docs: add interfaces-forward(5) manual page

Makefile

@@ -162,6 +162,7 @@ MANPAGES_5 = \
 	doc/interfaces-bond.5 \
 	doc/interfaces-batman.5 \
 	doc/interfaces-bridge.5 \
+	doc/interfaces-forward.5 \
 	doc/interfaces-ppp.5 \
 	doc/interfaces-vrf.5 \
 	doc/interfaces-vxlan.5 \

doc/interfaces-forward.scd

@@ -0,0 +1,45 @@
+interfaces-forward(5)
+
+# NAME
+
+*interfaces-forward* - forwarding vocabulary for the interfaces(5) file format
+
+# DESCRIPTION
+
+Linux allows for configuration of IP packet forwarding behavior on a protocol
+and interface basis.  The following options allow for this configuration.
+
+# FORWARDING-RELATED OPTIONS
+
+*forward-ipv4* _yes|no_
+	Whether the interface should forward unicast IPv4 packets.
+
+*forward-ipv6* _yes|no_
+	Whether the interface should forward unicast IPv6 packets.
+
+*forward-ipv4-mc* _yes|no_
+	Whether the interface should forward multicast IPv4 packets.
+
+*forward-ipv6-mc* _yes|no_
+	Whether the interface should forward multicast IPv6 packets.
+
+# EXAMPLES
+
+The typical home router scenario will want to forward both IPv4 and IPv6
+packets:
+
+```
+iface WAN
+	use dhcp
+	forward-ipv4 yes
+	forward-ipv6 yes
+
+iface LAN
+	address 192.168.0.1/24
+	forward-ipv4 yes
+	forward-ipv6 yes
+```
+
+# AUTHORS
+
+Ariadne Conill <ariadne@dereferenced.org>

doc/interfaces.scd

@@ -158,6 +158,9 @@ most common executors are:
 	Use a DHCP client to learn the IPv4 address of an
 	interface.
 
+*forward*
+	Configures forwarding settings on the interface.
+
 *loopback*
 	Designates the interface as a loopback device.