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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-dhc-dhcpv4-over-dhcpv6-ra-06" docName="draft-ietf-dhc-dhcpv4-over-dhcpv6-ra" category="std" consensus="true" submissionType="IETF" xml:lang="en" number="9928" tocInclude="true" sortRefs="true" symRefs="true" version="3">
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  <link href="https://datatracker.ietf.org/doc/draft-ietf-dhc-dhcpv4-over-dhcpv6-ra" rel="prev"/>
  <front>
    <title abbrev="DHCP 4o6 Relay Agent">DHCPv4-over-DHCPv6 Agent">DHCPv4 over DHCPv6 with Relay Agent Support</title>
    <seriesInfo name="Internet-Draft" value="draft-ietf-dhc-dhcpv4-over-dhcpv6-ra-06"/> name="RFC" value="9928"/>
    <author initials="C." surname="Porfiri" fullname="Claudio Porfiri">
      <organization>Ericsson</organization>
      <address>
        <email>claudio.porfiri@ericsson.com</email>
      </address>
    </author>
    <author initials="S." surname="Krishnan" fullname="Suresh Krishnan">
      <organization>Cisco</organization>
      <address>
        <email>suresh.krishnan@gmail.com</email>
      </address>
    </author>
    <author initials="J." surname="Arkko" fullname="Jari Arkko">
      <organization>Ericsson</organization>
      <address>
        <email>jari.arkko@ericsson.com</email>
      </address>
    </author>
    <author initials="M." surname="Kühlewind" fullname="Mirja Kühlewind">
      <organization>Ericsson</organization>
      <address>
        <email>mirja.kuehlewind@ericsson.com</email>
      </address>
    </author>
    <date year="2025" month="August" day="26"/>
    <area>Internet</area>
    <workgroup>Dynamic Host Configuration</workgroup> year="2026" month="February"/>
    <area>INT</area>
    <workgroup>dhc</workgroup>
    <keyword>dhcp</keyword>
    <abstract>
      <?line 59?> 54?>

<t>This document describes a mechanism for networks
with legacy IPv4-only clients to use services provided by
DHCPv4-over-DHCPv6
DHCPv4 over DHCPv6 in a Relay Agent.
RFC7341
RFC 7341 specifies the use of DHCPv4-over-DHCPv6 DHCPv4 over DHCPv6 in the client only.
This document specifies a RFC7341-based an approach based on RFC 7341 that
allows a Relay Agent to implement the DHCP 4o6 encapsulation and
decapsulation of DHCPv4 messages in DHCPv6 messages on behalf of a
DHCPv4 client.</t>
    </abstract>
    <note removeInRFC="true">
      <name>About This Document</name>
      <t>
        Status information for this document may be found at <eref target="https://datatracker.ietf.org/doc/draft-ietf-dhc-dhcpv4-over-dhcpv6-ra/"/>.
      </t>
      <t>Source for this draft and an issue tracker can be found at
        <eref target="https://github.com/mirjak/draft-dhc-dhcpv4-over-dhcpv6-ra"/>.</t>
    </note>
  </front>
  <middle>
    <?line 71?> 66?>

<section anchor="introduction">
      <name>Introduction</name>
      <t><xref target="RFC7341"/> describes a transport mechanism for carrying DHCPv4 <xref target="RFC2131"/>
messages using DHCPv6 <xref target="draft-ietf-dhc-rfc8415bis"/> target="RFC9915"/> for dynamic provisioning
of IPv4 addresses and other DHCPv4 specific DHCPv4-specific configuration parameters
across IPv6-only networks. The deployment of <xref target="RFC7341"/> requires support in
DHCP clients and at the DHCPv6 server.
However, if a client is embedded in a host that only supports IPv4
and cannot easily be replaced or updated (which could be due to any
number of technical or business reasons), this approach does not
work.</t>
      <!-- [rfced] Please review the text below. We were unable to find "L3RA" used in
[draft-ietf-dhc-rfc8415bis] (now published as RFC 9915).

Original:

   Similarly, the specifications for DHCPv6 Relay Agents such as
   Lightweight DHCPv6 Relay Agent (LDRA) [RFC6221] or DHCPv6 Relay Agent
   (L3RA) [draft-ietf-dhc-rfc8415bis] do not foresee the possibility to
   handle legacy DHCPv4, other than implementing DHCP 4o6 in the client.

-->

<t>Similarly, the specifications for DHCPv6 Relay Agents such as Lightweight
DHCPv6 Relay Agent (LDRA) <xref target="RFC6221"/> or DHCPv6 Relay Agent (L3RA)
<xref target="draft-ietf-dhc-rfc8415bis"/> target="RFC9915"/> do not foresee the possibility to handle legacy DHCPv4,
other than implementing DHCP 4o6 in the client.</t>
      <t>This document specifies an a solution based on <xref target="RFC7341"/> based solution that can be
implemented in intermediate nodes such as switches or routers,
without putting any requirements on clients. No new protocols or extensions are needed;
instead, this document specifies a new use case for <xref target="RFC7341"/> that allows
a Relay Agent to perform the DHCP 4o6 encapsulation and decapsulation instead of
the client.</t>
      <section anchor="applicability">
        <name>Applicability Scope</name>
        <t>The mechanisms described in this document apply to the configuration phase
of hosts that need to receive an IPv4 address when a DHCP server for IPv4 <xref target="RFC2131"/> is not
reachable directly from the host. Furthermore, the host is unable to implement
a DHCP client conformant to <xref target="RFC7341"/> target="RFC7341"/>, as it is connected to an IPv4-only
network. But However, there is a DHCPv6 server that can provide IPv4 addresses by means of
the mechanisms specified in <xref target="RFC7341"/>.</t>
        <!-- [rfced] Section 2:

a) May we adjust the items in this list to appear in alphabetical order?

b) May we make these list items consistent as follows?

