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Versions: 00 01 02 03

Network Working Group                                       F. Brockners
Internet-Draft                                               S. Bhandari
Intended status: Informational                                   S. Dara
Expires: September 14, 2017                                 C. Pignataro
                                                                   Cisco
                                                              H. Gredler
                                                            RtBrick Inc.
                                                                J. Leddy
                                                                 Comcast
                                                               S. Youell
                                                                    JMPC
                                                                D. Mozes
                                              Mellanox Technologies Ltd.
                                                              T. Mizrahi
                                                                 Marvell
                                                             P. Lapukhov
                                                                Facebook
                                                                R. Chang
                                                       Barefoot Networks
                                                          March 13, 2017


                      Requirements for In-situ OAM
               draft-brockners-inband-oam-requirements-03

Abstract

   This document discusses the motivation and requirements for including
   specific operational and telemetry information into data packets
   while the data packet traverses a path between two points in the
   network.  This method is referred to as "in-situ" Operations,
   Administration, and Maintenance (OAM), given that the OAM information
   is carried with the data packets as opposed to in "out-of-band"
   packets dedicated to OAM.  In situ OAM complements other OAM
   mechanisms which use dedicated probe packets to convey OAM
   information.

Status of This Memo

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

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





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   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 September 14, 2017.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Motivation for in-situ OAM  . . . . . . . . . . . . . . . . .   5
     3.1.  Path Congruency Issues with Dedicated OAM Packets . . . .   5
     3.2.  Results Sent to a System Other Than the Sender  . . . . .   6
     3.3.  Overlay and Underlay Correlation  . . . . . . . . . . . .   6
     3.4.  SLA Verification  . . . . . . . . . . . . . . . . . . . .   7
     3.5.  Analytics and Diagnostics . . . . . . . . . . . . . . . .   7
     3.6.  Frame Replication/Elimination Decision for Bi-casting
           /Active-active Networks . . . . . . . . . . . . . . . . .   8
     3.7.  Proof of Transit  . . . . . . . . . . . . . . . . . . . .   8
     3.8.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Considerations for In-situ OAM  . . . . . . . . . . . . . . .  11
     4.1.  Type of Information to be Recorded  . . . . . . . . . . .  11
     4.2.  MTU and Packet Size . . . . . . . . . . . . . . . . . . .  12
     4.3.  Administrative Boundaries . . . . . . . . . . . . . . . .  13
       4.3.1.  Layered In-Situ OAM Domains . . . . . . . . . . . . .  13
     4.4.  Selective Enablement  . . . . . . . . . . . . . . . . . .  14
     4.5.  Forwarding Behavior . . . . . . . . . . . . . . . . . . .  14
     4.6.  Optimization of Node and Interface Identifiers  . . . . .  14
     4.7.  Loop Communication Path (IPv6-specifics)  . . . . . . . .  15
   5.  Requirements for In-situ OAM Data Types . . . . . . . . . . .  15
     5.1.  Generic Requirements  . . . . . . . . . . . . . . . . . .  15
     5.2.  In-situ OAM Data with Per-hop Scope . . . . . . . . . . .  17



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     5.3.  In-situ OAM with Selected Hop Scope . . . . . . . . . . .  18
     5.4.  In-situ OAM with End-to-end Scope . . . . . . . . . . . .  18
   6.  Security Considerations and Requirements  . . . . . . . . . .  19
     6.1.  General considerations  . . . . . . . . . . . . . . . . .  19
     6.2.  Proof of Transit  . . . . . . . . . . . . . . . . . . . .  19
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   This document discusses requirements for "in-situ" Operations,
   Administration, and Maintenance (OAM) mechanisms.  In this context,
   "in-situ OAM" refers to the concept of directly encoding telemetry
   information within the data packet as it traverses the network or
   telemetry domain.  Mechanisms which add tracing or other types of
   telemetry information to the regular data traffic, sometimes also
   referred to as "in-band" OAM can complement active, probe-based
   mechanisms such as ping or traceroute, which are sometimes considered
   as "out-of-band", because the messages are transported independently
   from regular data traffic.  In terms of "active" or "passive" OAM,
   "in-situ" OAM can be considered a hybrid OAM type.  While no extra
   packets are sent, in-situ OAM adds information to the packets
   therefore cannot be considered passive.  In terms of the
   classification given in [RFC7799] in-situ OAM could be portrayed as
   "hybrid OAM, type 1".  "In-situ" mechanisms do not require extra
   packets to be sent and hence don't change the packet traffic mix
   within the network.  Traceroute and ping for example use ICMP
   messages: New packets are injected to get tracing information.  Those
   add to the number of messages in a network, which already might be
   highly loaded or suffering performance issues for a particular path
   or traffic type.

