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<rfc category="std" xmlns:xi="http://www.w3.org/2001/XInclude" docName="draft-ietf-6man-spring-srv6-oam-13"
     ipr="trust200902"> number="9259" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" category="std" consensus="true" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

  <!-- xml2rfc v2v3 conversion 3.12.2 -->
  <front>
    <title abbrev="SRv6 OAM">Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with over IPv6 Data plane (SRv6)</title>
    <seriesInfo name="RFC" value="9259"/>
    <author fullname="Zafar Ali" initials="Z" surname="Ali">
      <organization>Cisco Systems</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>zali@cisco.com</email>
      </address>
    </author>
    <author fullname="Clarence Filsfils" initials="C." surname="Filsfils">
      <organization>Cisco Systems</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>cfilsfil@cisco.com</email>
      </address>
    </author>
    <author fullname="Satoru Matsushima" initials="S" surname="Matsushima">
      <organization>Softbank</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>satoru.matsushima@g.softbank.co.jp</email>
      </address>
    </author>
    <author fullname="Daniel Voyer" initials="D" surname="Voyer">
      <organization>Bell Canada</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>daniel.voyer@bell.ca</email>
      </address>
    </author>
    <author fullname="Mach fullname="Mach(Guoyi) Chen" initials="M" surname="Chen">
      <organization>Huawei</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>mach.chen@huawei.com</email>
      </address>
    </author>
    <date year="2022"/>

    <area>Routing</area> year="2022" month="June" />
    <area>int</area>
    <workgroup>6man</workgroup>
    <keyword>SRv6</keyword>
    <keyword>Segment Routing</keyword>
    <keyword>OAM</keyword>
    <abstract>
      <t>This document describes how the existing IPv6 mechanisms for ping
      and traceroute can be used in an SRv6 a Segment Routing over IPv6 (SRv6) network.
      The document also specifies the OAM flag (O-flag) in the Segment Routing Header (SRH)
      for performing controllable and predictable flow sampling from segment endpoints.
      In addition, the document describes how a centralized monitoring system performs a
      path continuity check between any nodes within an SRv6 domain.
      </t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>
   As Segment Routing with over IPv6 data plane (SRv6) <xref target="RFC8402"/> target="RFC8402" format="default"/>
   simply adds a new type
   of Routing Extension Header, existing IPv6 OAM mechanisms can be used
   in an SRv6 network.  This document describes how the existing
   IPv6 mechanisms for ping and traceroute can be used in an SRv6 network.
   This includes illustrations of pinging an SRv6 SID Segment Identifier (SID) to
   verify that the SID is reachable and is locally programmed at the target node.
   This also includes illustrations for
   tracerouting to an SRv6 SID for hop-by-hop
   fault localization as well as path tracing to a SID.

      </t>
      <t>
   The
   This document also introduces enhancements for the OAM mechanism for SRv6
   networks for
   performing that allow controllable and predictable flow sampling from segment
   endpoints using, e.g., the IP Flow Information Export (IPFIX) protocol
   <xref target="RFC7011"/>. target="RFC7011" format="default"/>. Specifically, the document
   specifies the
   O-flag OAM flag (O-flag) in the SRH as a marking-bit marking bit in the user
   packets to trigger the telemetry data collection and export at the segment
   endpoints.
      </t>
      <t>
   The
   This document also outlines how the centralized OAM technique in
   <xref target="RFC8403"/> target="RFC8403" format="default"/> can be extended for SRv6 to perform a path continuity check between
   any nodes within an SRv6 domain.
   Specifically, the document illustrates how a centralized monitoring system can
   monitor arbitrary SRv6 paths by
   creating the loopback probes that
   originate and terminate at the centralized monitoring system.

      </t>
      <section title="Requirements Language">
    <t>The numbered="true" toc="default">
        <name>Requirements Language</name>
        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
    described in
    BCP 14 BCP&nbsp;14 <xref target="RFC2119" /> target="RFC2119"/> <xref target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>

      </section>
      <section title="Abbreviations"> numbered="true" toc="default">
        <name>Abbreviations</name>
        <t> The following abbreviations are used in this document:

        <list style="hanging">

            <t> SID: Segment ID.
        </t>

            <t> SL: Segments Left.
           </t>

            <t> SR: Segment Routing.
           </t>

            <t> SRH: Segment
        <dl newline="false" spacing="normal">
          <dt>SID:</dt>
          <dd>Segment Identifier
            </dd>
          <dt>SL:</dt>
          <dd>Segments Left
           </dd>
          <dt>SR:</dt>
          <dd>Segment Routing
           </dd>
          <dt>SRH:</dt>
          <dd>Segment Routing Header <xref target="RFC8754"/>.
           </t>

            <t> SRv6: Segment target="RFC8754" format="default"/>
           </dd>
          <dt>SRv6:</dt>
          <dd>Segment Routing with over IPv6 Data plane.
           </t>

            <t> PSP: Penultimate <xref target="RFC8402" format="default"/>
           </dd>
          <dt>PSP:</dt>
          <dd>Penultimate Segment Pop of the SRH <xref target="RFC8986"/>.
           </t>

           <t> USP: Ultimate target="RFC8986" format="default"/>
           </dd>
          <dt>USP:</dt>
          <dd>Ultimate Segment Pop of the SRH <xref target="RFC8986"/>.
           </t>

           <t> ICMPv6: ICMPv6 Specification target="RFC8986" format="default"/>
           </dd>
          <dt>ICMPv6:</dt>
          <dd>Internet Control Message Protocol for the Internet Protocol version 6 <xref target="RFC4443"/>.
           </t>

           <t>  IS-IS: Intermediate target="RFC4443" format="default"/>
           </dd>
          <dt>IS-IS:</dt>
          <dd>Intermediate System to Intermediate System
           </t>

           <t> OSPF: Open
           </dd>
          <dt>OSPF:</dt>
          <dd>Open Shortest Path First protocol <xref target="RFC2328"/>
           </t>

           <t> IGP: Interior target="RFC2328" format="default"/>
          </dd>
          <dt>IGP:</dt>
          <dd>Interior Gateway Protocols Protocol (e.g., OSPF, IS-IS).
           </t>

           <t> BGP-LS: Border OSPF and IS-IS)
           </dd>
          <dt>BGP-LS:</dt>
          <dd>Border Gateway Protocol - Link State Extensions <xref target="RFC8571"/>
           </t>

          </list></t> target="RFC8571" format="default"/>
          </dd>
        </dl>
      </section>
      <section title="Terminology numbered="true" toc="default">
        <name>Terminology and Reference Topology">

     <t> Throughout the document, the following Topology</name>
        <t>The terminology and
     simple topology is in this section are used for illustration. illustration throughout the document. </t>

      <figure> <artwork><![CDATA[
     <figure anchor="ref-top">
       <name>Reference Topology</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
+--------------------------| N100 |---------------------------------+
|                                                                   |
|  ====== link1====== link3------ link5====== link9------   ======  |
   ||N1||------||N2||------| N3 |------||N4||------| N5 |---||N7||
   ||  ||------||  ||------|    |------||  ||------|    |---||  ||
   ====== link2====== link4------ link6======link10------   ======
      |            |                      |                   |
   ---+--          |       ------         |                 --+---
      |CE 1|
   |CE1 |          +-------| N6 |---------+                 |CE 2|                 |CE2 |
   ------            link7 |    | link8                     ------
                           ------

                           Figure 1 Reference Topology
	  ]]>
	  </artwork>
]]></artwork>
     </figure>
     <t> In the reference topology:

