond.

   Wraparound:

      This time format wraps around every 2^32 seconds, which is roughly
      136 years.  The next wraparound will occur in the year 2106.

   Synchronization Aspects:

      It is assumed that nodes that use this timestamp format run Linux
      operating system, and hence use the POSIX time.  In some cases
      nodes may be synchronized to UTC using a
         specific tube which synchronization mechanism
      that is used outside the scope of this document, such as NTP [RFC5905].
      Thus, the timestamp may be derived from the NTP-synchronized
      clock, allowing the timestamp to identify packet loss and
         reordering for be measured with respect to the
      clock of an NTP server.

      The POSIX-based timestamp format is affected by leap seconds; it
      represents the number of seconds since the epoch minus the number
      of leap seconds that tube.

5. have occurred since the epoch.  The value of
      a timestamp during or slightly after a leap second may be
      temporarily inaccurate.

6.  IOAM Data Export

   IOAM nodes collect information for packets traversing a domain that
   supports IOAM.  IOAM decapsulating nodes as well as IOAM transit
   nodes can choose to retrieve IOAM information from the packet,
   process the information further and export the information using
   e.g., IPFIX.

   The discussion of IOAM data processing and export is left for a
   future version of this document.

6.

7.  IANA Considerations

   This document requests the following IANA Actions.

6.1.

7.1.  Creation of a new In-Situ OAM Protocol Parameters Registry (IOAM)
      Protocol Parameters IANA registry

   IANA is requested to create a new protocol registry for "In-Situ OAM
   (IOAM) Protocol Parameters".  This is the common registry that will
   include registrations for all IOAM namespaces.  Each Registry, whose
   names are listed below:

      IOAM Type

      IOAM Trace Type

      IOAM Trace flags

      IOAM POT Type

      IOAM POT flags

      IOAM E2E Type

   will contain the current set of possibilities defined in this
   document.  New registries in this name space are created via RFC
   Required process as per [RFC8126].

   The subsequent sub-sections detail the registries herein contained.

7.2.  IOAM Type Registry

   This registry defines 128 code points for the IOAM-Type field for
   identifying IOAM options as explained in Section 4.  The following
   code points are defined in this draft:

   0  IOAM Pre-allocated Trace Option Type

   1  IOAM Incremental Trace flags Option Type

   2  IOAM POT Option Type

   3  IOAM E2E Option Type

   will contain the current set of possibilities defined in this
   document.  New registries in this name space

   4 - 127 are created available for assignment via RFC Required process as per
   [RFC8126].

   The subsequent sub-sections detail the registries herein contained.

6.2.

7.3.  IOAM Trace Type Registry

   This registry defines code point for each bit in the 16-bit IOAM-
   Trace-Type field for Pre-allocated trace option and Incremental trace
   option defined in Section 4.1.  The meaning of Bit 0 - 11 for trace
   type are defined in this document in Paragraph 1 of (Section 4.1.1).
   The meaning for Bit 12 - 15 are available for assignment via RFC
   Required process as per [RFC8126].

6.3.

7.4.  IOAM Trace Flags Registry

   This registry defines code point for each bit in the 5 4 bit flags for
   Pre-allocated trace option and Incremental trace option defined in
   Section 4.1.  The meaning of Bit 0 - 1 for trace flags are defined in
   this document in Paragraph 5 of Section 4.1.1.  The meaning for Bit 2
   - 4 3 are available for assignment via RFC Required process as per
   [RFC8126].

6.4.

7.5.  IOAM POT Type Registry

   This registry defines 128 256 code points to define IOAM POT Type for
   IOAM proof of transit option Section 4.2.  The code point value 0 is
   defined in this document, 1 - 127 255 are available for assignment via
   RFC Required process as per [RFC8126].

7.6.  IOAM POT Flags Registry

   This registry defines code point for each bit in the 8 bit flags for
   IOAM POT option defined in Section 4.2.  The meaning of Bit 0 for
   IOAM POT flags is defined in this document in Section 4.2.  The
   meaning for Bit 1 - 7 are available for assignment via RFC Required
   process as per [RFC8126].

6.5.

7.7.  IOAM E2E Type Registry

   This registry defines 256 code points to define IOAM-E2E-Type for each bit in the 16 bit IOAM-
   E2E-Type field for IOAM E2E option Section 4.3.  The code point value meaning of Bit 0 is
   - 3 are defined in this document, 1 document.  The meaning of Bit 4 - 255 15 are
   available for assignments via RFC Required process as per [RFC8126].

7.

8.  Manageability Considerations

   Manageability considerations will be addressed in a later version of
   this document..

8.

9.  Security Considerations

   Security considerations will be addressed in a later version of this
   document.  For a discussion of security requirements of in-situ OAM,
   please refer to [I-D.brockners-inband-oam-requirements].

9.

10.  Acknowledgements

   The authors would like to thank Eric Vyncke, Nalini Elkins, Srihari
   Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya
   Nadahalli, LJ Wobker, Erik Nordmark, Vengada Prasad Govindan, and
   Andrew Yourtchenko for the comments and advice.

   This document leverages and builds on top of several concepts
   described in [I-D.kitamura-ipv6-record-route].  The authors would
   like to acknowledge the work done by the author Hiroshi Kitamura and
   people involved in writing it.

   The authors would like to gracefully acknowledge useful review and
   insightful comments received from Joe Clarke, Al Morton, and Mickey
   Spiegel.

