Fine-tune the MTU discovery multiplier for the maxmtu < MTU case.

[tinc] / src / net_packet.c

diff --git a/src/net_packet.c b/src/net_packet.c
index 34bdd26..84d4915 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -998,8 +998,11 @@ static void try_mtu(node_t *n) {
                /* 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;
+                  this fine-tuning allows tinc to cover a lot of ground very quickly.
+                  This fine-tuning is only valid for maxmtu = MTU; if maxmtu is smaller,
+                  then it's better to use a multiplier of 1. Indeed, this leads to an interesting scenario
+                  if choose_initial_maxmtu() returns the actual MTU value - it will get confirmed with one single probe. */
+               const float multiplier = (n->maxmtu == MTU) ? 0.97 : 1;
 
                const float cycle_position = probes_per_cycle - (n->mtuprobes % probes_per_cycle) - 1;
                const length_t minmtu = MAX(n->minmtu, 512);