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man: document DHCP relay configuration

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Yu Watanabe
2026-05-11 08:56:40 +09:00
parent 08b3ebf5f1
commit aa063e593b
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61
man/networkd.conf.xml
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@@ -393,6 +393,67 @@ DUIDRawData=00:00:ab:11:f9:2a:c2:77:29:f9:5c:00</programlisting>
</variablelist>
</refsect1>
<refsect1>
<title>[DHCPRelay] Section Options</title>
<para>The [DHCPRelay] section contains host-wide settings for the DHCP relay agent.</para>
<variablelist class='network-directives'>
<varlistentry>
<term><varname>ServerAddress=</varname></term>
<listitem>
<para>Specifies the IPv4 address of the upstream DHCP server. This is required for the host to act
as a DHCP relay agent.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>OverrideServerIdentifier=</varname></term>
<listitem>
<para>Takes a boolean value. When enabled, the Server Identifier Override sub-option and the Relay
Agent Flags sub-option in the Relay Agent Information option will be appended to the DHCP message
forwarded to the upstream DHCP server. Defaults to false.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>RemoteId=</varname></term>
<listitem>
<para>Specifies the remote ID, which is typically used by DHCP servers to identify the DHCP relay
agent. Takes a data type and data separated with a colon
(<literal><replaceable>type</replaceable>:<replaceable>value</replaceable></literal>). The type
takes one of <literal>uint8</literal>, <literal>uint16</literal>, <literal>uint32</literal>,
<literal>ipv4address</literal>, <literal>ipv6address</literal>, or <literal>string</literal>.
Special characters in the data string may be escaped using
<ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escapes</ulink>.
If unset, a UUID generated from the local machine ID will be used.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExtraOption=</varname></term>
<listitem>
<para>Specifies an extra sub-option in the Relay Agent Information option, which is appended to
DHCP messages forwarded to the upstream DHCP server. Takes a sub-option code, data type, and data
separated with a colon
(<literal><replaceable>code</replaceable>:<replaceable>type</replaceable>:<replaceable>value</replaceable></literal>).
The code is an integer in 1…254. See <varname>RemoteId=</varname> in the above for the acceptable
type and data. This setting can be specified multiple times. When an empty string is specified,
all previous assignments are cleared. Defaults to unset, and no extra sub-option will be appended.
</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[DHCPServer] Section Options</title>

118
man/systemd.network.xml
View File

@@ -435,6 +435,26 @@
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DHCPRelay=</varname></term>
<listitem>
<para>Takes one of <literal>upstream</literal> or <literal>downstream</literal>. When specified,
the host acts as a DHCP relay agent. When set to <literal>upstream</literal>, the interface behaves
as an upstream interface of the DHCP relay agent. When set to <literal>downstream</literal>, the
interface behaves as a downstream interface of the DHCP relay agent. To make the DHCP relay agent
work, at least one upstream interface and one downstream interface must be configured on the host.
This requires <varname>ServerAddress=</varname> in the [DHCPRelay] section to be configured in
<filename>networkd.conf</filename>. If <varname>ServerAddress=</varname> is not configured, this
setting is ignored. See
<citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more details about <varname>ServerAddress=</varname> and other host-wide settings.
Also, further per-interface settings can be configured in the [DHCPRelay] section described below.
Defaults to unset, and the interface is not used for DHCP relay forwarding.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DHCPServer=</varname></term>
<listitem>
@@ -3868,6 +3888,104 @@ Token=prefixstable:2002:da8:1::</programlisting></para>
</variablelist>
</refsect1>
<refsect1>
<title>[DHCPRelay] Section Options</title>
<para>The [DHCPRelay] section contains per-interface settings for the DHCP relay agent. The settings in
this section are only used when <varname>DHCPRelay=</varname> in the [Network] section is configured.
</para>
<variablelist class='network-directives'>
<varlistentry>
<term><varname>AgentAddress=</varname></term>
<listitem>
<para>Takes an IPv4 address. The specified address is used as the source IP address of packets
forwarded to the upstream DHCP server. The address may also be used for the Server Identifier
Override sub-option and the Link Selection sub-option in the Relay Agent Information option
appended to DHCP messages forwarded to the upstream DHCP server. This setting applies to both
upstream and downstream interfaces. Defaults to unset. If unset, a statically configured IPv4
address in the .network file is selected automatically. When multiple static IPv4 addresses are
configured, it is recommended to specify this setting explicitly.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>GatewayAddress=</varname></term>
<listitem>
<para>Takes an IPv4 address. The specified address is set to the <literal>giaddr</literal> field of
the DHCP message header when the DHCP message is forwarded to the upstream DHCP server. This is
used only when <varname>DHCPRelay=downstream</varname>, and ignored otherwise. Defaults to unset,
and the same address specified with <varname>AgentAddress=</varname> will be used.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>CircuitId=</varname></term>
<listitem>
<para>Specifies the circuit ID of the downstream interface. This is set as the Circuit ID
sub-option in the Relay Agent Information option in the forwarded DHCP message. Takes a data type
and data separated with a colon
(<literal><replaceable>type</replaceable>:<replaceable>value</replaceable></literal>). The type
takes one of <literal>uint8</literal>, <literal>uint16</literal>, <literal>uint32</literal>,
<literal>ipv4address</literal>, <literal>ipv6address</literal>, or <literal>string</literal>.
Special characters in the data string may be escaped using
<ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escapes</ulink>.
This is used only when <varname>DHCPRelay=downstream</varname>, and ignored otherwise. If unset,
the name of the interface will be used.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>VirtualSubnetSelection=</varname></term>
<listitem>
<para>Specifies a unique identifier used by the DHCP server to select the downstream subnet
independently of giaddr. This value is used as the Virtual Subnet Selection sub-option in the Relay
Agent Information option in the forwarded DHCP message. Takes a value in the same format as
<varname>CircuitId=</varname>. This is used only when <varname>DHCPRelay=downstream</varname>, and
ignored otherwise. Defaults to unset, and the sub-option is not set.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExtraOption=</varname></term>
<listitem>
<para>Specifies an extra sub-option in the Relay Agent Information option, which is appended to
DHCP messages forwarded to the upstream DHCP server. Takes a sub-option code, data type, and data
separated with a colon
(<literal><replaceable>code</replaceable>:<replaceable>type</replaceable>:<replaceable>value</replaceable></literal>).
The code is an integer in 1…254. See <varname>CircuitId=</varname> in the above for the acceptable
type and data. This setting can be specified multiple times. When an empty string is specified,
all previous assignments are cleared. This is used only when
<varname>DHCPRelay=downstream</varname>, and ignored otherwise. Defaults to unset, and no extra
sub-option will be appended.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>InterfacePriority=</varname></term>
<listitem>
<para>Specifies the priority of the upstream interface. Takes an integer value. When the host has
multiple upstream interfaces, the upstream interface with the highest (largest) priority will be
used for forwarding DHCP messages to the upstream DHCP server. When multiple interfaces have the
same priority, which interface is used is unspecified. This is used only when
<varname>DHCPRelay=upstream</varname>, and ignored otherwise. Defaults to zero.</para>
<xi:include href="version-info.xml" xpointer="v261"/>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[DHCPServer] Section Options</title>
<para>The [DHCPServer] section contains settings for the DHCP server, if enabled via the