10.

11.  References

10.1.

11.1.  Normative References

   [IEEE1588v2]
              Institute of Electrical and Electronics Engineers,
              "1588-2008 "IEEE
              Std 1588-2008 - IEEE Standard for a Precision Clock
              Synchronization Protocol for Networked Measurement and
              Control Systems",  IEEE Std 1588-2008, 2008,
              <http://standards.ieee.org/findstds/
              standard/1588-2008.html>.

   [POSIX]    Institute of Electrical and Electronics Engineers, "IEEE
              Std 1003.1-2008 (Revision of IEEE Std 1003.1-2004) - IEEE
              Standard for Information Technology - Portable Operating
              System Interface (POSIX(R))",  IEEE Std 1003.1-2008, 2008,
              <https://standards.ieee.org/findstds/
              standard/1003.1-2008.html>.

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

   [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,
              <https://www.rfc-editor.org/info/rfc5905>.

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

10.2.

11.2.  Informative References

   [I-D.brockners-inband-oam-requirements]
              Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
              Gredler, H., Leddy, J., Youell, S., Mozes, D., Mizrahi,
              T., <>, P., and r. remy@barefootnetworks.com,
              "Requirements for In-situ OAM", draft-brockners-inband-
              oam-requirements-03 (work in progress), March 2017.

   [I-D.brockners-inband-oam-transport]
              Brockners, F., Bhandari, S., Govindan, V., Pignataro, C.,
              Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Mozes,
              D., Lapukhov, P., and R. Chang, "Encapsulations for In-
              situ OAM Data", draft-brockners-inband-oam-transport-05
              (work in progress), July 2017.

   [I-D.hildebrand-spud-prototype]
              Hildebrand, J. and B. Trammell, "Substrate Protocol for
              User Datagrams (SPUD) Prototype", draft-hildebrand-spud-
              prototype-03 (work in progress), March 2015.

   [I-D.ietf-ntp-packet-timestamps]
              Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
              Defining Packet Timestamps", draft-ietf-ntp-packet-
              timestamps-00 (work in progress), October 2017.

   [I-D.ietf-nvo3-geneve]
              Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
              Network Virtualization Encapsulation", draft-ietf-
              nvo3-geneve-05 (work in progress), September 2017.

   [I-D.ietf-nvo3-vxlan-gpe]
              Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
              Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-04 draft-ietf-nvo3-vxlan-gpe-05 (work
              in progress), April October 2017.

   [I-D.ietf-sfc-nsh]
              Quinn, P., Elzur, U., and C. Pignataro, "Network Service
              Header (NSH)", draft-ietf-sfc-nsh-27 draft-ietf-sfc-nsh-28 (work in progress),
              October
              November 2017.

   [I-D.kitamura-ipv6-record-route]
              Kitamura, H., "Record Route for IPv6 (PR6) Hop-by-Hop
              Option Extension", draft-kitamura-ipv6-record-route-00
              (work in progress), November 2000.

   [I-D.lapukhov-dataplane-probe]
              Lapukhov, P. and r. remy@barefootnetworks.com, "Data-plane
              probe for in-band telemetry collection", draft-lapukhov-
              dataplane-probe-01 (work in progress), June 2016.

   [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>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC7820]  Mizrahi, T., "UDP Checksum Complement in the One-Way
              Active Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7820,
              DOI 10.17487/RFC7820, March 2016, <https://www.rfc-
              editor.org/info/rfc7820>.

   [RFC7821]  Mizrahi, T., "UDP Checksum Complement in the Network Time
              Protocol (NTP)", RFC 7821, DOI 10.17487/RFC7821, March
              2016, <https://www.rfc-editor.org/info/rfc7821>.

Authors' Addresses

   Frank Brockners
   Cisco Systems, Inc.
   Hansaallee 249, 3rd Floor
   DUESSELDORF, NORDRHEIN-WESTFALEN  40549
   Germany

   Email: fbrockne@cisco.com

   Shwetha Bhandari
   Cisco Systems, Inc.
   Cessna Business Park, Sarjapura Marathalli Outer Ring Road
   Bangalore, KARNATAKA 560 087
   India

   Email: shwethab@cisco.com

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC  27709
   United States

   Email: cpignata@cisco.com
   Hannes Gredler
   RtBrick Inc.

   Email: hannes@rtbrick.com

   John Leddy
   Comcast
   United States

   Email: John_Leddy@cable.comcast.com

   Stephen Youell
   JP Morgan Chase
   25 Bank Street
   London  E14 5JP
   United Kingdom

   Email: stephen.youell@jpmorgan.com

   Tal Mizrahi
   Marvell
   6 Hamada St.
   Yokneam  2066721
   Israel

   Email: talmi@marvell.com

   David Mozes
   Mellanox Technologies Ltd.

   Email: davidm@mellanox.com mosesster@gmail.com

   Petr Lapukhov
   Facebook
   1 Hacker Way
   Menlo Park, CA  94025
   US

   Email: petr@fb.com
   Remy Chang
   Barefoot Networks
   2185 Park Boulevard
   Palo Alto,
   4750 Patrick Henry Drive
   Santa Clara, CA  94306  95054
   US

   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca

   John Lemon
   Broadcom
   270 Innovation Drive
   San Jose, CA  95134
   US

   Email: john.lemon@broadcom.com