PR: 2755

Submitted by: Robin Seggelmann <seggelmann@fh-muenster.de>

Reduce MTU after failed transmissions.

ssl/d1_lib.c

@@ -424,6 +424,11 @@ int dtls1_handle_timeout(SSL *s)
 		state->timeout.read_timeouts = 1;
 		}
 
+	if (state->timeout_duration > 2)
+		{
+		s->d1->mtu = BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_GET_FALLBACK_MTU, 0, NULL);		
+		}
+
 #ifndef OPENSSL_NO_HEARTBEATS
 	if (s->tlsext_hb_pending)
 		{