+@cindex BroadcastSubnet
+@item BroadcastSubnet = @var{address}[/@var{prefixlength}]
+Declares a broadcast subnet.
+Any packet with a destination address falling into such a subnet will be routed as a broadcast
+(provided all nodes have it declared).
+This is most useful to declare subnet broadcast addresses (e.g. 10.42.255.255),
+otherwise tinc won't know what to do with them.
+
+Note that global broadcast addresses (MAC ff:ff:ff:ff:ff:ff, IPv4 255.255.255.255),
+as well as multicast space (IPv4 224.0.0.0/4, IPv6 ff00::/8)
+are always considered broadcast addresses and don't need to be declared.
+