--- Net2/net/if_dl.h	2018/04/24 18:04:02	1.1.1.1
+++ Net2/net/if_dl.h	2018/04/24 18:21:47	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)if_dl.h	7.2 (Berkeley) 2/22/91
+ *	from: @(#)if_dl.h	7.2 (Berkeley) 2/22/91
+ *	if_dl.h,v 1.3 1993/05/20 03:05:58 cgd Exp
  */
 
+#ifndef _NET_IF_DL_H_
+#define _NET_IF_DL_H_
+
 /* 
  * A Link-Level Sockaddr may specify the interface in one of two
  * ways: either by means of a system-provided index number (computed
@@ -78,3 +82,5 @@ char	*link_ntoa __P((const struct sockad
 __END_DECLS
 
 #endif /* !KERNEL */
+
+#endif /* !_NET_IF_DL_H_ */