X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=blobdiff_plain;f=src%2Fnet_packet.c;h=626114c8a63673e2125ef19d65f14a2acebd86dd;hp=c2552619857c89f7f53df2a7d7c6a82f27ff6dea;hb=c1532035e2850dc4ec0eb22a6d51208e3128eb94;hpb=9b9230a0a79c670b86f54fadd2807b864ff9d91f

diff --git a/src/net_packet.c b/src/net_packet.c
index c2552619..626114c8 100644
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -1,7 +1,7 @@
 /*
     net_packet.c -- Handles in- and outgoing VPN packets
     Copyright (C) 1998-2005 Ivo Timmermans,
-                  2000-2013 Guus Sliepen <guus@tinc-vpn.org>
+                  2000-2014 Guus Sliepen <guus@tinc-vpn.org>
                   2010      Timothy Redaelli <timothy@redaelli.eu>
                   2010      Brandon Black <blblack@gmail.com>
 
@@ -42,11 +42,14 @@
 #include "net.h"
 #include "netutl.h"
 #include "protocol.h"
-#include "process.h"
 #include "route.h"
 #include "utils.h"
 #include "xalloc.h"
 
+#ifndef MAX
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
 int keylifetime = 0;
 #ifdef HAVE_LZO
 static char lzo_wrkmem[LZO1X_999_MEM_COMPRESS > LZO1X_1_MEM_COMPRESS ? LZO1X_999_MEM_COMPRESS : LZO1X_1_MEM_COMPRESS];
@@ -55,135 +58,60 @@ 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;
+bool localdiscovery = true;
+bool udp_discovery = true;
+int udp_discovery_interval = 9;
+int udp_discovery_timeout = 30;
 
 #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
-
-   Probes are sent in batches of at least three, with random sizes between the
-   lower and upper boundaries for the MTU thus far discovered.
-
-   After the initial discovery, a fourth packet is added to each batch with a
-   size larger than the currently known PMTU, to test if the PMTU has increased.
-
-   In case local discovery is enabled, another packet is added to each batch,
-   which will be broadcast to the local network.
-
-*/
-
-static void send_mtu_probe_handler(void *data) {
-	node_t *n = data;
-	int timeout = 1;
-
-	n->mtuprobes++;
-
-	if(!n->status.reachable || !n->status.validkey) {
-		logger(DEBUG_TRAFFIC, LOG_INFO, "Trying to send MTU probe to unreachable or rekeying node %s (%s)", n->name, n->hostname);
-		n->mtuprobes = 0;
+static void try_fix_mtu(node_t *n) {
+	if(n->mtuprobes < 0)
 		return;
-	}
-
-	if(n->mtuprobes > 32) {
-		if(!n->minmtu) {
-			n->mtuprobes = 31;
-			timeout = pinginterval;
-			goto end;
-		}
 
-		logger(DEBUG_TRAFFIC, LOG_INFO, "%s (%s) did not respond to UDP ping, restarting PMTU discovery", n->name, n->hostname);
-		n->status.udp_confirmed = false;
-		n->mtuprobes = 1;
-		n->minmtu = 0;
-		n->maxmtu = MTU;
-	}
-
-	if(n->mtuprobes >= 10 && n->mtuprobes < 32 && !n->minmtu) {
-		logger(DEBUG_TRAFFIC, LOG_INFO, "No response to MTU probes from %s (%s)", n->name, n->hostname);
-		n->mtuprobes = 31;
-	}
-
-	if(n->mtuprobes == 30 || (n->mtuprobes < 30 && n->minmtu >= n->maxmtu)) {
+	if(n->mtuprobes == 20 || n->minmtu >= n->maxmtu) {
 		if(n->minmtu > n->maxmtu)
 			n->minmtu = n->maxmtu;
 		else
 			n->maxmtu = n->minmtu;
 		n->mtu = n->minmtu;
 		logger(DEBUG_TRAFFIC, LOG_INFO, "Fixing MTU of %s (%s) to %d after %d probes", n->name, n->hostname, n->mtu, n->mtuprobes);
-		n->mtuprobes = 31;
-	}
-
-	if(n->mtuprobes == 31) {
-		timeout = pinginterval;
-		goto end;
-	} else if(n->mtuprobes == 32) {
-		timeout = pingtimeout;
+		n->mtuprobes = -1;
 	}
-
-	for(int i = 0; i < 4 + localdiscovery; i++) {
-		int len;
-
-		if(i == 0) {
-			if(n->mtuprobes < 30 || n->maxmtu + 8 >= MTU)
-				continue;
-			len = n->maxmtu + 8;
-		} else if(n->maxmtu <= n->minmtu) {
-			len = n->maxmtu;
-		} else {
-			len = n->minmtu + 1 + rand() % (n->maxmtu - n->minmtu);
-		}
-
-		if(len < 64)
-			len = 64;
-
-		vpn_packet_t packet;
-		memset(packet.data, 0, 14);
-		randomize(packet.data + 14, len - 14);
-		packet.len = len;
-		if(i >= 4 && n->mtuprobes <= 10)
-			packet.priority = -1;
-		else
-			packet.priority = 0;
-
-		logger(DEBUG_TRAFFIC, LOG_INFO, "Sending MTU probe length %d to %s (%s)", len, n->name, n->hostname);
-
-		send_udppacket(n, &packet);
-	}
-
-	n->probe_counter = 0;
-	gettimeofday(&n->probe_time, NULL);
-
-	/* Calculate the packet loss of incoming traffic by comparing the rate of
-	   packets received to the rate with which the sequence number has increased.
-	 */
-
-	if(n->received > n->prev_received)
-		n->packetloss = 1.0 - (n->received - n->prev_received) / (float)(n->received_seqno - n->prev_received_seqno);
-	else
-		n->packetloss = n->received_seqno <= n->prev_received_seqno;
-
-	n->prev_received_seqno = n->received_seqno;
-	n->prev_received = n->received;
-
-end:
-	timeout_set(&n->mtutimeout, &(struct timeval){timeout, rand() % 100000});
 }
 
-void send_mtu_probe(node_t *n) {
-	timeout_add(&n->mtutimeout, send_mtu_probe_handler, n, &(struct timeval){1, 0});
-	send_mtu_probe_handler(n);
+static void udp_probe_timeout_handler(void *data) {
+	node_t *n = data;
+	if(!n->status.udp_confirmed)
+		return;
+
+	logger(DEBUG_TRAFFIC, LOG_INFO, "Too much time has elapsed since last UDP ping response from %s (%s), stopping UDP communication", n->name, n->hostname);
+	n->status.udp_confirmed = false;
+	n->mtuprobes = 0;
+	n->minmtu = 0;
+	n->maxmtu = MTU;
 }
 
-static void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
-	logger(DEBUG_TRAFFIC, LOG_INFO, "Got MTU probe length %d from %s (%s)", packet->len, n->name, n->hostname);
+static void udp_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
+	if(!DATA(packet)[0]) {
+		logger(DEBUG_TRAFFIC, LOG_INFO, "Got UDP probe request %d from %s (%s)", packet->len, n->name, n->hostname);
 
