ippm                                                        F. Brockners
Internet-Draft                                               S. Bhandari
Intended status: Standards Track                            C. Pignataro
Expires: April 26, September 9, 2020                                         Cisco
                                                              H. Gredler
                                                            RtBrick Inc.
                                                                J. Leddy

                                                               S. Youell
                                                                    JPMC
                                                              T. Mizrahi
                                        Huawei Network.IO Innovation Lab
                                                                D. Mozes

                                                             P. Lapukhov
                                                                Facebook
                                                                R. Chang
                                                       Barefoot Networks
                                                              D. Bernier
                                                             Bell Canada
                                                                J. Lemon
                                                                Broadcom
                                                        October 24, 2019
                                                          March 08, 2020

                      Data Fields for In-situ OAM
                      draft-ietf-ippm-ioam-data-08
                      draft-ietf-ippm-ioam-data-09

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 encapsulated into a variety of transports
   protocols 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 https://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 April 26, September 9, 2020.

Copyright Notice

   Copyright (c) 2019 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Scope, Applicability, and Assumptions . . . . . . . . . . . .   4
   4.  IOAM Data-Fields, Types, Nodes  . . . . . . . . . . . . . . .   5   6
     4.1.  IOAM Data-Fields and Option-Types . . . . . . . . . . . .   5   6
     4.2.  IOAM-Domains and types of IOAM Nodes  . . . . . . . . . .   6
     4.3.  IOAM-Namespaces . . . . . . . . . . . . . . . . . . . . .   7   8
     4.4.  IOAM Trace Option-Types . . . . . . . . . . . . . . . . .   9  10
       4.4.1.  Pre-allocated and Incremental Trace Option-Types  . .  12
       4.4.2.  IOAM node data fields and associated formats  . . . .  15  16
       4.4.3.  Examples of IOAM node data  . . . . . . . . . . . . .  21  22
     4.5.  IOAM Proof of Transit Option-Type . . . . . . . . . . . .  23  24
       4.5.1.  IOAM Proof of Transit Type 0  . . . . . . . . . . . .  25  26
     4.6.  IOAM Edge-to-Edge Option-Type . . . . . . . . . . . . . .  26  27
   5.  Timestamp Formats . . . . . . . . . . . . . . . . . . . . . .  28  29
     5.1.  PTP Truncated Timestamp Format  . . . . . . . . . . . . .  28  29
     5.2.  NTP 64-bit Timestamp Format . . . . . . . . . . . . . . .  29  30
     5.3.  POSIX-based Timestamp Format  . . . . . . . . . . . . . .  30  32
   6.  IOAM Data Export  . . . . . . . . . . . . . . . . . . . . . .  32  33
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32  33
     7.1.  Creation of a new In-Situ OAM  Protocol Parameters
           Registry (IOAM) Protocol Parameters IANA registry . . . .  32  33
     7.2.  IOAM Option-Type Registry . . . . . . . . . . . . . . . .  33  34
     7.3.  IOAM Trace-Type Registry  . . . . . . . . . . . . . . . .  33  34
     7.4.  IOAM Trace-Flags Registry . . . . . . . . . . . . . . . .  34  35
     7.5.  IOAM POT-Type Registry  . . . . . . . . . . . . . . . . .  34  35
     7.6.  IOAM POT-Flags Registry . . . . . . . . . . . . . . . . .  34  36
     7.7.  IOAM E2E-Type Registry  . . . . . . . . . . . . . . . . .  35  36
     7.8.  IOAM Namespace-ID Registry  . . . . . . . . . . . . . . .  35  36
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  35  37
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  36  38
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  37  38
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  37  39
     10.2.  Informative References . . . . . . . . . . . . . . . . .  37  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39  41

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.  IOAM is to complement
   mechanisms such as Ping or Traceroute, or more recent active probing
   mechanisms as described in [I-D.lapukhov-dataplane-probe]. Traceroute.  In terms of "active" or
   "passive" OAM, "in-situ" OAM can be considered a hybrid OAM type.
   "In-situ" mechanisms do not require extra packets to be sent.  IOAM
   adds information to the already available data packets and therefore
   cannot be considered passive.  In terms of the classification given
   in [RFC7799] IOAM could be portrayed as Hybrid Type 1.  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.

   IOAM use cases and mechanisms have expanded as this document matured,
   resulting in additional flags and options that may trigger creation
   of additional packets dedicated to OAM.  The term IOAM continues to
   be used for such mechanisms, in addition to the "in-situ" mechanisms
   that motivated this terminology.

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 [RFC8300]

   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
   encapsulated in 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
   protocol encapsulations 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. domain
   using for example packet filtering methods.  The operator should
   consider the 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, IPv6, IOAM support for
   ICMPv6 Echo Request/Reply could is desired which would translate into
   ICMPv6 extensions to enable IOAM-Data-
   Fields 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 which form an IOAM-Domain can add, update or remove IOAM-
   Data-Fields.  Edge devices of an IOAM-Domain 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  Using 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 could
   be defined useful in deployments where the cost of processing IOAM-Data-
   Fields by encapsulating, transit, or decapsulating node(s) might be a transport-independent manner.
   concern from a performance or operational perspective.  Thus limiting
   the amount of traffic IOAM applies is applied to a variety could be beneficial in some
   deployments.