   A number of in-situ as well as in-band OAM mechanisms have been
   discussed, such as the INT spec for the P4 programming language [P4]
   or the SPUD prototype [I-D.hildebrand-spud-prototype].  The SPUD
   prototype uses a similar logic that allows network devices on the
   path between endpoints to participate explicitly in the tube outside
   the end-to-end context.  Even the IPv4 route-record option defined in
   [RFC0791] can be considered an in-situ OAM mechanism.  Per what was
   already stated, in-situ OAM complements "out-of-band" mechanisms such
   as ping or traceroute, or more recent active probing mechanisms, as
   described in [I-D.lapukhov-dataplane-probe].  In-situ OAM mechanisms
   can be leveraged where current out-of-band mechanisms do not apply or
   do not offer the desired characteristics or requirements, such as



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   proving that a certain set of traffic takes a pre-defined path,
   strict congruency between overlay and underlay transports is in
   place, checking service level agreements for the live data traffic,
   detailed statistics or verification of path selections within a
   domain, or scenarios where probe traffic is potentially handled
   differently from regular data traffic by the network devices.
   [RFC7276] presents an overview of OAM tools.

   Compared to probably the most basic example of "in-situ OAM" which is
   IPv4 route recording [RFC0791], an in-situ OAM approach has the
   following capabilities:

   a.  A flexible data format to allow different types of information to
       be captured as part of an in-situ OAM operation, including but
       not limited to path tracing information, operational and
       telemetry information such as timestamps, sequence numbers, or
       even generic data such as queue size, geo-location of the node
       that forwarded the packet, etc.

   b.  A data format to express node as well as link identifiers to
       record the path a packet takes with a fixed amount of added data.

   c.  The ability to determine whether any nodes were skipped while
       recording in-situ OAM information (i.e., in-situ OAM is not
       supported or not enabled on those nodes).

   d.  The ability to actively process information in the packet, for
       example to prove in a cryptographically secure way that a packet
       really took a pre-defined path using some traffic steering method
       such as service chaining or traffic engineering.

   e.  The ability to include OAM data beyond simple path information,
       such as timestamps or even generic data of a particular use case.

   f.  The ability to carry in-situ OAM data in various different
       transport protocols.

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:

   ECMP:      Equal Cost Multi-Path

   IOAM:      In-situ Operations, Administration, and Maintenance



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   LISP:      Locator/ID Separation Protocol

   MTU:       Maximum Transmit Unit

   NSH:       Network Service Header

   NFV:       Network Function Virtualization

   OAM:       Operations, Administration, and Maintenance

   PMTU:      Path MTU

   SFC:       Service Function Chain

   SLA:       Service Level Agreement

   SR:        Segment Routing

   SID:       Segment Identifier

   VXLAN-GPE: Virtual eXtensible Local Area Network, Generic Protocol
              Extension

   This document defines in-situ Operations, Administration, and
   Maintenance (in-situ OAM), as the subset in which OAM information is
   carried along with data packets.  This is as opposed to "out-of-band
   OAM", where specific packets are dedicated to carrying OAM
   information.

3.  Motivation for in-situ OAM

   In several scenarios it is beneficial to make information about the
   path a packet took through the network or through a network device as
   well as associated telemetry information available to the operator.
   This includes not only tasks like debugging, troubleshooting, as well
   as network planning and network optimization but also policy or
   service level agreement compliance checks.  This section discusses
   the motivation to introduce new methods for enhanced in-situ network
   diagnostics.

3.1.  Path Congruency Issues with Dedicated OAM Packets

   Packet scheduling algorithms, especially for balancing traffic across
   equal cost paths or links, often leverage information contained
   within the packet, such as protocol number, IP-address or MAC-
   address.  Probe packets would thus either need to be sent from the
   exact same endpoints with the exact same parameters, or probe packets
   would need to be artificially constructed as "fake" packets and



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   inserted along the path.  Both approaches are often not feasible from
   an operational perspective, be it that access to the end-system is
   not feasible, or that the diversity of parameters and associated
   probe packets to be created is simply too large.  An in-situ
   mechanism is an alternative in those cases.

   In-situ mechanisms are not impacted by differences in the handling of
   probe traffic compared to other data packets, where probe traffic is
   handled differently (and potentially forwarded differently) by a
   router than regular data traffic.  This obviously assumes that the
   addition of in-situ information does not change the forwarding
   behavior of the packet.  Note that in certain implementations, the
   addition information to a transport protocol changes the forwarding
   behavior.  IPv6 extension header processing is one example.  Some
   implementations process IPv6 packets with extension headers in the
   "slow" path of a router, as opposed to the "fast" path.

3.2.  Results Sent to a System Other Than the Sender

   Traditional ping and traceroute tools return the OAM results to the
   sender of the probe.  Even when the ICMP messages that are used with
   these tools are enhanced, and additional telemetry is collected
   (e.g., ICMP Multi-Part [RFC4884] supporting MPLS information
   [RFC4950], Interface and Next-Hop Identification [RFC5837], etc.), it
   would be advantageous to separate the sending of an OAM probe from
   the receiving of the telemetry data.  In this context, it is helpful
   to eliminate the requirement that there be a working bidirectional
   path.