-	if(!packet->data[0]) {
 		/* It's a probe request, send back a reply */
 
-		packet->data[0] = 1;
+		/* Type 2 probe replies were introduced in protocol 17.3 */
+		if ((n->options >> 24) >= 3) {
+			uint8_t *data = DATA(packet);
+			*data++ = 2;
+			uint16_t len16 = htons(len); memcpy(data, &len16, 2); data += 2;
+			struct timeval now;
+			gettimeofday(&now, NULL);
+			uint32_t sec = htonl(now.tv_sec); memcpy(data, &sec, 4); data += 4;
+			uint32_t usec = htonl(now.tv_usec); memcpy(data, &usec, 4); data += 4;
+			packet->len -= 10;
+		} else {
+			/* Legacy protocol: n won't understand type 2 probe replies. */
+			DATA(packet)[0] = 1;
+		}
 
 		/* Temporarily set udp_confirmed, so that the reply is sent
 		   back exactly the way it came in. */
@@ -193,52 +121,65 @@ static void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
 		send_udppacket(n, packet);
 		n->status.udp_confirmed = udp_confirmed;
 	} else {
+		length_t probelen = len;
+		if (DATA(packet)[0] == 2) {
+			if (len < 3)
+				logger(DEBUG_TRAFFIC, LOG_WARNING, "Received invalid (too short) UDP probe reply from %s (%s)", n->name, n->hostname);
+			else {
+				uint16_t probelen16; memcpy(&probelen16, DATA(packet) + 1, 2); probelen = ntohs(probelen16);
+			}
+		}
+		logger(DEBUG_TRAFFIC, LOG_INFO, "Got type %d UDP probe reply %d from %s (%s)", DATA(packet)[0], probelen, n->name, n->hostname);
+
 		/* It's a valid reply: now we know bidirectional communication
 		   is possible using the address and socket that the reply
 		   packet used. */
-
 		n->status.udp_confirmed = true;
 
-		/* If we haven't established the PMTU yet, restart the discovery process. */
-
-		if(n->mtuprobes > 30) {
-			if (len == n->maxmtu + 8) {
-				logger(DEBUG_TRAFFIC, LOG_INFO, "Increase in PMTU to %s (%s) detected, restarting PMTU discovery", n->name, n->hostname);
-				n->maxmtu = MTU;
-				n->mtuprobes = 10;
-				return;
-			}
+		if(udp_discovery) {
+			timeout_del(&n->udp_ping_timeout);
+			timeout_add(&n->udp_ping_timeout, &udp_probe_timeout_handler, n, &(struct timeval){udp_discovery_timeout, 0});
+		}
 
-			if(n->minmtu)
-				n->mtuprobes = 30;
-			else
-				n->mtuprobes = 1;
+		if(probelen >= n->maxmtu + 1) {
+			logger(DEBUG_TRAFFIC, LOG_INFO, "Increase in PMTU to %s (%s) detected, restarting PMTU discovery", n->name, n->hostname);
+			n->maxmtu = MTU;
+			n->mtuprobes = 0;
+			return;
 		}
 
 		/* If applicable, raise the minimum supported MTU */
 
-		if(len > n->maxmtu)
-			len = n->maxmtu;
-		if(n->minmtu < len)
-			n->minmtu = len;
+		if(probelen > n->maxmtu)
+			probelen = n->maxmtu;
+		if(n->minmtu < probelen) {
+			n->minmtu = probelen;
+			try_fix_mtu(n);
+		}
 
-		/* Calculate RTT and bandwidth.
+		/* Calculate RTT.
 		   The RTT is the time between the MTU probe burst was sent and the first
-		   reply is received. The bandwidth is measured using the time between the
-		   arrival of the first and third probe reply.
+		   reply is received.
 		 */
 
 		struct timeval now, diff;
 		gettimeofday(&now, NULL);
 		timersub(&now, &n->probe_time, &diff);
+
+		struct timeval probe_timestamp = now;
+		if (DATA(packet)[0] == 2 && packet->len >= 11) {
+			uint32_t sec; memcpy(&sec, DATA(packet) + 3, 4);
+			uint32_t usec; memcpy(&usec, DATA(packet) + 7, 4);
+			probe_timestamp.tv_sec = ntohl(sec);
+			probe_timestamp.tv_usec = ntohl(usec);
+		}
+		
 		n->probe_counter++;
 
 		if(n->probe_counter == 1) {
 			n->rtt = diff.tv_sec + diff.tv_usec * 1e-6;
-			n->probe_time = now;
-		} else if(n->probe_counter == 3) {
-			n->bandwidth = 2.0 * len / (diff.tv_sec + diff.tv_usec * 1e-6);
-			logger(DEBUG_TRAFFIC, LOG_DEBUG, "%s (%s) RTT %.2f ms, burst bandwidth %.3f Mbit/s, rx packet loss %.2f %%", n->name, n->hostname, n->rtt * 1e3, n->bandwidth * 8e-6, n->packetloss * 1e2);
+			n->probe_time = probe_timestamp;
+			logger(DEBUG_TRAFFIC, LOG_DEBUG, "%s (%s) RTT %.2f ms, rx packet loss %.2f %%", n->name, n->hostname, n->rtt * 1e3, n->packetloss * 1e2);
 		}
 	}
 }
@@ -316,58 +257,82 @@ static void receive_packet(node_t *n, vpn_packet_t *packet) {
 
 static bool try_mac(node_t *n, const vpn_packet_t *inpkt) {
 	if(n->status.sptps)
-		return sptps_verify_datagram(&n->sptps, (char *)&inpkt->seqno, inpkt->len);
+		return sptps_verify_datagram(&n->sptps, DATA(inpkt), inpkt->len);
 
-	if(!digest_active(n->indigest) || inpkt->len < sizeof inpkt->seqno + digest_length(n->indigest))
+#ifdef DISABLE_LEGACY
+	return false;
+#else
+	if(!digest_active(n->indigest) || inpkt->len < sizeof(seqno_t) + digest_length(n->indigest))
 		return false;
 
-	return digest_verify(n->indigest, &inpkt->seqno, inpkt->len - digest_length(n->indigest), (const char *)&inpkt->seqno + inpkt->len - digest_length(n->indigest));
+	return digest_verify(n->indigest, SEQNO(inpkt), inpkt->len - digest_length(n->indigest), DATA(inpkt) + inpkt->len - digest_length(n->indigest));
+#endif
 }
 