   Encapsulation independence: The definition of IOAM-Data-Fields is
   independent from the protocols the IOAM-Data-Fields are encapsulated
   into.  IOAM-Data-Fields can be encapsulated into several
   encapsulating protocols.  A definition  The specification of how IOAM-Data-Fields
   are encapsulated into "parent" protocols, like e.g., NSH or IPv6 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-Fields could
   be present at multiple layers.  The behavior follows the ships-in-
   the-night model, i.e. IOAM-Data-Fields in one layer are independent
   from IOAM-Data-Fields in another layer.  Layering allows operators to
   instrument the protocol layer they want to measure.  The different
   layers could, but do not have to share the same IOAM encapsulation
   mechanisms.

   IOAM implementation: The definition of the IOAM-Data-Fields take the
   specifics of devices with hardware data-plane and software data-plane
   into account.

4.  IOAM Data-Fields, Types, Nodes

   This section details IOAM-related nomenclature and describes data
   types such as IOAM-Data-Fields, IOAM-Types, IOAM-Namespaces as well
   as the different types of IOAM nodes.

4.1.  IOAM Data-Fields and Option-Types

   An IOAM-Data-Field is a set of bits with a defined format and
   meaning, which can be stored at a certain place in a packet for the
   purpose of IOAM.

   To accommodate the different uses of IOAM, IOAM-Data-Fields fall into
   different categories.  In IOAM these categories are referred to as
   IOAM-Option-Types.  A common registry is maintained for IOAM-Option-
   Types, see Section 7.2 for details.  Corresponding to these IOAM-
   Option-Types, different IOAM-Data-Fields are defined.  IOAM-Data-
   Fields can be encapsulated into a variety of protocols, such as NSH,
   Geneve, IPv6, etc.  The definition of how IOAM-Data-Fields are
   encapsulated into other protocols is outside the scope of this
   document.

   This document defines four IOAM-Option-Types:

   o  Pre-allocated Trace Option-Type

   o  Incremental Trace Option-Type

   o  Proof of Transit (POT) Option-Type

   o  Edge-to-Edge (E2E) Option-Type

4.2.  IOAM-Domains and types of IOAM Nodes

   IOAM is expected to be deployed in a specific domain.  The part of
   the network which employs IOAM is referred to as the "IOAM-Domain".
   One or more IOAM-Option-Types are added to a packet upon entering the
   IOAM-Domain and are removed from the packet when exiting the domain.
   Within the IOAM-Domain, the IOAM-Data-Fields MAY be updated by
   network nodes that the packet traverses.  An IOAM-Domain consists of
   "IOAM encapsulating nodes", "IOAM decapsulating nodes" and "IOAM
   transit nodes".  The role of a node (i.e. encapsulating, transit,
   decapsulating) is defined within an IOAM-Namespace (see below).  A
   node can have different roles in different IOAM-Namespaces.

   A device which adds at least one IOAM-Option-Type to the packet is
   called the "IOAM encapsulating node", whereas a device which removes
   an IOAM-Option-Type 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-Fields can also update the
   IOAM-Data-Fields at the same time.  Or in other words, IOAM
   encapsulating 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 deployment might
   require that packets traverse a set of firewalls which support IOAM.
   In that case, only the set of firewall nodes would be IOAM transit
   nodes rather than all nodes.

   An "IOAM encapsulating node" incorporates one or more IOAM-Option-
   Types (from the list of IOAM-Types, see Section 7.2) into packets
   that IOAM is enabled for.  If IOAM is enabled for a selected subset
   of the traffic, the IOAM encapsulating node is responsible for
   applying the IOAM functionality to the selected subset.

   An "IOAM transit node" updates one or more of the IOAM-Data-Fields.
   If both the Pre-allocated and the Incremental Trace Option-Types are
   present in the packet, each IOAM transit node will update at most one
   of these Option-Types.  A transit node MUST NOT add new IOAM-Option-
   Types to a packet, and MUST NOT change the IOAM-Data-Fields of an
   IOAM Edge-to-Edge Option-Type.

   An "IOAM decapsulating node" removes IOAM-Option-Type(s) from
   packets.

   The role of an IOAM-encapsulating, IOAM-transit or IOAM-decapsulating
   node is always performed within a specific IOAM-Namespace.  This
   means that an IOAM node which is e.g. an IOAM-decapsulating node for
   IOAM-Namespace "A" but not for IOAM-Namespace "B" will only remove
   the IOAM-Option-Types for IOAM-Namespace "A" from the packet.  An
   IOAM decapsulating node situated at the edge of an IOAM domain MUST
   remove all IOAM-Option-Types and associated encapsulation headers for
   all IOAM-Namespaces from the packet.

   IOAM-Namespaces allow for a namespace-specific definition and
   interpretation of IOAM-Data-Fields.  An interface-id could for
   example 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).  Please refer to
   Section 4.3 for details on IOAM-Namespaces.

4.3.  IOAM-Namespaces

   A subset or all of the IOAM-Option-Types and their corresponding
   IOAM-Data-Fields can be associated to an IOAM-Namespace.  IOAM-
   Namespaces add further context to IOAM-Option-Types and associated
   IOAM-Data-Fields.  Any IOAM-Namespace MUST interpret the IOAM-Option-
   Types and associated IOAM-Data-Fields per the definition in this
   document.  IOAM-Namespaces group nodes to support different
   deployment approaches of IOAM (see a few example use-cases below) as
   well as resolve issues which can occur due to IOAM-Data-Fields not
   being globally unique (e.g.  IOAM node identifiers do not have to be
   globally unique).  IOAM-Data-Fields significance is always within a
   particular IOAM-Namespace.

