diff --git a/sys/net/if.c b/sys/net/if.c
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -1289,6 +1289,11 @@
 	if (rc != 0)
 		return (rc);
 
+	/*
+	 * Release old unit number or accquire a new one.
+	 */
+	ifc_reassign_unit_vnet(ifp, new_vnet);
+
 	/*
 	 * Perform interface-specific reassignment tasks, if provided by
 	 * the driver.
@@ -2762,12 +2767,21 @@
 		 * ifunit() checks not being atomic with namespace
 		 * changes (renames, vmoves, if_attach, etc).
 		 */
+		/* FIXME atomic bit flag */
+		if (ifp->if_flags & IFF_RENAMING)
+			return (EBUSY);
 		ifp->if_flags |= IFF_RENAMING;
-		
+
 		EVENTHANDLER_INVOKE(ifnet_departure_event, ifp);
 
 		if_printf(ifp, "changing name to '%s'\n", new_name);
 
+		if ((error = ifc_reassign_unit(ifp, new_name)) != 0) {
+			EVENTHANDLER_INVOKE(ifnet_arrival_event, ifp);
+
+			ifp->if_flags &= ~IFF_RENAMING;
+			return (error);
+		}
 		IF_ADDR_WLOCK(ifp);
 		strlcpy(old_name, ifp->if_xname, sizeof(old_name));
 		strlcpy(ifp->if_xname, new_name, sizeof(ifp->if_xname));
diff --git a/sys/net/if_clone.h b/sys/net/if_clone.h
--- a/sys/net/if_clone.h
+++ b/sys/net/if_clone.h
@@ -119,6 +119,8 @@
 int	if_clone_destroy(const char *);
 int	if_clone_list(struct if_clonereq *);
 void	if_clone_restoregroup(struct ifnet *);
+int	ifc_reassign_unit(struct ifnet *, char *);
+void	ifc_reassign_unit_vnet(struct ifnet *, struct vnet *);
 
 /* The below interfaces are used only by epair(4). */
 void	if_clone_addif(struct if_clone *, struct ifnet *);
diff --git a/sys/net/if_clone.c b/sys/net/if_clone.c
--- a/sys/net/if_clone.c
+++ b/sys/net/if_clone.c
@@ -381,8 +381,11 @@
 
 	if (err != 0)
 		ifc_link_ifp(ifc, ifp);
-	else if (ifc->ifc_flags & IFC_F_AUTOUNIT)
-		ifc_free_unit(ifc, unit);
+	else if (ifc->ifc_flags & IFC_F_AUTOUNIT) {
+		if (unit != IF_DUNIT_NONE)
+			free_unr(ifc->ifc_unrhdr, unit);
+		IF_CLONE_REMREF(ifc);
+	}
 	CURVNET_RESTORE();
 	return (err);
 }
@@ -517,7 +520,9 @@
 static int
 ifc_simple_destroy_wrapper(struct if_clone *ifc, struct ifnet *ifp, uint32_t flags)
 {
-	if (ifp->if_dunit < ifc->ifcs_minifs && (flags & IFC_F_FORCE) == 0)
+	if (ifp->if_dunit != IF_DUNIT_NONE &&
+	    ifp->if_dunit < ifc->ifcs_minifs &&
+	    (flags & IFC_F_FORCE) == 0)
 		return (EINVAL);
 
 	ifc->ifcs_destroy(ifp);
@@ -781,6 +786,7 @@
 ifc_free_unit(struct if_clone *ifc, int unit)
 {
 
+	KASSERT(unit != IF_DUNIT_NONE, ("Invalid unit"));
 	free_unr(ifc->ifc_unrhdr, unit);
 	IF_CLONE_REMREF(ifc);
 }
@@ -872,3 +878,86 @@
 {
 	return (ifc->ifc_flags);
 }
+
+/*
+ * Reassign unit number from new name.
+ */
+int
+ifc_reassign_unit(struct ifnet *ifp, char *new_name)
+{
+	struct if_clone *ifc, *nifc;
+
+	KASSERT(new_name[0] != '\0', ("Invalid interface name"));
+
+	if (ifp->if_vnet != ifp->if_home_vnet)
+		return (0);
+	/* XXX lock cloners ??? */
+	ifc = ifc_find_cloner_in_vnet(ifp->if_dname, ifp->if_home_vnet);
+	/* Physical interfaces do not have cloner */
+	if (ifc == NULL || (ifc->ifc_flags & IFC_F_AUTOUNIT) == 0)
+		return (0);
+
+	CURVNET_SET_QUIET(ifp->if_home_vnet);
+	nifc = ifc_find_cloner_match(new_name);
+	CURVNET_RESTORE();
+	if (nifc == ifc) {
+		int unit = -1;
+		ifc_name2unit(new_name, &unit);
+		if (unit >= 0) {
+			if (unit > ifc->ifc_maxunit)
+				return (ENOSPC);
+			if (alloc_unr_specific(ifc->ifc_unrhdr, unit) == -1)
+				return (EEXIST);
+			if (ifp->if_dunit != IF_DUNIT_NONE)
+				free_unr(ifc->ifc_unrhdr, ifp->if_dunit);
+			/* FIXME need lock ??? */
+			ifp->if_dunit = unit;
+			return (0);
+		}
+	}
+	if (ifp->if_dunit != IF_DUNIT_NONE) {
+		free_unr(ifc->ifc_unrhdr, ifp->if_dunit);
+		/* FIXME need lock ??? */
+		ifp->if_dunit = IF_DUNIT_NONE;
+	}
+	return (0);
+}
+
+void
+ifc_reassign_unit_vnet(struct ifnet *ifp, struct vnet *new_vnet)
+{
+	struct if_clone *ifc;
+	KASSERT(ifp->if_vnet != new_vnet, ("Require different vnet"));
+
+	ifc = ifc_find_cloner_in_vnet(ifp->if_dname, ifp->if_home_vnet);
+	if (ifc == NULL || (ifc->ifc_flags & IFC_F_AUTOUNIT) == 0)
+		return;
+
+	if (new_vnet != ifp->if_home_vnet) {
+		if (ifp->if_vnet == ifp->if_home_vnet &&
+		    ifp->if_dunit != IF_DUNIT_NONE) {
+			free_unr(ifc->ifc_unrhdr, ifp->if_dunit);
+			/* FIXME need lock ??? */
+			ifp->if_dunit = IF_DUNIT_NONE;
+		}
+	} else {
+		KASSERT(ifp->if_dunit == IF_DUNIT_NONE, ("Unit number is not released"));
+
+		struct if_clone *nifc;
+		CURVNET_SET_QUIET(ifp->if_home_vnet);
+		nifc = ifc_find_cloner_match(ifp->if_xname);
+		CURVNET_RESTORE();
+		if (nifc != ifc)
+			return;
+
+		int unit = -1;
+		ifc_name2unit(ifp->if_xname, &unit);
+		if (unit < 0 || unit > ifc->ifc_maxunit)
+			return;
+		if (alloc_unr_specific(ifc->ifc_unrhdr, unit) == -1)
+			return;
+
+		/* FIXME need lock ??? */
+		ifp->if_dunit = unit;
+	}
+}