+/* 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;
+ 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->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;
+ }
+
+ 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 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);
+
+ if(!packet->data[0]) {
+ /* It's a probe request, send back a reply */
+
+ packet->data[0] = 1;
+
+ /* Temporarily set udp_confirmed, so that the reply is sent
+ back exactly the way it came in. */
+
+ bool udp_confirmed = n->status.udp_confirmed;
+ n->status.udp_confirmed = true;
+ send_udppacket(n, packet);
+ n->status.udp_confirmed = udp_confirmed;
+ } else {
+ /* 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(n->minmtu)
+ n->mtuprobes = 30;
+ else
+ n->mtuprobes = 1;
+ }
+
+ /* If applicable, raise the minimum supported MTU */
+
+ if(len > n->maxmtu)
+ len = n->maxmtu;
+ if(n->minmtu < len)
+ n->minmtu = len;
+
+ /* Calculate RTT and bandwidth.
+ 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.
+ */
+
+ struct timeval now, diff;
+ gettimeofday(&now, NULL);
+ timersub(&now, &n->probe_time, &diff);
+ 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);
+ }
+ }
+}
+
+static length_t compress_packet(uint8_t *dest, const uint8_t *source, length_t len, int level) {
+ if(level == 0) {
+ memcpy(dest, source, len);
+ return len;
+ } else if(level == 10) {
+#ifdef HAVE_LZO
+ lzo_uint lzolen = MAXSIZE;
+ lzo1x_1_compress(source, len, dest, &lzolen, lzo_wrkmem);
+ return lzolen;
+#else
+ return -1;
+#endif
+ } else if(level < 10) {
+#ifdef HAVE_ZLIB
+ unsigned long destlen = MAXSIZE;
+ if(compress2(dest, &destlen, source, len, level) == Z_OK)
+ return destlen;
+ else
+#endif
+ return -1;
+ } else {
+#ifdef HAVE_LZO
+ lzo_uint lzolen = MAXSIZE;
+ lzo1x_999_compress(source, len, dest, &lzolen, lzo_wrkmem);
+ return lzolen;
+#else
+ return -1;
+#endif
+ }
+
+ return -1;
+}
+
+static length_t uncompress_packet(uint8_t *dest, const uint8_t *source, length_t len, int level) {
+ if(level == 0) {
+ memcpy(dest, source, len);
+ return len;
+ } else if(level > 9) {
+#ifdef HAVE_LZO
+ lzo_uint lzolen = MAXSIZE;
+ if(lzo1x_decompress_safe(source, len, dest, &lzolen, NULL) == LZO_E_OK)
+ return lzolen;
+ else
+#endif
+ return -1;
+ }
+#ifdef HAVE_ZLIB
+ else {
+ unsigned long destlen = MAXSIZE;
+ if(uncompress(dest, &destlen, source, len) == Z_OK)
+ return destlen;
+ else
+ return -1;
+ }
+#endif
+
+ return -1;
+}
+