+/* this is a portability hack */
+#ifndef IPV6_ADD_MEMBERSHIP
+#ifdef IPV6_JOIN_GROUP
+#define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
+#endif
+#endif
+
+#ifndef IPV6_DROP_MEMBERSHIP
+#ifdef IPV6_LEAVE_GROUP
+#define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
+#endif
+#endif
+