diff --git a/waterutil/tap.go b/waterutil/tap.go
index d81da37..5ad78fd 100644
--- a/waterutil/tap.go
+++ b/waterutil/tap.go
@@ -38,3 +38,11 @@ func MACEthertype(macFrame []byte) Ethertype {
 func MACPayload(macFrame []byte) []byte {
 	return macFrame[12+MACTagging(macFrame)+2:]
 }
+
+func IsBroadcast(addr net.HardwareAddr) bool {
+	return addr[0] == 0xff && addr[1] == 0xff && addr[2] == 0xff && addr[3] == 0xff && addr[4] == 0xff && addr[5] == 0xff
+}
+
+func IsIPv4Multicast(addr net.HardwareAddr) bool {
+	return addr[0] == 0x01 && addr[1] == 0x00 && addr[2] == 0x5e
+}