Allow broadcast packets to be sent directly instead of via the MST.

When the "Broadcast = direct" option is used, broadcast packets are not sent
and forwarded via the Minimum Spanning Tree to all nodes, but are sent directly
to all nodes that can be reached in one hop.

One use for this is to allow running ad-hoc routing protocols, such as OLSR, on
top of tinc.

doc/tinc.conf.5.in

@@ -159,8 +159,25 @@ It is possible to bind only to a single interface with this variable.
 .Pp
 This option may not work on all platforms.
 
-.It Va Broadcast Li = yes | no Po yes Pc Bq experimental
-When disabled, tinc will drop all broadcast and multicast packets, in both router and switch mode.
+.It Va Broadcast Li = no | mst | direct Po mst Pc Bq experimental
+This option selects the way broadcast packets are sent to other daemons.
+NOTE: all nodes in a VPN must use the same
+.Va Broadcast
+mode, otherwise routing loops can form.
+
+.Bl -tag -width indent
+.It no
+Broadcast packets are never sent to other nodes.
+
+.It mst
+Broadcast packets are sent and forwarded via the VPN's Minimum Spanning Tree.
+This ensures broadcast packets reach all nodes.
+
+.It direct
+Broadcast packets are sent directly to all nodes that can be reached directly.
+Broadcast packets received from other nodes are never forwarded.
+If the IndirectData option is also set, broadcast packets will only be sent to nodes which we have a meta connection to.
+.El
 
 .It Va ConnectTo Li = Ar name
 Specifies which other tinc daemon to connect to on startup.

doc/tinc.texi

@@ -778,8 +778,23 @@ variable.
 This option may not work on all platforms.
 
 @cindex Broadcast
-@item Broadcast = <yes | no> (yes) [experimental]
-When disabled, tinc will drop all broadcast and multicast packets, in both router and switch mode.
+@item Broadcast = <no | mst | direct> (mst) [experimental]
+This option selects the way broadcast packets are sent to other daemons.
+@emph{NOTE: all nodes in a VPN must use the same Broadcast mode, otherwise routing loops can form.}
+
+@table @asis
+@item no
+Broadcast packets are never sent to other nodes.
+
+@item mst
+Broadcast packets are sent and forwarded via the VPN's Minimum Spanning Tree.
+This ensures broadcast packets reach all nodes.
+
+@item direct
+Broadcast packets are sent directly to all nodes that can be reached directly.
+Broadcast packets received from other nodes are never forwarded.
+If the IndirectData option is also set, broadcast packets will only be sent to nodes which we have a meta connection to.
+@end table
 
 @cindex ConnectTo
 @item ConnectTo = <@var{name}>

src/net_packet.c

@@ -584,24 +584,50 @@ void send_packet(const node_t *n, vpn_packet_t *packet) {
 void broadcast_packet(const node_t *from, vpn_packet_t *packet) {
 	avl_node_t *node;
 	connection_t *c;
+	node_t *n;
+
+	// Always give ourself a copy of the packet.
+	if(from != myself)
+		send_packet(myself, packet);
+
+	// In TunnelServer mode, do not forward broadcast packets.
+        // The MST might not be valid and create loops.
+	if(tunnelserver || broadcast_mode == BMODE_NONE)
+		return;
 
 	ifdebug(TRAFFIC) logger(LOG_INFO, "Broadcasting packet of %d bytes from %s (%s)",
 			   packet->len, from->name, from->hostname);
 
-	if(from != myself) {
-		send_packet(myself, packet);
+	switch(broadcast_mode) {
+		// In MST mode, broadcast packets travel via the Minimum Spanning Tree.
+		// This guarantees all nodes receive the broadcast packet, and
+		// usually distributes the sending of broadcast packets over all nodes.
+		case BMODE_MST:
+			for(node = connection_tree->head; node; node = node->next) {
+				c = node->data;
 
-		// In TunnelServer mode, do not forward broadcast packets.
-                // The MST might not be valid and create loops.
-		if(tunnelserver)
-			return;
-	}
+				if(c->status.active && c->status.mst && c != from->nexthop->connection)
+					send_packet(c->node, packet);
+			}
+			break;
 
