Add LocalDiscovery option which tries to detect peers on the local network.

Currently, this is implemented by sending IPv4 broadcast packets to the
LAN during path MTU discovery.

src/graph.c

@@ -174,6 +174,7 @@ static void sssp_bfs(void) {
 	myself->status.visited = true;
 	myself->status.indirect = false;
 	myself->nexthop = myself;
+	myself->prevedge = NULL;
 	myself->via = myself;
 	list_insert_head(todo_list, myself);
 
@@ -214,6 +215,7 @@ static void sssp_bfs(void) {
 			e->to->status.visited = true;
 			e->to->status.indirect = indirect;
 			e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
+			e->to->prevedge = e;
 			e->to->via = indirect ? n->via : e->to;
 			e->to->options = e->options;
 

src/net.h

@@ -107,6 +107,7 @@ extern int maxoutbufsize;
 extern int seconds_till_retry;
 extern int addressfamily;
 extern unsigned replaywin;
+extern bool localdiscovery;
 
 extern listen_socket_t listen_socket[MAXSOCKETS];
 extern int listen_sockets;

src/net_packet.c

@@ -61,13 +61,21 @@ static char lzo_wrkmem[LZO1X_999_MEM_COMPRESS > LZO1X_1_MEM_COMPRESS ? LZO1X_999
 static void send_udppacket(node_t *, vpn_packet_t *);
 
 unsigned replaywin = 16;
+bool localdiscovery = false;
 
 #define MAX_SEQNO 1073741824
 
-// mtuprobes == 1..30: initial discovery, send bursts with 1 second interval
-// mtuprobes ==    31: sleep pinginterval seconds
-// mtuprobes ==    32: send 1 burst, sleep pingtimeout second
-// mtuprobes ==    33: no response from other side, restart PMTU discovery process
+/* mtuprobes == 1..30: initial discovery, send bursts with 1 second interval
+   mtuprobes ==    31: sleep pinginterval seconds
+   mtuprobes ==    32: send 1 burst, sleep pingtimeout second
+   mtuprobes ==    33: no response from other side, restart PMTU discovery process
+
+   Probes are sent in batches of three, with random sizes between the lower and
+   upper boundaries for the MTU thus far discovered.
+
+   In case local discovery is enabled, a fourth packet is added to each batch,
+   which will be broadcast to the local network.
+*/
 
 void send_mtu_probe(node_t *n) {
 	vpn_packet_t packet;
@@ -118,7 +126,7 @@ void send_mtu_probe(node_t *n) {
 		timeout = pingtimeout;
 	}
 
-	for(i = 0; i < 3; i++) {
+	for(i = 0; i < 3 + localdiscovery; i++) {
 		if(n->maxmtu <= n->minmtu)
 			len = n->maxmtu;
 		else
@@ -130,7 +138,7 @@ void send_mtu_probe(node_t *n) {
 		memset(packet.data, 0, 14);
 		RAND_pseudo_bytes(packet.data + 14, len - 14);
 		packet.len = len;
-		packet.priority = 0;
+		packet.priority = i < 3 ? 0 : -1;
 
 		ifdebug(TRAFFIC) logger(LOG_INFO, "Sending MTU probe length %d to %s (%s)", len, n->name, n->hostname);
 
@@ -486,6 +494,29 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 
 	/* Send the packet */
 
+	struct sockaddr *sa;
+	socklen_t sl;
+	int sock;
+
+	/* Overloaded use of priority field: -1 means local broadcast */
+
+	if(origpriority == -1 && n->prevedge) {
+		struct sockaddr_in in;
+		in.sin_family = AF_INET;
+		in.sin_addr.s_addr = -1;
+		in.sin_port = n->prevedge->address.in.sin_port;
+		sa = (struct sockaddr *)&in;
+		sl = sizeof in;
+		sock = 0;
+	} else {
+		if(origpriority == -1)
+			origpriority = 0;
+
+		sa = &(n->address.sa);
+		sl = SALEN(n->address.sa);
+		sock = n->sock;
+	}
+
 #if defined(SOL_IP) && defined(IP_TOS)
 	if(priorityinheritance && origpriority != priority
 	   && listen_socket[n->sock].sa.sa.sa_family == AF_INET) {
@@ -496,7 +527,7 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 	}
 #endif
 
-	if(sendto(listen_socket[n->sock].udp, (char *) &inpkt->seqno, inpkt->len, 0, &(n->address.sa), SALEN(n->address.sa)) < 0 && !sockwouldblock(sockerrno)) {
+	if(sendto(listen_socket[sock].udp, (char *) &inpkt->seqno, inpkt->len, 0, sa, sl) < 0 && !sockwouldblock(sockerrno)) {
 		if(sockmsgsize(sockerrno)) {
 			if(n->maxmtu >= origlen)
 				n->maxmtu = origlen - 1;
@@ -600,6 +631,7 @@ static node_t *try_harder(const sockaddr_t *from, const vpn_packet_t *pkt) {
 	if(hard)
 		last_hard_try = now;
 
+	last_hard_try = now;
 	return n;
 }
 

src/net_setup.c

@@ -356,6 +356,7 @@ static bool setup_myself(void) {
 	get_config_bool(lookup_config(config_tree, "DirectOnly"), &directonly);
 	get_config_bool(lookup_config(config_tree, "StrictSubnets"), &strictsubnets);
 	get_config_bool(lookup_config(config_tree, "TunnelServer"), &tunnelserver);
+	get_config_bool(lookup_config(config_tree, "LocalDiscovery"), &localdiscovery);
 	strictsubnets |= tunnelserver;
 
 	if(get_config_string(lookup_config(config_tree, "Mode"), &mode)) {

src/net_socket.c

@@ -211,6 +211,7 @@ int setup_vpn_in_socket(const sockaddr_t *sa) {
 
 	option = 1;
 	setsockopt(nfd, SOL_SOCKET, SO_REUSEADDR, (void *)&option, sizeof(option));
+	setsockopt(nfd, SOL_SOCKET, SO_BROADCAST, (void *)&option, sizeof(option));
 
 	if(udp_rcvbuf && setsockopt(nfd, SOL_SOCKET, SO_RCVBUF, (void *)&udp_rcvbuf, sizeof(udp_rcvbuf)))
 		logger(LOG_WARNING, "Can't set UDP SO_RCVBUF to %i: %s", udp_rcvbuf, strerror(errno));

src/node.h

@@ -67,6 +67,7 @@ typedef struct node_t {
 	int outcompression;			/* Compressionlevel, 0 = no compression */
 
 	struct node_t *nexthop;			/* nearest node from us to him */
+	struct edge_t *prevedge;		/* nearest node from him to us */
 	struct node_t *via;			/* next hop for UDP packets */
 
 	avl_tree_t *subnet_tree;		/* Pointer to a tree of subnets belonging to this node */