man: suggest to enable global IPv6Forwarding= setting to make IPv6 packets forwarded

Closes #33414.

(cherry picked from commit 175cdefd33788eced7fd6d76fb0b1676eb6ba799)

diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index 42a31b4cdd12416771163253ade77c78e91571f7..68d0c9be59be6c6a4da15e07623b284296a7919c 100644 (file)
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -853,7 +853,7 @@ DuplicateAddressDetection=none</programlisting></para>
       <varlistentry>
         <term><varname>IPv6Forwarding=</varname></term>
         <listitem>
-          <para>Configures IPv6 packet forwarding for the interface. Takes a boolean value. This controls the
+          <para>Configures interface-specific host/router behaviour. Takes a boolean value. This controls the
           <filename>net.ipv6.conf.<replaceable>INTERFACE</replaceable>.forwarding</filename> sysctl option of
           the network interface. See
           <ulink url="https://docs.kernel.org/networking/ip-sysctl.html">IP Sysctl</ulink>
@@ -867,6 +867,14 @@ DuplicateAddressDetection=none</programlisting></para>
           <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
           </para>
 
+          <para>Note, unlike <varname>IPv4Forwarding=</varname>, enabling per-interface
+          <varname>IPv6Forwarding=</varname> on two or more interfaces <emphasis>DOES NOT</emphasis> make IPv6
+          packets forwarded within the interfaces. This setting just controls the per-interface sysctl value,
+          and the sysctl value is not directly correlated to whether packets are forwarded. To ensure IPv6
+          packets forwarded, the global setting in
+          <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+          needs to be enabled.</para>
+
           <xi:include href="version-info.xml" xpointer="v256"/>
         </listitem>
       </varlistentry>