Original:

   *  DHCP: If not otherwise specified, DHCP refers to DHCPv4 and/or
      DHCPv6.

   *  DHCPv4: DHCP as defined in [RFC2131].

   *  DHCPv4 over DHCPv6 (or 4o6): The architecture, the procedures, and
      the protocols specified in the DHCPv4-over-DHCPv6 document
      [RFC7341].

   *  DHCP Relay Agent: This is a concept in all of the following
      protocols, although the details differ between them: BOOTP
      [RFC951] [RFC1542], DHCPv4 [RFC2131] [RFC2132], and DHCPv6
      [draft-ietf-dhc-rfc8415bis].

   *  Lightweight DHCPv6 Relay Agent (or LDRA): This is an extension of
      the original DHCPv6 Relay Agent specification, to allow layer-
      2-only devices to perform a Relay Agent function [RFC6221].

   *  DHCPv4 over DHCPv6 Relay Agent (or 4o6RA): Refers to a Relay Agent
      that implements the 4o6 transport as specified in this document.

Perhaps:

   DHCP:
     Refers to DHCPv4 and/or DHCPv6 if not otherwise specified.

   DHCPv4:
     Refers to DHCP as defined in [RFC2131].

   DHCPv4 over DHCPv6 (DHCP 4o6):
      Refers to the architecture, the procedures, and the protocols specified in
      the DHCPv4-over-DHCPv6 document [RFC7341].

   (etc.)

-->

</section>
    </section>
    <section anchor="conventions-and-definitions">
      <name>Conventions and Definitions</name>
      <t>The following terms and acronyms abbreviations are used in this document:</t>
      <ul spacing="normal">
        <li>
          <t>DHCP:
If
      <dl newline="true">
        <dt>DHCP:</dt>
        <dd>
          <t>If not otherwise specified, DHCP refers to DHCPv4 and/or DHCPv6.</t>
        </li>
        <li>
          <t>DHCPv4:
 DHCP
        </dd>
        <dt>DHCPv4:</dt>
        <dd>
          <t>DHCP as defined in <xref target="RFC2131"/>.</t>
        </li>
        <li>
          <t>DHCPv4
        </dd>
        <dt>DHCPv4 over DHCPv6 (or 4o6):
 The (DHCP 4o6):</dt>
        <dd>
          <t>The architecture, the procedures, and the protocols specified in the
DHCPv4-over-DHCPv6 document <xref target="RFC7341"/>.</t>
        </li>
        <li>
          <t>DHCP
        </dd>
        <dt>DHCP Relay Agent:
 This Agent:</dt>
        <dd>
          <t>This is a concept in all of the following protocols, although the details differ
between them: BOOTP the Bootstrap Protocol (BOOTP) <xref target="RFC951"/> target="RFC0951"/> <xref target="RFC1542"/>, DHCPv4
<xref target="RFC2131"/> <xref target="RFC2132"/>, and DHCPv6 <xref target="draft-ietf-dhc-rfc8415bis"/>.</t>
        </li>
        <li>
          <t>Lightweight target="RFC9915"/>.</t>
        </dd>
        <dt>Lightweight DHCPv6 Relay Agent (or LDRA):
 This (LDRA):</dt>
        <dd>
          <t>This is an extension of the original DHCPv6 Relay Agent specification, to allow
 layer-2-only
Layer 2 (L2) only devices to perform a Relay Agent function <xref target="RFC6221"/>.</t>
        </li>
        <li>
          <t>DHCPv4 over DHCPv6
        </dd>
        <dt>DHCPv4-over-DHCPv6 Relay Agent (or 4o6RA):
 Refers (4o6RA):</dt>
        <dd>
          <t>Refers to a Relay Agent that implements the 4o6
transport as specified in this document.</t>
        </li>
      </ul>
        </dd>
      </dl>
      <t>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"/> <xref target="RFC8174"/> when, and only when, they
appear in all capitals, as shown here.</t>
      <?line -18?>

</section>
    <section anchor="dhcpv4-over-dhcpv6-relay-agent-4o6ra">
      <name>DHCPv4 over DHCPv6
      <name>DHCPv4-over-DHCPv6 Relay Agent (4o6RA)</name>
      <t>This document assumes a network, network where IPv4-only hosts are connected
to a network that supports IPv6 and limited IPv4 services.</t>
      <t>To address such a network setup, this document extends
DHCPv6 Relay Agents with DHCPv4-over-DHCPv6, DHCPv4 over DHCPv6, as shown in <xref target="fig_4o6RA"/>.</t>
      <figure anchor="fig_4o6RA">
        <name>Architecture Example with Legacy DHCP Client</name>
        <artset>
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              <g class="text">
                <text x="140" y="68">L2</text>
                <text x="340" y="68">IPv6</text>
                <text x="52" y="84">DHCPv4</text>
                <text x="136" y="84">Network</text>
                <text x="236" y="84">DHCPv6</text>
                <text x="344" y="84">Network</text>
                <text x="412" y="84">DHCP</text>
                <text x="448" y="84">4o6</text>
                <text x="52" y="100">Client</text>
                <text x="216" y="100">Relay</text>
                <text x="264" y="100">Agent</text>
                <text x="428" y="100">Server</text>
                <text x="220" y="116">with</text>
                <text x="264" y="116">4o6RA</text>
              </g>
            </svg>
          </artwork>
          <artwork type="ascii-art" align="center"><![CDATA[
           .-----------.             .-----------.
          |             |           |             |
 +--------+-+    L2   +-+-----------+-+  IPv6   +-+--------+
 |  DHCPv4  | Network |    DHCPv6     | Network | DHCP 4o6 |
 |  Client  +---------+  Relay Agent  +---------+  Server  |
 |          |         |   with 4o6RA  |         |          |
 +--------+-+         +-+-----------+-+         +-+--------+
          |             |           |             |
           '-----------'             '-----------'