        <list style="empty">

            <t>
        </t>
        <ul spacing="normal">
          <li> Node j has a an IPv6 loopback address 2001:db8:L:j::/128.
           </t>

            <t>
           </li>
          <li> Nodes N1, N2, N4 N4, and N7 are SRv6-capable nodes.
            </t>

            <t>
            </li>
          <li> Nodes N3, N5 N5, and N6 are IPv6 nodes that are not SRv6-capable. SRv6-capable nodes.
            Such nodes are referred to as non-SRv6 capable nodes.
           </t>

			<t> "non-SRv6-capable nodes".
           </li>
          <li> CE1 and CE2 are Customer Edge devices of any data plane
			capability (e.g., IPv4, IPv6, L2, etc.).
           </t>

            <t> and L2).
           </li>
          <li> A SID at node j with locator block 2001:db8:K::/48 and function U is represented
     by 2001:db8:K:j:U::.
           </t>

            <t>
           </li>
          <li> Node N100 is a controller.
           </t>

           <t>
           </li>

           <li> The IPv6 address of the nth Link link between node nodes i and j at the i side
     is represented as 2001:db8:i:j:in::, e.g., 2001:db8:i:j:in::. For example, in <xref target="ref-top"/>, the IPv6 address of link6
     (the 2nd second link between nodes N3 and N4) at node N3 in Figure 1 is
     2001:db8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st first
     link between nodes N3 and N4) at node N3 is 2001:db8:3:4:31::.
           </t>

           <t>
           </li>
          <li> 2001:db8:K:j:Xin:: is explicitly allocated as the End.X SID
            at node j
     towards neighbor node i via the nth Link link between node nodes i and node j.
     e.g.,
     For example, 2001:db8:K:2:X31:: represents End.X at node N2 towards node N3 via link3 (the 1st first
     link between nodes N2 and N3). Similarly, 2001:db8:K:4:X52:: represents the End.X at
     node N4 towards node N5 via link10 (the 2nd second
     link between nodes N4 and N5). Please refer to <xref target="RFC8986"/> target="RFC8986" format="default"/> for
     a description of End.X SID.
           </t>

            <t>
           </li>
          <li> A SID list is represented as &lt;S1, S2, S3&gt; S3&gt;, where
            S1 is the first SID
   to visit, S2 is the second SID to visit visit, and S3 is the last SID to
   visit along the SR path.
           </t>
           </li>
          <li>
            <t> (SA,DA) (S3, S2, S1; SL)(payload) represents an IPv6 packet with:

        <list style="symbols">

            <t>

            </t>
            <ul spacing="normal">
              <li> IPv6 header with source address SA, destination addresses DA address DA, and
     SRH as next-header
            </t>

            <t> SRH the next header
            </li>
              <li><t>SRH with SID list &lt;S1, S2, S3&gt; with SegmentsLeft = SL
           </t> SL</t>

              <t> Note the difference between the &lt; &gt; and () symbols:
            &lt;S1, S2, S3&gt;
     represents a SID list where S1 is the first SID and S3 is the last
     SID to traverse.  (S3, S2, S1; SL) represents the same SID list but
     encoded in the SRH format where the rightmost SID in the SRH is the
     first SID and the leftmost SID in the SRH is the last SID.  When
     referring to an SR policy Policy in a high-level use-case, use case, it is simpler
     to use the &lt;S1, S2, S3&gt; notation.  When referring to an
     illustration of the detailed packet behavior, the (S3, S2, S1; SL)
     notation is more convenient.
           </t>

            <t> convenient.</t>
           </li>
              <li> (payload) represents the the payload of the packet.
           </t>

          </list></t>

          </list></t>
           </li>
            </ul>
          </li>
        </ul>
      </section>
    </section>
    <!--end: Introduction -->

    <section title="OAM Mechanisms"> numbered="true" toc="default">
      <name>OAM Mechanisms</name>
      <t>This section defines OAM enhancement enhancements for the SRv6 networks.
      </t>
      <section title="O-flag numbered="true" toc="default">
        <name>OAM Flag in the Segment Routing Header"> Header</name>
        <t><xref target="RFC8754"/> target="RFC8754" format="default"/> describes the Segment
     Routing Header (SRH) and how SR capable SR-capable nodes use it. The SRH
     contains an 8-bit "Flags" Flags field. </t>
        <t> This document defines the following bit in the
     SRH Flags field to carry the O-flag: </t>

      <figure> <artwork><![CDATA[
<artwork name="" type="" align="left" alt=""><![CDATA[
               0 1 2 3 4 5 6 7
              +-+-+-+-+-+-+-+-+
              |   |O|         |
              +-+-+-+-+-+-+-+-+
	  ]]>
	  </artwork> </figure>
]]></artwork>
        <t> Where:

        <list style="hanging">

            <t> O-flag: OAM

        </t>
        <dl newline="false" spacing="normal">
          <dt>O-flag:</dt>
          <dd>OAM flag in the SRH Flags field defined in <xref target="RFC8754"/>.
            </t>

          </list>
          </t> target="RFC8754" format="default"/>.
            </dd>
        </dl>
        <section title="O-flag Processing"> anchor="oflag-proc" numbered="true" toc="default">
          <name>OAM Flag Processing</name>
          <t> The O-flag in the SRH is used as a marking-bit marking bit in the user packets to trigger
	the
	telemetry data collection and export at the segment endpoints.
          </t>
          <t> An SR domain ingress edge node encapsulates packets traversing the SR
    domain as defined in <xref target="RFC8754"/>. target="RFC8754" format="default"/>. The SR domain ingress edge node
    MAY
    <bcp14>MAY</bcp14> use the O-flag in the SRH for marking the packet to trigger
	the telemetry data collection and export at the segment endpoints.
	Based on a local configuration, the SR domain ingress edge node
	may implement a classification and sampling mechanism to mark a packet with the O-flag in the SRH.
	Specification of the classification and sampling method is outside the scope of this
    document.
          </t>
          <t>
	This document does not specify the data elements that need to be exported
	and the associated configurations.
	Similarly, this document does not define any formats for exporting the data
	elements.
	Nonetheless, without the loss of generality, this document assumes that the
	IP Flow Information Export (IPFIX) protocol <xref target="RFC7011"/> target="RFC7011" format="default"/> is used for exporting
	the traffic flow information from the network devices to a controller for
	monitoring and analytics.
	Similarly, without the loss of generality, this document assumes that requested information
	elements are configured
    by the management plane through data set templates (e.g., as in IPFIX
    <xref target="RFC7012"/>). target="RFC7012" format="default"/>).
          </t>
          <t>Implementation of the O-flag is OPTIONAL. <bcp14>OPTIONAL</bcp14>. If a node does not support the
     O-flag, then upon reception it simply ignores it. it upon reception.  If a node supports
     the O-flag, it can optionally advertise its potential via
     control plane protocol(s).
          </t>

      <t> When N receives a packet destined to S and S

	  <t>The following is a local SID,
the appended to line S01 of the pseudo-code pseudocode
	  associated with the SID S, as S (as defined in section 4.3.1.1 of <xref target="RFC8754"/>,
is appended target="RFC8754"
	  sectionFormat="of" section="4.3.1.1" format="default"/>) when N
	  receives a packet destined to as follows for S, S is a local SID, and the O-flag processing. is
	  processed.
          </t>