-static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
+static bool receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
 	vpn_packet_t pkt1, pkt2;
 	vpn_packet_t *pkt[] = { &pkt1, &pkt2, &pkt1, &pkt2 };
 	int nextpkt = 0;
-	vpn_packet_t *outpkt = pkt[0];
 	size_t outlen;
+	pkt1.offset = DEFAULT_PACKET_OFFSET;
+	pkt2.offset = DEFAULT_PACKET_OFFSET;
 
 	if(n->status.sptps) {
-		sptps_receive_data(&n->sptps, (char *)&inpkt->seqno, inpkt->len);
-		return;
+		if(!n->sptps.state) {
+			if(!n->status.waitingforkey) {
+				logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got packet from %s (%s) but we haven't exchanged keys yet", n->name, n->hostname);
+				send_req_key(n);
+			} else {
+				logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got packet from %s (%s) but he hasn't got our key yet", n->name, n->hostname);
+			}
+			return false;
+		}
+		inpkt->offset += 2 * sizeof(node_id_t);
+		if(!sptps_receive_data(&n->sptps, DATA(inpkt), inpkt->len - 2 * sizeof(node_id_t))) {
+			logger(DEBUG_TRAFFIC, LOG_ERR, "Got bad packet from %s (%s)", n->name, n->hostname);
+			return false;
+		}
+		return true;
 	}
 
-	if(!cipher_active(n->incipher)) {
-		logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got packet from %s (%s) but he hasn't got our key yet",
-					n->name, n->hostname);
-		return;
+#ifdef DISABLE_LEGACY
+	return false;
+#else
+	if(!n->status.validkey) {
+		logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got packet from %s (%s) but he hasn't got our key yet", n->name, n->hostname);
+		return false;
 	}
 
 	/* Check packet length */
 
-	if(inpkt->len < sizeof inpkt->seqno + digest_length(n->indigest)) {
+	if(inpkt->len < sizeof(seqno_t) + digest_length(n->indigest)) {
 		logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got too short packet from %s (%s)",
 					n->name, n->hostname);
-		return;
+		return false;
 	}
 
+	/* It's a legacy UDP packet, the data starts after the seqno */
+
+	inpkt->offset += sizeof(seqno_t);
+
 	/* Check the message authentication code */
 
 	if(digest_active(n->indigest)) {
 		inpkt->len -= digest_length(n->indigest);
-		if(!digest_verify(n->indigest, &inpkt->seqno, inpkt->len, (const char *)&inpkt->seqno + inpkt->len)) {
+		if(!digest_verify(n->indigest, SEQNO(inpkt), inpkt->len, SEQNO(inpkt) + inpkt->len)) {
 			logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got unauthenticated packet from %s (%s)", n->name, n->hostname);
-			return;
+			return false;
 		}
 	}
 	/* Decrypt the packet */
 
 	if(cipher_active(n->incipher)) {
-		outpkt = pkt[nextpkt++];
+		vpn_packet_t *outpkt = pkt[nextpkt++];
 		outlen = MAXSIZE;
 
-		if(!cipher_decrypt(n->incipher, &inpkt->seqno, inpkt->len, &outpkt->seqno, &outlen, true)) {
+		if(!cipher_decrypt(n->incipher, SEQNO(inpkt), inpkt->len, SEQNO(outpkt), &outlen, true)) {
 			logger(DEBUG_TRAFFIC, LOG_DEBUG, "Error decrypting packet from %s (%s)", n->name, n->hostname);
-			return;
+			return false;
 		}
 
 		outpkt->len = outlen;
@@ -376,38 +341,40 @@ static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
 
 	/* Check the sequence number */
 
-	inpkt->len -= sizeof inpkt->seqno;
-	inpkt->seqno = ntohl(inpkt->seqno);
+	seqno_t seqno;
+	memcpy(&seqno, SEQNO(inpkt), sizeof seqno);
+	seqno = ntohl(seqno);
+	inpkt->len -= sizeof seqno;
 
 	if(replaywin) {
-		if(inpkt->seqno != n->received_seqno + 1) {
-			if(inpkt->seqno >= n->received_seqno + replaywin * 8) {
+		if(seqno != n->received_seqno + 1) {
+			if(seqno >= n->received_seqno + replaywin * 8) {
 				if(n->farfuture++ < replaywin >> 2) {
 					logger(DEBUG_ALWAYS, LOG_WARNING, "Packet from %s (%s) is %d seqs in the future, dropped (%u)",
-						n->name, n->hostname, inpkt->seqno - n->received_seqno - 1, n->farfuture);
-					return;
+						n->name, n->hostname, seqno - n->received_seqno - 1, n->farfuture);
+					return false;
 				}
 				logger(DEBUG_ALWAYS, LOG_WARNING, "Lost %d packets from %s (%s)",
-						inpkt->seqno - n->received_seqno - 1, n->name, n->hostname);
+						seqno - n->received_seqno - 1, n->name, n->hostname);
 				memset(n->late, 0, replaywin);
-			} else if (inpkt->seqno <= n->received_seqno) {
-				if((n->received_seqno >= replaywin * 8 && inpkt->seqno <= n->received_seqno - replaywin * 8) || !(n->late[(inpkt->seqno / 8) % replaywin] & (1 << inpkt->seqno % 8))) {
+			} else if (seqno <= n->received_seqno) {
+				if((n->received_seqno >= replaywin * 8 && seqno <= n->received_seqno - replaywin * 8) || !(n->late[(seqno / 8) % replaywin] & (1 << seqno % 8))) {
 					logger(DEBUG_ALWAYS, LOG_WARNING, "Got late or replayed packet from %s (%s), seqno %d, last received %d",
-						n->name, n->hostname, inpkt->seqno, n->received_seqno);
-					return;
+						n->name, n->hostname, seqno, n->received_seqno);
+					return false;
 				}
 			} else {
-				for(int i = n->received_seqno + 1; i < inpkt->seqno; i++)
+				for(int i = n->received_seqno + 1; i < seqno; i++)
 					n->late[(i / 8) % replaywin] |= 1 << i % 8;
 			}
 		}
 
 		n->farfuture = 0;
-		n->late[(inpkt->seqno / 8) % replaywin] &= ~(1 << inpkt->seqno % 8);
+		n->late[(seqno / 8) % replaywin] &= ~(1 << seqno % 8);
 	}
 
-	if(inpkt->seqno > n->received_seqno)
-		n->received_seqno = inpkt->seqno;
+	if(seqno > n->received_seqno)
+		n->received_seqno = seqno;
 
 	n->received++;
 
@@ -419,12 +386,12 @@ static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
 	length_t origlen = inpkt->len;
 
 	if(n->incompression) {
-		outpkt = pkt[nextpkt++];
+		vpn_packet_t *outpkt = pkt[nextpkt++];
 
-		if((outpkt->len = uncompress_packet(outpkt->data, inpkt->data, inpkt->len, n->incompression)) < 0) {
+		if((outpkt->len = uncompress_packet(DATA(outpkt), DATA(inpkt), inpkt->len, n->incompression)) < 0) {
 			logger(DEBUG_TRAFFIC, LOG_ERR, "Error while uncompressing packet from %s (%s)",
 						 n->name, n->hostname);
-			return;
+			return false;
 		}
 
 		inpkt = outpkt;
@@ -434,16 +401,19 @@ static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
 
 	inpkt->priority = 0;
 
