--- Net2/netinet/ip.h	2018/04/24 18:03:54	1.1
+++ Net2/netinet/ip.h	2018/04/24 18:13:47	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)ip.h	7.10 (Berkeley) 6/28/90
+ *	from: @(#)ip.h	7.10 (Berkeley) 6/28/90
+ *	ip.h,v 1.3 1993/05/20 03:50:15 cgd Exp
  */
 
+#ifndef _NETINET_IP_H_
+#define _NETINET_IP_H_
+
 /*
  * Definitions for internet protocol version 4.
  * Per RFC 791, September 1981.
@@ -164,3 +168,5 @@ struct	ip_timestamp {
 #define	IPTTLDEC	1		/* subtracted when forwarding */
 
 #define	IP_MSS		576		/* default maximum segment size */
+
+#endif /* !_NETINET_IP_H_ */