   An IOAM-Namespace is identified by a 16-bit namespace identifier
   (Namespace-ID).  IOAM-Namespace identifiers MUST be present and
   populated in all IOAM-Option-Types.  The Namespace-ID value is
   divided into two sub-ranges:

   o  An operator-assigned range from 0x0001 to 0x7FFF

   o  An IANA-assigned range from 0x8000 to 0xFFFF

   The IANA-assigned range is intended to allow future extensions to
   have new and interoperable IOAM functionality, while the operator-
   assigned range is intended to be domain specific, and managed by the
   network operator.  The Namespace-ID value of 0x0000 is default and
   known to all the nodes implementing IOAM.

   Namespace identifiers allow devices which are IOAM capable to
   determine:

   o  whether IOAM-Option-Type(s) need to be processed by a device: If
      the Namespace-ID contained in a packet does not match any
      Namespace-ID the node is configured to operate on, then the node
      MUST NOT change the contents of the IOAM-Data-Fields.

   o  which IOAM-Option-Type needs to be processed/updated in case there
      are multiple IOAM-Option-Types present in the packet.  Multiple
      IOAM-Option-Types can be present in a packet in case of
      overlapping IOAM-Domains or in case of a layered IOAM deployment.

   o  whether IOAM-Option-Type(s) should be removed from the packet,
      e.g. at a domain edge or domain boundary.

   IOAM-Namespaces support several different uses:

   o  IOAM-Namespaces can be used by an operator to distinguish
      different operational domains.  Devices at domain edges can filter
      on Namespace-IDs to provide for proper IOAM-Domain isolation.

   o  IOAM-Namespaces provide additional context for IOAM-Data-Fields
      and thus ensure that IOAM-Data-Fields are unique and can be
      interpreted properly by management stations or network
      controllers.  While, for example, the node identifier field
      (node_id, see below) does not need to be unique in a deployment
      (e.g. an operator may wish to use different node identifiers for
      different IOAM layers, even within the same device; or node
      identifiers might not be unique for other organizational reasons,
      such as after a merger of two formerly separated organizations),
      the combination of node_id and Namespace-ID will always be unique.
      Similarly, IOAM-Namespaces can be used to define how certain IOAM-
      Data-Fields are interpreted: IOAM offers three different timestamp
      format options.  The Namespace-ID can be used to determine the
      timestamp format.  IOAM-Data-Fields (e.g. buffer occupancy) which
      do not have a unit associated are to be interpreted within the
      context of a IOAM-Namespace.

   o  IOAM-Namespaces can be used to identify different sets of devices
      (e.g., different types of devices) in a deployment: If an operator
      desires to insert different IOAM-Data-Fields based on the device,
      the devices could be grouped into multiple IOAM-Namespaces.  This
      could be due to the fact that the IOAM feature set differs between
      different sets of devices, or it could be for reasons of optimized
      space usage in the packet header.  It could also stem from
      hardware or operational limitations on the size of the trace data
      that can be added and processed, preventing collection of a full
      trace for a flow.

      *  Assigning different IOAM Namespace-IDs to different sets of
         nodes or network partitions and using the Namespace-ID as a
         selector at the IOAM encapsulating node, a full trace for a
         flow could be collected and constructed via partial traces in
         different packets of the same flow.  Example: An operator could
         choose to group the devices of a domain into two IOAM-
         Namespaces, in a way that at average, only every second hop
         would be recorded by any device.  To retrieve a full view of
         the deployment, the captured IOAM-Data-Fields of the two IOAM-
         Namespaces need to be correlated.

      *  Assigning different IOAM Namespace-IDs to different sets of
         nodes or network partitions and using a separate instance of an
         IOAM-Option-Type for each Namespace-ID, a full trace for a flow
         could be collected and constructed via partial traces from each
         IOAM-Option-Type in each of the packets in the flow.  Example:

         An operator could choose to group the devices of a domain into
         two IOAM-Namespaces, in a way that each IOAM-Namespace is
         represented by one of two IOAM-Option-Types in the packet.
         Each node would record data only for the IOAM-Namespace that it
         belongs to, ignoring the other IOAM-Option-Type with a IOAM-
         Namespace to which it doesn't belong.  To retrieve a full view
         of the deployment, the captured IOAM-Data-Fields of the two
         IOAM-Namespaces need to be correlated.

4.4.  IOAM Trace Option-Types

   "IOAM tracing data" is expected to be either collected at every IOAM
   transit 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 IOAM-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 support IOAM capable, functionality
   as defined in this document, IOAM tracing information (i.e., node
   data, see below) will only be collected on those nodes which are support
   IOAM capable. functionality as defined in this document.  Nodes which are do not
   support IOAM capable functionality as defined in this document will forward
   the packet without any changes to the IOAM-
   Data-Fields. 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 IOAM tracing is
   defined as two separate options.  Any deployment MAY choose to
   configure and support one or both of the following options.

   Pre-allocated Trace-Option:  This trace option is defined as a
      container of node data fields (see below) with pre-allocated space
      for each node to populate its information.  This option is useful
      for implementations where it is efficient to allocate the space
      once and index into the array to populate the data during transit
      (e.g., software forwarders often fall into this class).  The IOAM
      encapsulating node allocates space for Pre-allocated Trace Option-
      Type in the packet and sets corresponding fields in this IOAM-
      Option-Type.  The IOAM 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, and possibly update the checksums of outer
      headers.  A pointer which is part of the IOAM trace data, points
      to the next empty slot in the array.  An IOAM transit node that
      updates the content of the pre-allocated option also updates the
      value of the pointer, which specifies where the next IOAM transit
      node fills in its data.The "node data list" array (see below) 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.

   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.  This type
      of trace recording is useful for some of the hardware
      implementations as it 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 IOAM
      encapsulating node allocates space for the Incremental Trace
      Option-Type.  Based on operational state and configuration, the
      IOAM encapsulating node sets the fields in the Option-Type that
      control what IOAM-Data-Fields should be collected and how large
      the node data list can grow.  IOAM transit nodes push their node
      data to the node data list, decrease the remaining length
      available to subsequent nodes and adjust the lengths and possibly
      checksums in outer headers.