-	if(!inpkt->data[12] && !inpkt->data[13])
-		mtu_probe_h(n, inpkt, origlen);
+	if(!DATA(inpkt)[12] && !DATA(inpkt)[13])
+		udp_probe_h(n, inpkt, origlen);
 	else
 		receive_packet(n, inpkt);
+	return true;
+#endif
 }
 
 void receive_tcppacket(connection_t *c, const char *buffer, int len) {
 	vpn_packet_t outpkt;
+	outpkt.offset = DEFAULT_PACKET_OFFSET;
 
-	if(len > sizeof outpkt.data)
+	if(len > sizeof outpkt.data - outpkt.offset)
 		return;
 
 	outpkt.len = len;
@@ -451,30 +421,20 @@ void receive_tcppacket(connection_t *c, const char *buffer, int len) {
 		outpkt.priority = 0;
 	else
 		outpkt.priority = -1;
-	memcpy(outpkt.data, buffer, len);
+	memcpy(DATA(&outpkt), buffer, len);
 
 	receive_packet(c->node, &outpkt);
 }
 
 static void send_sptps_packet(node_t *n, vpn_packet_t *origpkt) {
-	if(!n->status.validkey) {
-		logger(DEBUG_TRAFFIC, LOG_INFO, "No valid key known yet for %s (%s)", n->name, n->hostname);
-		if(!n->status.waitingforkey)
-			send_req_key(n);
-		else if(n->last_req_key + 10 < now.tv_sec) {
-			logger(DEBUG_ALWAYS, LOG_DEBUG, "No key from %s after 10 seconds, restarting SPTPS", n->name);
-			sptps_stop(&n->sptps);
-			n->status.waitingforkey = false;
-			send_req_key(n);
-		}
+	if(!n->status.validkey && !n->connection)
 		return;
-	}
 
 	uint8_t type = 0;
 	int offset = 0;
 
-	if(!(origpkt->data[12] | origpkt->data[13])) {
-		sptps_send_record(&n->sptps, PKT_PROBE, (char *)origpkt->data, origpkt->len);
+	if(!(DATA(origpkt)[12] | DATA(origpkt)[13])) {
+		sptps_send_record(&n->sptps, PKT_PROBE, (char *)DATA(origpkt), origpkt->len);
 		return;
 	}
 
@@ -489,7 +449,8 @@ static void send_sptps_packet(node_t *n, vpn_packet_t *origpkt) {
 	vpn_packet_t outpkt;
 
 	if(n->outcompression) {
-		int len = compress_packet(outpkt.data + offset, origpkt->data + offset, origpkt->len - offset, n->outcompression);
+		outpkt.offset = 0;
+		int len = compress_packet(DATA(&outpkt) + offset, DATA(origpkt) + offset, origpkt->len - offset, n->outcompression);
 		if(len < 0) {
 			logger(DEBUG_TRAFFIC, LOG_ERR, "Error while compressing packet to %s (%s)", n->name, n->hostname);
 		} else if(len < origpkt->len - offset) {
@@ -499,10 +460,29 @@ static void send_sptps_packet(node_t *n, vpn_packet_t *origpkt) {
 		}
 	}
 
-	sptps_send_record(&n->sptps, type, (char *)origpkt->data + offset, origpkt->len - offset);
+	/* If we have a direct metaconnection to n, and we can't use UDP, then
+	   don't bother with SPTPS and just use a "plaintext" PACKET message.
+	   We don't really care about end-to-end security since we're not
+	   sending the message through any intermediate nodes. */
+	if(n->connection && origpkt->len > n->minmtu)
+		send_tcppacket(n->connection, origpkt);
+	else
+		sptps_send_record(&n->sptps, type, DATA(origpkt) + offset, origpkt->len - offset);
 	return;
 }
 
+static void adapt_socket(const sockaddr_t *sa, int *sock) {
+	/* Make sure we have a suitable socket for the chosen address */
+	if(listen_socket[*sock].sa.sa.sa_family != sa->sa.sa_family) {
+		for(int i = 0; i < listen_sockets; i++) {
+			if(listen_socket[i].sa.sa.sa_family == sa->sa.sa_family) {
+				*sock = i;
+				break;
+			}
+		}
+	}
+}
+
 static void choose_udp_address(const node_t *n, const sockaddr_t **sa, int *sock) {
 	/* Latest guess */
 	*sa = &n->address;
@@ -541,43 +521,29 @@ static void choose_udp_address(const node_t *n, const sockaddr_t **sa, int *sock
 		*sock = rand() % listen_sockets;
 	}
 
-	/* Make sure we have a suitable socket for the chosen address */
-	if(listen_socket[*sock].sa.sa.sa_family != (*sa)->sa.sa_family) {
-		for(int i = 0; i < listen_sockets; i++) {
-			if(listen_socket[i].sa.sa.sa_family == (*sa)->sa.sa_family) {
-				*sock = i;
-				break;
-			}
-		}
-	}
+	adapt_socket(*sa, sock);
 }
 
-static void choose_broadcast_address(const node_t *n, const sockaddr_t **sa, int *sock) {
-	static sockaddr_t broadcast_ipv4 = {
-		.in = {
-			.sin_family = AF_INET,
-			.sin_addr.s_addr = -1,
-		}
-	};
+static void choose_local_address(const node_t *n, const sockaddr_t **sa, int *sock) {
+	*sa = NULL;
 
-	static sockaddr_t broadcast_ipv6 = {
-		.in6 = {
-			.sin6_family = AF_INET6,
-			.sin6_addr.s6_addr[0x0] = 0xff,
-			.sin6_addr.s6_addr[0x1] = 0x02,
-			.sin6_addr.s6_addr[0xf] = 0x01,
-		}
-	};
+	/* Pick one of the edges from this node at random, then use its local address. */
 
-	*sock = rand() % listen_sockets;
+	int i = 0;
+	int j = rand() % n->edge_tree->count;
+	edge_t *candidate = NULL;
 
-	if(listen_socket[*sock].sa.sa.sa_family == AF_INET6) {
-		broadcast_ipv6.in6.sin6_port = n->prevedge->address.in.sin_port;
-		broadcast_ipv6.in6.sin6_scope_id = listen_socket[*sock].sa.in6.sin6_scope_id;
-		*sa = &broadcast_ipv6;
-	} else {
-		broadcast_ipv4.in.sin_port = n->prevedge->address.in.sin_port;
-		*sa = &broadcast_ipv4;
+	for splay_each(edge_t, e, n->edge_tree) {
+		if(i++ == j) {
+			candidate = e;
+			break;
+		}
+	}
+
+	if (candidate && candidate->local_address.sa.sa_family) {
+		*sa = &candidate->local_address;
+		*sock = rand() % listen_sockets;
+		adapt_socket(*sa, sock);
 	}
 }
 
@@ -591,8 +557,11 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 	size_t outlen;
 #if defined(SOL_IP) && defined(IP_TOS)
 	static int priority = 0;
-#endif
 	int origpriority = origpkt->priority;
+#endif
+
+	pkt1.offset = DEFAULT_PACKET_OFFSET;
+	pkt2.offset = DEFAULT_PACKET_OFFSET;
 
 	if(!n->status.reachable) {
 		logger(DEBUG_TRAFFIC, LOG_INFO, "Trying to send UDP packet to unreachable node %s (%s)", n->name, n->hostname);
@@ -602,24 +571,20 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 	if(n->status.sptps)
 		return send_sptps_packet(n, origpkt);
 
