X-Git-Url: https://www.tinc-vpn.org/git/browse?a=blobdiff_plain;f=src%2Fnet_packet.c;h=db571ba3830c3846e922afdf0bea5703f19509e7;hb=42b222ecb66b1957d7b439e5d8be8b287aef0054;hp=c034f852e604d39ec7fcb114c3804d703c7c66b8;hpb=87416bcd8bd3e8816750150e2dbe90a970400a00;p=tinc

diff --git a/src/net_packet.c b/src/net_packet.c
index c034f852..db571ba3 100644
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -70,11 +70,15 @@ bool localdiscovery = false;
    mtuprobes ==    32: send 1 burst, sleep pingtimeout second
    mtuprobes ==    33: no response from other side, restart PMTU discovery process
 
-   Probes are sent in batches of three, with random sizes between the lower and
-   upper boundaries for the MTU thus far discovered.
+   Probes are sent in batches of at least three, with random sizes between the
+   lower and upper boundaries for the MTU thus far discovered.
 
-   In case local discovery is enabled, a fourth packet is added to each batch,
+   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) {
@@ -125,13 +129,18 @@ static void send_mtu_probe_handler(void *data) {
 		timeout = pingtimeout;
 	}
 
-	for(int i = 0; i < 3 + localdiscovery; i++) {
+	for(int i = 0; i < 4 + localdiscovery; i++) {
 		int len;
 
-		if(n->maxmtu <= n->minmtu)
+		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
+		} else {
 			len = n->minmtu + 1 + rand() % (n->maxmtu - n->minmtu);
+		}
 
 		if(len < 64)
 			len = 64;
@@ -140,7 +149,7 @@ static void send_mtu_probe_handler(void *data) {
 		memset(packet.data, 0, 14);
 		randomize(packet.data + 14, len - 14);
 		packet.len = len;
-		if(i >= 3 && n->mtuprobes <= 10)
+		if(i >= 4 && n->mtuprobes <= 10)
 			packet.priority = -1;
 		else
 			packet.priority = 0;
@@ -199,6 +208,13 @@ static void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
 		/* 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