func isLocalNetwork(ip net.IP) bool {
	if classA.Contains(ip) {
		return true
	}
	if classB.Contains(ip) {
		return true
	}
	if classC.Contains(ip) {
		return true
	}
	if ip.IsLinkLocalUnicast() {
		return true
	}
	if ip.IsLoopback() {
		return true
	}
	return false
}
func isLocalNetwork(ip net.IP) bool {
	if classA.Contains(ip) {
		return true
	}
	if classB.Contains(ip) {
		return true
	}
	if classC.Contains(ip) {
		return true
	}
	if ip.IsLinkLocalUnicast() {
		return true
	}
	if ip.IsLoopback() {
		return true
	}
	return false
}
// Per http://www.libtorrent.org/dht_sec.html#enforcement, the IP is
// considered a local network address and should be exempted from node ID
// verification.