3.3.  Overlay and Underlay Correlation

   Several network deployments leverage tunneling mechanisms to create
   overlay or service-layer networks.  Examples include VXLAN-GPE, GRE,
   or LISP.  One often observed attribute of overlay networks is that
   they do not offer the user of the overlay any insight into the
   underlay network.  This means that the path that a particular
   tunneled packet takes, nor other operational details such as the per-
   hop delay/jitter in the underlay are visible to the user of the
   overlay network, giving rise to diagnosis and debugging challenges in
   case of connectivity or performance issues.  The scope of OAM tools
   like ping or traceroute is limited to either the overlay or the
   underlay which means that the user of the overlay has typically no
   access to OAM in the underlay, unless specific operational procedures
   are put in place.  With in-situ OAM the operator of the underlay can
   offer details of the connectivity in the underlay to the user of the
   overlay.  This could include the ability to find out which underlay
   elements are shared by overlays and ability to know which overlays
   are mapped to the same underlay elements.  Deployment dependent



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   underlay transit nodes can be configured to update OAM information in
   the overlay transport encapsulation.  The operator of the egress
   tunnel router could choose to share the recorded information about
   the path with the user of the overlay.

   Coupled with mechanisms such as Segment Routing (SR)
   [I-D.ietf-spring-segment-routing], overlay network and underlay
   network can be more tightly coupled: The user of the overlay has
   detailed diagnostic information available in case of failure
   conditions.  The user of the overlay can also use the path recording
   information as input to traffic steering or traffic engineering
   mechanisms, to for example achieve path symmetry for the traffic
   between two endpoints.  [I-D.brockners-lisp-sr] is an example for how
   these methods can be applied to LISP.

3.4.  SLA Verification

   In-situ OAM can help users of an overlay-service to verify that
   negotiated SLAs for the real traffic are met by the underlay network
   provider.  Different from solutions which rely on active probes to
   test an SLA, in-situ OAM based mechanisms avoid wrong interpretations
   and "cheating", which can happen if the probe traffic that is used to
   perform SLA-check is prioritized by the network provider of the
   underlay.  In active/standby deployments in-situ OAM would only allow
   for SLA verification of the active path.

3.5.  Analytics and Diagnostics

   Network planners and operators benefit from knowledge of the actual
   traffic distribution in the network.  When deriving an overall
   network connectivity traffic matrix one typically needs to correlate
   data gathered from each individual device in the network.  If the
   path of a packet is recorded while the packet is forwarded, the
   entire path that a packet took through the network is available to
   the egress system.  This obviates the need to retrieve individual
   traffic statistics from every device in the network and correlate
   those statistics, or employ other mechanisms such as leveraging
   traffic engineering with null-bandwidth tunnels just to retrieve the
   appropriate statistics to generate the traffic matrix.

   In addition, with individual path tracing, information is available
   at packet level granularity, rather than only at aggregate level - as
   is usually the case with IPFIX-style methods which employ flow-
   filters at the network elements.  Data-center networks which use
   equal-cost multipath (ECMP) forwarding are one example where detailed
   statistics on flow distribution in the network are highly desired.
   If a network supports ECMP, one can create detailed statistics for
   the different paths packets take through the network at the egress



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   system, without a need to correlate/aggregate statistics from every
   router in the system.  Transit devices are off-loaded from the task
   of gathering packet statistics.

   In high-speed networks one can leverage and benefit from packet-
   accurate measurements with for example hardware-accurate timestamping
   (i.e., nanosecond-level verification) to support optimized packet
   scheduling and queuing mechanisms.

3.6.  Frame Replication/Elimination Decision for Bi-casting/Active-
      active Networks

   Bandwidth- and power-constrained, time-sensitive, or loss-intolerant
   networks (e.g., networks for industry automation/control, health
   care) require efficient OAM methods to decide when to replicate
   packets to a secondary path in order to keep the loss/error-rate for
   the receiver at a tolerable level - and also when to stop replication
   and eliminate the redundant flow.  Many Internet of Things (IoT)
   networks are time sensitive and cannot leverage automatic
   retransmission requests (ARQ) to cope with transmission errors or
   lost packets.  Transmitting the data over multiple disparate paths
   (often called bi-casting or live-live) is a method used to reduce the
   error rate observed by the receiver.  Time sensitive networks (TSN)
   receive a lot of attention from the manufacturing industry as shown
   by a various standardization activities and industry forums being
   formed (see e.g., IETF 6TiSCH, IEEE P802.1CB, AVnu).

3.7.  Proof of Transit

   Several deployments use traffic engineering, policy routing, segment
   routing or Service Function Chaining (SFC) [RFC7665] to steer packets
   through a specific set of nodes.  In certain cases regulatory
   obligations or a compliance policy require to prove that all packets
   that are supposed to follow a specific path are indeed being
   forwarded across the exact set of nodes specified.  If a packet flow
   is supposed to go through a series of service functions or network
   nodes, it has to be proven that all packets of the flow actually went
   through the service chain or collection of nodes specified by the
   policy.  In case the packets of a flow weren't appropriately
   processed, a verification device would be required to identify the
   policy violation and take corresponding actions (e.g., drop or
   redirect the packet, send an alert etc.) corresponding to the policy.
   In today's deployments, the proof that a packet traversed a
   particular service chain is typically delivered in an indirect way:
   Service appliances and network forwarding are in different trust
   domains.  Physical hand-off-points are defined between these trust
   domains (i.e., physical interfaces).  Or in other terms, in the
   "network forwarding domain" things are wired up in a way that traffic



