diff --git a/sys/net/if.c b/sys/net/if.c
index c82aafc1f2c9..975bf780761d 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if.c	8.3 (Berkeley) 1/4/94
- * $Id$
+ * $Id: if.c,v 1.2 1994/08/02 07:46:05 davidg Exp $
  */
 
 #include <sys/param.h>
@@ -486,6 +486,10 @@ ifioctl(so, cmd, data, p)
 		ifr->ifr_metric = ifp->if_metric;
 		break;
 
+	case SIOCGIFMTU:
+		ifr->ifr_mtu = ifp->if_mtu;
+		break;
+
 	case SIOCSIFFLAGS:
 		if (error = suser(p->p_ucred, &p->p_acflag))
 			return (error);
@@ -511,6 +515,13 @@ ifioctl(so, cmd, data, p)
 		ifp->if_metric = ifr->ifr_metric;
 		break;
 
+	case SIOCSIFMTU:
+		if (error = suser(p->p_ucred, &p->p_acflag))
+			return (error);
+		if (ifp->if_ioctl == NULL)
+			return (EOPNOTSUPP);
+		return ((*ifp->if_ioctl)(ifp, cmd, data));
+
 	case SIOCADDMULTI:
 	case SIOCDELMULTI:
 		if (error = suser(p->p_ucred, &p->p_acflag))
diff --git a/sys/net/if.h b/sys/net/if.h
index b1b7de913abf..107d7e705a8c 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if.h	8.1 (Berkeley) 6/10/93
- * $Id$
+ * $Id: if.h,v 1.3 1994/08/02 07:46:07 davidg Exp $
  */
 
 /*
@@ -282,6 +282,7 @@ struct	ifreq {
 		struct	sockaddr ifru_broadaddr;
 		short	ifru_flags;
 		int	ifru_metric;
+		int	ifru_mtu;
 		caddr_t	ifru_data;
 	} ifr_ifru;
 #define	ifr_addr	ifr_ifru.ifru_addr	/* address */
@@ -289,6 +290,7 @@ struct	ifreq {
 #define	ifr_broadaddr	ifr_ifru.ifru_broadaddr	/* broadcast address */
 #define	ifr_flags	ifr_ifru.ifru_flags	/* flags */
 #define	ifr_metric	ifr_ifru.ifru_metric	/* metric */
+#define	ifr_mtu		ifr_ifru.ifru_mtu	/* mtu */
 #define	ifr_data	ifr_ifru.ifru_data	/* for use by interface */
 };
 
diff --git a/sys/sys/sockio.h b/sys/sys/sockio.h
index ab696b1675c9..b253044fc0d1 100644
--- a/sys/sys/sockio.h
+++ b/sys/sys/sockio.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)sockio.h	8.1 (Berkeley) 3/28/94
- * $Id$
+ * $Id: sockio.h,v 1.2 1994/08/02 07:53:37 davidg Exp $
  */
 
 #ifndef	_SYS_SOCKIO_H_
@@ -74,5 +74,7 @@
 
 #define	SIOCADDMULTI	 _IOW('i', 49, struct ifreq)	/* add m'cast addr */
 #define	SIOCDELMULTI	 _IOW('i', 50, struct ifreq)	/* del m'cast addr */
+#define SIOCGIFMTU	_IOWR('i', 51, struct ifreq)	/* get IF mtu */
+#define SIOCSIFMTU	 _IOW('i', 52, struct ifreq)	/* set IF mtu */
 
 #endif /* !_SYS_SOCKIO_H_ */