]]></artwork>
        </artset>
      </figure>
      <t>This document specifies the encapsulation
and decapsulation specified in <xref target="RFC7341"/> to be performed in the Relay Agent
without requiring any changes on the DHCPv4 client.
In this case case, it is up to the Relay Agent to provide the full DHCP
4o6 support support, and the legacy DHCPv4 client is not aware that it is being served
via a DHCP 4o6 service.
As the 4o6RA acts as a DHCP 4o6 client, all prerequisites and configuration configurations
that apply to the DHCP client in <xref section="5" sectionFormat="of" target="RFC7341"/> are also applied to the 4o6RA.</t>
      <t>As the 4o6RA takes the role of the client in respect to <xref target="RFC7341"/>,
it is responsible for determining a suitable interface where it acts as a
DHCPv6 client, and it is responsible for locating a suitable DHCPv6
server or relay agent Relay Agent and obtain obtaining the necessary IPv6 configuration.. configuration.
As specified in <xref target="RFC7341"/>, the 4o6RA, acting as 4o6 client, therefore has to request
the DHCP 4o6 Server Address option from the server by sending the
Option Request option as described in <xref target="draft-ietf-dhc-rfc8415bis"/> target="RFC9915"/>
before it can use the 4o6 transport.</t>
      <t>To maintain interoperability with existing DHCPv6 relays and servers,
the message format is unchanged from <xref target="draft-ietf-dhc-rfc8415bis"/>. target="RFC9915"/>. The 4o6RA implements
the same message types as a DHCPv6 Relay Agent (see <xref section="6" sectionFormat="of" target="RFC7341"/>.</t> target="RFC7341"/>).</t>
      <t>However, in this specification, the 4o6RA, instead of the client, creates the DHCPV4-QUERY Message message
and encapsulates the DHCP request message received from the legacy DHCPv4 client.</t>
      <t>When the DHCPV4-RESPONSE Message message is received by the 4o6 Relay Agent,
it looks for the DHCPv4 Message message option within this message.
If this option is not found or the DHCPv4-RESPONSE message is not well-formed,
it <bcp14>MUST</bcp14> be discarded.
If the DHCPv4 Message message option is present and correct, the 4o6RA <bcp14>MUST</bcp14> extract the DHCPv4
message and forward the encapsulated DHCPv4-response DHCPv4-RESPONSE to the requesting DHCPv4
client, given that the encapsulated DHCPv4-response DHCPv4-RESPONSE is correct and can be
actually forwarded.</t>
      <t>Layer-2
      <t>Layer 2 (L2) Relay Agents receiving DHCPV4-QUERY or DHCPV4-RESPONSE messages
<bcp14>MUST</bcp14> handle them as specified in <xref section="6" sectionFormat="of" target="RFC6221"/>.</t>
      <t>In any given environment, DHCPv6 servers to which DHCPV4-QUERY
requests are routed are expected to be compliant with 4o6 according
to <xref target="RFC7341"/>.  No additional requirements on DHCPv6 servers are set
by this specification.</t>
      <section anchor="intermediate-relays">
        <name>Intermediate relays</name> Relays</name>
        <t>Intermediate relays shall behave according to section 10 of <xref section="10" sectionFormat="of" target="RFC7341"/>.</t>
      </section>
      <section anchor="topology_considerations">
        <name>4o6RA and Topology Discovery</name>
        <t>In some networks, the configuration of a host may depend on the topology.
However, when a new host attaches to a network, it may be unaware
of the topology and, consequently, how it has to be configured.</t>
        <t>DHCPv4 <xref target="RFC2131"/> and DHCPv6 <xref target="draft-ietf-dhc-rfc8415bis"/> target="RFC9915"/> specifications
describe how addresses can typically be allocated to clients based on network
topology information provided by a DHCP relay, typically.</t> relay.</t>
        <t>Address/prefix allocation decisions are integral to the allocation of
addresses and prefixes in DHCP, as described in detail
in <xref target="RFC7969"/>. This specification aims to guarantee that the 4o6RA does not
break any legacy capability when used for topology discovery.</t>
        <t>Topology discovery as described in <xref target="RFC7969"/> differs between
IPv4 and IPv6:</t> IPv6 as follows:</t>
        <ul spacing="normal">
          <li>
            <t>IPv4:
when When using DHCP on IPv4 IPv4, only the first Relay Agent <bcp14>SHOULD</bcp14>
set the giaddr field (section 3.1 of <xref (<xref section="3.1" sectionFormat="of" target="RFC7969"/>). Thus, in a
network that has more than one Relay Agent Agent, only part of the topology
is transported via DHCPv4.</t>
          </li>
          <li>
            <t>IPv6:
when When using DHCPv6, all Relay Agents <bcp14>SHOULD</bcp14> send
link-address and Interface-ID options, options that provide
information about the complete path
between the DHCPv6 client and the DHCPv6 server to the DHCPv6 server.</t>
          </li>
        </ul>
        <t>In Layer-2 Layer 2 networks, Lightweight DHCPv6 Relay Agents (LDRAs) <xref target="RFC6221"/>
can be used.</t>
        <t>When provided, the topology information is available at the DHCPv6
server in the form of a sequence of the link-address field and Interface-ID option.</t>
        <t>Then, topology information for the given IP address
can be obtained from the DHCPv6 server and used for configuration
or other purposes.</t>
        <t><xref target="RFC7341"/> enables the client to use DHCPv6 for topology discovery
even within a DHCPv4 context, as the DHCPv6 Relay Agent knows
the interface where the encapsulated DHCP request is received.
As
However, as shown in <xref target="fig_4o6RA_RA"/>, however, the introduction of 4o6 at
the edge of the IPv6 network hides the Layer-2 Layer 2 network from the DHCPv6 RA.
As such, moving 4o6 to a an intermediate node rather than performing it at the client breaks
the topology propagation, as 4o6RA-only solutions does do not provide any interface
information in the encapsulated message.</t>
        <figure anchor="fig_4o6RA_RA">
          <name>Broken topology information</name> Topology Information</name>
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                  <text x="124" y="52">L2</text>
                  <text x="168" y="52">Network</text>
                  <text x="356" y="52">IPv6</text>
                  <text x="408" y="52">Network</text>
                  <text x="52" y="84">DHCPv4</text>
                  <text x="156" y="84">L2</text>
                  <text x="256" y="84">4o6</text>
                  <text x="380" y="84">DHCPv6</text>
                  <text x="508" y="84">DHCP</text>
                  <text x="544" y="84">4o6</text>
                  <text x="52" y="100">Client</text>
                  <text x="156" y="100">Switch</text>
                  <text x="264" y="100">Relay</text>
                  <text x="376" y="100">Relay</text>
                  <text x="524" y="100">Server</text>
                  <text x="264" y="116">Agent</text>
                  <text x="376" y="116">Agent</text>
                </g>
              </svg>
            </artwork>
            <artwork type="ascii-art" align="center"><![CDATA[
           .-----------------.     .-------------------------.
          |    L2 Network     |   |        IPv6 Network       |
 +--------+-+  +---------+  +-+---+---+    +--------+       +-+--------+
 |  DHCPv4  |  |   L2    |  |  4o6    |    | DHCPv6 |       | DHCP 4o6 |
 |  Client  +--+ Switch  +--+  Relay  +----+ Relay  +-------+  Server  |
 |          |  |         |  |  Agent  |    | Agent  |       |          |
 +--------+-+  +---------+  +-+---+---+    +--------+       +-+--------+
          |                   |   |                           |
           '-----------------'     '-------------------------'