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   is delivered to the ingress interface of a service appliance and
   received back from an egress interface of a service appliance.  This
   "wiring" is verified and trusted.  The evolution to Network Function
   Virtualization (NFV) and modern service chaining concepts (using
   technologies such as Locator/ID Separation Protocol (LISP), Network
   Service Header (NSH), Segment Routing (SR), etc.) blurs the line
   between the different trust domains, because the hand-off-points are
   no longer clearly defined physical interfaces, but are virtual
   interfaces.  Because of that very reason, networks operators require
   that different trust layers not to be mixed in the same device.  For
   an NFV scenario a different proof is required.  Offering a proof that
   a packet traversed a specific set of service functions would allow
   network operators to move away from the above described indirect
   methods of proving that a service chain is in place for a particular
   application.

   Deployed service chains without the presence of a "proof of transit"
   mechanism are typically operated as fail-open system: The packets
   that arrive at the end of a service chain are processed.  Adding
   "proof of transit" capabilities to a service chain allows an operator
   to turn a fail-open system into a fail-close system, i.e.  packets
   that did not properly traverse the service chain can be blocked.

   A solution approach could be based on OAM data which is added to
   every packet for achieving Proof Of Transit (POT).The OAM data is
   updated at every hop and is used to verify whether a packet traversed
   all required nodes.  When the verifier receives each packet, it can
   validate whether the packet traversed the service chain correctly.
   The detailed mechanisms used for path verification along with the
   procedures applied to the OAM data carried in the packet for path
   verification are beyond the scope of this document.  Details are
   addressed in [I-D.brockners-proof-of-transit].  In this document the
   term "proof" refers to a discrete set of bits that represents an
   integer or string carried as OAM data.  The OAM data is used to
   verify whether a packet traversed the nodes it is supposed to
   traverse.

3.8.  Use Cases

   In-situ OAM could be leveraged for several use cases, including:

   o  Traffic Matrix: Derive the network traffic matrix: Traffic for a
      given time interval between any two edge nodes of a given domain.
      Could be performed for all traffic or on a per Quality of Service
      (QoS) class.

   o  Flow Debugging: Discover which path(s) a particular set of traffic
      (identified by an n-tuple) takes in the network.  Such a procedure



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      is particularly useful in case traffic is balanced across multiple
      paths, like with link aggregation (LACP) or equal cost multi-
      pathing (ECMP).

   o  Loss Statistics per Path: Retrieve loss statistics per flow and
      path in the network.

   o  Path Heat Maps: Discover highly utilized links in the network.

   o  Trend Analysis on Traffic Patterns: Analyze if (and if so how) the
      forwarding path for a specific set of traffic changes over time
      (can give hints to routing issues, unstable links etc.)

   o  Network Delay Distribution: Show delay distribution across network
      by node or links.  If enabled per application or for a specific
      flow then display the path taken along with the delay incurred at
      every hop.

   o  SLA Verification: Verify that a negotiated service level agreement
      (SLA), e.g., for packet drop rates or delay/jitter is conformed to
      by the actual traffic.

   o  Low-power Networks: Include application level OAM information
      (e.g., battery charge level, cache or buffer fill level) into data
      traffic to avoid sending extra OAM traffic which incur an extra
      cost on the devices.  Using the battery charge level as example,
      one could avoid sending extra OAM packets just to communicate
      battery health, and as such would save battery on sensors.

   o  Path Verification or Service Function Path Verification: Proof and
      verification of packets traversing check points in the network,
      where check points can be nodes in the network or service
      functions.

   o  Geo-location Policy: Network policy implemented based on which
      path packets took.  Example: Only if packets originated and stayed
      within the trading-floor department, access to specific
      applications or servers is granted.

   o  Device-level Troubleshooting and Optimization: In many cases,
      network operators could benefit from information specific to a
      single device.  A non-exhaustive list of useful information
      includes: queue-depths, buffer utilization (either shared or per-
      port), packet latency measured from a known starting point, packet
      latency introduced by a single device, and resource utilization
      (CPU, memory, link bandwidth) of a given device or link.  In some
      cases, this information changes over per-packet timescales (i.e.,
      nanoseconds) and as such it is extremely challenging to collect



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      and report this info in an accurate and scalable manner.  By
      encoding the information from the forwarding element directly
      within a data packet (i.e., within the 'fast-path') this
      information can be added to some or all data packets and then
      collected and analyzed by human or machine tools.  This type of
      information is particularly valuable for troubleshooting low-level
      device errors as well as providing a knowledge feedback loop for
      network and device optimization.

   o  Custom Network Probing: Active network probing and in-situ OAM can
      be combined for customized and efficient network probing.  This
      could for example be a customized traceroute.

4.  Considerations for In-situ OAM

   The implementation of an in-situ OAM mechanism needs to take several
   considerations into account, including administrative boundaries, how
   information is recorded, Maximum Transfer Unit (MTU), Path MTU
   Discovery (PMTUD) and packet size, etc.