+#ifdef DISABLE_LEGACY
+	return;
+#else
 	/* Make sure we have a valid key */
 
 	if(!n->status.validkey) {
 		logger(DEBUG_TRAFFIC, LOG_INFO,
 				   "No valid key known yet for %s (%s), forwarding via TCP",
 				   n->name, n->hostname);
-
-		if(n->last_req_key + 10 <= now.tv_sec) {
-			send_req_key(n);
-			n->last_req_key = now.tv_sec;
-		}
-
 		send_tcppacket(n->nexthop->connection, origpkt);
-
 		return;
 	}
 
-	if(n->options & OPTION_PMTU_DISCOVERY && inpkt->len > n->minmtu && (inpkt->data[12] | inpkt->data[13])) {
+	if(n->options & OPTION_PMTU_DISCOVERY && inpkt->len > n->minmtu && (DATA(inpkt)[12] | DATA(inpkt)[13])) {
 		logger(DEBUG_TRAFFIC, LOG_INFO,
 				"Packet for %s (%s) larger than minimum MTU, forwarding via %s",
 				n->name, n->hostname, n != n->nexthop ? n->nexthop->name : "TCP");
@@ -637,7 +602,7 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 	if(n->outcompression) {
 		outpkt = pkt[nextpkt++];
 
-		if((outpkt->len = compress_packet(outpkt->data, inpkt->data, inpkt->len, n->outcompression)) < 0) {
+		if((outpkt->len = compress_packet(DATA(outpkt), DATA(inpkt), inpkt->len, n->outcompression)) < 0) {
 			logger(DEBUG_TRAFFIC, LOG_ERR, "Error while compressing packet to %s (%s)",
 				   n->name, n->hostname);
 			return;
@@ -648,8 +613,9 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 
 	/* Add sequence number */
 
-	inpkt->seqno = htonl(++(n->sent_seqno));
-	inpkt->len += sizeof inpkt->seqno;
+	seqno_t seqno = htonl(++(n->sent_seqno));
+	memcpy(SEQNO(inpkt), &seqno, sizeof seqno);
+	inpkt->len += sizeof seqno;
 
 	/* Encrypt the packet */
 
@@ -657,7 +623,7 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 		outpkt = pkt[nextpkt++];
 		outlen = MAXSIZE;
 
-		if(!cipher_encrypt(n->outcipher, &inpkt->seqno, inpkt->len, &outpkt->seqno, &outlen, true)) {
+		if(!cipher_encrypt(n->outcipher, SEQNO(inpkt), inpkt->len, SEQNO(outpkt), &outlen, true)) {
 			logger(DEBUG_TRAFFIC, LOG_ERR, "Error while encrypting packet to %s (%s)", n->name, n->hostname);
 			goto end;
 		}
@@ -669,20 +635,22 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 	/* Add the message authentication code */
 
 	if(digest_active(n->outdigest)) {
-		digest_create(n->outdigest, &inpkt->seqno, inpkt->len, (char *)&inpkt->seqno + inpkt->len);
+		if(!digest_create(n->outdigest, SEQNO(inpkt), inpkt->len, SEQNO(inpkt) + inpkt->len)) {
+			logger(DEBUG_TRAFFIC, LOG_ERR, "Error while encrypting packet to %s (%s)", n->name, n->hostname);
+			goto end;
+		}
+
 		inpkt->len += digest_length(n->outdigest);
 	}
 
 	/* Send the packet */
 
-	const sockaddr_t *sa;
+	const sockaddr_t *sa = NULL;
 	int sock;
 
-	/* Overloaded use of priority field: -1 means local broadcast */
-
-	if(origpriority == -1 && n->prevedge)
-		choose_broadcast_address(n, &sa, &sock);
-	else
+	if(n->status.send_locally)
+		choose_local_address(n, &sa, &sock);
+	if(!sa)
 		choose_udp_address(n, &sa, &sock);
 
 #if defined(SOL_IP) && defined(IP_TOS)
@@ -691,55 +659,84 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 		priority = origpriority;
 		logger(DEBUG_TRAFFIC, LOG_DEBUG, "Setting outgoing packet priority to %d", priority);
 		if(setsockopt(listen_socket[n->sock].udp.fd, SOL_IP, IP_TOS, &priority, sizeof(priority))) /* SO_PRIORITY doesn't seem to work */
-			logger(DEBUG_ALWAYS, LOG_ERR, "System call `%s' failed: %s", "setsockopt", strerror(errno));
+			logger(DEBUG_ALWAYS, LOG_ERR, "System call `%s' failed: %s", "setsockopt", sockstrerror(sockerrno));
 	}
 #endif
 
-	if(sendto(listen_socket[sock].udp.fd, (char *) &inpkt->seqno, inpkt->len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
+	if(sendto(listen_socket[sock].udp.fd, SEQNO(inpkt), inpkt->len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
 		if(sockmsgsize(sockerrno)) {
 			if(n->maxmtu >= origlen)
 				n->maxmtu = origlen - 1;
 			if(n->mtu >= origlen)
 				n->mtu = origlen - 1;
+			try_fix_mtu(n);
 		} else
 			logger(DEBUG_TRAFFIC, LOG_WARNING, "Error sending packet to %s (%s): %s", n->name, n->hostname, sockstrerror(sockerrno));
 	}
 
 end:
 	origpkt->len = origlen;
+#endif
 }
 
-bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
-	node_t *to = handle;
+static bool send_sptps_data_priv(node_t *to, node_t *from, int type, const void *data, size_t len) {
+	node_t *relay = (to->via != myself && (type == PKT_PROBE || (len - SPTPS_DATAGRAM_OVERHEAD) <= to->via->minmtu)) ? to->via : to->nexthop;
+	bool direct = from == myself && to == relay;
+	bool relay_supported = (relay->options >> 24) >= 4;
+	bool tcponly = (myself->options | relay->options) & OPTION_TCPONLY;
 
-	/* Send it via TCP if it is a handshake packet, TCPOnly is in use, or this packet is larger than the MTU. */
+	/* Send it via TCP if it is a handshake packet, TCPOnly is in use, this is a relay packet that the other node cannot understand, or this packet is larger than the MTU.
+	   TODO: When relaying, the original sender does not know the end-to-end PMTU (it only knows the PMTU of the first hop).
+	         This can lead to scenarios where large packets are sent over UDP to relay, but then relay has no choice but fall back to TCP. */
 
