Add MTU_INFO protocol message.

[tinc] / src / net_packet.c

diff --git a/src/net_packet.c b/src/net_packet.c
index 40cb2ba..2e47df4 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -687,9 +687,7 @@ static bool send_sptps_data_priv(node_t *to, node_t *from, int type, const void
        bool relay_supported = (relay->options >> 24) >= 4;
        bool tcponly = (myself->options | relay->options) & OPTION_TCPONLY;
 
-       /* Send it via TCP if it is a handshake packet, TCPOnly is in use, this is a relay packet that the other node cannot understand, or this packet is larger than the MTU.
-          TODO: When relaying, the original sender does not know the end-to-end PMTU (it only knows the PMTU of the first hop).
-                This can lead to scenarios where large packets are sent over UDP to relay, but then relay has no choice but fall back to TCP. */
+       /* Send it via TCP if it is a handshake packet, TCPOnly is in use, this is a relay packet that the other node cannot understand, or this packet is larger than the MTU. */
 
        if(type == SPTPS_HANDSHAKE || tcponly || (!direct && !relay_supported) || (type != PKT_PROBE && (len - SPTPS_DATAGRAM_OVERHEAD) > relay->minmtu)) {
                char buf[len * 4 / 3 + 5];
@@ -1422,6 +1420,12 @@ skip_harder:
        n->sock = ls - listen_socket;
        if(direct && sockaddrcmp(&addr, &n->address))
                update_node_udp(n, &addr);
+
+       /* If the packet went through a relay, help the sender find the appropriate MTU
+          through the relay path. */
+
+       if(!direct)
+               send_mtu_info(myself, n, MTU);
 }
 
 void handle_device_data(void *data, int flags) {