     <figure> <artwork><![CDATA[
<sourcecode type="pseudocode"><![CDATA[
   S01.1. IF the O-flag is set and local configuration permits
          O-flag processing {
             a. Make a copy of the packet.
             b. Send the copied packet, along with a timestamp timestamp,
             to the OAM process for telemetry data collection
             and export.      ;; Ref1
             }
   Ref1: To provide an accurate timestamp, an implementation should
   copy and record the timestamp as soon as possible during packet
   processing. Timestamp and any other metadata is are not carried in
   the packet forwarded to the next hop.
	]]>
	</artwork> </figure>
]]></sourcecode>
          <t> Please note that the O-flag processing happens before execution of regular
	processing of the local SID S. Specifically, the line S01.1 of the pseudo-code pseudocode
	specified in this document is inserted between line lines S01
    and S02 of the pseudo-code pseudocode defined in section 4.3.1.1 of <xref target="RFC8754"/>. target="RFC8754" sectionFormat="of" section="4.3.1.1" format="default"/>.
          </t>
          <t>
      Based on the
      requested information elements configured
      by the management plane through data set templates <xref target="RFC7012"/>, target="RFC7012" format="default"/>,
      the OAM process exports the requested information elements.
   The information elements include parts of the packet header and/or parts of
   the packet payload for flow identification.
   The OAM process uses information elements defined in
   IPFIX <xref target="RFC7011"/> target="RFC7011" format="default"/> and PSAMP Packet Sampling (PSAMP) <xref target="RFC5476"/> target="RFC5476" format="default"/> for exporting the requested sections
   of the mirrored packets.
          </t>
          <t>

    If the penultimate segment of a segment-list segment list is a Penultimate Segment Pop (PSP) PSP SID,
    telemetry data from the ultimate segment cannot be requested. This is because,
    when the penultimate segment is a PSP SID,
   the SRH is removed at the penultimate segment segment, and the O-flag is
   not processed at the ultimate segment.

          </t>
          <t>
      The processing node MUST <bcp14>MUST</bcp14>
      rate-limit the number of packets punted to the OAM process
      to a configurable rate.
      This is to avoid hitting any impacting the
      performance impact on of the OAM and
      the
      telemetry collection processes. Failure in implementing to implement the rate
      limit can lead to a denial-of-service attack, as detailed in section 4. <xref target="Security" format="default"/>.

          </t>
          <t>
     The OAM process MUST NOT <bcp14>MUST NOT</bcp14> process the copy of the packet or respond
      to any upper-layer Upper-Layer header
      (like ICMP, UDP,
      etc.) payload to prevent multiple evaluations of the datagram.
          </t>
          <t>
      The OAM process is expected to be located on the routing node processing the packet.
      Although the specification of the OAM process or the external controller
      operations are beyond the scope of this document, the OAM process SHOULD NOT <bcp14>SHOULD NOT</bcp14> be
      topologically distant from the routing node, as this is likely to create significant security
      and congestion issues.
      How to correlate the data collected from different nodes at an
      external controller is also outside the scope of the this document.
      Appendix A
      <xref target="app-illustrations" /> illustrates use of the O-flag for implementing
      a hybrid OAM mechanism, where the "hybrid" classification
      is based on RFC7799 <xref target="RFC7799"/>. target="RFC7799" format="default"/>.

          </t>
        </section>
        <!--end: O-flag Processing -->
    </section>
      <!--end: O-flag  -->

	<section title="OAM Operations"> numbered="true" toc="default">
        <name>OAM Operations</name>
        <t> IPv6 OAM operations can be performed for any SRv6 SID whose behavior
   allows Upper Layer Header Upper-Layer header processing for an applicable OAM payload
   (e.g., ICMP, UDP).
</t>

<t> Ping to an SRv6 SID is used to verify
   that the SID is reachable and is locally programmed at the target node.
   Traceroute to a SID is used for hop-by-hop
   fault localization as well as path tracing to a SID.  Appendix A  <xref target="app-illustrations" />
   illustrates the ICMPv6 based ICMPv6-based ping and the UDP based UDP-based traceroute mechanisms
   for ping and traceroute to an SRv6 SID.  Although this document only
   illustrates ICMPv6 ICMPv6-based ping and UDP based UDP-based traceroute to an SRv6 SID, the procedures are
   equally applicable to other IPv6 OAM probing to mechanisms that probe an SRv6 SID
   (e.g., Bidirectional Forwarding Detection (BFD) <xref target="RFC5880"/>, target="RFC5880" format="default"/>,
Seamless BFD (SBFD) (S-BFD) <xref target="RFC7880"/>, STAMP target="RFC7880" format="default"/>, and Simple Two-way Active Measurement Protocol (STAMP) probe message processing
[I-D.gandhi-spring-stamp-srpm], etc.).
<xref target="I-D.ietf-spring-stamp-srpm" format="default"/>).
Specifically, as
   long as local configuration allows the Upper-layer Header Upper-Layer header processing of
   the applicable OAM payload for SRv6 SIDs, the existing IPv6 OAM
   techniques can be used to target a probe to a (remote) SID.
</t>
        <t> IPv6 OAM operations can be performed with the target SID in the IPv6
destination address without an SRH or with an SRH where the target SID is the last segment.
In general, OAM operations to a target SID may not exercise all of its
processing depending on its behavior definition.
For example, ping to an End.X SID <xref target="RFC8986"/> target="RFC8986" format="default"/>
only validates the SID is locally programmed at the target node
and does not validate switching to the
correct outgoing interface.
To exercise the behavior
of a target SID, the OAM operation should construct the probe in a manner
similar to a data packet that exercises the SID behavior, i.e. to include
that SID as a transit SID in either an SRH or IPv6 DA of an outer IPv6 header
or as appropriate
based on the definition of the SID behavior.

</t>
      </section>
      <!--end: Ping and Traceroute  -->

    </section>
    <!--end: OAM Mechanisms -->

    <section anchor="Status" title="Implementation Status">
     <t>  This section is to be removed prior to publishing as an RFC.
     </t>

     <t>  See [I-D.matsushima-spring-srv6-deployment-status] for updated
   deployment and interoperability reports.
     </t>

    </section> <!--end: Implementation Status-->

    <section anchor="Security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>  <xref target="RFC8754"/> target="RFC8754" format="default"/> defines the notion of an SR domain and
     use of the SRH within the SR domain.
     The use of OAM procedures described in this document is restricted to an SR domain.
     For example, similar to the SID manipulation, O-flag manipulation is not considered
     as
     a threat within the SR domain.
     Procedures for securing an SR domain are defined the section 5.1 in Sections <xref target="RFC8754" format="default" section="5.1" sectionFormat="bare"/> and section 7 <xref target="RFC8754" format="default" section="7" sectionFormat="bare"/> of
     <xref target="RFC8754"/>. target="RFC8754" format="default"/>.
      </t>
      <t>
     As noted in section 7.1 of <xref target="RFC8754"/>, target="RFC8754" format="default" sectionFormat="of" section="7.1"/>,
     compromised nodes within the SR domain may mount attacks. The O-flag
     may be set by an attacking node attempting a denial-of-service attack on the
     OAM process at the segment endpoint node.
     An implementation correctly implementing
     the rate limiting described in section 2.1.1 <xref target="oflag-proc" /> is not susceptible to that
     denial-of-service attack.
     Additionally, SRH Flags flags are protected by the HMAC Hashed Message Authentication Code (HMAC) TLV, as
     described in section 2.1.2.1 of <xref target="RFC8754"/>. target="RFC8754" format="default" sectionFormat="of" section="2.1.2.1"/>.
     Once an HMAC is generated for a segment list with the O-flag set,
     it can be used for an arbitrary amount of traffic using that
     segment list with the O-flag set.