   A particular implementation of IOAM MAY choose to support only one of
   the two trace option types.  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.  Deployments which mix
   devices which either the Incremental Trace-Option or the Pre-
   allocated Trace-Option could result in both Option-Types being
   present in a packet.  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 used for a
   particular domain.

   Every node data entry holds information for a particular IOAM transit
   node that is traversed by a packet.  The IOAM decapsulating node
   removes the IOAM-Option-Type(s) and processes and/or exports the
   associated data.  Like all IOAM-Data-Fields, the IOAM-Data-Fields of
   the IOAM-Trace-Option-Types are defined in the context of an IOAM-
   Namespace.

   IOAM tracing can collect the following types of information:

   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 as well as
      the transit delay.  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 IOAM-Namespace, 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  Information to detect whether IOAM trace data was added at every
      hop or whether certain hops in the domain weren't IOAM transit
      nodes.

4.4.1.  Pre-allocated and Incremental Trace Option-Types

   The IOAM Pre-allocated Trace-Option and the IOAM Incremental Trace-
   Option have similar formats.  Except where noted below, the internal
   formats and fields of the two trace options are identical.  Both
   Trace-Options consist of a fixed size "trace option header" and a
   variable data space to store gathered data, the "node data list":

   Pre-allocated and incremental trace option headers:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 list".  An
   IOAM transit node (that is not an IOAM encapsulating node or IOAM
   decapsulating node) MUST NOT modify any of the fields in the fixed
   size "trace option header", other than "flags" and "RemainingLen",
   i.e. an IOAM transit node MUST NOT modify the Namespace-ID, NodeLen,
   IOAM-Trace-Type, or Reserved fields.

   Pre-allocated and incremental trace option 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Namespace-ID           |NodeLen  | Flags | RemainingLen|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               IOAM-Trace-Type                 |  Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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]                     |  |
   |                                                               |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

   Namespace-ID:  16-bit identifier of an IOAM-Namespace.  The
      Namespace-ID value of 0x0000 is defined as the default value and
      MUST be known to all the nodes implementing IOAM.  For any other
      Namespace-ID value that does not match any Namespace-ID the node
      is configured to operate on, the node MUST NOT change the contents
      of the IOAM-Data-Fields.

   NodeLen:  5-bit unsigned integer.  This field specifies the length of
      data added by each node in multiples of 4-octets, excluding the
      length of the "Opaque State Snapshot" field.

      If IOAM-Trace-Type bit 22 is not set, then NodeLen specifies the
      actual length added by each node.  If IOAM-Trace-Type bit 22 is
      set, then the actual length added by a node would be (NodeLen +
      Opaque Data Length).
      length of the "Opaque State Snapshot" field) in 4 octet units.

      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 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 (see
      below).

   Flags  4-bit field.  Flags are allocated by IANA, as specified in
      Section 7.4.  This document allocates a single flag as follows:

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

   RemainingLen:  7-bit unsigned integer.  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.
      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 pre-allocated
      trace option, RemainingLength is used to derive the offset in data
      space to record the node data element.  Specifically, the
      recording of the node data element would start from RemainingLen -
      NodeLen - sizeof(opaque snapshot) in 4 octet units.

   IOAM-Trace-Type:  A 24-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 bits are
      defined in this document, with details on each bit described in
      the Section 4.4.2.  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 (short format) 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.

      Bit 3    When set indicates presence of timestamp 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 IOAM-Namespace specific
               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 the Checksum Complement
               node data.

      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 IOAM-Namespace specific
               data in wide format in the node data.

      Bit 11   When set indicates presence of buffer occupancy in the
               node data.

      Bit 12-21  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 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.

      Bit 22   When set indicates presence of variable length Opaque
               State Snapshot field.

      Bit 23   Reserved: Must be set to zero upon transmission and
               ignored upon receipt.

      Section 4.4.2 describes the IOAM-Data-Types and their formats.
      Within an IOAM-Domain possible combinations of these bits making
      the IOAM-Trace-Type can be restricted by configuration knobs.

   Reserved:  8-bits.  Must be zero.  An IOAM encapsulating node MUST set the value to
      zero upon transmission.  IOAM transit nodes must ignore the
      received value.

   Node data List [n]:  Variable-length field.  The type  This is a list of which node
      data elements where the content of each node data element is
      determined by the IOAM-Trace-Type bit representing IOAM-Trace-Type.  The order of packing the n-th node data
      fields in the node data list.  The each node data list is encoded
      starting from element follows the last node data bit order of the path.  The first
      IOAM-Trace-Type field.  Each node MUST prepend its node data
      element in front of the node data list (node data list [0]) contains elements that it received, such
      that the last transmitted node
      of data list begins with this node's data
      element as the path while first populated element in the list.  The last node
      data of element in this list is the node data list (node
      data list[n]) contains of the first IOAM
      capable node data of in the path traced. path.  Populating the node data list in this
      way ensures that the order of node data list is the same for
      incremental and pre-allocated trace options.  In the pre-allocated
      trace option, the index contained in RemainingLen identifies the
      offset for current active node data to be populated.

4.4.2.  IOAM node data fields and associated formats

   All the IOAM-Data-Fields MUST be 4-octet aligned.  If a node which is
   supposed to update an IOAM-Data-Field is not capable of populating
   the value of a field set in the IOAM-Trace-Type, the 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 the field description below.

