<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="std" ipr="trust200902" docName="draft-ietf-bfd-unaffiliated-echo-14" number="9747" obsoletes="" updates="5880" consensus="true" submissionType="IETF" tocInclude="true" symRefs="true" sortRefs="true" xml:lang="en" prepTime="2025-03-26T16:52:29" indexInclude="true" scripts="Common,Latin" tocDepth="3">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-bfd-unaffiliated-echo-14" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9747" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title abbrev="Unaffiliated BFD Echo">Unaffiliated Bidirectional Forwarding Detection (BFD) Echo</title>
    <seriesInfo name="RFC" value="9747" stream="IETF"/>
    <author fullname="Weiqiang Cheng" initials="W" surname="Cheng">
      <organization showOnFrontPage="true">China Mobile</organization>
      <address>
        <postal>
          <city>Beijing</city>
          <country>China</country>
        </postal>
        <email>chengweiqiang@chinamobile.com</email>
      </address>
    </author>
    <author fullname="Ruixue Wang" initials="R" surname="Wang">
      <organization showOnFrontPage="true">China Mobile</organization>
      <address>
        <postal>
          <city>Beijing</city>
          <country>China</country>
        </postal>
        <email>wangruixue@chinamobile.com</email>
      </address>
    </author>
    <author fullname="Xiao Min" initials="X" surname="Min" role="editor">
      <organization showOnFrontPage="true">ZTE Corp.</organization>
      <address>
        <postal>
          <city>Nanjing</city>
          <country>China</country>
        </postal>
        <email>xiao.min2@zte.com.cn</email>
      </address>
    </author>
    <author fullname="Reshad Rahman" initials="R" surname="Rahman">
      <organization showOnFrontPage="true">Equinix</organization>
      <address>
        <postal>
          <city>Ottawa</city>
          <country>Canada</country>
        </postal>
        <email>reshad@yahoo.com</email>
      </address>
    </author>
    <author fullname="Raj Chetan Boddireddy" initials="R" surname="Boddireddy">
      <organization showOnFrontPage="true">Juniper Networks</organization>
      <address>
        <email>rchetan@juniper.net</email>
      </address>
    </author>
    <date month="03" year="2025"/>
    <area>RTG</area>
    <workgroup>bfd</workgroup>
    <keyword>single-ended BFD</keyword>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1"> 
	This document specifies an extension to the Bidirectional Forwarding Detection (BFD) 
	protocol that enables the use of the BFD Echo function without the need for an associated 
	BFD control session. This "Unaffiliated BFD Echo" mechanism allows rapid detection of 
	forwarding path failures in networks where establishing BFD control sessions is impractical 
	or undesirable. By decoupling the Echo function from the control plane, network devices can 
	utilize BFD's fast failure detection capabilities in a simplified manner, enhancing network 
	resiliency and operational efficiency.
      </t>
      <t indent="0" pn="section-abstract-2"> 
	This document updates RFC 5880 by defining a new Unaffiliated BFD Echo mechanism.
      </t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This is an Internet Standards Track document.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.
        </t>
        <t indent="0" pn="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <eref target="https://www.rfc-editor.org/info/rfc9747" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2025 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.1.2">
              <li pn="section-toc.1-1.1.2.1">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.1.1"><xref derivedContent="1.1" format="counter" sectionFormat="of" target="section-1.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-conventions-used-in-this-do">Conventions Used in This Document</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-unaffiliated-bfd-echo-proce">Unaffiliated BFD Echo Procedures</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-updates-to-rfc-5880">Updates to RFC 5880</xref></t>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-operational-considerations">Operational Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" format="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.7.2">
              <li pn="section-toc.1-1.7.2.1">
                <t indent="0" pn="section-toc.1-1.7.2.1.1"><xref derivedContent="7.1" format="counter" sectionFormat="of" target="section-7.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.7.2.2">
                <t indent="0" pn="section-toc.1-1.7.2.2.1"><xref derivedContent="7.2" format="counter" sectionFormat="of" target="section-7.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgements">Acknowledgements</xref></t>
          </li>
          <li pn="section-toc.1-1.9">
            <t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-contributors">Contributors</xref></t>
          </li>
          <li pn="section-toc.1-1.10">
            <t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.c"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-addresses">Authors' Addresses</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">
	To minimize the impact of device and link faults on services and to improve network availability 
	in single-hop scenarios, a network device needs the capability to quickly detect communication 
	faults with adjacent devices. Prompt detection allows for timely remedial actions to ensure 
	service continuity.
      </t>
      <t indent="0" pn="section-1-2"> 
	BFD <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> provides a low-overhead, short-interval method for detecting faults 
	on the communication path between adjacent forwarding engines, which may include interfaces, data 
	links, and the forwarding engines themselves. BFD offers a unified mechanism to monitor any media 
	and protocol layers in real time.