      </t>
      <t>

     The security properties of the channel used to send exported packets marked
     by the O-flag will depend on the specific OAM processes used.
     An on-path attacker able to observe this OAM channel could conduct
     traffic analysis, or potentially eavesdropping (depending on the OAM configuration),
     of this telemetry for the entire SR domain from such a vantage point.

      </t>
      <t>
     This document does not
     impose any additional security challenges to be considered beyond the
     security threats described in <xref target="RFC4884"/>, target="RFC4884" format="default"/>, <xref target="RFC4443"/>, target="RFC4443" format="default"/>,
     <xref target="RFC0792"/>, target="RFC0792" format="default"/>,
    <xref target="RFC8754"/> target="RFC8754" format="default"/>, and <xref target="RFC8986"/>. target="RFC8986" format="default"/>.
      </t>
    </section>
    <!--end: Security Considerations-->

    <section anchor="PRIVACY" title="Privacy Considerations"> numbered="true" toc="default">
      <name>Privacy Considerations</name>
      <t> The per-packet marking capabilities of the O-flag provides provide a granular
     mechanism to collect telemetry.  When this collection is deployed by an operator
     with the knowledge and consent of the users, it will enable a variety of diagnostics
     and monitoring to support the OAM and security operations use cases needed for
     resilient network operations.  However, this collection mechanism will also
     provide an explicit protocol mechanism to operators for surveillance and
     pervasive monitoring use cases done contrary to the user's consent.
      </t>
    </section>
    <!--end: asd -->

    <section anchor="IANA" title="IANA Considerations">

     <t>  This document requests that IANA allocate numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>IANA has registered the following
     registration in the "Segment
	   Routing Header Flags" sub-registry for subregistry in the "Internet Protocol Version
	   6 (IPv6) Parameters" registry maintained by IANA:
     <figure> <artwork><![CDATA[

         +-------+------------------------------+---------------+
         | Bit   | Description                  | Reference     |
         +=======+==============================+===============+
         | 2     | O-flag                       | This document |
         +-------+------------------------------+---------------+

	]]>
	</artwork> </figure> registry:
      </t>

<table anchor="iana-table">
  <name></name>
  <thead>
    <tr>
      <th>Bit</th>
      <th>Description</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>2</td>
      <td>O-flag</td>
      <td>RFC 9259</td>
    </tr>
  </tbody>
</table>

    </section>
    <!--end: IANA Considerations-->

</middle>
  <back>
    <references title="Normative References">
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8754.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8986.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8174.xml"?>

<displayreference target="I-D.ietf-spring-stamp-srpm" to="STAMP-SR"/>

    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8754.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8986.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.0792.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4443.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4884.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5837.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8403.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8402.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7011.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5476.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7012.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7799.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5880.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7880.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8571.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9197.xml"/>

<!-- [I-D.gandhi-spring-stamp-srpm] Replaced by [I-D.ietf-spring-stamp-srpm] IESG state I-D Exists -->

<reference anchor="I-D.ietf-spring-stamp-srpm">
   <front>
      <title>Performance Measurement Using Simple TWAMP (STAMP) for Segment Routing Networks</title>
      <author fullname="Rakesh Gandhi" role="editor">
	 <organization>Cisco Systems, Inc.</organization>
      </author>
      <author fullname="Clarence Filsfils">
	 <organization>Cisco Systems, Inc.</organization>
      </author>
      <author fullname="Daniel Voyer">
	 <organization>Bell Canada</organization>
      </author>
      <author fullname="Mach(Guoyi) Chen">
	 <organization>Huawei</organization>
      </author>
      <author fullname="Bart Janssens">
	 <organization>Colt</organization>
      </author>
      <author fullname="Richard Foote">
	 <organization>Nokia</organization>
      </author>
      <date month="February" day="1" year="2022" />
   </front>
   <seriesInfo name="Internet-Draft" value="draft-ietf-spring-stamp-srpm-03" />
   <format type="TXT" target="https://www.ietf.org/archive/id/draft-ietf-spring-stamp-srpm-03.txt" />
</reference>

      </references>

    <references title="Informative References">
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.0792.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4443.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4884.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5837.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8403.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8402.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7011.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5476.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7012.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7799.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5880.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7880.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2328.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8571.xml"?>

      <?rfc include="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.matsushima-spring-srv6-deployment-status.xml"?>
      <?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.gandhi-spring-stamp-srpm.xml"?>
      <?rfc include="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-ietf-ippm-ioam-data-11.xml"?>
    </references>
    <section title="Illustrations"> anchor="app-illustrations" numbered="true" toc="default">
      <name>Illustrations</name>
      <t> This appendix shows how some of the
   existing IPv6 OAM mechanisms can be used in an SRv6 network. It also
   illustrates an OAM mechanism for
   performing controllable and predictable flow sampling from segment
   endpoints. How the centralized OAM technique in
   <xref target="RFC8403"/> target="RFC8403" format="default"/> can be extended for SRv6 is also described in this appendix.
      </t>
      <section title="Ping numbered="true" toc="default">
        <name>Ping in SRv6 Networks"> Networks</name>
        <t> The existing mechanism to perform the reachability checks,
     along the shortest path, continues to work without any modification.
     Any IPv6 node (SRv6 capable (SRv6-capable or a non-SRv6 capable) non-SRv6-capable) can initiate, transit,
     and egress a ping packet.

        </t>
        <t> The following subsections outline some additional use cases of the ICMPv6 ping in
     the
     SRv6 networks.
        </t>
        <section title="Pinging numbered="true" toc="default">
          <name>Pinging an IPv6 Address via a Segment-list"> Segment List</name>
          <t> If an SRv6-capable ingress node wants to ping an IPv6 address via an
     arbitrary segment list &lt;S1, S2, S3&gt;, it needs to initiate an ICMPv6
     ping with an SR header containing the SID list &lt;S1, S2, S3&gt;. This is
     illustrated using the topology in Figure 1. User <xref target="ref-top"/>. The user issues a ping from node N1 to a
     loopback of node N5, N5 via segment list &lt;2001:db8:K:2:X31::, 2001:db8:K:4:X52::&gt;.
     The SID behavior used in the example is End.X SID, End.X,
     as described in <xref target="RFC8986"/>, target="RFC8986" format="default"/>, but the procedure is
     equally applicable to any other (transit) SID type.
          </t>

     <t> Figure 2
          <t><xref target="sample-ping"/> contains sample output for a ping request initiated at node
     N1 to a loopback address of node N5 via a segment list &lt;2001:db8:K:2:X31::,
     2001:db8:K:4:X52::&gt;.
          </t>

     <figure> <artwork><![CDATA[
	  <figure anchor="sample-ping">
	    <name>Sample Ping Output at an SRv6-Capable Node</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
    > ping 2001:db8:L:5:: via segment-list segment list 2001:db8:K:2:X31::,
           2001:db8:K:4:X52::

    Sending 5, 100-byte ICMPv6 Echos to B5::, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625
    /0.749/0.931 ms

             Figure 2 A sample ping output at an SRv6-capable node
	]]>
	</artwork>
]]></artwork>
	  </figure>
          <t> All transit nodes process the echo request message like any other
     data packet carrying an SR header and hence do not require any change.
     Similarly, the egress node does not
     require any change to process the ICMPv6 echo request. For example,
     in the ping example of Figure 2:

      <list style="symbols">
          <t>Node in <xref target="sample-ping"/>:

          </t>
          <ul spacing="normal">
            <li>Node N1 initiates an ICMPv6 ping packet with the SRH as follows follows:
          (2001:db8:L:1::, 2001:db8:K:2:X31::)
          (2001:db8:L:5::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::, SL=2,
          NH = ICMPv6)(ICMPv6 Echo Request).
          </t>