]]></artwork>
          </artset>
        </figure>
        <t>In order to provide full topology information, it is <bcp14>RECOMMENDED</bcp14> that
any implementation of 4o6RA be combined
with an LDRA implementation <xref target="RFC6221"/> in a back-to-back structure, structure and that the
LDRA implementation includes a mechanism to obtain interface information that
can be used to provide the Interface-ID option to outgoing
DHCPV4-QUERY messages, as specified in Section 5.3.2 of <xref section="5.3.2" sectionFormat="of" target="RFC6221"/>.</t>
        <t>The internal mechanisms to exchange interface information,
their format format, and whether the interface information contains an indication that a 4o6RA
is involved involved, are out of the scope for this document.</t>
        <t>The resulting architecture is shown in <xref target="fig_4o6LDRA"/> where
the Relay Agent is implementing 4o6RA and LDRA, LDRA and has an internal interface to
propagate topology information from 4o6RA to LDRA.</t>
        <figure anchor="fig_4o6LDRA">
          <name>Topology information preserved Information Preserved with LDRA</name>
          <artset>
            <artwork type="svg" align="center"><svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="224" width="528" viewBox="0 0 528 224" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
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                <path d="M 472,176 C 480.83064,176 488,168.83064 488,160" fill="none" stroke="black"/>
                <g class="text">
                  <text x="108" y="52">L2</text>
                  <text x="152" y="52">Network</text>
                  <text x="196" y="52">or</text>
                  <text x="348" y="52">IPv6</text>
                  <text x="400" y="52">Network</text>
                  <text x="136" y="68">IPv6-only</text> y="68">IPv6-Only</text>
                  <text x="196" y="68">link</text> y="68">Link</text>
                  <text x="52" y="100">DHCPv4</text>
                  <text x="156" y="100">L2</text>
                  <text x="256" y="100">4o6</text>
                  <text x="332" y="100">LDRA</text>
                  <text x="460" y="100">DHCP</text>
                  <text x="496" y="100">4o6</text>
                  <text x="52" y="116">Client</text>
                  <text x="156" y="116">Switch</text>
                  <text x="264" y="116">Relay</text>
                  <text x="336" y="116">RFC6221</text> x="320" y="116">RFC</text>
                  <text x="356" y="116">6221</text>
                  <text x="476" y="116">Server</text>
                  <text x="264" y="132">Agent</text>
                </g>
              </svg>
            </artwork>
            <artwork type="ascii-art" align="center"><![CDATA[
           .-----------------.     .------------------------.
          |  L2 Network or    |   |       IPv6 Network       |
          |  IPv6-only link  IPv6-Only Link   |   |                          |
 +--------+-+  +---------+  +-+---+--+---------+      +------+---+
 |  DHCPv4  |  |   L2    |  |  4o6   |  LDRA   |      | DHCP 4o6 |
 |  Client  +--+ Switch  +--+  Relay + RFC6221 +------+ RFC 6221+------+  Server  |
 |          |  |         |  |  Agent |         |      |          |
 +--------+-+  +---------+  +-+---+--+---------+      +------+---+
          |                   |   |                          |
           '-----------------'     '------------------------'