      </t>
      <t indent="0" pn="section-1-3"> 
	BFD defines two primary modes -- Asynchronous mode and Demand mode -- to accommodate various deployment 
	scenarios. Additionally, it supports an Echo function that reduces the level of BFD support required 
	in device implementations, as described in <xref section="3.2" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-3.2" derivedContent="RFC5880"/>. When the Echo 
	function is activated, the local system sends BFD Echo packets, and the remote system loops back the 
	received Echo packets through the forwarding path, as described in <xref section="5" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-5" derivedContent="RFC5880"/> 
	and <xref section="4" sectionFormat="of" target="RFC5881" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5881#section-4" derivedContent="RFC5881"/>. If several consecutive BFD Echo packets are not received 
	by the local system, the BFD session is declared Down.
      </t>
      <t indent="0" pn="section-1-4"> 
	There are two typical scenarios when using the BFD Echo function:
      </t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-1-5">
        <li pn="section-1-5.1">
          <t indent="0" pn="section-1-5.1.1"> 
	Full BFD protocol capability with adjunct Echo function (Affiliated BFD Echo): This scenario requires 
	both the local device and the adjacent device to support the full BFD protocol. This operation remains 
	unchanged from <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>.
          </t>
        </li>
        <li pn="section-1-5.2">
          <t indent="0" pn="section-1-5.2.1">
	BFD Echo-Only method without full BFD protocol capability (Unaffiliated BFD Echo): This scenario requires 
	only the local device to support sending and demultiplexing BFD Control packets. In this case, BFD 
	Control packets are sent over the BFD Echo port, and the processing procedures for Asynchronous mode 
	are used with the modifications specified in this document. Note that this method requires the local device 
	to send packets with one of its own IP addresses as the destination address, upon receipt of which the adjacent 
	device loops them back to the local device. Also note that this method monitors the connectivity to a device 
	over a specific interface and does not verify the availability of a specific IP address at that device.
          </t>
        </li>
      </ul>
      <t indent="0" pn="section-1-6">
	This document specifies the Unaffiliated BFD Echo scenario.
      </t>
      <t indent="0" pn="section-1-7"> 
	<xref section="5" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-5" derivedContent="RFC5880"/> indicates that the payload of an Affiliated BFD Echo packet is a local 
	matter; therefore, its contents are outside the scope of that specification. This document, however, 
	specifies the contents of the Unaffiliated BFD Echo packet and the procedures for handling them. While this 
	may appear to contravene <xref section="5" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-5" derivedContent="RFC5880"/>, the core behavior in that RFC states that the 
	contents of BFD Echo packets are a local matter; this document is defining that "local matter". Regarding the 
	selection of IP addresses, the rules stated in <xref section="4" sectionFormat="of" target="RFC5881" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5881#section-4" derivedContent="RFC5881"/> are applicable to the 
	encapsulation of an Unaffiliated BFD Echo packet.
      </t>
      <t indent="0" pn="section-1-8"> 
	Section 6.2.2 of <xref target="BBF-TR-146" format="default" sectionFormat="of" derivedContent="BBF-TR-146"/> describes a use case for the Unaffiliated BFD Echo.
      </t>
      <t indent="0" pn="section-1-9"> 
	This document updates <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> by defining a new method of BFD Echo-only operation which only 
	impacts the sender of BFD Echo packets without requiring an implementation to support the BFD protocol at the 
	loopback device, such that any IP forwarder can loop back the BFD Echo packets. It specifies the use of the 
	Unaffiliated BFD Echo over IPv4 and IPv6 for a single IP hop. The reason why it cannot be used for multihop 
	paths is that the Unaffiliated BFD Echo packets would be looped back by the first hop. A full description of 
	the updates to <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> is provided in <xref target="updates-to-rfc-5880" format="default" sectionFormat="of" derivedContent="Section 3"/>.
      </t>
      <section numbered="true" removeInRFC="false" toc="include" pn="section-1.1">
        <name slugifiedName="name-conventions-used-in-this-do">Conventions Used in This Document</name>
        <t indent="0" pn="section-1.1-1">
    The key words "<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 "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
        </t>
      </section>
    </section>
    <section anchor="unaffiliated-bfd-echo-procedures" numbered="true" removeInRFC="false" toc="include" pn="section-2">
      <name slugifiedName="name-unaffiliated-bfd-echo-proce">Unaffiliated BFD Echo Procedures</name>
      <t indent="0" pn="section-2-1"> 
	This section specifies the Unaffiliated BFD Echo procedures.
