Better address MTU issues.

Signed-off-by: Kurt Garloff <kurt@garloff.de>

Author: garloff

01-kind-cluster.sh

@@ -4,9 +4,12 @@ set -e
 DEV=$(ip route show default | head -n1 | sed 's/^.*dev \([^ ]*\).*$/\1/')
 CLOUDMTU=$(ip link show $DEV | head -n1 | sed 's/^.*mtu \([0-9]*\) .*$/\1/')
 DOCKERMTU=$(ip link show docker0 | head -n1 | sed 's/^.*mtu \([0-9]*\) .*$/\1/')
-if test $((DOCKERMTU+50)) -gt $CLOUDMTU; then
-	echo "WARNING: Consider ip link set dev docker0 mtu $((CLOUDMTU-50))"
-	echo "   ... and you may want to do the same for kind's bridge device br-*"
+if test $DOCKERMTU -gt $CLOUDMTU; then
+	echo "WARNING: Consider setting mtu to $((8*($CLOUDMTU/8))) in /etc/docker/daemon.json"
+	echo "  and restart docker and do docker network rm kind ..."
+	sudo ip link set dev docker0 mtu $((8*($CLOUDMTU/8)))
+	# Just in case ...
+	sudo sysctl net.ipv4.tcp_mtu_probing=1
 fi
 # Create kind cluster
 if test "$(kind get clusters)" != "kind"; then