]]></artwork>
          </artset>
        </figure>
        <t>In a simple case, where the same node hosts the 4o6RA and the DHCP4o6 DHCP 4o6 server,
it might be enough to only use 4o6RA, as shown in <xref target="fig_4o6RAserver"/>.</t>
        <!-- [rfced] Per Section 3.6 of RFC 7322 ("RFC Style Guide"), abbreviations
should be expanded upon first use. How and where should "CPE" be expanded as
it appears in Figure 4?

Original:

   In a simple case, where the same node hosts the 4o6RA and the DHCP4o6
   server, it might be enough to only use 4o6RA, as shown in Figure 4.

Perhaps:

   In a simple case, where the same node hosts the 4o6RA and the DHCP 4o6
   server, it might be enough to only use 4o6RA, as shown in Figure 4, where
   CPE stands for "Customer Premises Equipment".

-->

<figure anchor="fig_4o6RAserver">
          <name>Topology information preserved Information Preserved by 4o6 Relay Agent in DHCP server</name> Server</name>
          <artset>
            <artwork type="svg" align="center"><svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="208" width="344" viewBox="0 0 344 208" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
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                <g class="text">
                  <text x="100" y="52">L2</text>
                  <text x="144" y="52">Network</text>
                  <text x="52" y="84">DHCP</text>
                  <text x="208" y="84">4o6</text>
                  <text x="276" y="84">DHCP</text>
                  <text x="312" y="84">4o6</text>
                  <text x="52" y="100">Client</text>
                  <text x="216" y="100">Relay</text>
                  <text x="292" y="100">Server</text>
                  <text x="36" y="116">on</text>
                  <text x="64" y="116">CPE</text>
                  <text x="216" y="116">Agent</text>
                </g>
              </svg>
            </artwork>
            <artwork type="ascii-art" align="center"><![CDATA[
           .-----------.
          | L2 Network  |
 +--------+-+         +-+------+----------+
 |   DHCP   |         |  4o6   | DHCP 4o6 |
 |  Client  +---------+  Relay +  Server  |
 |  on CPE  |         |  Agent |          |
 +--------+-+         +-+------+----------+
          |             |
           '-----------'

]]></artwork>
          </artset>
        </figure>
      </section>
    </section>
    <section anchor="deployment-considerations">
      <name>Deployment Considerations</name>
      <t>As clients are unaware of the presence of 4o6RA, the network
deployment needs to ensure that all DHCPv4 broadcast and unicast messages to and
from clients are steered via a 4o6RA.
This can be achieved by placing the 4o6RA in a central position
that can intercept all traffic from the clients or by using Network Address
Translation (NAT) with the 4o6RA address for unicast messages.</t>
      <!-- [rfced] Security Considerations:

a) Would the following adjustment clarify what "the 4o6 DHCP specification"
refers to?

b) Please note that we have changed "4o6 DHCP" to "DHCP 4o6" in this
section for consistency with the rest of the document.

Original:

   This document does not change anything else in the 4o6 DHCP specification
   and therefore the security considerations of [RFC7341] still apply.

Perhaps:

   This document does not change anything else in the DHCP 4o6 specification [RFC7341];
   therefore, the security considerations of that document still apply.