      </t>
      <figure anchor="Figure_1" align="left" suppress-title="false" pn="figure-1">
        <name slugifiedName="name-unaffiliated-bfd-echo">Unaffiliated BFD Echo</name>
        <artset pn="section-2-2.1">
          <artwork type="svg" align="left" pn="section-2-2.1.1">
      <svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="272" width="512" viewBox="0 0 512 272" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
              <path d="M 8,32 L 8,240" fill="none" stroke="black"/>
              <path d="M 40,64 L 40,192" fill="none" stroke="black"/>
              <path d="M 144,32 L 144,88" fill="none" stroke="black"/>
              <path d="M 144,104 L 144,136" fill="none" stroke="black"/>
              <path d="M 144,184 L 144,240" fill="none" stroke="black"/>
              <path d="M 368,32 L 368,136" fill="none" stroke="black"/>
              <path d="M 368,184 L 368,240" fill="none" stroke="black"/>
              <path d="M 384,144 L 384,176" fill="none" stroke="black"/>
              <path d="M 504,32 L 504,240" fill="none" stroke="black"/>
              <path d="M 8,32 L 144,32" fill="none" stroke="black"/>
              <path d="M 368,32 L 504,32" fill="none" stroke="black"/>
              <path d="M 48,64 L 136,64" fill="none" stroke="black"/>
              <path d="M 136,96 L 160,96" fill="none" stroke="black"/>
              <path d="M 136,144 L 376,144" fill="none" stroke="black"/>
              <path d="M 128,176 L 376,176" fill="none" stroke="black"/>
              <path d="M 48,192 L 136,192" fill="none" stroke="black"/>
              <path d="M 8,240 L 144,240" fill="none" stroke="black"/>
              <path d="M 368,240 L 504,240" fill="none" stroke="black"/>
              <polygon class="arrowhead" points="168,96 156,90.4 156,101.6" fill="black" transform="rotate(0,160,96)"/>
              <polygon class="arrowhead" points="136,176 124,170.4 124,181.6" fill="black" transform="rotate(180,128,176)"/>
              <g class="text">
                <text x="76" y="20">Device A</text>
                <text x="436" y="20">Device B</text>
                <text x="92" y="84">Unaffiliated</text>
                <text x="84" y="100">BFD Echo</text>
                <text x="80" y="116">Session</text>
                <text x="256" y="132">Unaffiliated BFD Echo</text>
                <text x="408" y="148">BFD</text>
                <text x="144" y="164">|</text>
                <text x="424" y="164">packets</text>
                <text x="420" y="180">looped</text>
                <text x="72" y="260">BFD supported</text>
                <text x="440" y="260">BFD not supported</text>
              </g>
            </svg>
          </artwork>
          <artwork type="ascii-art" align="left" pn="section-2-2.1.2">
        Device A                                     Device B
   +----------------+                           +----------------+
   |                |                           |                |
   |   |------------|                           |                |
   |   |Unaffiliated|                           |                |
   |   | BFD Echo  ---&gt;                         |                |
   |   | Session    |                           |                |
   |   |            |   Unaffiliated BFD Echo   |                |
   |   |           -------------------------------| BFD          |
   |   |            |                             | packets      |
   |   |          &lt;-------------------------------| looped       |
   |   |------------|                           |                |
   |                |                           |                |
   |                |                           |                |
   +----------------+                           +----------------+
     BFD supported                               BFD not supported
</artwork>
        </artset>
      </figure>
      <t indent="0" pn="section-2-3">
    As shown in <xref target="Figure_1" format="default" sectionFormat="of" derivedContent="Figure 1"/>, device A supports BFD, whereas device B is a regular IP forwarder that does not support 
	BFD. Device A would send Unaffiliated BFD Echo packets, and after receiving the Unaffiliated BFD Echo packets 
	sent from device A, the one-hop-away BFD peer device B immediately loops them back by normal IP forwarding. This 
	allows device A to rapidly detect a connectivity loss to device B. Note that device B would not intercept any 
	received Unaffiliated BFD Echo packet or parse any BFD protocol field within the Unaffiliated BFD Echo packet.
      </t>
      <t indent="0" pn="section-2-4">
    An Unaffiliated BFD Echo session is not actually a BFD session because there is no coordination of BFD protocol 
	state between the two link ends: the remote end does not support BFD and so cannot engage in a BFD session. 

   From the standpoint of the local end (as an initiator),
   the Unaffiliated BFD Echo session may be regarded as a BFD session.
      </t>
      <t indent="0" pn="section-2-5">
	For the Unaffiliated Echo procedure, an Unaffiliated BFD Echo session is established on device A. The session 
	<bcp14>MUST</bcp14> adhere to the BFD state machine specified in <xref section="6.2" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.2" derivedContent="RFC5880"/>, with the exception 
	that the received state is not derived from BFD Control packets originating from the remote system, but rather 
	from packets that are generated by the local system and looped back from the remote system. Consequently, the 
	AdminDown state is not utilized in Unaffiliated BFD Echo.
      </t>
      <t indent="0" pn="section-2-6">
	BFD Control packets are transmitted and received as Unaffiliated BFD Echo packets, using UDP destination port 
	3785, as defined in <xref target="RFC5881" format="default" sectionFormat="of" derivedContent="RFC5881"/>. The standard procedures for BFD Asynchronous sessions are applied 
	to the looped BFD Control packets, including packet validation and authentication, in accordance with <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>.
      </t>
      <t indent="0" pn="section-2-7">
	Once an Unaffiliated BFD Echo session is created on device A, it starts sending Unaffiliated BFD Echo packets. 
   Unaffiliated BFD Echo
   packets with zeroed "Your Discriminator" field are demultiplexed to
   the proper session based on the source IP address or UDP source port.
