--- Net2/netinet/in.h	2018/04/24 18:03:54	1.1
+++ Net2/netinet/in.h	2018/04/24 18:13:53	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)in.h	7.11 (Berkeley) 4/20/91
+ *	from: @(#)in.h	7.11 (Berkeley) 4/20/91
+ *	in.h,v 1.3 1993/05/20 03:50:02 cgd Exp
  */
 
+#ifndef _NETINET_IN_H_
+#define _NETINET_IN_H_
+
 /*
  * Constants and structures defined by the internet system,
  * Per RFC 790, September 1981.
@@ -149,3 +153,5 @@ struct ip_opts {
 struct	in_addr in_makeaddr();
 u_long	in_netof(), in_lnaof();
 #endif
+
+#endif /* !_NETINET_IN_H_ */