   Some IOAM-Data-Fields defined below, such as interface identifiers or
   IOAM-Namespace specific data, are defined in both "short format" as
   well as "wide format".  Their use is not exclusive.  A deployment
   could choose to leverage both.  For example, ingress_if_id_(short
   format) could be an identifier for the physical interface, whereas
   ingress_if_id_(wide format) could be an identifier for a logical sub-
   interface of that physical interface.

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

   Hop_Lim and node_id: node_id short format:  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.  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, e.g., TTL value in IPv4 header or hop limit field from
         IPv6 header of the packet when the packet is ready for
         transmission.  The semantics of the Hop_Lim field depend on the
         lower layer protocol that IOAM is encapsulated over, into, and
         therefore its specific semantics are outside the scope of this
         memo.  The value of this field MUST be set to 0xff when the
         lower level does not have a TTL/Hop limit equivalent field.

      node_id:  3-octet unsigned integer.  Node identifier field to
         uniquely identify a node within the IOAM-Namespace and
         associated IOAM-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:  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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ingress_if_id             |         egress_if_id          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      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.

      Note that due to the fact that IOAM uses its own IOAM-Namespaces
      for IOAM-Data-Fields, data fields like interface identifiers can
      be used in a flexible way to represent system resources that are
      associated with ingressing or egressing packets, i.e.
      ingress_if_id could represent a physical interface, a virtual or
      logical interface, or even a queue.

   timestamp seconds:  4-octet unsigned integer.  Absolute timestamp in
      seconds that specifies the time at which the packet was received
      by the 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 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.

   timestamp subseconds:  4-octet unsigned integer.  Absolute timestamp
      in subseconds that specifies the time at which the packet was
      received by the 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 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 value 0xFFFFFFFF.  Note that this is a legitimate
      value in the NTP format, valid for approximately 233 picoseconds
      in every second.  If the NTP format is used the analyzer should
      correlate several packets in order to detect the error indication.

   transit delay:  4-octet unsigned integer in the range 0 to 2^31-1.
      It is the time in nanoseconds the packet spent in the transit
      node.  This can serve as an indication of the queuing delay at the
      node.  If the transit delay exceeds 2^31-1 nanoseconds then the
      top bit 'O' is set to indicate overflow and 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |O|                     transit delay                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   namespace specific data:  4-octet field which can be used by the node
      to add IOAM-Namespace specific data.  This represents a "free-
      format" 4-octet bit field with its semantics defined in the
      context of a specific IOAM-Namespace.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    namespace specific data                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   queue depth:  4-octet unsigned integer field.  This field indicates
      the current length of the egress interface queue of the interface
      from where the packet is forwarded out.  The queue depth is
      expressed as the current number of memory buffers used by the
      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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       queue depth                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Hop_Lim     |              node_id                          ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                         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,
         into, and therefore its specific semantics are outside the
         scope of this memo.

      node_id:  7-octet unsigned integer.  Node identifier  The value of this field MUST be set to
         uniquely identify a
         0xff when the lower level does not have a TTL/Hop limit
         equivalent field.

      node_id:  7-octet unsigned integer.  Node identifier field to
         uniquely identify a node within the IOAM-Namespace and
         associated IOAM-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.

   namespace specific data wide:  8-octet field which can be used by the
      node to add IOAM-Namespace specific data.  This represents a
      "free-format" 8-octet bit field with its semantics defined in the
      context of a specific IOAM-Namespace.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    namespace specific data                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                namespace specific data (contd)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   buffer occupancy:  4-octet unsigned integer field.  This field
      indicates the current status of the occupancy of the common buffer
      pool used by a set of queues.  The units of this field depend on may be
      implementation specific.  Hence, the equipment type and deployment and has units may need to be
      interpreted within the context of an IOAM-Namespace and/or node-id
      if used.  The authors acknowledge that in some operational cases
      there is a need for the units to be consistent across a packet
      path through the network, hence recommend the implementations to
      use standard unit such as Bytes.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       buffer occupancy                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Checksum Complement:  4-octet node data which contains a 4-octet
      Checksum Complement field.  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 Checksum
      Complement, nodes adding IOAM node data must update the UDP
      Checksum field.  When the Checksum Complement is present, an IOAM
      encapsulating node or IOAM transit node adding node data MUST
      carry out one of the following two alternatives in order to
      maintain the correctness of the 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 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.

      IOAM decapsulating nodes MUST recompute the UDP Checksum field,
      since they do not know whether previous hops modified the UDP
      Checksum field 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Checksum Complement                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Opaque State Snapshot:  Opaque State Snapshot is a variable length
      field and immediately follows the fixed length IOAM-Data-Fields
      defined above.  It allows the network element to store an
      arbitrary state in the node data field, without a pre-defined
      schema.  The schema is to be defined within the context of an
      IOAM-Namespace.  The schema needs to be made known to the analyzer
      by some out-of-band mechanism.  The specification of this
      mechanism is beyond the scope of this document.  A 24-bit "Schema
      Id" field, interpreted within the context of an IOAM-Namespace,
      indicates which particular schema is used, and should be
      configured on the network element by the 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 length in multiples
         of 4-octets of the Opaque data field that follows Schema Id.

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

      Opaque data:  Variable length field.  This field is 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 has no opaque state data to report, the Length must be
      set to 0 and the Schema ID must be set to 0xFFFFFF to mean no
      schema.

4.4.3.  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 provides example entries of the "node data list".