-->

</section>
    <section anchor="seccons">
      <name>Security Considerations</name>
      <t>This document specifies the applicability of 4o6 DHCP 4o6 in a scenario where legacy IPv4 clients are
connected to 4o6 DHCP Relay Agents that perform the encapsulation and decapsulation. This document
does not change anything else in the 4o6 DHCP specification and therefore 4o6 specification; therefore, the
security considerations of <xref target="RFC7341"/> still apply.
Specifically, since the legacy IPv4 client is not aware of the encapsulation and decapsulation,
it is
4o6RA has to provide the protections that are specficed specified in the security
considerations in <xref section="12" sectionFormat="of" target="RFC7341"/>.</t>
      <t>The mechanisms defined here differ from <xref target="RFC7341"/> as they allow the DHCP client
to send and receive DHCPv4 messages, whereas in <xref target="RFC7341"/> target="RFC7341"/>, the client
only sends DHCPv6 messages. This makes it possible that in improperly configured
networks where the client is located on the same Layer-2 Layer 2 scope of a DHCPv4 server,
DHCPv4 messages could reach a DHCPv4 server without using the 4o6RA.
While this can cause erroneous state in both clients and servers
and potentially even lead to misconfigurations that impact reachability,
this is seen as a deployment error rather than a security concern.
Further, even though this mechanism may be used for attacks from within the network,
this is not a new concern introduced by this specification.</t>
      <t>More generally, legacy IPv4 clients are not aware of this mechanism, mechanism; however, even
when DHCP 4o6 is used, the client does not have any control about the
information provided by the Relay agent. Agent.
As such such, this change does not raise any additional security concerns.</t>
    </section>
    <section anchor="iana-considerations">
      <name>IANA Considerations</name>
      <t>This document has no IANA actions.</t>
    </section>
  </middle>
  <back>
    <references anchor="sec-combined-references">
      <name>References</name>
      <references anchor="sec-normative-references">
        <name>Normative References</name>
        <reference anchor="RFC6221">
          <front>
            <title>Lightweight DHCPv6 Relay Agent</title>
            <author fullname="D. Miles" initials="D." role="editor" surname="Miles"/>
            <author fullname="S. Ooghe" initials="S." surname="Ooghe"/>
            <author fullname="W. Dec" initials="W." surname="Dec"/>
            <author fullname="S. Krishnan" initials="S." surname="Krishnan"/>
            <author fullname="A. Kavanagh" initials="A." surname="Kavanagh"/>
            <date month="May" year="2011"/>
            <abstract>
              <t>This document proposes a Lightweight DHCPv6 Relay Agent (LDRA) that is used to insert relay agent options in DHCPv6 message exchanges identifying client-facing interfaces. The LDRA can be implemented in existing access nodes (such as Digital Subscriber Link Access Multiplexers (DSLAMs) and Ethernet switches) that do not support IPv6 control or routing functions. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6221"/>
          <seriesInfo name="DOI" value="10.17487/RFC6221"/>
        </reference>
        <reference anchor="RFC7341">
          <front>
            <title>DHCPv4-over-DHCPv6 (DHCP 4o6) Transport</title>
            <author fullname="Q. Sun" initials="Q." surname="Sun"/>
            <author fullname="Y. Cui" initials="Y." surname="Cui"/>
            <author fullname="M. Siodelski" initials="M." surname="Siodelski"/>
            <author fullname="S. Krishnan" initials="S." surname="Krishnan"/>
            <author fullname="I. Farrer" initials="I." surname="Farrer"/>
            <date month="August" year="2014"/>
            <abstract>
              <t>IPv4 connectivity is still needed as networks migrate towards IPv6. Users require IPv4 configuration even if the uplink to their service provider supports IPv6 only. This document describes a mechanism for obtaining IPv4 configuration information dynamically in IPv6 networks by carrying DHCPv4 messages over DHCPv6 transport. Two new DHCPv6 messages and two new DHCPv6 options are defined for this purpose.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7341"/>
          <seriesInfo name="DOI" value="10.17487/RFC7341"/>
        </reference>
        <reference anchor="draft-ietf-dhc-rfc8415bis" target="https://datatracker.ietf.org/doc/draft-ietf-dhc-rfc8415bis/">
          <front>
            <title>Dynamic Host Configuration Protocol for IPv6 (DHCPv6)</title>
            <author>
              <organization/>
            </author>
            <date year="2025" month="June"/>
          </front>
        </reference>
        <reference anchor="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>In many standards track documents several words are used
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6221.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7341.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9915.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      </references>
      <references anchor="sec-informative-references">
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.0951.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1542.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2131.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2132.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7969.xml"/>
      </references>
    </references>
    <?line 467?>

<!-- [rfced] Appendix A: Please review our questions and suggested updates to signify
the requirements in text below, including 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 following items:

a) Should the Internet Community, and requests discussion and suggestions abbreviation 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="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>RFC 2119 specifies common key words that may "Baseband Units (BB)" be used in protocol specifications. This document aims updated to reduce "Baseband Units (BBUs)"
as seen in the ambiguity by clarifying text below? If so, please note that only UPPERCASE usage we would also update instances 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 anchor="sec-informative-references">
        <name>Informative References</name>
        <reference anchor="RFC951">
          <front>
            <title>Bootstrap Protocol</title>
            <author fullname="W.J. Croft" initials="W.J." surname="Croft"/>
            <author fullname="J. Gilmore" initials="J." surname="Gilmore"/>
            <date month="September" year="1985"/>
            <abstract>
              <t>This RFC describes an IP/UDP bootstrap protocol (BOOTP) which allows a diskless client machine
"BB"/"BBs" to discover its own IP address, "BBU"/"BBUs" accordingly throughout the address of a server host, and the name of a file to be loaded into memory and executed. The bootstrap operation can be thought rest of this section as consisting of TWO PHASES. This RFC describes well.

b) Should the first phase, which could abbreviation for "Radio Fronthaul Network (FH)" be labeled `address determination and bootfile selection'. After this address and filename information is obtained, control passes to the second phase of the bootstrap where a file transfer occurs. The file transfer will typically use adjusted for
clarity?

Original:

   In 3GPP mobile network architecture, the TFTP protocol, since it User Equipments (UE) are
   connected via Radio Access Network (RAN).  RAN is intended that both phases reside in PROM on the client. However BOOTP could also work built up with other protocols such as SFTP or FTP. This RFC suggests a proposed protocol for the ARPA-Internet community, and requests discussion
   Baseband Units (BB) and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="951"/>
          <seriesInfo name="DOI" value="10.17487/RFC0951"/>
        </reference>
        <reference anchor="RFC1542">
          <front>
            <title>Clarifications Radio Units (RU).  Radio Fronthaul Network
   (FH) connects RU and Extensions for the Bootstrap Protocol</title>
            <author fullname="W. Wimer" initials="W." surname="Wimer"/>
            <date month="October" year="1993"/>
            <abstract>
              <t>Some aspects BB, each of the BOOTP protocol were rather loosely defined in its original specification. In particular, RU and BB is an IP host, they may
   support IPv4 only, IPv6 only a general description was provided for or both depending on the behavior of "BOOTP relay agents" (originally called "BOOTP forwarding agents"). The client behavior description also suffered in certain ways. This memo attempts to clarify vendor and strengthen the specification in these areas. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="1542"/>
          <seriesInfo name="DOI" value="10.17487/RFC1542"/>
        </reference>
        <reference anchor="RFC2131">
          <front>
            <title>Dynamic Host Configuration Protocol</title>
            <author fullname="R. Droms" initials="R." surname="Droms"/>
            <date month="March" year="1997"/>
            <abstract>
              <t>The Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuration information to hosts on
   model.