-	for(node = connection_tree->head; node; node = node->next) {
-		c = node->data;
+		// In direct mode, we send copies to each node we know of.
+	        // However, this only reaches nodes that can be reached in a single hop.
+		// We don't have enough information to forward broadcast packets in this case.
+		case BMODE_DIRECT:
+			if(from != myself)
+				break;
 
-		if(c->status.active && c->status.mst && c != from->nexthop->connection)
-			send_packet(c->node, packet);
+			for(node = node_udp_tree->head; node; node = node->next) {
+				n = node->data;
+
+				if(n->status.reachable && ((n->via == myself && n->nexthop == n) || n->via == n))
+					send_packet(c->node, packet);
+			}
+			break;
+
+		default:
+			break;
 	}
 }
 

src/net_setup.c

@@ -429,7 +429,19 @@ static bool setup_myself(void) {
 
 	get_config_bool(lookup_config(config_tree, "PriorityInheritance"), &priorityinheritance);
 	get_config_bool(lookup_config(config_tree, "DecrementTTL"), &decrement_ttl);
-	get_config_bool(lookup_config(config_tree, "Broadcast"), &broadcast);
+	if(get_config_string(lookup_config(config_tree, "Broadcast"), &mode)) {
+		if(!strcasecmp(mode, "no"))
+			broadcast_mode = BMODE_NONE;
+		else if(!strcasecmp(mode, "yes") || !strcasecmp(mode, "mst"))
+			broadcast_mode = BMODE_MST;
+		else if(!strcasecmp(mode, "direct"))
+			broadcast_mode = BMODE_DIRECT;
+		else {
+			logger(LOG_ERR, "Invalid broadcast mode!");
+			return false;
+		}
+		free(mode);
+	}
 
 #if !defined(SOL_IP) || !defined(IP_TOS)
 	if(priorityinheritance)

src/route.c

@@ -34,12 +34,12 @@
 
 rmode_t routing_mode = RMODE_ROUTER;
 fmode_t forwarding_mode = FMODE_INTERNAL;
+bmode_t broadcast_mode = BMODE_MST;
 bool decrement_ttl = false;
 bool directonly = false;
 bool priorityinheritance = false;
 int macexpire = 600;
 bool overwrite_mac = false;
-bool broadcast = true;
 mac_t mymac = {{0xFE, 0xFD, 0, 0, 0, 0}};
 
 /* Sizes of various headers */
@@ -430,7 +430,7 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 	if(!checklength(source, packet, ether_size + ip_size))
 		return;
 
-	if(broadcast && (((packet->data[30] & 0xf0) == 0xe0) || (
+	if(broadcast_mode && (((packet->data[30] & 0xf0) == 0xe0) || (
 			packet->data[30] == 255 &&
 			packet->data[31] == 255 &&
 			packet->data[32] == 255 &&
@@ -727,7 +727,7 @@ static void route_ipv6(node_t *source, vpn_packet_t *packet) {
 		return;
 	}
 
-	if(broadcast && packet->data[38] == 255)
+	if(broadcast_mode && packet->data[38] == 255)
 		broadcast_packet(source, packet);
 	else
 		route_ipv6_unicast(source, packet);
@@ -817,8 +817,7 @@ static void route_mac(node_t *source, vpn_packet_t *packet) {
 	subnet = lookup_subnet_mac(NULL, &dest);
 
 	if(!subnet) {
-		if(broadcast)
-			broadcast_packet(source, packet);
+		broadcast_packet(source, packet);
 		return;
 	}
 

src/route.h

@@ -36,12 +36,18 @@ typedef enum fmode_t {
 	FMODE_KERNEL,
 } fmode_t;
 
+typedef enum bmode_t {
+	BMODE_NONE = 0,
+	BMODE_MST,
+	BMODE_DIRECT,
+} bmode_t;
+
 extern rmode_t routing_mode;
 extern fmode_t forwarding_mode;
+extern bmode_t broadcast_mode;
 extern bool decrement_ttl;
 extern bool directonly;
 extern bool overwrite_mac;
-extern bool broadcast;
 extern bool priorityinheritance;
 extern int macexpire;