   0xD40000:  IOAM-Trace-Type is 0xD40000 (0b110101000000000000000000)
      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     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id             |         egress_if_id          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     timestamp subseconds                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    namespace specific data                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0xC00000:  IOAM-Trace-Type is 0xC00000 (0b110000000000000000000000)
      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                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     ingress_if_id             |         egress_if_id          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x900000:  IOAM-Trace-Type is 0x900000 (0b100100000000000000000000)
      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 subseconds                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x840000:  IOAM-Trace-Type is 0x840000 (0b100001000000000000000000)
      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                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    namespace specific data                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x940000:  IOAM-Trace-Type is 0x940000 (0b100101000000000000000000)
      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 subseconds                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    namespace specific data                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   0x308002:  IOAM-Trace-Type is 0x308002 (0b001100001000000000000010)
      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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      timestamp seconds                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    timestamp subseconds                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Hop_Lim     |              node_id                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         node_id(contd)                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Length      |                     Schema Id                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                                                               |
       |                        Opaque data                            |
       ~                                                               ~
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.5.  IOAM Proof of Transit Option-Type

   IOAM Proof of Transit Option-Type is to support 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-
   Fields 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.

   The IOAM Proof of Transit Option-Type consist of a fixed size "IOAM
   proof of transit option header" and "IOAM proof of transit option
   data fields":

   IOAM proof of transit 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Namespace-ID            |IOAM POT Type  | IOAM POT flags|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IOAM proof of transit Option-Type IOAM-Data-Fields 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       POT Option data field determined by IOAM-POT-Type       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Namespace-ID:  16-bit identifier of an IOAM-Namespace.  The
      Namespace-ID value of 0x0000 is defined as the default value and
      MUST be known to all the nodes implementing IOAM.  For any other
      Namespace-ID value that does not match any Namespace-ID the node
      is configured to operate on, the node MUST NOT change the contents
      of the IOAM-Data-Fields.

   IOAM POT Type:  8-bit identifier of a particular POT variant that
      specifies the POT data that is 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.

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

4.5.1.  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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Namespace-ID           |IOAM POT Type=0|P|R R R R R R R|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
   |                        Random                                 |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  P
   |                        Random(contd)                          |  O
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  T
   |                        Cumulative                             |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
   |                        Cumulative (contd)                     |  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

   Namespace-ID:  16-bit identifier of an IOAM-Namespace.  The
      Namespace-ID value of 0x0000 is defined as the default value and
      MUST be known to all the nodes implementing IOAM.  For any other
      Namespace-ID value that does not match any Namespace-ID the node
      is configured to operate on, the node MUST NOT change the contents
      of the IOAM-Data-Fields.

   IOAM POT Type:  8-bit identifier of 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 the 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.

   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 encapsulation protocols used).  Future
   versions of this document will
   documents may address different sizes of data for "proof of transit".

4.6.  IOAM Edge-to-Edge Option-Type

   The IOAM Edge-to-Edge Option-Type 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 but MUST NOT
   modify it.

   The IOAM Edge-to-Edge Option-Type consist of a fixed size "IOAM Edge-
   to-Edge Option-Type header" and "IOAM Edge-to-Edge Option-Type data
   fields":

   IOAM Edge-to-Edge Option-Type 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Namespace-ID           |         IOAM-E2E-Type         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IOAM Edge-to-Edge Option-Type IOAM-Data-Fields 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       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Namespace-ID:  16-bit identifier of an IOAM-Namespace.  The
      Namespace-ID value of 0x0000 is defined as the default value and
      MUST be known to all the nodes implementing IOAM.  For any other
      Namespace-ID value that does not match any Namespace-ID the node
      is configured to operate on, then the node MUST NOT change the
      contents of the IOAM-Data-Fields.

   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 "packet group"
               which is used to detect packet loss, packet reordering,
               or packet duplication within the group.  The "packet
               group" is deployment dependent and defined at the IOAM
               encapsulating node e.g. by n-tuple based classification
               of packets.

      Bit 1    When set indicates presence of a 32-bit sequence number
               added to a specific "packet group" which is used to
               detect packet loss, packet reordering, or packet
               duplication within that group.  The "packet group" is
               deployment dependent and defined at the IOAM
               encapsulating node e.g. by n-tuple based classification
               of packets.

      Bit 2    When set indicates presence of timestamp seconds for seconds,
               representing the
               transmission of time at which the packet entered the
               IOAM domain.  Within the IOAM encapsulating node, the
               time that the timestamp is retrieved can depend on the
               implementation.  Some possibilities are: 1) the time at
               which the packet was received by the node, 2) the time at
               which the frame. packet was transmitted by the node, 3) when a
               tunnel encapsulation is used, the point at which the
               packet is encapsulated into the tunnel.  Each
               implementation should document when the E2E timestamp
               that is going to be put in the packet is retrieved.  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 subseconds,
               representing the transmission of time at which the frame. packet entered the
               IOAM domain.  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 value 0xFFFFFFFF.

               Note that this is a legitimate value in the NTP format,
               valid for approximately 233 picoseconds in every second.
               If the NTP format is used the analyzer should correlate
               several packets in order to detect the error indication.

      Bit 4-15 Undefined.  An IOAM encapsulating node Must set the value
               of these bits to zero upon transmission and ignore upon
               receipt.

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

5.  Timestamp Formats

   The IOAM-Data-Fields include a timestamp field which is represented
   in one of three possible timestamp formats.  It is assumed that the
   management plane is responsible for 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 a 64-bit field,
   which is the 64 least significant bits of the 80-bit PTP timestamp.
   The PTP truncated format is specified in Section 4.3 of
   [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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Seconds                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Nanoseconds                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 1: PTP [IEEE1588v2] Truncated Timestamp Format

   Timestamp field format:

      Seconds: specifies the integer portion of the 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 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 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 run this protocol are synchronized
      among themselves.  Nodes may be synchronized to 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 the 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 Section 4.2.1 of
   [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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Seconds                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Fraction                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 2: NTP [RFC5905] 64-bit Timestamp Format

   Timestamp field format:

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

      + Size: 32 bits.