Perhaps:

   In 3GPP mobile network architecture, the User Equipment (UE) is
   connected via a TCPIP network. DHCP Radio Access Network (RAN).  RAN is based on the Bootstrap Protocol (BOOTP), adding the capability of automatic allocation of reusable built up with
   Baseband Units (BBUs) and Radio Units (RUs). A radio Fronthaul (FH) network addresses
   connects RUs and additional configuration options. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="2131"/>
          <seriesInfo name="DOI" value="10.17487/RFC2131"/>
        </reference>
        <reference anchor="RFC2132">
          <front>
            <title>DHCP Options BBUs.  Each RU and BOOTP Vendor Extensions</title>
            <author fullname="S. Alexander" initials="S." surname="Alexander"/>
            <author fullname="R. Droms" initials="R." surname="Droms"/>
            <date month="March" year="1997"/>
            <abstract>
              <t>This document specifies the current set of DHCP options. Future options will be specified in separate RFCs. The current list of valid options BBU is also available in ftp://ftp.isi.edu/in-notes/iana/assignments. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="2132"/>
          <seriesInfo name="DOI" value="10.17487/RFC2132"/>
        </reference>
        <reference anchor="RFC7969">
          <front>
            <title>Customizing DHCP Configuration an IP host, and they may
   support IPv4 only, IPv6 only, or both, depending on the Basis of Network Topology</title>
            <author fullname="T. Lemon" initials="T." surname="Lemon"/>
            <author fullname="T. Mrugalski" initials="T." surname="Mrugalski"/>
            <date month="October" year="2016"/>
            <abstract>
              <t>DHCP servers have evolved over the years to provide significant functionality beyond that described in the DHCP base specifications. One aspect of this functionality is support for context-specific configuration information. This memo describes some such features vendor and explains their operation.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7969"/>
          <seriesInfo name="DOI" value="10.17487/RFC7969"/>
        </reference>
      </references>
    </references>
    <?line 379?> the
   model.