4.1.  Type of Information to be Recorded

   The information gathered for in-situ OAM can be categorized into
   three main categories: Information with a per-hop scope, such as path
   tracing; information which applies to a specific set of hops, such as
   path or service chain verification; information which only applies to
   the edges of a domain, such as sequence numbers.  Note that a single
   network device could comprise several in-situ OAM hops, for example
   in case one wants to trace the path of a packet through that device.

   o  "edge to edge": Information that needs to be shared between
      network edges (the "edge" of a network could either be a host or a
      domain edge device): Edge to edge data e.g., packet and octet
      count of data entering a well-defined domain and leaving it is
      helpful in building traffic matrix, sequence number (also called
      "path packet counters") is useful for the flow to detect packet
      loss.

   o  "selected hops": Information that applies to a specific set of
      nodes only.  In case of path verification, only the nodes which
      are "check points" are required to interpret and update the
      information in the packet.

   o  "per hop": Information that is gathered at every hop along the
      path a packet traverses within an administrative domain:

      *  Hop by Hop information e.g., Nodes visited for path tracing,
         Timestamps at each hop to find delays along the path



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      *  Stats collection at each hop to optimize communication in
         resource constrained networks e.g., battery, CPU, memory status
         of each node piggy backed in a data packet is useful in low
         power lossy networks where network nodes are mostly asleep and
         communication is expensive

4.2.  MTU and Packet Size

   The recorded data at every hop might lead to packet size exceeding
   the Maximum Transmit Unit (MTU).  A detailed discussion of the
   implications of oversized IPv6 header chains is found in [RFC7112].
   The Path MTU restricts the amount of data that can be recorded for
   purpose of OAM within a data packet.

   If in-situ OAM data is inserted at the edge of the domain (e.g., by
   intermediate routers) then the MTU on all interfaces with the domain
   (MTU_INT) MUST be >= the maximum MTU on any "external" facing
   interfaces (MTU_EXT) and the total size of in-situ OAM data to be
   recorded MUST be <= (MTU_INT - MTU_EXT).

   In-situ OAM comprises two approaches to insert OAM data fields in the
   packets:

   o  Pre-allocated: In this case, the encapsulating node inserts empty
      data fields into the packet to cover the entire domain.  The data
      fields will be incrementally updated/filled as the packet
      progresses through the network.  With pre-allocation the packet
      size is only changed at the encapsulating node and is kept
      constant throughout the domain.  The pre-allocated approach is
      beneficial for software data-plane implementations where
      allocating the required space only once and index into the array
      to populate the data during transit avoids copy operations at
      every hop.

   o  Incremental: Every node that desires to include in-situ OAM
      information extends the packet as needed.  The incremental
      approach is beneficial for hardware data-plane implementations as
      it eliminates the need for the transit nodes to read the full
      array and lookup the pointer in the option prior to updating the
      data fields contents.

   The "incremental" or the "pre-allocated" approaches could even be
   combined in the same deployment - in which case two in-situ OAM
   headers would be present in the packet: One for the incremental
   approach and one for the pre-allocated approach.  In such a case one
   would expect that nodes with a hardware data-plane would update the
   incremental header, whereas nodes with a software data-plane would
   process the pre-allocated header.



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4.3.  Administrative Boundaries

   There are several challenges in enabling in-situ OAM in the public
   Internet as well as in corporate/enterprise networks across
   administrative domains, which include but are not limited to:

   o  Deployment dependent, the data fields that in-situ OAM requires as
      part of a specific transport protocol may not be supported across
      administrative boundaries.

   o  Current OAM implementations are often done in the slow path, i.e.,
      OAM packets are punted to router's CPU for processing.  This leads
      to performance and scaling issues and opens up routers for attacks
      such as Denial of Service (DoS) attacks.

   o  Discovery of network topology and details of the network devices
      across administrative boundaries may open up attack vectors
      compromising network security.

   o  Specifically on IPv6: At the administrative boundaries IPv6
      packets with extension headers are dropped for several reasons
      described in [RFC7872].

   The following considerations will be discussed in a future version of
   this document: If the packet is dropped due to the presence of the
   in-situ OAM; If the policy failure is treated as feature disablement
   and any further recording is stopped but the packet itself is not
   dropped, it may lead to every node in the path to make this policy
   decision.

4.3.1.  Layered In-Situ OAM Domains

   Like any OAM domain, in-situ OAM domains could also be layered/
   nested.  Layering/nesting of in-situ OAM follows the general approach
   of OAM layering: An in-situ OAM domain consists of maintenance end-
   points (MEP) and maintenance intermediate points (MIP).  MEP add to
   or remove the entire set of in-situ OAM data fields from the traffic,
   while only MIP update or add in-situ OAM data fields.  When in-situ
   OAM layering is employed, a MEP of one layer becomes a MIP in the
   layer above, while MIP of the lower layer are not visible to the
   layer above - unless specifically configured otherwise.

