--- kernel/bsd/net/if.c	2018/04/24 18:26:07	1.1
+++ kernel/bsd/net/if.c	2018/04/24 18:31:40	1.1.1.2
@@ -351,7 +351,8 @@ link_rtrequest(cmd, rt, sa)
 	if ((ifa = ifaof_ifpforaddr(dst, ifp))) {
 		IFAFREE(rt->rt_ifa);
 		rt->rt_ifa = ifa;
-		ifa->ifa_refcnt++;
+		if (++ifa->ifa_refcnt <= 0)
+			panic("link_rtrequest ifa_refcnt");
 		if (ifa->ifa_rtrequest && ifa->ifa_rtrequest != link_rtrequest)
 			ifa->ifa_rtrequest(cmd, rt, sa);
 	}