          <t>Node
          </li>
            <li>Node N2, which is an SRv6-capable node, performs the standard
          SRH processing. Specifically, it executes the End.X behavior
          indicated by the 2001:db8:K:2:X31:: SID and forwards the packet on link3 to N3.</t>

          <t> node N3.</li>
            <li> Node N3, which is a non-SRv6 capable non-SRv6-capable node, performs the standard
          IPv6 processing. Specifically, it forwards the echo request
          based on the DA 2001:db8:K:4:X52:: in the IPv6 header. </t>

          <t> </li>
            <li> Node N4, which is an SRv6-capable node, performs the standard
          SRH processing. Specifically, it observes the End.X behavior
          (2001:db8:K:4:X52::) and forwards the packet on link10 towards node N5.
          If 2001:db8:K:4:X52:: is a PSP SID,
          the penultimate node (Node (node N4) does not, should not not, and cannot differentiate
          between the data packets and OAM probes.
          Specifically, if 2001:db8:K:4:X52:: is a PSP SID,
          node N4 executes the SID like any other data packet with DA = 2001:db8:K:4:X52::
          and removes the SRH.
          </t>

          <t>
          </li>
            <li> The echo request packet at node N5 arrives as an IPv6 packet with or
          without an SRH. If node N5 receives the packet with an SRH, it skips SRH processing (SL=0).
          In either case, Node node N5 performs the
          standard ICMPv6 processing on the echo request and responds with the
          echo reply message to node N1. The echo reply message is IP routed.

          </t>

        </list> </t>

          </li>
          </ul>
        </section>
        <!--end: Pinging an IPv6 address via a sid-list -->

	<section title="Pinging numbered="true" toc="default">
          <name>Pinging a SID"> SID</name>
<t>
   The ping mechanism described above applies equally can also be used to perform SID
   reachability check checks and to validate that the SID is locally programmed at
   the target node.
 	   This is explained using an example in the
   following.
   following example. The example uses ping to an END End SID, as described in <xref target="RFC8986"/>, target="RFC8986" format="default"/>,
   but the procedure is
     equally applicable to ping any other SID behaviors.
          </t>
          <t>  Consider the example where the user wants to ping a remote
          SID 2001:db8:K:4::, via 2001:db8:K:2:X31::, from node N1.
          The ICMPv6 echo request is processed at the individual nodes
          along the path as follows:

          <list style="symbols">
          <t>Node

          </t>
          <ul spacing="normal">
            <li>Node N1 initiates an ICMPv6 ping packet with the SRH as follows follows:
          (2001:db8:L:1::, 2001:db8:K:2:X31::)
          (2001:db8:K:4::, 2001:db8:K:2:X31::; SL=1;
          NH=ICMPv6)(ICMPv6 Echo Request).  </t>

          <t>Node  </li>
            <li>Node N2, which is an SRv6-capable node, performs the standard
          SRH processing. Specifically, it executes the End.X behavior
          indicated by the 2001:db8:K:2:X31:: SID on the echo request packet. If
          2001:db8:K:2:X31:: is a PSP SID, node N4 executes the SID like any
      other data packet with DA = 2001:db8:K:2:X31:: and removes the
      SRH.
          </t>
          <t>
          </li>
            <li> Node N3, which is a non-SRv6 capable non-SRv6-capable node, performs
          the standard IPv6 processing. Specifically, it forwards the
          echo request based on DA = 2001:db8:K:4:: in the IPv6 header.</t>

          <t>When header.</li>
            <li>When node N4 receives the packet, it
          processes the target SID (2001:db8:K:4::). </t>

          <t> </li>
            <li> If the target SID (2001:db8:K:4::) is not locally instantiated
          and does not represent a local interface,
          the packet is discarded </t>

          <t> </li>
            <li>
          If the target SID (2001:db8:K:4::) is locally instantiated or
          represents a local interface, the node processes
          the upper layer Upper-Layer header.
          As part of the upper layer Upper-Layer header processing processing, node N4 respond responds
          to the ICMPv6 echo request message and responds with the an
          echo reply message. The echo reply message is IP routed.

          </t>

          </list>

     </t>

          </li>
          </ul>
        </section>
        <!--end: SID Ping -->

    </section>
      <!--end: Ping-->

	<section title="Traceroute"> numbered="true" toc="default">
        <name>Traceroute in SRv6 Networks</name>
        <t>  The existing traceroute
     mechanisms, along the shortest path, continues continue to work without any modification.
     Any IPv6 node (SRv6 capable (SRv6-capable or a non-SRv6 capable) non-SRv6-capable) can initiate, transit,
     and egress a traceroute probe.

        </t>
        <t>
     The following subsections outline some additional use cases of the traceroute
     in the SRv6 networks.
        </t>
        <section title="Traceroute numbered="true" toc="default">
          <name>Traceroute to an IPv6 Address via a Segment-list"> Segment List</name>
          <t>  If an SRv6-capable ingress node wants to traceroute to an IPv6 address
     via an arbitrary segment list &lt;S1, S2, S3&gt;, it needs to initiate
     a traceroute probe with an SR header containing the SID list
     &lt;S1, S2, S3&gt;. User The user issues a traceroute
     from node N1 to a loopback of node N5, N5 via segment list
     &lt;2001:db8:K:2:X31::, 2001:db8:K:4:X52::&gt;.
     The SID behavior used in the example is End.X SID, End.X, as described in
      <xref target="RFC8986"/>, target="RFC8986" format="default"/>,
 	   but the procedure is equally applicable to any other (transit) SID
 	   type.

     Figure 3

     <xref target="sample-traceroute"/> contains sample output for the traceroute
     request.
          </t>

     <figure> <artwork><![CDATA[
	  <figure anchor="sample-traceroute">
	    <name>Sample Traceroute Output at an SRv6-Capable Node</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
> traceroute 2001:db8:L:5:: via segment-list segment list 2001:db8:K:2:X31::,
             2001:db8:K:4:X52::

Tracing the route to 2001:db8:L:5::
1  2001:db8:2:1:21:: 0.512 msec 0.425 msec 0.374 msec
   DA: 2001:db8:K:2:X31::,
   SRH:(2001:db8:L:5::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::, SL=2)
2  2001:db8:3:2:31:: 0.721 msec 0.810 msec 0.795 msec
   DA: 2001:db8:K:4:X52::,
   SRH:(2001:db8:L:5::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::, SL=1)
3  2001:db8:4:3::41:: 0.921 msec 0.816 msec 0.759 msec
   DA: 2001:db8:K:4:X52::,
   SRH:(2001:db8:L:5::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::, SL=1)
4  2001:db8:5:4::52:: 0.879 msec 0.916 msec 1.024 msec
   DA: 2001:db8:L:5::

      Figure 3 A sample traceroute output at an SRv6-capable node
	]]>
	</artwork>
]]></artwork>
	  </figure>
          <t>  In the sample traceroute output, the information displayed at each hop
	is obtained using the contents of the "Time Exceeded" or
	"Destination Unreachable" ICMPv6 responses. These ICMPv6 responses
	are IP routed.