   Consider the following examples:

   o  NSH over IPv6: In-situ OAM data fields could be present in both
      transport protocols: NSH and IPv6, with NSH forming the overlay
      network and IPv6 forming the underlay network.  The network which
      deploys NSH would form an in-situ OAM domain.  In addition each



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      IPv6 underlay network which connects two NSH nodes forms an in-
      situ OAM domain.  The in-situ OAM domain with NSH as transport
      could be considered as layered on top of the different in-situ OAM
      domains which use IPv6 as transport.

   o  NSH using an in-situ OAM aware transport: Consider a case where
      the underlay network would not natively support in-situ OAM, still
      the individual transport nodes would have the capability to "look
      deep into the packet" and update/add in-situ OAM information in
      the NSH header.  The in-situ OAM domain with NSH as transport
      could be considered as layered on top of the different in-situ OAM
      domains which are in-situ OAM aware and connect the individual NSH
      nodes.

4.4.  Selective Enablement

   The ability to selectively enable in-situ OAM is valuable.  While it
   may be desirable to enable data collection on all traffic or devices,
   this may not always be feasible.  In-situ OAM collection may also
   come with a performance impact to forwarding rates or feature
   capabilities, which may be acceptable in only some locations.  For
   example, the SPUD prototype uses the notion of "pipes" to describe
   the portion of the traffic that could be subject to in-path
   inspection.  Mechanisms to decide which traffic would be subject to
   in-situ OAM are outside the scope of this document.

4.5.  Forwarding Behavior

   In-situ OAM adds additional data fields to live user traffic and as
   such changes the packet which is also why in-situ OAM is
   characterized as "hybrid, type 1" OAM.  The effectiveness of in-situ
   OAM as a tool for operations depends on forwarding nodes not altering
   their forwarding behavior in case of in-situ OAM data fields being
   present in the packet.  As a consequence, an implementation of in-
   situ OAM should not change the forwarding behavior of the packet,
   i.e.  packets with or without in-situ OAM data fields should be
   handled the same way by a forwarding node (see also the associated
   requirement further below).  Note that there are implementations
   where the addition of meta-data to live user traffic might cause the
   forwarding behavior of the packet to change, e.g. certain
   implementation handle IPv6 packets with or without extension headers
   differently (see [RFC7872]).

4.6.  Optimization of Node and Interface Identifiers

   Since packets have a finite maximum size, the data recording or
   carrying capacity of one packet in which the in-situ OAM metadata is
   present is limited.  In-situ OAM should use its own dedicated



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   namespace (confined to the domain in-situ OAM operates in) to
   represent node and interface IDs to save space in the header.
   Generic representations of node and interface identifiers which are
   globally unique (such as a UUID) would consume significantly more
   bits of in-situ OAM data.

4.7.  Loop Communication Path (IPv6-specifics)

   When recorded data is required to be analyzed on a source node that
   issues a packet and inserts in-situ OAM data, the recorded data needs
   to be carried back to the source node.

   One way to carry the in-situ OAM data back to the source is to
   utilize an ICMP Echo Request/Reply (ping) or ICMPv6 Echo Request/
   Reply (ping6) mechanism.  In order to run the in-situ OAM mechanism
   appropriately on the ping/ping6 mechanism, the following two
   operations should be implemented by the ping/ping6 target node:

   1.  All of the in-situ OAM fields would be copied from an Echo
       Request message to an Echo Reply message.

   2.  The Hop Limit field of the IPv6 header of these messages would be
       copied as a continuous sequence.  Further considerations are
       addressed in a future version of this document.

5.  Requirements for In-situ OAM Data Types

   The above discussed use cases require different types of in-situ OAM
   data.  This section details requirements for in-situ OAM derived from
   the discussion above.

5.1.  Generic Requirements

   REQ-G1:   Classification: It should be possible to enable in-situ OAM
             on a selected set of traffic (e.g., per interface, based on
             an access control list specifying a specific set of
             traffic, etc.)  The selected set of traffic can also be all
             traffic.

   REQ-G2:   Scope: If in-situ OAM is used only within a specific
             domain, provisions need to be put in place to ensure that
             in-situ OAM data stays within the specific domain only.

   REQ-G3:   Transport independence: Data formats for in-situ OAM shall
             be defined in a transport independent way.  In-situ OAM
             applies to a variety of transport protocols.
             Encapsulations should be defined how the generic data
             formats are carried by a specific protocol.



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   REQ-G4:   Layering: It should be possible to have in-situ OAM
             information for different transport protocol layers be
             present in several fields within a single packet.  This
             could for example be the case when tunnels are employed and
             in-situ OAM information is to be gathered for both the
             underlay as well as the overlay network.  Layering support
             should not be limited to just underlay and overlay, but
             include more than two layers.

   REQ-G5:   MTU size: With in-situ OAM information added, packets MUST
             NOT become larger than the path MTU.

             REQ-G5.1:  If due to some reason a packet which contains in
                        situ OAM data fields cannot be forwarded due to
                        the presence of in-situ OAM data fields, the
                        node SHOULD remove the in situ OAM data fields
                        and forward the packet, rather than drop the
                        entire packet.