-	if(type >= SPTPS_HANDSHAKE || ((myself->options | to->options) & OPTION_TCPONLY) || (type != PKT_PROBE && len > to->minmtu)) {
+	if(type == SPTPS_HANDSHAKE || tcponly || (!direct && !relay_supported) || (type != PKT_PROBE && (len - SPTPS_DATAGRAM_OVERHEAD) > relay->minmtu)) {
 		char buf[len * 4 / 3 + 5];
 		b64encode(data, buf, len);
 		/* If no valid key is known yet, send the packets using ANS_KEY requests,
 		   to ensure we get to learn the reflexive UDP address. */
-		if(!to->status.validkey)
-			return send_request(to->nexthop->connection, "%d %s %s %s -1 -1 -1 %d", ANS_KEY, myself->name, to->name, buf, myself->incompression);
-		else
-			return send_request(to->nexthop->connection, "%d %s %s %d %s", REQ_KEY, myself->name, to->name, REQ_SPTPS, buf);
+		if(from == myself && !to->status.validkey) {
+			to->incompression = myself->incompression;
+			return send_request(to->nexthop->connection, "%d %s %s %s -1 -1 -1 %d", ANS_KEY, from->name, to->name, buf, to->incompression);
+		} else {
+			return send_request(to->nexthop->connection, "%d %s %s %d %s", REQ_KEY, from->name, to->name, REQ_SPTPS, buf);
+		}
 	}
 
-	/* Otherwise, send the packet via UDP */
-
-	const sockaddr_t *sa;
-	int sock;
+	size_t overhead = 0;
+	if(relay_supported) overhead += sizeof to->id + sizeof from->id;
+	char buf[len + overhead]; char* buf_ptr = buf;
+	if(relay_supported) {
+		if(direct) {
+			/* Inform the recipient that this packet was sent directly. */
+			node_id_t nullid = {};
+			memcpy(buf_ptr, &nullid, sizeof nullid); buf_ptr += sizeof nullid;
+		} else {
+			memcpy(buf_ptr, &to->id, sizeof to->id); buf_ptr += sizeof to->id;
+		}
+		memcpy(buf_ptr, &from->id, sizeof from->id); buf_ptr += sizeof from->id;
 
-	choose_udp_address(to, &sa, &sock);
+	}
+	/* TODO: if this copy turns out to be a performance concern, change sptps_send_record() to add some "pre-padding" to the buffer and use that instead */
+	memcpy(buf_ptr, data, len); buf_ptr += len;
 
-	if(sendto(listen_socket[sock].udp.fd, data, len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
+	const sockaddr_t *sa = NULL;
+	int sock;
+	if(relay->status.send_locally)
+		choose_local_address(relay, &sa, &sock);
+	if(!sa)
+		choose_udp_address(relay, &sa, &sock);
+	logger(DEBUG_TRAFFIC, LOG_INFO, "Sending packet from %s (%s) to %s (%s) via %s (%s)", from->name, from->hostname, to->name, to->hostname, relay->name, relay->hostname);
+	if(sendto(listen_socket[sock].udp.fd, buf, buf_ptr - buf, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
 		if(sockmsgsize(sockerrno)) {
-			if(to->maxmtu >= len)
-				to->maxmtu = len - 1;
-			if(to->mtu >= len)
-				to->mtu = len - 1;
+			// Compensate for SPTPS overhead
+			len -= SPTPS_DATAGRAM_OVERHEAD;
+			if(relay->maxmtu >= len)
+				relay->maxmtu = len - 1;
+			if(relay->mtu >= len)
+				relay->mtu = len - 1;
+			try_fix_mtu(relay);
 		} else {
-			logger(DEBUG_TRAFFIC, LOG_WARNING, "Error sending UDP SPTPS packet to %s (%s): %s", to->name, to->hostname, sockstrerror(sockerrno));
+			logger(DEBUG_TRAFFIC, LOG_WARNING, "Error sending UDP SPTPS packet to %s (%s): %s", relay->name, relay->hostname, sockstrerror(sockerrno));
 			return false;
 		}
 	}
@@ -747,7 +744,11 @@ bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
 	return true;
 }
 
-bool receive_sptps_record(void *handle, uint8_t type, const char *data, uint16_t len) {
+bool send_sptps_data(void *handle, uint8_t type, const void *data, size_t len) {
+	return send_sptps_data_priv(handle, myself, type, data, len);
+}
+
+bool receive_sptps_record(void *handle, uint8_t type, const void *data, uint16_t len) {
 	node_t *from = handle;
 
 	if(type == SPTPS_HANDSHAKE) {
@@ -765,11 +766,12 @@ bool receive_sptps_record(void *handle, uint8_t type, const char *data, uint16_t
 	}
 
 	vpn_packet_t inpkt;
+	inpkt.offset = DEFAULT_PACKET_OFFSET;
 
 	if(type == PKT_PROBE) {
 		inpkt.len = len;
-		memcpy(inpkt.data, data, len);
-		mtu_probe_h(from, &inpkt, len);
+		memcpy(DATA(&inpkt), data, len);
+		udp_probe_h(from, &inpkt, len);
 		return true;
 	}
 
@@ -788,7 +790,7 @@ bool receive_sptps_record(void *handle, uint8_t type, const char *data, uint16_t
 
 	int offset = (type & PKT_MAC) ? 0 : 14;
 	if(type & PKT_COMPRESSED) {
-		length_t ulen = uncompress_packet(inpkt.data + offset, (const uint8_t *)data, len, from->incompression);
+		length_t ulen = uncompress_packet(DATA(&inpkt) + offset, (const uint8_t *)data, len, from->incompression);
 		if(ulen < 0) {
 			return false;
 		} else {
@@ -797,25 +799,25 @@ bool receive_sptps_record(void *handle, uint8_t type, const char *data, uint16_t
 		if(inpkt.len > MAXSIZE)
 			abort();
 	} else {
-		memcpy(inpkt.data + offset, data, len);
+		memcpy(DATA(&inpkt) + offset, data, len);
 		inpkt.len = len + offset;
 	}
 
 	/* Generate the Ethernet packet type if necessary */
 	if(offset) {
-		switch(inpkt.data[14] >> 4) {
+		switch(DATA(&inpkt)[14] >> 4) {
 			case 4:
-				inpkt.data[12] = 0x08;
-				inpkt.data[13] = 0x00;
+				DATA(&inpkt)[12] = 0x08;
+				DATA(&inpkt)[13] = 0x00;
 				break;
 			case 6:
-				inpkt.data[12] = 0x86;
-				inpkt.data[13] = 0xDD;
+				DATA(&inpkt)[12] = 0x86;
+				DATA(&inpkt)[13] = 0xDD;
 				break;
 			default:
 				logger(DEBUG_TRAFFIC, LOG_ERR,
 						   "Unknown IP version %d while reading packet from %s (%s)",
-						   inpkt.data[14] >> 4, from->name, from->hostname);
+						   DATA(&inpkt)[14] >> 4, from->name, from->hostname);
 				return false;
 		}
 	}
@@ -824,6 +826,181 @@ bool receive_sptps_record(void *handle, uint8_t type, const char *data, uint16_t
 	return true;
 }
 