          </t>
          <t> In the sample traceroute output, the information for link3 is
     returned by node N3, which is a
     non-SRv6 capable
     non-SRv6-capable node. Nonetheless, the ingress node is able to display
     SR header contents as the packet travels through the non-SRv6 capable non-SRv6-capable node.
     This is because the "Time Exceeded Message" Exceeded" ICMPv6 message can
     contain as much of the invoking packet as possible without the
     ICMPv6 packet exceeding the minimum IPv6 MTU <xref target="RFC4443"/>. target="RFC4443" format="default"/>. The SR
     header is included in these ICMPv6 messages initiated by the
     non-SRv6 capable
     non-SRv6-capable transit nodes that are not running SRv6 software.
     Specifically, a node generating an ICMPv6 message containing a copy of
     the invoking packet does not need to understand the extension
     header(s) in the invoking packet.
          </t>
          <t>  The segment list information returned for the first hop is returned by node N2,
     which is an SRv6-capable node. Just like for the second hop, the ingress node
     is able to display SR header contents for the first hop.
          </t>
          <t>  There is no difference in processing of the traceroute probe at an
     SRv6-capable and a non-SRv6 capable non-SRv6-capable node. Similarly, both SRv6-capable and
     non-SRv6 capable
     non-SRv6-capable nodes may use the address of the interface on
     which probe was received as the source address in the ICMPv6
     response. ICMPv6 extensions defined in <xref target="RFC5837"/> target="RFC5837" format="default"/> can be used to
     display information about the IP interface through which the
     datagram would have been forwarded had it been forwardable, and the
     IP next hop to which the datagram would have been forwarded, the IP
     interface upon which a the datagram arrived, and the sub-IP component of an
     IP interface upon which a the datagram arrived.
          </t>

	  <t>  The IP address of the interface on which the traceroute probe was received
     is useful. This information can also be used to verify if SIDs
     2001:db8:K:2:X31:: and 2001:db8:K:4:X52:: are executed correctly by nodes N2 and N4,
     respectively. Specifically, the information displayed for the second hop
     contains the incoming interface address 2001:db8:2:3:31:: at node N3.
     This matches with the expected interface bound to End.X behavior
     2001:db8:K:2:X31:: (link3). Similarly, the information displayed for the fourth hop
     contains the incoming interface address 2001:db8:4:5::52:: at node N5.
     This matches with the expected interface bound to the End.X behavior
     2001:db8:K:4:X52:: (link10).
          </t>
        </section>
        <!--end: Tracerouting an IPv6 Address via a Segment-list Segment list -->

	<section title="Traceroute numbered="true" toc="default">
          <name>Traceroute to a SID">

     <t>  The SID</name>

          <t>The mechanism to traceroute an IPv6 Address address via a Segment-list segment list
          described in the previous section applies
     equally can also be used to traceroute a
          remote SID behavior, as explained using an
     example in the following. following example.  The
          example uses traceroute to an END End SID, as described in <xref target="RFC8986"/>,
          target="RFC8986" format="default"/>, but the procedure is equally
          applicable to tracerouting any other SID behaviors.
          </t>
          <t>  Please note that traceroute to a SID is
     exemplified using UDP probes. However, the procedure is equally
     applicable to other implementations of traceroute mechanism.
     The UDP encoded message to traceroute a SID would use the UDP ports
     assigned by IANA for "traceroute use".
          </t>
          <t> Consider the example where the user wants to traceroute a remote SID
    2001:db8:K:4::, via 2001:db8:K:2:X31::, from node N1. The
     traceroute probe is processed at the individual nodes along the path
     as follows:

     <list style="symbols">
          <t>Node

          </t>
          <ul spacing="normal">
            <li>Node N1 initiates a traceroute probe packet as follows
          (2001:db8:L:1::, 2001:db8:K:2:X31::)
          (2001:db8:K:4::, 2001:db8:K:2:X31::; SL=1; NH=UDP)(Traceroute probe).
          The first traceroute probe is sent with the hop-count value set to 1.
          The hop-count value is incremented by 1 for each following subsequent traceroute probes.

           </t>

          <t>When probe.

           </li>
            <li>When node N2 receives the packet with hop-count = 1, it
          processes the hop-count expiry. Specifically, the node N2
          responds with the ICMPv6 message (Type: with type "Time Exceeded", Code:
          "Hop Exceeded" and code
          "hop limit exceeded in transit"). transit". The ICMPv6 response
	      is IP routed.

          </t>
          <t>When Node

          </li>
            <li>When node N2 receives the packet with hop-count > &gt; 1, it
          performs the standard SRH processing. Specifically, it executes
          the End.X behavior indicated by the
          2001:db8:K:2:X31:: SID on the traceroute probe.
          If 2001:db8:K:2:X31:: is a PSP SID,
      node N2 executes the SID like any other data packet with DA = 2001:db8:K:2:X31::
      and removes the SRH.
          </t>
          <t>When
          </li>
            <li>When node N3, which is a non-SRv6 capable non-SRv6-capable node, receives the packet
          with hop-count = 1, it processes the
          hop-count expiry. Specifically, the node N3 responds with the
          ICMPv6 message (Type: with type "Time Exceeded", Code: Exceeded" and code "Hop limit
          exceeded in Transit"). transit". The ICMPv6 response is IP routed.

          </t>
          <t>When

          </li>
            <li>When node N3, which is a non-SRv6 capable non-SRv6-capable node, receives the packet
          with hop-count > &gt; 1, it performs the standard IPv6 processing.
          Specifically, it forwards the traceroute probe based on DA
          2001:db8:K:4:: in the IPv6 header. </t>
          <t>When </li>
            <li>When node N4 receives the packet with DA set to the local SID 2001:db8:K:4::, it
          processes the END End SID. </t>

     <t> </li>
            <li>  If the target SID (2001:db8:K:4::) is not locally instantiated and
          does not represent a local interface, the packet is discarded.
     </t>

          <t>
     </li>
            <li>
          If the target SID (2001:db8:K:4::) is locally instantiated or represents a
          local interface, the node processes
          the upper layer Upper-Layer header.
	  As part of the upper layer Upper-Layer header processing processing, node N4 responds
          with the ICMPv6 message (Type: Destination unreachable, Code:
          Port Unreachable). with type "Destination Unreachable" and code
          "Port Unreachable". The ICMPv6 response
	     is IP routed.

          </t>
    </list>
     </t>

     <t> Figure 4

          </li>
          </ul>
          <t><xref target="sample-output"/> displays a sample traceroute output for this example.

     <figure> <artwork><![CDATA[

          </t>
	  <figure anchor="sample-output">
	    <name>Sample Output for Hop-by-Hop Traceroute to a SID</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
  > traceroute 2001:db8:K:4:X52:: via segment-list segment list 2001:db8:K:2:X31::

  Tracing the route to SID 2001:db8:K:4:X52::
  1  2001:db8:2:1:21:: 0.512 msec 0.425 msec 0.374 msec
     DA: 2001:db8:K:2:X31::,
     SRH:(2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=1)
  2  2001:db8:3:2:21:: 0.721 msec 0.810 msec 0.795 msec
     DA: 2001:db8:K:4:X52::,
     SRH:(2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=0)
  3  2001:db8:4:3:41:: 0.921 msec 0.816 msec 0.759 msec
     DA: 2001:db8:K:4:X52::,
     SRH:(2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=0)

        Figure 4 A sample output for hop-by-hop traceroute to a SID

	]]>
	</artwork>
]]></artwork>
	  </figure>
     </t>
        </section>
        <!--end: Traceroute to a SID behavior-->

    </section>
      <!--end: Traceroute -->

	<section title="A Hybrid numbered="true" toc="default">
        <name>Hybrid OAM Using O-flag"> the OAM Flag</name>
        <t> This section illustrates a hybrid OAM mechanism using
    the the O-flag. Without loss of the generality, the illustration
    assumes node N100 is a centralized controller.
        </t>
        <t>
    The
    This illustration is different than from the In-situ OAM "in situ OAM" defined in
   [I.D-draft-ietf-ippm-ioam-data]. <xref
    target="RFC9197" format="default"/>.  This is because In-situ in situ OAM records
    operational and telemetry information in the packet as the packet
    traverses a path between two points in the network [I.D-draft-ietf-
   ippm-ioam-data]. <xref target="RFC9197"
    format="default"/>.  The illustration in this subsection does not require
    the recording of OAM data in the packet.

