Don't send MTU probes smaller than 512 bytes.
[tinc] / src / net_packet.c
index 26e4907..626114c 100644 (file)
@@ -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>
 
 #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;
+               n->mtuprobes = -1;
        }
-
-       if(n->mtuprobes == 31) {
-               timeout = pinginterval;
-               goto end;
-       } else if(n->mtuprobes == 32) {
-               timeout = pingtimeout;
-       }
-
-       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);
                }
        }
 }
@@ -316,20 +257,25 @@ 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) {
                if(!n->sptps.state) {
@@ -339,43 +285,54 @@ static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
                        } else {
                                logger(DEBUG_TRAFFIC, LOG_DEBUG, "Got packet from %s (%s) but he hasn't got our key yet", n->name, n->hostname);
                        }
-                       return;
+                       return false;
                }
-               sptps_receive_data(&n->sptps, (char *)&inpkt->seqno, inpkt->len);
-               return;
+               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)) {
+#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;
+               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;
@@ -384,38 +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++;
 
@@ -427,12 +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;
@@ -442,16 +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;
@@ -459,30 +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;
        }
 
@@ -497,7 +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) {
@@ -507,10 +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;
@@ -549,43 +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);
        }
 }
 
@@ -599,8 +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);
@@ -610,24 +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");
@@ -645,7 +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;
@@ -656,8 +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 */
 
@@ -665,7 +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;
                }
@@ -677,7 +635,7 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
        /* Add the message authentication code */
 
        if(digest_active(n->outdigest)) {
-               if(!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;
                }
@@ -687,14 +645,12 @@ static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 
        /* 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)
@@ -703,55 +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;
                }
        }
@@ -759,7 +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) {
@@ -777,11 +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;
        }
 
@@ -800,7 +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 {
@@ -809,25 +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;
                }
        }
@@ -836,6 +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.
 */
@@ -844,7 +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);
@@ -865,7 +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;
@@ -879,6 +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 */
@@ -902,7 +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;
 
@@ -914,7 +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;
 
@@ -956,12 +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))
@@ -971,32 +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.
 
-       n = lookup_node_udp(&from);
+       node_t *n = lookup_node_udp(&addr);
 
        if(!n) {
-               n = try_harder(&from, &pkt);
-               if(n)
-                       update_node_udp(n, &from);
-               else if(debug_level >= DEBUG_PROTOCOL) {
-                       hostname = sockaddr2hostname(&from);
+               // 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) {
+               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)) {