handle environments without direct connectivity

Change-Id: I62dc89af231745b9af61a8f071734e6f02804c44

cmd/kindnetd/routes.go

@@ -26,7 +26,24 @@ import (
 
 func syncRoute(nodeIP string, podCIDRs []string) error {
 	ip := net.ParseIP(nodeIP)
-
+	mask := net.CIDRMask(32, 32)
+	if ip.To4() == nil {
+		mask = net.CIDRMask(128, 128)
+	}
+	// check if nodeIP is reachable, this happens when nodes are in the same l2 domain
+	// Environments like GCE implement IP alias, and assign /24 to the VMs so there is
+	// no l2 domain for the instances, and the traffic is handled by the underneath SDN
+	routeToNode := netlink.Route{Dst: &net.IPNet{IP: ip, Mask: mask}}
+	routes, err := netlink.RouteListFiltered(nl.GetIPFamily(ip), &routeToNode, netlink.RT_FILTER_DST)
+	if err != nil {
+		return err
+	}
+	for _, route := range routes {
+		if route.Gw != nil {
+			klog.Infof("Route to Node %s via %s, no direct routing needed, if pods can not communicate please configure your router correctly", ip, route.Gw.String())
+			return nil
+		}
+	}
 	for _, podCIDR := range podCIDRs {
 		// parse subnet
 		dst, err := netlink.ParseIPNet(podCIDR)