--- Net2/net/if_arp.h	2018/04/24 18:04:02	1.1.1.1
+++ Net2/net/if_arp.h	2018/04/24 18:21:50	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_arp.h	7.4 (Berkeley) 6/28/90
+ *	from: @(#)if_arp.h	7.4 (Berkeley) 6/28/90
+ *	if_arp.h,v 1.3 1993/05/20 03:05:57 cgd Exp
  */
 
+#ifndef _NET_IF_ARP_H_
+#define _NET_IF_ARP_H_
+
 /*
  * Address Resolution Protocol.
  *
@@ -76,3 +80,5 @@ struct arpreq {
 #define	ATF_PERM	0x04	/* permanent entry */
 #define	ATF_PUBL	0x08	/* publish entry (respond for other host) */
 #define	ATF_USETRAILERS	0x10	/* has requested trailers */
+
+#endif /* !_NET_IF_ARP_H_ */