   After the remote system loops back the local discriminator, all
   further received packets are demultiplexed based on the "Your                      
   Discriminator" field only, which conforms to the procedure
   specified in 
<xref section="6.3" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.3" derivedContent="RFC5880"/>. An Unaffiliated BFD Echo packet follows the same encapsulation 
	rules as for a BFD Echo packet as specified in <xref section="4" sectionFormat="of" target="RFC5881" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5881#section-4" derivedContent="RFC5881"/>. All Unaffiliated BFD Echo packets 
	for the session <bcp14>MUST</bcp14> be sent with a TTL or Hop Limit value of 255. Received packets <bcp14>MUST</bcp14> have a TTL or Hop Limit 
	value of 254 (similar to <xref section="A" sectionFormat="of" target="RFC5082" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5082#appendix-A" derivedContent="RFC5082"/> to verify against a configured number of hops); otherwise, 
	the received packets <bcp14>MUST</bcp14> be dropped.
      </t>
      <t indent="0" pn="section-2-8">
	In the context of an Unaffiliated BFD Echo packet, the "Desired Min TX Interval" and "Required Min RX Interval" fields, 
	as defined in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>, <bcp14>MUST</bcp14> be populated with a specific value to prevent the potential exposure of 
	uninitialized memory. It is <bcp14>RECOMMENDED</bcp14> that these fields be set to a value of 1 second (1,000,000 microseconds). However, 
	upon receipt, these values <bcp14>MUST</bcp14> be ignored and <bcp14>MUST NOT</bcp14> be used in the calculation of the Detection Time.
      </t>
      <t indent="0" pn="section-2-9">
	The "Required Min Echo RX Interval" field, as defined in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>, <bcp14>MUST</bcp14> be populated with a specific value 
	to prevent the potential exposure of uninitialized memory. It is <bcp14>RECOMMENDED</bcp14> that this field be set to 0. However, this value 
	<bcp14>MUST</bcp14> be ignored upon receipt. The transmission interval for Unaffiliated BFD Echo packets when in the Up state <bcp14>MUST</bcp14> be 
	provisioned on device A.
      </t>
      <t indent="0" pn="section-2-10">
	The functionality of the Unaffiliated BFD Echo feature is dependent on device B performing IP forwarding. While this capability 
	is typically expected to be supported on routers, it may not be enabled by default on hosts. The method for provisioning device 
	B to loop back Unaffiliated BFD Echo packets is outside the scope of this document.
      </t>
      <t indent="0" pn="section-2-11">
	Similar to what's specified in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>, the Unaffiliated BFD Echo session begins with the 
	periodic, slow transmission of Unaffiliated BFD Echo packets. The slow transmission rate should be no greater than 
	one packet per second, until the session on device A is Up. After the session is Up, the provisioned transmission interval is 
	used. When the Unaffiliated BFD Echo session on device A goes Down, the slow transmission rate is resumed. The "Detect Mult" field 
	defined in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> <bcp14>MUST</bcp14> be set to a value provisioned on device A. When the bfd.SessionState is 
	Up and a "Detect Mult" number of Unaffiliated BFD Echo packets have not arrived at device A as they should, the device 
	A "<bcp14>MUST</bcp14> set bfd.SessionState to Down and bfd.LocalDiag to 2 (Echo Function Failed)", as specified in 
	<xref section="6.8.5" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.8.5" derivedContent="RFC5880"/>.
      </t>
      <t indent="0" pn="section-2-12">
	In summary, the Unaffiliated BFD Echo packet reuses the format of the BFD Control packet defined in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>, 
	and the fields within the Unaffiliated BFD Echo packet are populated as follows:
      </t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-2-13">
        <li pn="section-2-13.1">
          <t indent="0" pn="section-2-13.1.1">My Discriminator: <bcp14>MUST</bcp14> be set to the provisioned local discriminator.</t>
        </li>
        <li pn="section-2-13.2">
          <t indent="0" pn="section-2-13.2.1">Your Discriminator: <bcp14>MUST</bcp14> initially be set to 0, and then <bcp14>MUST</bcp14> be set to the value of "My Discriminator" looped back 
		 from the remote system.</t>
        </li>
        <li pn="section-2-13.3">
          <t indent="0" pn="section-2-13.3.1">Desired Min TX Interval: <bcp14>MUST</bcp14> be set to a specific value, with a suggested value of 1 second (1,000,000 microseconds).</t>
        </li>
        <li pn="section-2-13.4">
          <t indent="0" pn="section-2-13.4.1">Required Min RX Interval: <bcp14>MUST</bcp14> be set to a specific value, with a suggested value of 1 second (1,000,000 microseconds).</t>
        </li>
        <li pn="section-2-13.5">
          <t indent="0" pn="section-2-13.5.1">Required Min Echo RX Interval: <bcp14>MUST</bcp14> be set to a specific value, with a suggested value of 0.</t>
        </li>
        <li pn="section-2-13.6">
          <t indent="0" pn="section-2-13.6.1">Detect Mult: <bcp14>MUST</bcp14> be set to the provisioned maximum allowable number of consecutively lost Unaffiliated BFD Echo packets.</t>
        </li>
      </ul>
    </section>
    <section anchor="updates-to-rfc-5880" numbered="true" removeInRFC="false" toc="include" pn="section-3">
      <name slugifiedName="name-updates-to-rfc-5880">Updates to RFC 5880</name>
      <t indent="0" pn="section-3-1"> 
	The Unaffiliated BFD Echo described in this document reuses the BFD
	Echo function as described in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> and <xref target="RFC5881" format="default" sectionFormat="of" derivedContent="RFC5881"/>, but does not require BFD Asynchronous or Demand
	mode. In the Unaffiliated BFD Echo operation, only the local system
	has the BFD protocol enabled, while the remote system simply loops
	back the received BFD Echo packets as ordinary data packets, without
	engaging in the BFD protocol.