             REQ-G5.2:  If the encapsulating router is unable to insert
                        in-situ OAM data fields into a packet, e.g., due
                        to MTU issues, even though it is configured to
                        do so, it should use some operational means to
                        inform the operator (e.g., syslog) about the
                        inability to add in-situ OAM data fields.  Even
                        if the in-situ OAM encapsulating node fails to
                        add in-situ OAM data fields, it should forward
                        the packet normally.

             REQ-G5.3:  MTU size consideration for in-situ OAM MUST take
                        domain specifics into account, e.g., changes of
                        the domain topology due to path protection
                        mechanisms might extend the hop count of a path
                        etc.

   REQ-G6:   Data structure reuse: The data fields and associated types
             defined and used for in-situ OAM ought to be reusable for
             out-of-band OAM telemetry as well.

   REQ-G7:   Data fields: It is desirable that the format of in-situ OAM
             data fields leverages already defined data formats for OAM
             as much as feasible.

   REQ-G8:   Combination with active OAM mechanisms: In-situ OAM should
             be usable for active network probing, like for example a
             customized version of traceroute.  Decapsulating in-situ
             OAM nodes may have an ability to send the in-situ OAM




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             information retrieved from the packet back to the source
             address of the packet or to the encapsulating node.

   REQ-G9:   Unaltered forwarding behavior of in-situ OAM nodes: The
             addition of in-situ OAM data fields should not change the
             way packets are forwarded within the in-situ OAM domain.

   REQ-G10:  Layering of in-situ OAM domains: It should be possible to
             layer in-situ OAM domains on each other.  Layering should
             be supported within the same, as well as with different
             transport protocols which carry in-situ OAM data fields.

5.2.  In-situ OAM Data with Per-hop Scope

   REQ-H1:  Missing nodes detection: Data shall be present that allows a
            node to detect whether all nodes that might participate in
            in-situ OAM operations have indeed participated.

   REQ-H2:  Node, instance or device identifier: Data shall be present
            that allows to retrieve the identity of the entity reporting
            telemetry information.  The entity can be a device, or a
            subsystem/component within a device.  The latter will allow
            for packet tracing within a device in much the same way as
            between devices.

   REQ-H3:  Ingress interface identifier: Data shall be present that
            allows the identification of the interface a particular
            packet was received from.  The interface can be a logical
            and/or physical entity.

   REQ-H4:  Egress interface identifier: Data shall be present that
            allows the identification of the interface a particular
            packet was forwarded to.  Interface can be a logical or
            physical entity.

   REQ-H5:  Time-related requirements

            REQ-H5.1:  Delay: Data shall be present that allows to
                       retrieve the delay between two or more points of
                       interest within the system.  Those points can be
                       within the same device or on different devices.

            REQ-H5.2:  Jitter: Data shall be present that allows to
                       retrieve the jitter between two or more points of
                       interest within the system.  Those points can be
                       within the same device or on different devices.
                       Jitter can be derived from the different




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                       timestamps gathered and does not necessarily need
                       to be an explicit data field.

            REQ-H5.3:  Wall-clock time: Data shall be present that
                       allows to retrieve the wall-clock time visited a
                       particular point of interest in the system.

            REQ-H5.4:  Time precision: Time with different precision
                       should be supported.  Use-case dependent, the
                       required precision could e.g., be nanoseconds,
                       microseconds, milliseconds, or seconds.

   REQ-H6:  Generic data fields (like e.g., GPS/Geo-location
            information): It should be possible to add user-defined OAM
            data at select hops to the packet.  The semantics of the
            data are defined by the user.

5.3.  In-situ OAM with Selected Hop Scope

   REQ-S1:  Proof of transit: Data shall be present which allows to
            securely prove that a packet has visited or ore several
            particular points of interest (i.e., a particular set of
            nodes).

            REQ-S1.1:  In case "Shamir's secret sharing scheme" is used
                       for proof of transit, two data fields, "random"
                       and "cumulative" shall be present.  The number of
                       bits used for "random" and "cumulative" data
                       fields can vary between deployments and should
                       thus be configurable.

            REQ-S1.2:  Enable a fail-open service chaining system to be
                       converted into a fail-closed service chaining
                       system.

5.4.  In-situ OAM with End-to-end Scope

   REQ-E1:  Sequence numbering:

            REQ-E1.1:  Reordering detection: It should be possible to
                       detect whether packets have been reordered while
                       traversing an in situ OAM domain.

            REQ-E1.2:  Duplicates detection: It should be possible to
                       detect whether packets have been duplicated while
                       traversing an in situ OAM domain.





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            REQ-E1.3:  Detection of packet drops: It should be possible
                       to detect whether packets have been dropped while
                       traversing an in-situ OAM domain.

6.  Security Considerations and Requirements

6.1.  General considerations

   General Security considerations will be expanded on in a later
   version of this document.

   In-situ OAM is considered a "per domain" feature, where one or
   several operators decide on leveraging and configuring in-situ OAM
   according to their needs.  Still operators need to properly secure
   the in-situ OAM domain to avoid malicious configuration and use,
   which could include injecting malicious in-situ OAM packets into a
   domain.