</t>
        <t>
The illustration does not assume any formats for exporting the data
	elements or the data elements that need to be exported.
	The illustration assumes system clocks among all nodes in the SR domain are synchronized.
</t>
        <t>  Consider the example where the user wants to monitor sampled IPv4
    VPN 999 traffic going from CE1 to CE2 via a low latency low-latency SR policy Policy P installed
    at Node node N1.
    To exercise a low latency low-latency path, the SR Policy P forces the packet via segments
    2001:db8:K:2:X31:: and 2001:db8:K:4:X52::.
    The VPN SID at node N7 associated with VPN 999 is 2001:db8:K:7:DT999::.
    2001:db8:K:7:DT999:: is a USP SID.
    Nodes N1, N4, and N7 are capable of processing O-flag the O-flag, but
    node N2 is not capable of processing the O-flag.
    Node N100 is the centralized controller capable of processing and correlating
    the copy of the packets sent from nodes N1, N4, and N7.
    Node N100 is aware of O-flag processing capabilities.
    Controller N100
    Node N100, with the help from nodes N1, N4, N7 and N7, implements a hybrid
    OAM mechanism using the O-flag as follows:

     <list style="symbols">
          <t> A

        </t>
        <ul spacing="normal">
          <li> <t>A packet P1:(IPv4 header)(payload) P1 is sent from CE1 to Node node N1. </t>
          <t> Node The packet is:</t>
	<t>P1: (IPv4 header)(payload)</t></li>
          <li> <t>Node N1 steers the packet P1 through the SR Policy P.
          Based on a local configuration, Node node N1 also implements logic to sample
          traffic steered through policy SR Policy P for hybrid OAM purposes.
          Specification for the sampling logic is beyond the scope of this document.
          Consider the case where packet P1 is classified as a packet to be monitored
          via the hybrid OAM.
          Node N1 sets the O-flag during the encapsulation required by policy SR Policy P.
          As part of setting the O-flag, node N1 also sends a timestamped copy
          of the packet P1: P1 to a local
          OAM process. The packet is:</t>
	  <t>P1: (2001:db8:L:1::, 2001:db8:K:2:X31::) (2001:db8:K:7:DT999::,
	  2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=2; O-flag=1;
	  NH=IPv4)(IPv4 header)(payload) to a local
          OAM process. The header)(payload)</t>
	  <t>The local OAM process sends a full or partial copy of
          the
          packet P1 to the controller node N100.
          The OAM process includes the
          recorded timestamp, additional
          OAM information like (like incoming and outgoing interface, etc. along
          with interface), and
          any applicable metadata.
          Node N1 forwards the original packet towards the next
          segment 2001:db8:K:2:X31::. </t>
          <t> When 2001:db8:K:2:X31::.</t> </li>
          <li> <t>When node N2 receives the packet with the O-flag set, it
          ignores the O-flag. This is because node N2 is not capable of
          processing the O-flag. Node N2 performs the standard SRv6 SID and
          SRH processing.  Specifically, it executes the End.X behavior <xref
          target="RFC8986" format="default"/>
          indicated by the 2001:db8:K:2:X31:: SID as described in <xref target="RFC8986"/> and forwards the packet P1 over
          link3 towards node N3. The packet is:</t>
	  <t>P1: (2001:db8:L:1::, 2001:db8:K:4:X52::) (2001:db8:K:7:DT999::,
	  2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=1; O-flag=1;
	  NH=IPv4)(IPv4 header)(payload) over link 3 towards Node N3.
	  </t>
          <t>When
          </li>
          <li>When node N3, which is a non-SRv6 capable non-SRv6-capable node, receives the packet P1
          , P1, it performs the standard IPv6 processing.
          Specifically, it forwards the packet P1 based on DA
          2001:db8:K:4:X52:: in the IPv6 header.
          </t>
          <t>When
          </li>
          <li><t>When node N4 receives packet P1, it processes the O-flag. The packet P1 is:</t>
	  <t>P1: (2001:db8:L:1::, 2001:db8:K:4:X52::)
          (2001:db8:K:7:DT999::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=1; O-flag=1;
          NH=IPv4)(IPv4 header)(payload), it processes the O-flag.
          As header)(payload)
	  </t>
          <t>As part of processing the O-flag, it sends a timestamped copy of
          the packet to a local OAM process.
          Based on a local configuration, the local OAM process sends a full or partial
          copy of the packet
          P1 to the controller node N100. The OAM process includes the
          recorded timestamp, additional
          OAM information like (like incoming and outgoing interface, etc. along
          with etc.), and
          any applicable metadata.
          Node N4 performs the standard SRv6 SID and SRH processing on the original packet P1.
          Specifically, it executes
          the End.X behavior indicated by the 2001:db8:K:4:X52:: SID and forwards the packet P1
          over link10 towards node N5. The packet is:</t>
	  <t>P1: (2001:db8:L:1::, 2001:db8:K:7:DT999::)
          (2001:db8:K:7:DT999::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=0; O-flag=1;
          NH=IPv4)(IPv4 header)(payload) over link 10 towards Node N5.
	  </t>
          <t>When
         </li>
          <li>When node N5, which is a non-SRv6 capable non-SRv6-capable node, receives the packet P1,
          it performs the standard IPv6 processing.
          Specifically, it forwards the packet based on DA
          2001:db8:K:7:DT999:: in the IPv6 header.
          </t>
          <t>When
          </li>
          <li><t>When node N7 receives packet P1, it processes the O-flag. The packet P1 is:</t>
	  <t>P1: (2001:db8:L:1::, 2001:db8:K:7:DT999::)
          (2001:db8:K:7:DT999::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::; SL=0; O-flag=1;
          NH=IPv4)(IPv4 header)(payload), it processes the O-flag.
           As header)(payload)
	  </t>
          <t>As part of processing the O-flag, it sends a timestamped copy of
          the packet to a local OAM process.
          The local OAM process sends a full or partial copy of the packet
          P1 to the controller node N100. The OAM process includes the
          recorded timestamp, additional
          OAM information like (like incoming and outgoing interface, etc. along
          with etc.), and
          any applicable metadata.
          Node N7 performs the standard SRv6 SID and SRH processing on the original packet P1.
          Specifically, it executes the VPN SID indicated by the 2001:db8:K:7:DT999:: SID
          and
          and, based on lookup in table 100 100, forwards the packet P1
          towards CE2. The packet is:</t>
	  <t>P1: (IPv4 header)(payload) towards CE 2.
	  </t>

          <t>
          The controller
         </li>
          <li>
          Node N100 processes and correlates the copy of the packets
          sent from nodes N1, N4 N4, and N7 to find segment-by-segment delays and
          provide other hybrid OAM information related to packet P1.
          For segment-by-segment delay computation, it is assumed that clock clocks
          are synchronized time across the SR domain.