+// This function tries to get SPTPS keys, if they aren't already known.
+// This function makes no guarantees - it is up to the caller to check the node's state to figure out if the keys are available.
+static void try_sptps(node_t *n) {
+	if(n->status.validkey)
+		return;
+
+	logger(DEBUG_TRAFFIC, LOG_INFO, "No valid key known yet for %s (%s)", n->name, n->hostname);
+
+	if(!n->status.waitingforkey)
+		send_req_key(n);
+	else if(n->last_req_key + 10 < now.tv_sec) {
+		logger(DEBUG_ALWAYS, LOG_DEBUG, "No key from %s after 10 seconds, restarting SPTPS", n->name);
+		sptps_stop(&n->sptps);
+		n->status.waitingforkey = false;
+		send_req_key(n);
+	}
+
+	return;
+}
+
+static void send_udp_probe_packet(node_t *n, int len) {
+	vpn_packet_t packet;
+	packet.offset = DEFAULT_PACKET_OFFSET;
+	memset(DATA(&packet), 0, 14);
+	randomize(DATA(&packet) + 14, len - 14);
+	packet.len = len;
+	packet.priority = 0;
+
+	logger(DEBUG_TRAFFIC, LOG_INFO, "Sending UDP probe length %d to %s (%s)", len, n->name, n->hostname);
+
+	send_udppacket(n, &packet);
+}
+
+// This function tries to establish a UDP tunnel to a node so that packets can be sent.
+// If a tunnel is already established, it makes sure it stays up.
+// This function makes no guarantees - it is up to the caller to check the node's state to figure out if UDP is usable.
+static void try_udp(node_t* n) {
+	if(!udp_discovery)
+		return;
+
+	struct timeval now;
+	gettimeofday(&now, NULL);
+	struct timeval ping_tx_elapsed;
+	timersub(&now, &n->udp_ping_sent, &ping_tx_elapsed);
+
+	if(ping_tx_elapsed.tv_sec >= udp_discovery_interval) {
+		send_udp_probe_packet(n, MAX(n->minmtu, 16));
+		n->udp_ping_sent = now;
+
+		if(localdiscovery && !n->status.udp_confirmed && n->prevedge) {
+			n->status.send_locally = true;
+			send_udp_probe_packet(n, 16);
+			n->status.send_locally = false;
+		}
+	}
+}
+
+// This function tries to determines the MTU of a node.
+// By calling this function repeatedly, n->minmtu will be progressively increased, and at some point, n->mtu will be fixed to n->minmtu.
+// If the MTU is already fixed, this function checks if it can be increased.
+static void try_mtu(node_t *n) {
+	if(!(n->options & OPTION_PMTU_DISCOVERY))
+		return;
+
+	if(udp_discovery && !n->status.udp_confirmed) {
+		n->mtuprobes = 0;
+		n->minmtu = 0;
+		n->maxmtu = MTU;
+		return;
+	}
+
+	/* mtuprobes == 0..19: initial discovery, send bursts with 1 second interval, mtuprobes++
+	   mtuprobes ==    20: fix MTU, and go to -1
+	   mtuprobes ==    -1: send one >maxmtu probe every pingtimeout */
+
+	struct timeval now;
+	gettimeofday(&now, NULL);
+	struct timeval elapsed;
+	timersub(&now, &n->probe_sent_time, &elapsed);
+	if(n->mtuprobes >= 0) {
+		if(n->mtuprobes != 0 && elapsed.tv_sec == 0 && elapsed.tv_usec < 333333)
+			return;
+	} else {
+		if(elapsed.tv_sec < pingtimeout)
+			return;
+	}
+
+	try_fix_mtu(n);
+
+	int timeout;
+	if(n->mtuprobes < 0) {
+		/* After the initial discovery, we only send one >maxmtu probe
+		   to detect PMTU increases. */
+		if(n->maxmtu + 1 < MTU)
+			send_udp_probe_packet(n, n->maxmtu + 1);
+	} else {
+		/* Decreasing the number of probes per cycle might make the algorithm react faster to lost packets,
+		   but it will typically increase convergence time in the no-loss case. */
+		const length_t probes_per_cycle = 8;
+
+		/* This magic value was determined using math simulations.
+		   It will result in a 1329-byte first probe, followed (if there was a reply) by a 1407-byte probe.
+		   Since 1407 is just below the range of tinc MTUs over typical networks,
+		   this fine-tuning allows tinc to cover a lot of ground very quickly. */
+		const float multiplier = 0.97;
+
+		const float cycle_position = probes_per_cycle - (n->mtuprobes % probes_per_cycle) - 1;
+		const length_t minmtu = MAX(n->minmtu, 512);
+		const float interval = n->maxmtu - minmtu;
+
+		/* The core of the discovery algorithm is this exponential.
+		   It produces very large probes early in the cycle, and then it very quickly decreases the probe size.
+		   This reflects the fact that in the most difficult cases, we don't get any feedback for probes that
+		   are too large, and therefore we need to concentrate on small offsets so that we can quickly converge
+		   on the precise MTU as we are approaching it.
+		   The last probe of the cycle is always 1 byte in size - this is to make sure we'll get at least one
+		   reply per cycle so that we can make progress. */
+		const length_t offset = powf(interval, multiplier * cycle_position / (probes_per_cycle - 1));
+
+		send_udp_probe_packet(n, minmtu + offset);
+		if(n->mtuprobes >= 0)
+			n->mtuprobes++;
+	}
+
+	n->probe_counter = 0;
+	n->probe_sent_time = now;
+	n->probe_time = now;
+
+	/* Calculate the packet loss of incoming traffic by comparing the rate of
+	   packets received to the rate with which the sequence number has increased.
+	   TODO: this is unrelated to PMTU discovery - it should be moved elsewhere.
+	 */
+
+	if(n->received > n->prev_received)
+		n->packetloss = 1.0 - (n->received - n->prev_received) / (float)(n->received_seqno - n->prev_received_seqno);
+	else
+		n->packetloss = n->received_seqno <= n->prev_received_seqno;
+
+	n->prev_received_seqno = n->received_seqno;
+	n->prev_received = n->received;
+}
+
+// This function tries to establish a tunnel to a node (or its relay) so that packets can be sent (e.g. get SPTPS keys).
+// If a tunnel is already established, it tries to improve it (e.g. by trying to establish a UDP tunnel instead of TCP).
+// This function makes no guarantees - it is up to the caller to check the node's state to figure out if TCP and/or UDP is usable.
+// By calling this function repeatedly, the tunnel is gradually improved until we hit the wall imposed by the underlying network environment.
+// It is recommended to call this function every time a packet is sent (or intended to be sent) to a node,
+// so that the tunnel keeps improving as packets flow, and then gracefully downgrades itself as it goes idle.
+static void try_tx(node_t *n) {
+	/* If n is a TCP-only neighbor, we'll only use "cleartext" PACKET
+	   messages anyway, so there's no need for SPTPS at all. Otherwise, get the keys. */
+	if(n->status.sptps && !(n->connection && ((myself->options | n->options) & OPTION_TCPONLY))) {
+		try_sptps(n);
+		if (!n->status.validkey)
+			return;
+	}
+
+	node_t *via = (n->via == myself) ? n->nexthop : n->via;
+	
+	if((myself->options | via->options) & OPTION_TCPONLY)
+		return;
+
+	if(!n->status.sptps && !via->status.validkey && via->last_req_key + 10 <= now.tv_sec) {
+		send_req_key(via);
+		via->last_req_key = now.tv_sec;
+	} else if(via == n || !n->status.sptps || (via->options >> 24) >= 4) {
+		try_udp(via);
+		try_mtu(via);
+	}
+
+	/* If we don't know how to reach "via" yet, then try to reach it through a relay. */
+	if(n->status.sptps && !via->status.udp_confirmed && via->nexthop != via && (via->nexthop->options >> 24) >= 4)
+		try_tx(via->nexthop);
+}
+
 /*
   send a packet to the given vpn ip.
 */
@@ -832,7 +1009,7 @@ void send_packet(node_t *n, vpn_packet_t *packet) {
 