6.2.  Proof of Transit

   Threat Model: Attacks on the deployments could be due to malicious
   administrators or accidental misconfiguration resulting in bypassing
   of certain nodes.  The solution approach should meet the following
   requirements:

   REQ-SEC1:  Sound Proof of Transit: A valid and verifiable proof that
              the packet definitively traversed through all the nodes as
              expected.  Probabilistic methods to achieve this should be
              avoided, as the same could be exploited by an attacker.

   REQ-SEC2:  Tampering of meta data: An active attacker should not be
              able to insert or modify or delete meta data in whole or
              in parts and bypass few (or all) nodes.  Any deviation
              from the expected path should be accurately determined.

   REQ-SEC3:  Replay Attacks: A attacker (active/passive) should not be
              able to reuse the POT bits in the packet by observing the
              OAM data in the packet, packet characteristics (like IP
              addresses, octets transferred, timestamps) or even the
              proof bits themselves.  The solution approach should
              consider usage of these parameters for deriving any
              secrets cautiously.  Mitigating replay attacks beyond a
              window of longer duration could be intractable to achieve
              with fixed number of bits allocated for proof.

   REQ-SEC4:  Pre-play Attacks: A active attacker should not be able to
              generate or reuse valid POT bits from legitimate packets,
              in order to prove to the verifier as valid packets.  This



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              slight variant of replay attacks.  The attacker extracts
              POT bits from legitimate packets and ensure they do not
              reach the verifier.  Subsequently reuse those POT bits in
              crafted packets.

   REQ-SEC5:  Recycle Secrets: Any configuration of the secrets (like
              cryptographic keys, initialization vectors etc.) either in
              the controller or service functions should be re-
              configurable.  Solution approach should enable controls,
              API calls etc. needed in order to perform such recycling.
              It is desirable to provide recommendations on the duration
              of rotation cycles needed for the secure functioning of
              the overall system.

   REQ-SEC6:  Secret storage and distribution: Secrets should be shared
              with the devices over secure channels.  Methods should be
              put in place so that secrets cannot be retrieved by non-
              authorized personnel from the devices.

7.  IANA Considerations

   [RFC Editor: please remove this section prior to publication.]

   This document has no IANA actions.

8.  Acknowledgements

   The authors would like to thank Jen Linkova, LJ Wobker, Eric Vyncke,
   Nalini Elkins, Srihari Raghavan, Ranganathan T S, Karthik Babu
   Harichandra Babu, Akshaya Nadahalli, Ignas Bagdonas, LJ Wobker, Erik
   Nordmark, Vengada Prasad Govindan, and Andrew Yourtchenko for the
   comments and advice.  This document leverages and builds on top of
   several concepts described in [I-D.kitamura-ipv6-record-route].  The
   authors would like to acknowledge the work done by the author Hiroshi
   Kitamura and people involved in writing it.

9.  References

9.1.  Normative References

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







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9.2.  Informative References

   [I-D.brockners-lisp-sr]
              Brockners, F., Bhandari, S., Maino, F., and D. Lewis,
              "LISP Extensions for Segment Routing", draft-brockners-
              lisp-sr-01 (work in progress), February 2014.

   [I-D.brockners-proof-of-transit]
              Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
              Leddy, J., Youell, S., Mozes, D., and T. Mizrahi, "Proof
              of Transit", draft-brockners-proof-of-transit-02 (work in
              progress), October 2016.

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

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-10 (work in progress), November
              2016.

   [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.

   [P4]       Kim, , "P4: In-band Network Telemetry (INT)", September
              2015.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <http://www.rfc-editor.org/info/rfc791>.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              DOI 10.17487/RFC4884, April 2007,
              <http://www.rfc-editor.org/info/rfc4884>.






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   [RFC4950]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
              Extensions for Multiprotocol Label Switching", RFC 4950,
              DOI 10.17487/RFC4950, August 2007,
              <http://www.rfc-editor.org/info/rfc4950>.

   [RFC5837]  Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
              N., and JR. Rivers, "Extending ICMP for Interface and
              Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
              April 2010, <http://www.rfc-editor.org/info/rfc5837>.

   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112,
              DOI 10.17487/RFC7112, January 2014,
              <http://www.rfc-editor.org/info/rfc7112>.

   [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,
              <http://www.rfc-editor.org/info/rfc7276>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <http://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, <http://www.rfc-editor.org/info/rfc7799>.

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,
              <http://www.rfc-editor.org/info/rfc7872>.

Authors' Addresses

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

   Email: fbrockne@cisco.com






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

   Email: shwethab@cisco.com


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

   Email: sadara@cisco.com


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

   Email: cpignata@cisco.com


   Hannes Gredler
   RtBrick Inc.

   Email: hannes@rtbrick.com


   John Leddy
   Comcast

   Email: John_Leddy@cable.comcast.com


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

   Email: stephen.youell@jpmorgan.com





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   David Mozes
   Mellanox Technologies Ltd.

   Email: davidm@mellanox.com


   Tal Mizrahi
   Marvell
   6 Hamada St.
   Yokneam  20692
   Israel

   Email: talmi@marvell.com


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

   URI:   petr@fb.com


   Remy Chang
   Barefoot Networks

   Email: remy@barefootnetworks.com























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