-->

<section anchor="usecase">
      <name>Example Use Case: Topology Discovery for IPv4-only IPv4-Only Radio Unit in 3GPP RAN with Switched Fronthaul</name>
      <t>In 3GPP mobile network architecture, the User Equipments Equipment (UE) are is connected
via Radio Access Network (RAN). RAN is built up with Baseband Units (BB) (BBs)
and Radio Units (RU). (RUs). Radio Fronthaul Network (FH) connects RU RUs and BB, each of BBs. Each
RU and BB is an IP host, and they may support IPv4 only, IPv6 only only, or both both,
depending on the vendor and the model.
Each RU is unique as it is tied to a set of antennas, and each antenna
is serving a specific Cell and Sector.
Each RU is configured by the BB depending on the Cell and Sectors it serves.
However, that dependency is only specified by the cabling between RU RUs and antennas.
BB
BBs can be cabled to RU RUs directly or via a Layer-2 Layer 2 switched network.</t>
      <figure anchor="bb_connected_to_ru">
        <name>3GPP RAN where RU are cabled directly Where RUs Are Cabled Directly to BB</name>
        <artset>
          <artwork type="svg" align="center"><svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="368" width="256" viewBox="0 0 256 368" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
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              <path d="M 80,304 L 128,304" fill="none" stroke="black"/>
              <path d="M 8,336 L 80,336" fill="none" stroke="black"/>
              <g class="text">
                <text x="40" y="52">RU2</text>
                <text x="40" y="132">RU3</text>
                <text x="196" y="180">Baseband</text>
                <text x="196" y="212">Unit</text>
                <text x="40" y="228">RU4</text>
                <text x="40" y="308">RU2</text>
              </g>
            </svg>
          </artwork>
          <artwork type="ascii-art" align="center"><![CDATA[
     +--------+
     |  RU2   +-----+
     |        |     |
     +--------+     |
                    |
     +--------+     |
     |  RU3   |     |
     |        +--+  |  +-----------+
     +--------+  |  +--|           |
                 +-----| Baseband  |
                       |           |
     +--------+  +-----|   Unit    |
     |  RU4   +--+  +--|           |
     |        |     |  +-----------+
     +--------+     |
                    |
     +--------+     |
     |  RU2   +-----+
     |        |
     +--------+
]]></artwork>
        </artset>
      </figure>
      <t>In <xref target="bb_connected_to_ru"/> target="bb_connected_to_ru"/>, the BB is directly cabled to a set of RUs, and the
BB can recognize the relationship between RUs and Cell/Sectors
based on the cabling between the RUs and antennas.</t>
      <t>When BBs and RUs are connected via a Layer-2 Layer 2 switched network,
the added level of complexity requires the BBs to have a deeper
knowledge of the topology in order to properly configure the RUs,
involving knowledge of all the cabling in the switched network.</t>
      <t>Examples for switched networks are shown in section 3 of <xref section="3" sectionFormat="of" target="RFC7969"/>
and demonstrate the different levels of complexity.
An example of a FH is depicted in <xref target="l2_switched_fh"/>.</t>
      <figure anchor="l2_switched_fh">
        <name>3GPP RAN with Layer-2 Layer 2 Switched Fronthaul Example</name>
        <artset>
          <artwork type="svg" align="center"><svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="352" width="544" viewBox="0 0 544 352" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
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              <g class="text">
                <text x="40" y="52">RU1</text>
                <text x="132" y="52">P1</text>
                <text x="196" y="68">L2RA</text>
                <text x="364" y="84">L3RA</text>
                <text x="180" y="100">L2</text>
                <text x="132" y="116">P2</text>
                <text x="188" y="116">switch</text> y="116">Switch</text>
                <text x="40" y="132">RU2</text>
                <text x="180" y="132">#1</text>
                <text x="348" y="132">Router</text>
                <text x="484" y="180">DHCP</text>
                <text x="492" y="196">Server</text>
                <text x="40" y="212">RU3</text>
                <text x="132" y="212">P1</text>
                <text x="492" y="212">#1</text>
                <text x="196" y="228">L2RA</text>
                <text x="180" y="260">L2</text>
                <text x="340" y="260">Baseband</text>
                <text x="132" y="276">P2</text>
                <text x="188" y="276">switch</text> y="276">Switch</text>
                <text x="340" y="276">Unit</text>
                <text x="40" y="292">RU4</text>
                <text x="180" y="292">#2</text>
              </g>
            </svg>
          </artwork>
          <artwork type="ascii-art" align="center"><![CDATA[
     +--------+
     |  RU1   |     P1 +-+------+     |                   |
     |        +--------| | L2RA |     |  +----+------+    |
     +--------+        | +------+     |  |    | L3RA |    |
                       |  L2    |     +--|    +------+    |
     +--------+     P2 | switch Switch |     |  |           |    |
     |  RU2   +--------|  #1    +-----|  |   Router  +----|
     |        |        +--------+     |  +-----------+    |  +---------+
     +--------+                       |                   |  |         |
                                      |                   +--| DHCP    |
     +--------+                       |                   |  | Server  |
     |  RU3   |     P1 +-+------+     |                   |  |   #1    |
     |        +--------| | L2RA |     |  +-----------+    |  +---------+
     +--------+        | +------+     |  |           |    |
                       |  L2    |     +--| Baseband  |    |
     +--------+     P2 | switch Switch |     |  |   Unit    |    |
     |  RU4   +--------|  #2    +-----|  |           +----|
     |        |        +--------+     |  +-----------+    |
     +--------+                       |                   |
]]></artwork>
        </artset>
      </figure>
      <t>If IPv6 is used and all RU RUs are capable of DHCPv6 in <xref target="l2_switched_fh"/>,
DHCP topology knowledge can be used for solving the RU configuration problem.
Such solution would use the topology discovery mechanisms described in section 3.2
of <xref section="3.2" sectionFormat="of" target="RFC7969"/>.</t>
      <t>If RU RUs are capable of IPv4 only but implement a 4o6 client according to <xref target="RFC7341"/>, the same topology discovery mechanisms are applicable.</t>
      <t>If RU RUs are capable of IPV4 IPv4 only and cannot implement a 4o6 client according to <xref target="RFC7341"/>,
the topology discovery mechanisms described in section 3.2
of <xref section="3.2" sectionFormat="of" target="RFC7969"/> can be used by introducing 4o6RA in the switches as decribed described in this document.</t>
    </section>
    <section numbered="false" anchor="acknowledgments">
      <name>Acknowledgments</name>
      <t>The authors would also like to acknowledge interesting discussions in
this problem space with Sarah Gannon, Ines Ramadza, and Siddharth Sharma <contact fullname="Sarah Gannon"/>, <contact fullname="Ines Ramadza"/>, and <contact fullname="Siddharth Sharma"/>,
as well as reviews and comments provided by Eric Vyncke, Mohamed Boucadair,
David Lamparter, Michael Richardson, Alan DeKok, Dale Worley, Paul Wouters,
Deb Cooley, Erik Kline, Ketan Talaulikar, Mike Bishop <contact fullname="Éric Vyncke"/>, <contact fullname="Mohamed Boucadair"/>,
<contact fullname="David Lamparter"/>, <contact fullname="Michael Richardson"/>, <contact fullname="Alan DeKok"/>, <contact fullname="Dale Worley"/>, <contact fullname="Paul Wouters"/>,
<contact fullname="Deb Cooley"/>, <contact fullname="Erik Kline"/>, <contact fullname="Ketan Talaulikar"/>, <contact fullname="Mike Bishop"/>, and <contact fullname="Roman Danyliw"/>.</t>
      <!-- [rfced] Terminology and Abbreviations:

a) We note that the phrase "4o6" appears a few times by itself throughout this
document. For consistency and Roman Danyliw.</t> context, should these instances be updated to "DHCP 4o6"?

We have provided a few examples below:

the 4o6 transport
are expected to be compliant with 4o6
the introduction of 4o6 at the edge
moving 4o6 to a intermediate node
a 4o6 client

b) We note the following phrases appear after their abbreviations are
introduced. For consistency, should these terms (on the left) be updated to
their abbreviated form (on the right) after first use?

Expansion -> Abbreviation

DHCPv4-over-DHCPv6  ->  DHCP 4o6
4o6 Relay Agent     ->  4o6RA
Layer 2             ->  L2

c) FYI - We have added expansions for abbreviations upon first use
per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please review each
expansion in the document carefully to ensure correctness.

Bootstrap Protocol (BOOTP)
Layer 2 (L2)

-->

<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.  Updates of this nature typically
result in more precise language, which is helpful for readers.

Note that our script did not flag any words in particular, but this should
still be reviewed as a best practice. -->

</section>
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