 	if(n == myself) {
 		if(overwrite_mac)
-			 memcpy(packet->data, mymac.x, ETH_ALEN);
+			 memcpy(DATA(packet), mymac.x, ETH_ALEN);
 		n->out_packets++;
 		n->out_bytes += packet->len;
 		devops.write(packet);
@@ -853,7 +1030,7 @@ void send_packet(node_t *n, vpn_packet_t *packet) {
 
 	if(n->status.sptps) {
 		send_sptps_packet(n, packet);
-		return;
+		goto end;
 	}
 
 	via = (packet->priority == -1 || n->via == myself) ? n->nexthop : n->via;
@@ -867,6 +1044,12 @@ void send_packet(node_t *n, vpn_packet_t *packet) {
 			terminate_connection(via->connection, true);
 	} else
 		send_udppacket(via, packet);
+
+end:
+	/* Try to improve the tunnel.
+	   Note that we do this *after* we send the packet because sending actual packets take priority
+	   with regard to the send buffer space and latency. */
+	try_tx(n);
 }
 
 /* Broadcast a packet using the minimum spanning tree */
@@ -890,7 +1073,7 @@ void broadcast_packet(const node_t *from, vpn_packet_t *packet) {
 		// usually distributes the sending of broadcast packets over all nodes.
 		case BMODE_MST:
 			for list_each(connection_t, c, connection_list)
-				if(c->status.active && c->status.mst && c != from->nexthop->connection)
+				if(c->edge && c->status.mst && c != from->nexthop->connection)
 					send_packet(c->node, packet);
 			break;
 
@@ -902,7 +1085,7 @@ void broadcast_packet(const node_t *from, vpn_packet_t *packet) {
 				break;
 
 			for splay_each(node_t, n, node_tree)
-				if(n->status.reachable && ((n->via == myself && n->nexthop == n) || n->via == n))
+				if(n->status.reachable && n != myself && ((n->via == myself && n->nexthop == n) || n->via == n))
 					send_packet(n, packet);
 			break;
 
@@ -944,12 +1127,14 @@ void handle_incoming_vpn_data(void *data, int flags) {
 	listen_socket_t *ls = data;
 	vpn_packet_t pkt;
 	char *hostname;
-	sockaddr_t from = {{0}};
-	socklen_t fromlen = sizeof from;
-	node_t *n;
-	int len;
+	node_id_t nullid = {};
+	sockaddr_t addr = {};
+	socklen_t addrlen = sizeof addr;
+	node_t *from, *to;
+	bool direct = false;
 
-	len = recvfrom(ls->udp.fd, (char *) &pkt.seqno, MAXSIZE, 0, &from.sa, &fromlen);
+	pkt.offset = 0;
+	int len = recvfrom(ls->udp.fd, DATA(&pkt), MAXSIZE, 0, &addr.sa, &addrlen);
 
 	if(len <= 0 || len > MAXSIZE) {
 		if(!sockwouldblock(sockerrno))
@@ -959,32 +1144,76 @@ void handle_incoming_vpn_data(void *data, int flags) {
 
 	pkt.len = len;
 
-	sockaddrunmap(&from); /* Some braindead IPv6 implementations do stupid things. */
+	sockaddrunmap(&addr); /* Some braindead IPv6 implementations do stupid things. */
+
+	// Try to figure out who sent this packet.
+
+	node_t *n = lookup_node_udp(&addr);
 
-	n = lookup_node_udp(&from);
+	if(!n) {
+		// It might be from a 1.1 node, which might have a source ID in the packet.
+		pkt.offset = 2 * sizeof(node_id_t);
+		from = lookup_node_id(SRCID(&pkt));
+		if(from && !memcmp(DSTID(&pkt), &nullid, sizeof nullid) && from->status.sptps) {
+			if(sptps_verify_datagram(&from->sptps, DATA(&pkt), pkt.len - 2 * sizeof(node_id_t)))
+				n = from;
+			else
+				goto skip_harder;
+		}
+	}
 
 	if(!n) {
-		n = try_harder(&from, &pkt);
-		if(n)
-			update_node_udp(n, &from);
-		else if(debug_level >= DEBUG_PROTOCOL) {
-			hostname = sockaddr2hostname(&from);
+		pkt.offset = 0;
+		n = try_harder(&addr, &pkt);
+	}
+
+skip_harder:
+	if(!n) {
+		if(debug_level >= DEBUG_PROTOCOL) {
+			hostname = sockaddr2hostname(&addr);
 			logger(DEBUG_PROTOCOL, LOG_WARNING, "Received UDP packet from unknown source %s", hostname);
 			free(hostname);
+		}
+		return;
+	}
+
+	if(n->status.sptps) {
+		pkt.offset = 2 * sizeof(node_id_t);
+
+		if(!memcmp(DSTID(&pkt), &nullid, sizeof nullid)) {
+			direct = true;
+			from = n;
+			to = myself;
+		} else {
+			from = lookup_node_id(SRCID(&pkt));
+			to = lookup_node_id(DSTID(&pkt));
+		}
+		if(!from || !to) {
+			logger(DEBUG_PROTOCOL, LOG_WARNING, "Received UDP packet from %s (%s) with unknown source and/or destination ID", n->name, n->hostname);
 			return;
 		}
-		else
+
+		if(to != myself) {
+			send_sptps_data_priv(to, n, 0, DATA(&pkt), pkt.len - 2 * sizeof(node_id_t));
 			return;
+		}
+	} else {
+		direct = true;
+		from = n;
 	}
 
-	n->sock = ls - listen_socket;
+	pkt.offset = 0;
+	if(!receive_udppacket(from, &pkt))
+		return;
 
-	receive_udppacket(n, &pkt);
+	n->sock = ls - listen_socket;
+	if(direct && sockaddrcmp(&addr, &n->address))
+		update_node_udp(n, &addr);
 }
 
 void handle_device_data(void *data, int flags) {
 	vpn_packet_t packet;
-
+	packet.offset = DEFAULT_PACKET_OFFSET;
 	packet.priority = 0;
 
 	if(devops.read(&packet)) {