      </t>
      <t indent="0" pn="section-3-2"> 
	This document updates <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> with respect to its
	descriptions on the BFD Echo function as follows.
      </t>
      <t indent="0" pn="section-3-3">
	The fourth paragraph of <xref section="3.2" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-3.2" derivedContent="RFC5880"/> is
	updated as below:
      </t>
      <t indent="0" pn="section-3-4">OLD TEXT</t>
      <blockquote pn="section-3-5">An adjunct to both modes is the Echo function.</blockquote>
      <t indent="0" pn="section-3-6">NEW TEXT</t>
      <blockquote pn="section-3-7">An adjunct to both modes is the Echo function, which can also be running independently.</blockquote>
      <t indent="0" pn="section-3-8">OLD TEXT</t>
      <blockquote pn="section-3-9">Since the Echo function is handling the task of detection,
      the rate of periodic transmission of Control packets may be reduced (in
      the case of Asynchronous mode) or eliminated completely (in the case of
      Demand mode).</blockquote>
      <t indent="0" pn="section-3-10">NEW TEXT</t>
      <blockquote pn="section-3-11">Since the Echo function is handling the task of detection,
      the rate of periodic transmission of Control packets may be reduced (in
      the case of Asynchronous mode) or eliminated completely (in the case of
      Demand mode).  The Echo function may also be used independently, with
      neither Asynchronous nor Demand mode.</blockquote>
      <t indent="0" pn="section-3-12">
	The third and ninth paragraphs of <xref section="6.1" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.1" derivedContent="RFC5880"/> are updated as below:
      </t>
      <t indent="0" pn="section-3-13">OLD TEXT</t>
      <blockquote pn="section-3-14">Once the BFD session is Up, a system can choose to start the
      Echo function if it desires and the other system signals that it will
      allow it. The rate of transmission of Control packets is typically kept
      low when the Echo function is active.</blockquote>
      <t indent="0" pn="section-3-15">NEW TEXT</t>
      <blockquote pn="section-3-16">When a system is running with Asynchronous or Demand mode,
      once the BFD session is Up, it can choose to start the Echo function if
      it desires and the other system signals that it will allow it. The rate
      of transmission of Control packets is typically kept low for
      Asynchronous mode or eliminated completely for Demand mode when the Echo
      function is active.</blockquote>
      <t indent="0" pn="section-3-17">OLD TEXT</t>
      <blockquote pn="section-3-18">If the session goes Down, the transmission of Echo packets
      (if any) ceases, and the transmission of Control packets goes back to
      the slow rate.</blockquote>
      <t indent="0" pn="section-3-19">NEW TEXT</t>
      <blockquote pn="section-3-20">In Asynchronous mode or Demand mode, if the session goes
      Down, the transmission of Echo packets (if any) ceases, and the
      transmission of Control packets goes back to the slow rate.</blockquote>
      <t indent="0" pn="section-3-21">
	The second paragraph of <xref section="6.4" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.4" derivedContent="RFC5880"/> is updated as below:
      </t>
      <t indent="0" pn="section-3-22">OLD TEXT</t>
      <blockquote pn="section-3-23">When a system is using the Echo function, it is advantageous
      to choose a sedate reception rate for Control packets, since liveness
      detection is being handled by the Echo packets. This can be controlled
      by manipulating the Required Min RX Interval field (see section 6.8.3).</blockquote>
      <t indent="0" pn="section-3-24">NEW TEXT</t>
      <blockquote pn="section-3-25">When a system is using the Echo function with Asynchronous
      mode, it is advantageous to choose a sedate reception rate for Control
      packets, since liveness detection is being handled by the Echo
      packets. This can be controlled by manipulating the Required Min RX
      Interval field (see section <xref target="RFC5880" section="6.8.3" sectionFormat="bare" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.8.3" derivedContent="RFC5880"/>).  Note that a system operating in
      Demand mode would direct the remote system to cease the periodic
      transmission of BFD Control packets, by setting the Demand (D) bit in
      its BFD Control packets.</blockquote>
      <t indent="0" pn="section-3-26">
	The second paragraph of <xref section="6.8" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.8" derivedContent="RFC5880"/> is updated as below:
      </t>
      <t indent="0" pn="section-3-27">OLD TEXT</t>
      <blockquote pn="section-3-28">When a system is said to have "the Echo function active" it
      means that the system is sending BFD Echo packets, implying that the
      session is Up and the other system has signaled its willingness to loop
      back Echo packets.</blockquote>
      <t indent="0" pn="section-3-29">NEW TEXT</t>
      <blockquote pn="section-3-30">When a system in Asynchronous or Demand mode is said to have
