add test for PMTU discovery and packet fragmentation

test/100_cross_hosts_2_test.sh

@@ -27,10 +27,4 @@ start_container $HOST2 net:$SUBNET_2 --name=c6
 C6=$(container_ip $HOST2 c6)
 assert_raises "exec_on $HOST1 c5 $PING $C6"
 
-# check large packets get through. The first attempt typically fails,
-# since the PMTU hasn't been discovered yet. The 2nd attempt should
-# succeed.
-exec_on $HOST1 c1 $PING -s 65000 $C2 2>&1 1>/dev/null || true
-assert_raises "exec_on $HOST1 c1 $PING -s 65000 $C2"
-
 end_suite

test/105_frag_2_test.sh

@@ -0,0 +1,30 @@
+#! /bin/bash
+
+. ./config.sh
+
+# 700 = Linux's minimum PMTU (552) + weave framing overheads
+# (currently about 60, but we leave some margin). That way the PMTUs
+# seen by containers is still >= 552.
+drop_large_udp_packets="FORWARD -p udp --destination-port 6783 -m length '!' --length 0:700 -j DROP"
+
+start_suite "PMTU discovery and packet fragmentation"
+
+run_on $HOST2 "sudo iptables -I $drop_large_udp_packets"
+
+weave_on $HOST1 launch
+weave_on $HOST2 launch $HOST1
+
+start_container $HOST1 --name=c1
+start_container $HOST2 --name=c2
+
+sleep 30 # give weave time to discover the PMTU
+
+# Check large packets get through. The first attempt typically fails,
+# since the sending container hasn't discovered the PMTU yet. The 2nd
+# attempt should succeed.
+exec_on $HOST2 c2 $PING -s 10000 c1 2>&1 1>/dev/null || true
+assert_raises "exec_on $HOST2 c2 $PING -s 10000 c1"
+
+run_on $HOST2 "sudo iptables -D $drop_large_udp_packets"
+
+end_suite