From 1d7b86cd9d1421f67d3717a52a52635155a29829 Mon Sep 17 00:00:00 2001 From: Guus Sliepen Date: Thu, 31 Jan 2013 15:58:33 +0100 Subject: [PATCH] Detect increases in PMTU. Tinc never restarts PMTU discovery unless a node becomes unreachable. However, it can be that the PMTU was very low during the initial discovery, but has increased later. To detect this, tinc now tries to send an extra packet every PingInterval, with a size slightly higher than the currently known PMTU. If this packet is succesfully received back, we partially restart PMTU discovery to find out the new maximum. --- src/net_packet.c | 30 +++++++++++++++++++++++------- 1 file changed, 23 insertions(+), 7 deletions(-) diff --git a/src/net_packet.c b/src/net_packet.c index 2780f518..c2092480 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. + */ void send_mtu_probe(node_t *n) { @@ -126,11 +130,16 @@ void send_mtu_probe(node_t *n) { timeout = pingtimeout; } - for(i = 0; i < 3 + localdiscovery; i++) { - if(n->maxmtu <= n->minmtu) + 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 + } else { len = n->minmtu + 1 + rand() % (n->maxmtu - n->minmtu); + } if(len < 64) len = 64; @@ -138,7 +147,7 @@ void send_mtu_probe(node_t *n) { memset(packet.data, 0, 14); RAND_pseudo_bytes(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; @@ -164,6 +173,13 @@ void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) { 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 -- 2.20.1