      + Units: seconds.

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

      + Size: 32 bits.

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

   Epoch:

      The epoch is 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 next wraparound will occur in the year 2036.

   Synchronization Aspects:

      Nodes that use this timestamp format will typically be
      synchronized to UTC using NTP [RFC5905].  Thus, the timestamp may
      be derived from the NTP-synchronized clock, allowing the timestamp
      to be measured with respect to 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 timestamp during or slightly after a leap second may be
      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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Seconds                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Microseconds                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: POSIX-based Timestamp Format

   Timestamp field format:

      Seconds: specifies the integer portion of 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
      the range 0 to (10^6)-1.

   Epoch:

      The epoch is 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 synchronization mechanism
      that is 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 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 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 mechanisms and associated data formats for
   exporting IOAM data is outside the scope of this document.

   Raw data export of IOAM data using IPFIX is discussed in
   [I-D.spiegel-ippm-ioam-rawexport].

7.  IANA Considerations

   This document requests the following IANA Actions.

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 Option-Type

      IOAM Trace-Type
      IOAM Trace-Flags

      IOAM POT-Type

      IOAM POT-Flags

      IOAM E2E-Type

      IOAM Namespace-ID

   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 Option-Type Registry

   This registry defines 128 code points for the IOAM Option-Type field
   for identifying IOAM Option-Types 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 Option-Type

   2  IOAM POT Option-Type

   3  IOAM E2E Option-Type

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

7.3.  IOAM Trace-Type Registry

   This registry defines code point for each bit in the 24-bit IOAM-
   Trace-Type field for Pre-allocated trace option and Incremental trace
   option defined in Section 4.4.  The meaning of Bits 0 - 11 for trace
   type are defined in this document in Paragraph 5 of Section 4.4.1:

   Bit 0  hop_Lim and node_id in short format

   Bit 1  ingress_if_id and egress_if_id in short format

   Bit 2  timestamp seconds

   Bit 3  timestamp subseconds
   Bit 4  transit delay

   Bit 5  namespace specific data in short format

   Bit 6  queue depth

   Bit 7  checksum complement

   Bit 8  hop_Lim and node_id in wide format

   Bit 9  ingress_if_id and egress_if_id in wide format

   Bit 10  namespace specific data in wide format

   Bit 11  buffer occupancy

   Bit 22  variable length Opaque State Snapshot

   Bit 23  reserved

   The meaning for Bits 12 - 21 are available for assignment via RFC
   Required process as per [RFC8126].

7.4.  IOAM Trace-Flags Registry

   This registry defines code points for each bit in the 4 bit flags for
   the Pre-allocated trace option and for the Incremental trace option
   defined in Section 4.4.  The meaning of Bit 0 (the most significant
   bit) for trace flags is defined in this document in Paragraph 3 of
   Section 4.4.1:

   Bit 0  "Overflow" (O-bit)

   Bit 1 - 3 are available for assignment via RFC Required process as
   per [RFC8126].

7.5.  IOAM POT-Type Registry

   This registry defines 256 code points to define IOAM POT Type for
   IOAM proof of transit option Section 4.5.  The code point value 0 is
   defined in this document:

   0: 16 Octet POT data

   1 - 255 are available for assignment via RFC Required process as per
   [RFC8126].

7.6.  IOAM POT-Flags Registry

   This registry defines code points for each bit in the 8 bit flags for
   IOAM POT option defined in Section 4.5.  The meaning of Bit 0 for
   IOAM POT flags is defined in this document in Section 4.5:

   Bit 0  "Profile-to-use" (P-bit)

   The meaning for Bits 1 - 7 are available for assignment via RFC
   Required process as per [RFC8126].

7.7.  IOAM E2E-Type Registry

   This registry defines code points for each bit in the 16 bit IOAM-
   E2E-Type field for IOAM E2E option Section 4.6.  The meaning of Bit 0
   - 3 are defined in this document:

   Bit 0  64-bit sequence number

   Bit 1  32-bit sequence number

   Bit 2  timestamp seconds

   Bit 3  timestamp subseconds

   The meaning of Bits 4 - 15 are available for assignment via RFC
   Required process as per [RFC8126].

7.8.  IOAM Namespace-ID Registry

   IANA is requested to set up an "IOAM Namespace-ID Registry",
   containing 16-bit values.  The meaning of Bit 0 is defined in this
   document.  IANA is requested to reserve the values 0x0001 to 0x7FFF
   for private use (managed by operators), as specified in Section 4.3
   of the current document.  Registry entries for the values 0x8000 to
   0xFFFF are to be assigned via the "Expert Review" policy defined in
   [RFC8126].

   0: default namespace (known to all IOAM nodes)

   0x0001 - 0x7FFF:  reserved for private use

   0x8000 - 0xFFFF:  unassigned

8.  Security Considerations

   As discussed in [RFC7276], a successful attack on an OAM protocol in
   general, and specifically on IOAM, can prevent the detection of
   failures or anomalies, or create a false illusion of nonexistent
   ones.  In particular, these threats are applicable by compromising
   the integrity of IOAM data, either by maliciously modifying IOAM
   options in transit, or by injecting packets with maliciously
   generated IOAM options

   The Proof of Transit Option-Type (Section Section 4.5) is used for
   verifying the path of data packets.  The security considerations of
   POT are further discussed in [I-D.ietf-sfc-proof-of-transit].