           </t>
          <t>

           </li>
          <li>
          The process continues for any other sampled packets.  </t>
    </list>
     </t>  </li>
        </ul>
      </section>
      <!--end: O-flag -->

	<section title="Monitoring numbered="true" toc="default">
        <name>Monitoring of SRv6 Paths"> Paths</name>
        <t>  In the recent past, network operators demonstrated interest in performing
   network OAM functions in a centralized manner.  <xref target='RFC8403'/> target="RFC8403" format="default"/>
     describes such a centralized OAM mechanism. Specifically, the document <xref target="RFC8403" format="default"/>
     describes a procedure that can be used to perform path continuity
     check
     checks between any nodes within an SR domain from a centralized
     monitoring system. However, the document while <xref target="RFC8403" format="default"/> focuses on SR networks with MPLS data
     plane. This
     plane, this document describes how
     the concept can be used to perform path monitoring in an SRv6 network
     from a centralized controller.
        </t>
        <t>  In the reference topology in Figure 1, <xref target="ref-top"/>, node N100 uses an IGP protocol
     like OSPF or IS-IS to get a view of the topology view within the IGP domain.
     Node N100 can also use BGP-LS to get the complete view of an inter-domain
     topology. The controller leverages the visibility of
     the topology to monitor the paths between the various endpoints.

        </t>

     <t>The controller
        <t>Node N100 advertises an END End
     SID <xref target="RFC8986"/> target="RFC8986" format="default"/> 2001:db8:K:100:1::. To monitor any
     arbitrary SRv6 paths, the controller can create a loopback probe that originates and
     terminates on Node node N100. To distinguish between a failure in the monitored path
     and loss of connectivity between the controller and the network,
     Node
     node N100 runs a suitable mechanism to monitor its connectivity to the monitored network.
        </t>
        <t>
     The following example illustrates loopback probes are exemplified using an example where controller in which node N100
     needs to verify a
     segment list &lt;2001:db8:K:2:X31::, 2001:db8:K:4:X52::&gt;:

     <list style="symbols">
     	<t>N100

        </t>
        <ul spacing="normal">
          <li>Node N100 generates an OAM packet (2001:db8:L:100::,
     	2001:db8:K:2:X31::)(2001:db8:K:100:1::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::,
     	SL=2)(OAM Payload). The controller routes the probe packet towards the first
     	segment, which is 2001:db8:K:2:X31::.
     	</t>

     	<t>Node
     	</li>
          <li>Node N2 executes the End.X behavior indicated by the 2001:db8:K:2:X31:: SID and
     	forwards the packet
     	 (2001:db8:L:100::,
     	2001:db8:K:4:X52::)(2001:db8:K:100:1::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::,
     	SL=1)(OAM Payload) on link3 to node N3.
     	</t>

        <t>
     	</li>
          <li> Node N3, which is a non-SRv6 capable non-SRv6-capable node, performs the standard
          IPv6 processing. Specifically, it forwards the packet
          based on the DA 2001:db8:K:4:X52:: in the IPv6 header. </t>

     	<t>Node </li>
          <li>Node N4 executes the End.X behavior indicated by the 2001:db8:K:4:X52:: SID and
     	forwards the packet
     	 (2001:db8:L:100::,
     	2001:db8:K:100:1::)(2001:db8:K:100:1::, 2001:db8:K:4:X52::, 2001:db8:K:2:X31::,
     	SL=0)(OAM Payload) on link10 to node N5.
     	</t>

        <t>
     	</li>
          <li> Node N5, which is a non-SRv6 capable non-SRv6-capable node, performs the standard
          IPv6 processing. Specifically, it forwards the packet
          based on the DA 2001:db8:K:100:1:: in the IPv6 header. </t>

     	<t>Node </li>
          <li>Node N100 executes the standard SRv6 END behavior. It
     	decapsulates the header and consume consumes the probe for OAM processing. The information
     	in the OAM payload is used to detect any missing probes, round trip round-trip delay, etc.
     	</t>

     </list>
     </t>
     	</li>
        </ul>
        <t> The OAM payload type or
     	the information carried in the OAM probe is a local implementation
     	decision at the controller and is outside the scope of this document.
        </t>
      </section>
      <!--end: Monitoring of SRv6 Paths -->

    </section>
    <!--end: Illustrations-->

    <section anchor="Acknowledgements" title="Acknowledgements"> numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t> The authors would like to thank Joel <contact fullname="Joel M. Halpern, Greg Mirsky,
      Bob Hinden, Loa Andersson, Gaurav Naik, Ketan Talaulikar and Haoyu Song Halpern"/>, <contact fullname="Greg Mirsky"/>,
      <contact fullname="Bob Hinden"/>, <contact fullname="Loa Andersson"/>, <contact fullname="Gaurav Naik"/>, <contact fullname="Ketan Talaulikar"/>, and <contact fullname="Haoyu Song"/>
      for their review comments. </t>
    </section>
    <section anchor="Contributors" title="Contributors"> numbered="false" toc="default">
      <name>Contributors</name>
      <t>The following people have contributed to this document:
      <figure>
      <artwork><![CDATA[
   Robert Raszuk
   Bloomberg LP
   Email: robert@raszuk.net
        ]]>
        </artwork>
        </figure>

    <figure>
      <artwork><![CDATA[
   John Leddy
   Individual
   Email: john@leddy.net
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Gaurav Dawra
   LinkedIn
   Email: gdawra.ietf@gmail.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Bart Peirens
   Proximus
   Email: bart.peirens@proximus.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Nagendra Kumar
   Cisco
      </t>
        <contact fullname="Robert Raszuk" >
        <organization>Bloomberg LP</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>robert@raszuk.net</email>
        </address>
      </contact>

      <contact fullname="John Leddy" >
        <organization>Individual</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>john@leddy.net</email>
        </address>
      </contact>

      <contact fullname="Gaurav Dawra" >
        <organization>LinkedIn</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>gdawra.ietf@gmail.com</email>
        </address>
      </contact>

      <contact fullname="Bart Peirens" >
        <organization>Proximus</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>bart.peirens@proximus.com</email>
        </address>
      </contact>

      <contact fullname="Nagendra Kumar" >
        <organization>Cisco Systems, Inc.
   Email: naikumar@cisco.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Carlos Pignataro
   Cisco Inc.</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>naikumar@cisco.com</email>
        </address>
      </contact>

      <contact fullname="Carlos Pignataro" >
        <organization>Cisco Systems, Inc.
   Email: cpignata@cisco.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Rakesh Gandhi
   Cisco Inc.</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>cpignata@cisco.com</email>
        </address>
      </contact>

      <contact fullname="Rakesh Gandhi" >
        <organization>Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Frank Brockners
   Cisco Inc.</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>rgandhi@cisco.com</email>
        </address>
      </contact>

      <contact fullname="Frank Brockners" >
        <organization>Cisco Systems, Inc.
   Germany
   Email: fbrockne@cisco.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Darren Dukes
   Cisco Inc.</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>fbrockne@cisco.com</email>
        </address>
      </contact>

      <contact fullname="Darren Dukes" >
        <organization>Cisco Systems, Inc.
   Email: ddukes@cisco.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Cheng Li
   Huawei
   Email: chengli13@huawei.com
        ]]>
        </artwork>
        </figure>

      <figure>
      <artwork><![CDATA[
   Faisal Iqbal
   Individual
   Email: faisal.ietf@gmail.com
        ]]>
        </artwork>
        </figure>
        </t> Inc.</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>ddukes@cisco.com</email>
        </address>
      </contact>

      <contact fullname="Cheng Li" >
        <organization>Huawei</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>chengli13@huawei.com</email>
        </address>
      </contact>

      <contact fullname="Faisal Iqbal" >
        <organization>Individual</organization>
        <address>
          <postal>
            <street></street>
            <city></city>
            <region></region><code></code>
            <country></country>
          </postal>
          <email>faisal.ietf@gmail.com</email>
        </address>
      </contact>
    </section>

  </back>
</rfc>