      "the Echo function active" it means that the system is sending BFD Echo
      packets, implying that the session is Up and the other system has
      signaled its willingness to loop back Echo packets.</blockquote>
      <t indent="0" pn="section-3-31">
	The seventh paragraph of <xref section="6.8.3" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.8.3" derivedContent="RFC5880"/> is updated as below:
      </t>
      <t indent="0" pn="section-3-32">OLD TEXT</t>
      <blockquote pn="section-3-33">When the Echo function is active, a system
      <bcp14>SHOULD</bcp14> set bfd.RequiredMinRxInterval to a value of not
      less than one second (1,000,000 microseconds). This is intended to keep
      received BFD Control traffic at a negligible level, since the actual
      detection function is being performed using BFD Echo
      packets.</blockquote>
      <t indent="0" pn="section-3-34">NEW TEXT</t>
      <blockquote pn="section-3-35">When the Echo function is active with Asynchronous mode, a
      system <bcp14>SHOULD</bcp14> set bfd.RequiredMinRxInterval to a value of
      not less than one second (1,000,000 microseconds). This is intended to
      keep received BFD Control traffic at a negligible level, since the
      actual detection function is being performed using BFD Echo packets. A
      system operating in Demand mode would not receive BFD Control traffic.</blockquote>
      <t indent="0" pn="section-3-36">
	The first and second paragraphs of <xref section="6.8.9" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-6.8.9" derivedContent="RFC5880"/> are updated as below:
      </t>
      <t indent="0" pn="section-3-37">OLD TEXT</t>
      <blockquote pn="section-3-38">
        <t indent="0" pn="section-3-38.1">BFD Echo packets <bcp14>MUST NOT</bcp14> be transmitted when
	bfd.SessionState is not Up.  BFD Echo packets <bcp14>MUST NOT</bcp14> be
	transmitted unless the last BFD Control packet received from the remote
	system contains a nonzero value in Required Min Echo RX Interval.</t>
        <t indent="0" pn="section-3-38.2">BFD Echo packets <bcp14>MAY</bcp14> be transmitted when
	bfd.SessionState is Up.  The interval between transmitted BFD Echo
	packets <bcp14>MUST NOT</bcp14> be less than the value advertised by the
	remote system in Required Min Echo RX Interval, except as follows: [...]
        </t>
      </blockquote>
      <t indent="0" pn="section-3-39">NEW TEXT</t>
      <blockquote pn="section-3-40">
        <t indent="0" pn="section-3-40.1">When a system is using the Echo function with either
	Asynchronous or Demand mode, BFD Echo packets <bcp14>MUST NOT</bcp14> be
	transmitted when bfd.SessionState is not Up, and BFD Echo packets
	<bcp14>MUST NOT</bcp14> be transmitted unless the last BFD Control
	packet received from the remote system contains a nonzero value in
	Required Min Echo RX Interval.</t>
        <t indent="0" pn="section-3-40.2">When a system is using the Echo function with either
	Asynchronous or Demand mode, BFD Echo packets <bcp14>MAY</bcp14> be
	transmitted when bfd.SessionState is Up, and the interval between
	transmitted BFD Echo packets <bcp14>MUST NOT</bcp14> be less than the
	value advertised by the remote system in Required Min Echo RX
	Interval, except as follows: [...]</t>
      </blockquote>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-4">
      <name slugifiedName="name-operational-considerations">Operational Considerations</name>
      <t indent="0" pn="section-4-1">
    All operational considerations from <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> apply. Since this mechanism leverages existing BFD machinery, 
	particularly periodic pacing of traffic based on configuration, there's no real possibility to create congestion. 
   Moreover, creating congestion would be 
   counterproductive to checking the bidirectional connectivity.
      </t>
      <t indent="0" pn="section-4-2">
    Some devices that would benefit from the use of BFD may be unable to support the full BFD protocol. Examples of such 
	devices include servers running virtual machines, or Internet of Things (IoT) devices. By using Unaffiliated BFD 
	Echo, these devices only need to support a basic loopback function.
      </t>
      <t indent="0" pn="section-4-3">
    As specified in <xref target="unaffiliated-bfd-echo-procedures" format="default" sectionFormat="of" derivedContent="Section 2"/> of this document, some configuration is needed to make the Unaffiliated BFD Echo work, 
	although the configuration won't go beyond the scope of <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/>. 
At a BFD-enabled local system, the 
	Unaffiliated BFD Echo session can coexist with other types of BFD sessions. In that scenario, the remote system for the 
	Unaffiliated BFD Echo session must be different from the remote system for any other type of BFD session, and the local 
	system's discriminators for different BFD sessions must be different. At the same time, it's not necessary for the local 
	system to differentiate the Unaffiliated BFD Echo session from the other types of BFD sessions.
