+/* 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.
+
+*/
+
+void send_mtu_probe(node_t *n) {
+ vpn_packet_t packet;
+ int len, i;
+ int timeout = 1;
+
+ n->mtuprobes++;
+ n->mtuevent = NULL;
+
+ if(!n->status.reachable || !n->status.validkey) {
+ ifdebug(TRAFFIC) logger(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;
+ }
+
+ ifdebug(TRAFFIC) logger(LOG_INFO, "%s (%s) did not respond to UDP ping, restarting PMTU discovery", n->name, n->hostname);
+ n->mtuprobes = 1;
+ n->minmtu = 0;
+ n->maxmtu = MTU;
+ }
+
+ if(n->mtuprobes >= 10 && n->mtuprobes < 32 && !n->minmtu) {
+ ifdebug(TRAFFIC) logger(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;
+ ifdebug(TRAFFIC) logger(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(i = 0; i < 4 + localdiscovery; i++) {
+ 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;
+
+ memset(packet.data, 0, 14);
+ RAND_bytes(packet.data + 14, len - 14);
+ packet.len = len;
+ if(i >= 4 && n->mtuprobes <= 10)
+ packet.priority = -1;
+ else
+ packet.priority = 0;
+
+ ifdebug(TRAFFIC) logger(LOG_INFO, "Sending MTU probe length %d to %s (%s)", len, n->name, n->hostname);
+
+ send_udppacket(n, &packet);
+ }
+
+end:
+ n->mtuevent = new_event();
+ n->mtuevent->handler = (event_handler_t)send_mtu_probe;
+ n->mtuevent->data = n;
+ n->mtuevent->time = now + timeout;
+ event_add(n->mtuevent);
+}
+
+void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
+ ifdebug(TRAFFIC) logger(LOG_INFO, "Got MTU probe length %d from %s (%s)", packet->len, n->name, n->hostname);
+
+ if(!packet->data[0]) {
+ packet->data[0] = 1;
+ send_udppacket(n, packet);
+ } else {
+ if(n->mtuprobes > 30) {
+ if (len == n->maxmtu + 8) {
+ ifdebug(TRAFFIC) logger(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(len > n->maxmtu)
+ len = n->maxmtu;
+ if(n->minmtu < len)
+ n->minmtu = len;
+ }
+}
+
+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