diff --git a/ospfd/ospf_interface.h b/ospfd/ospf_interface.h
index 60ee165..ca22c1a 100644
--- a/ospfd/ospf_interface.h
+++ b/ospfd/ospf_interface.h
@@ -44,7 +44,7 @@
   DECLARE_IF_PARAM (u_int32_t, transmit_delay); /* Interface Transmisson Delay */
   DECLARE_IF_PARAM (u_int32_t, output_cost_cmd);/* Command Interface Output Cost */
   DECLARE_IF_PARAM (u_int32_t, retransmit_interval); /* Retransmission Interval */
-  DECLARE_IF_PARAM (u_char, passive_interface);      /* OSPF Interface is passive */
+  DECLARE_IF_PARAM (u_char, passive_interface);      /* OSPF Interface is passive: no sending or receiving (no need to join multicast groups) */
   DECLARE_IF_PARAM (u_char, priority);               /* OSPF Interface priority */
   DECLARE_IF_PARAM (u_char, type);                   /* type of interface */
 #define OSPF_IF_ACTIVE                  0
@@ -126,6 +126,11 @@
   struct prefix *address;		/* Interface prefix */
   struct connected *connected;          /* Pointer to connected */ 
 
+  /* To which multicast groups do we currently belong? */
+  u_char multicast_memberships;
+#define MEMBER_ALLROUTERS	0x1
+#define MEMBER_DROUTERS		0x2
+
   /* Configured varables. */
   struct ospf_if_params *params;
   u_int32_t crypt_seqnum;		/* Cryptographic Sequence Number */ 
@@ -248,4 +253,8 @@
 
 u_char ospf_default_iftype(struct interface *ifp);
 
+/* Set all multicast memberships appropriately based on the type and
+   state of the interface. */
+extern void ospf_if_set_multicast(struct ospf_interface *);
+
 #endif /* _ZEBRA_OSPF_INTERFACE_H */