Fixes a bug with neighbor cache and overlapping IP prefixes.

When there are overlapping IP prefixes and one disappears,
neighbors associated with it was removed even if there
is another covering IP prefix.

nest/neighbor.c

@@ -114,7 +114,7 @@ neighbor *
 neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags)
 {
   neighbor *n;
-  int class, scope = -1;       ;
+  int class, scope = -1;
   unsigned int h = neigh_hash(p, a);
   struct iface *i;
 
@@ -240,7 +240,21 @@ neigh_down(neighbor *n)
     n->proto->neigh_notify(n);
   rem_node(&n->n);
   if (n->flags & NEF_STICKY)
-    add_tail(&sticky_neigh_list, &n->n);
+    {
+      add_tail(&sticky_neigh_list, &n->n);
+
+      /* Respawn neighbor if there is another matching prefix */
+      struct iface *i;
+      int scope;
+
+      if (!n->iface)
+	WALK_LIST(i, iface_list)
+	  if ((scope = if_connected(&n->addr, i)) >= 0)
+	    {
+	      neigh_up(n, i, scope);
+	      return;
+	    }
+    }
   else
     sl_free(neigh_slab, n);
 }