      </t>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-5">
      <name slugifiedName="name-security-considerations">Security Considerations</name>
      <t indent="0" pn="section-5-1">
	All security considerations from <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> and <xref target="RFC5881" format="default" sectionFormat="of" derivedContent="RFC5881"/> apply.
      </t>
      <t indent="0" pn="section-5-2">
	Unaffiliated BFD Echo requires the remote device to loop Unaffiliated BFD Echo packets. In order to provide this 
	service, the remote device cannot make use of Unicast Strict Reverse Path Forwarding (RPF) <xref target="RFC3704" format="default" sectionFormat="of" derivedContent="RFC3704"/>, 
	otherwise the Unaffiliated BFD Echo packets might not pass the RPF check at the remote device.
      </t>
      <t indent="0" pn="section-5-3">
	As described in <xref section="5" sectionFormat="of" target="RFC5880" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5880#section-5" derivedContent="RFC5880"/>, BFD Echo packets may be spoofed. Specifically for Unaffiliated 
	BFD Echo, a DoS attacker may send spoofed Unaffiliated BFD Echo packets to the loopback device, so some form of 
	authentication <bcp14>SHOULD</bcp14> be included. Considering the Unaffiliated BFD Echo packets in this document are also BFD 
	Control packets, the "Authentication Section" as defined in <xref target="RFC5880" format="default" sectionFormat="of" derivedContent="RFC5880"/> for a BFD Control packet is 
	<bcp14>RECOMMENDED</bcp14> to be included within the Unaffiliated BFD Echo packet.
      </t>
      <t indent="0" pn="section-5-4">
	As stated in <xref target="unaffiliated-bfd-echo-procedures" format="default" sectionFormat="of" derivedContent="Section 2"/>, in order to avoid unset values being a potential vector for disclosure of uninitialized 
	memory, all fields of the Unaffiliated BFD Echo packet <bcp14>MUST</bcp14> be populated with a certain value, even if some of the 
	fields are ignored on receipt.
      </t>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-6">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <t indent="0" pn="section-6-1"> This document has no IANA actions.</t>
    </section>
  </middle>
  <back>
    <references pn="section-7">
      <name slugifiedName="name-references">References</name>
      <references pn="section-7.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC5880" target="https://www.rfc-editor.org/info/rfc5880" quoteTitle="true" derivedAnchor="RFC5880">
          <front>
            <title>Bidirectional Forwarding Detection (BFD)</title>
            <author fullname="D. Katz" initials="D." surname="Katz"/>
            <author fullname="D. Ward" initials="D." surname="Ward"/>
            <date month="June" year="2010"/>
            <abstract>
              <t indent="0">This document describes a protocol intended to detect faults in the bidirectional path between two forwarding engines, including interfaces, data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. It operates independently of media, data protocols, and routing protocols. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5880"/>
          <seriesInfo name="DOI" value="10.17487/RFC5880"/>
        </reference>
        <reference anchor="RFC5881" target="https://www.rfc-editor.org/info/rfc5881" quoteTitle="true" derivedAnchor="RFC5881">
          <front>
            <title>Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)</title>
            <author fullname="D. Katz" initials="D." surname="Katz"/>
            <author fullname="D. Ward" initials="D." surname="Ward"/>
            <date month="June" year="2010"/>
            <abstract>
              <t indent="0">This document describes the use of the Bidirectional Forwarding Detection (BFD) protocol over IPv4 and IPv6 for single IP hops. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5881"/>
          <seriesInfo name="DOI" value="10.17487/RFC5881"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
      </references>
      <references pn="section-7.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="BBF-TR-146" target="https://www.broadband-forum.org/pdfs/tr-146-1-0-0.pdf" quoteTitle="true" derivedAnchor="BBF-TR-146">
          <front>
            <title>TR-146: Subscriber Sessions</title>
            <author>
              <organization showOnFrontPage="true">Broadband Forum</organization>
            </author>
            <date month="May" year="2013"/>
          </front>
          <refcontent>Broadband Forum Technical Report, TR-146, Issue 1</refcontent>
        </reference>
        <reference anchor="RFC3704" target="https://www.rfc-editor.org/info/rfc3704" quoteTitle="true" derivedAnchor="RFC3704">
          <front>
            <title>Ingress Filtering for Multihomed Networks</title>
            <author fullname="F. Baker" initials="F." surname="Baker"/>
            <author fullname="P. Savola" initials="P." surname="Savola"/>
            <date month="March" year="2004"/>
            <abstract>
              <t indent="0">BCP 38, RFC 2827, is designed to limit the impact of distributed denial of service attacks, by denying traffic with spoofed addresses access to the network, and to help ensure that traffic is traceable to its correct source network. As a side effect of protecting the Internet against such attacks, the network implementing the solution also protects itself from this and other attacks, such as spoofed management access to networking equipment. There are cases when this may create problems, e.g., with multihoming. This document describes the current ingress filtering operational mechanisms, examines generic issues related to ingress filtering, and delves into the effects on multihoming in particular. This memo updates RFC 2827. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="84"/>