   The data elements of

   From a confidentiality perspective, although IOAM options do not
   contain user data, they can be used for network reconnaissance,
   allowing attackers to collect information about network paths,
   performance, queue states, buffer occupancy and other information.
   Moreover, if IOAM data leaks from the IOAM domain it may enable
   reconnaissance beyond the scope of the IOAM domain.  Note that in
   case IOAM is used in "immediate export" "Direct Exporting" mode (reference
   to be added in a future revision),
   [I-D.ioamteam-ippm-ioam-direct-export], the IOAM related trace
   information would not be available in the customer data packets, but
   would trigger export of packet related IOAM information at every node.
   IOAM data export
   node, thus restricting the potential threat to the management plane
   and securing mitigating the leakage threat.  IOAM data export exporting and the way
   it is secured is outside the scope of this document.

   IOAM can be used as a means for implementing Denial of Service (DoS)
   attacks, or for amplifying them.  For example, a malicious attacker
   can add an IOAM header to packets in order to consume the resources
   of network devices that take part in IOAM or collectors entities that receive,
   collect or analyze the IOAM data.  Another example is a packet length
   attack, in which an attacker pushes headers associated with IOAM
   Option-Types into data packets, causing these packets to be increased
   beyond the MTU size, resulting in fragmentation or in packet drops.

   Since IOAM options may include timestamps, if network devices use
   synchronization protocols then any attack on the time protocol
   [RFC7384] can compromise the integrity of the timestamp-related data
   fields.

   At the management plane, attacks may be implemented by misconfiguring
   or by maliciously configuring IOAM-enabled nodes in a way that
   enables other attacks.  Thus, IOAM configuration should be secured in
   a way that authenticates authorized users and verifies the integrity
   of configuration procedures.

   The current document does not define a specific IOAM encapsulation.
   It should be noted that some IOAM encapsulation types may introduce
   specific security considerations.  A specification that defines an
   IOAM encapsulation is expected to address the respective
   encapsulation-specific security considerations.

   Notably, in most cases IOAM is expected to be deployed in specific
   network domains, thus confining the potential attack vectors to
   within the network domain.  A limited administrative domain provides
   the operator with the means to select, monitor, and control the
   access of all the network devices, making these devices trusted by
   the operator.  Indeed, in order to limit the scope of threats
   mentioned above to within the current network domain the network
   operator is expected to enforce policies that prevent IOAM traffic
   from leaking outside of the IOAM domain, and prevent IOAM data from
   outside the domain to be processed and used within the domain.  Note

   The security considerations of a system that the Immediate Export mode
   (reference to deploys IOAM, much like
   any system, should be added in reviewed on a future revision) can mitigate the
   potential per-deployment-scenario basis,
   based on a systems-specific threat analysis, which may lead to
   specific security solutions that are beyond the scope of the current
   document.  For example, in an IOAM data leaking through data packets. deployment that is not confined to
   a single LAN, but spans multiple inter-connected sites, the inter-
   site links may be secured (e.g., by IPsec) in order to avoid external
   threats.

9.  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, Andrew
   Yourtchenko, Aviv Kfir, Tianran Zhou and Zhenbin (Robin) 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, Tom Herbet, Herbert,
   Haoyu song, and Song, Mickey Spiegel.

   The authors would like to acknowledge the contribution of "Immediate
   export" of IOAM trace by Spiegel and Barak Gafni.

10.  References
10.1.  Normative References

   [IEEE1588v2]
              Institute of Electrical and Electronics Engineers, "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.  Informative References

   [I-D.ietf-ntp-packet-timestamps]
              Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
              Defining Packet Timestamps", draft-ietf-ntp-packet-
              timestamps-07
              timestamps-08 (work in progress), August 2019. February 2020.

   [I-D.ietf-nvo3-geneve]
              Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
              Network Virtualization Encapsulation", draft-ietf-
              nvo3-geneve-14
              nvo3-geneve-15 (work in progress), September 2019. February 2020.

   [I-D.ietf-nvo3-vxlan-gpe]
              Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
              Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-07 draft-ietf-nvo3-vxlan-gpe-09 (work
              in progress), April December 2019.

   [I-D.ietf-sfc-proof-of-transit]
              Brockners, F., Bhandari, S., Mizrahi, T., Dara, S., and S.
              Youell, "Proof of Transit", draft-ietf-sfc-proof-of-
              transit-03
              transit-04 (work in progress), September November 2019.

   [I-D.ioamteam-ippm-ioam-direct-export]
              Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F.,
              Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ
              OAM Direct Exporting", draft-ioamteam-ippm-ioam-direct-
              export-00 (work in progress), October 2019.

   [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.

   [I-D.spiegel-ippm-ioam-rawexport]
              Spiegel, M., Brockners, F., Bhandari, S., and R.
              Sivakolundu, "In-situ OAM raw data export with IPFIX",
              draft-spiegel-ippm-ioam-rawexport-02 (work in progress),
              July 2019.

   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,
              <https://www.rfc-editor.org/info/rfc7276>.

   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
              Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
              October 2014, <https://www.rfc-editor.org/info/rfc7384>.

   [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>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

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
   United States

   Email: john@leddy.net

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

   Email: stephen.youell@jpmorgan.com

   Tal Mizrahi
   Huawei Network.IO Innovation Lab
   Israel

   Email: tal.mizrahi.phd@gmail.com

   David Mozes

   Email: mosesster@gmail.com

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

   Email: petr@fb.com

   Remy Chang
   Barefoot Networks
   4750 Patrick Henry Drive
   Santa Clara, CA  95054
   US

   Email: remy@barefootnetworks.com
   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca

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

   Email: jennifer.lemon@broadcom.com