          <seriesInfo name="RFC" value="3704"/>
          <seriesInfo name="DOI" value="10.17487/RFC3704"/>
        </reference>
        <reference anchor="RFC5082" target="https://www.rfc-editor.org/info/rfc5082" quoteTitle="true" derivedAnchor="RFC5082">
          <front>
            <title>The Generalized TTL Security Mechanism (GTSM)</title>
            <author fullname="V. Gill" initials="V." surname="Gill"/>
            <author fullname="J. Heasley" initials="J." surname="Heasley"/>
            <author fullname="D. Meyer" initials="D." surname="Meyer"/>
            <author fullname="P. Savola" initials="P." role="editor" surname="Savola"/>
            <author fullname="C. Pignataro" initials="C." surname="Pignataro"/>
            <date month="October" year="2007"/>
            <abstract>
              <t indent="0">The use of a packet's Time to Live (TTL) (IPv4) or Hop Limit (IPv6) to verify whether the packet was originated by an adjacent node on a connected link has been used in many recent protocols. This document generalizes this technique. This document obsoletes Experimental RFC 3682. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5082"/>
          <seriesInfo name="DOI" value="10.17487/RFC5082"/>
        </reference>
      </references>
    </references>
    <section numbered="false" removeInRFC="false" toc="include" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgements">Acknowledgements</name>
      <t indent="0" pn="section-appendix.a-1"> The authors would like to acknowledge <contact fullname="Ketan       Talaulikar"/>, <contact fullname="Greg Mirsky"/>, <contact fullname="Santosh Pallagatti"/>, <contact fullname="Aijun Wang"/>,
      <contact fullname="Éric Vyncke"/>, <contact fullname="Adrian Farrel"/>,
      <contact fullname="Tim Wicinski"/>, <contact fullname="Dhruv Dhody"/>,
      <contact fullname="Stephen Farrell"/>, <contact fullname="Gunter Van de Velde"/>, <contact fullname="Gyan Mishra"/>, <contact fullname="Brian Trammell"/>, <contact fullname="Gorry Fairhurst"/>, <contact fullname="Mahesh Jethanandani"/>, <contact fullname="John Scudder"/>,
      <contact fullname="Murray Kucherawy"/>, and <contact fullname="Zaheduzzaman Sarker"/> for their careful reviews and very
      helpful comments.</t>
      <t indent="0" pn="section-appendix.a-2"> The authors would like to acknowledge <contact fullname="Jeff Haas"/> for his guidance, insightful review, and very helpful
      comments.</t>
      <t indent="0" pn="section-appendix.a-3"> The authors would like to acknowledge <contact fullname="Erik Auerswald"/> for his insightful comments during the discussion of this
      document.</t>
      <t indent="0" pn="section-appendix.a-4"> The authors would like to acknowledge <contact fullname="Detao Zhao"/> for the very helpful discussion.</t>
    </section>
    <section numbered="false" removeInRFC="false" toc="include" pn="section-appendix.b">
      <name slugifiedName="name-contributors">Contributors</name>
      <contact fullname="Liu Aihua">
        <organization showOnFrontPage="true">ZTE</organization>
        <address>
          <email>liu.aihua@zte.com.cn</email>
        </address>
      </contact>
      <contact fullname="Qian Xin">
        <organization showOnFrontPage="true">ZTE</organization>
        <address>
          <email>qian.xin2@zte.com.cn</email>
        </address>
      </contact>
      <contact fullname="Zhao Yanhua">
        <organization showOnFrontPage="true">ZTE</organization>
        <address>
          <email>zhao.yanhua3@zte.com.cn</email>
        </address>
      </contact>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.c">
      <name slugifiedName="name-authors-addresses">Authors' Addresses</name>
      <author fullname="Weiqiang Cheng" initials="W" surname="Cheng">
        <organization showOnFrontPage="true">China Mobile</organization>
        <address>
          <postal>
            <city>Beijing</city>
            <country>China</country>
          </postal>
          <email>chengweiqiang@chinamobile.com</email>
        </address>
      </author>
      <author fullname="Ruixue Wang" initials="R" surname="Wang">
        <organization showOnFrontPage="true">China Mobile</organization>
        <address>
          <postal>
            <city>Beijing</city>
            <country>China</country>
          </postal>
          <email>wangruixue@chinamobile.com</email>
        </address>
      </author>
      <author fullname="Xiao Min" initials="X" surname="Min" role="editor">
        <organization showOnFrontPage="true">ZTE Corp.</organization>
        <address>
          <postal>
            <city>Nanjing</city>
            <country>China</country>
          </postal>
          <email>xiao.min2@zte.com.cn</email>
        </address>
      </author>
      <author fullname="Reshad Rahman" initials="R" surname="Rahman">
        <organization showOnFrontPage="true">Equinix</organization>
        <address>
          <postal>
            <city>Ottawa</city>
            <country>Canada</country>
          </postal>
          <email>reshad@yahoo.com</email>
        </address>
      </author>
      <author fullname="Raj Chetan Boddireddy" initials="R" surname="Boddireddy">
        <organization showOnFrontPage="true">Juniper Networks</organization>
        <address>
          <email>rchetan@juniper.net</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
