Index: head/sys/net/if.c
===================================================================
--- head/sys/net/if.c
+++ head/sys/net/if.c
@@ -264,7 +264,6 @@
 static int	if_transmit(struct ifnet *ifp, struct mbuf *m);
 static void	if_unroute(struct ifnet *, int flag, int fam);
 static void	link_rtrequest(int, struct rtentry *, struct rt_addrinfo *);
-static int	ifhwioctl(u_long, struct ifnet *, caddr_t, struct thread *);
 static int	if_delmulti_locked(struct ifnet *, struct ifmultiaddr *, int);
 static void	do_link_state_change(void *, int);
 static int	if_getgroup(struct ifgroupreq *, struct ifnet *);
@@ -2512,7 +2511,7 @@
 /*
  * Hardware specific interface ioctls.
  */
-static int
+int
 ifhwioctl(u_long cmd, struct ifnet *ifp, caddr_t data, struct thread *td)
 {
 	struct ifreq *ifr;
Index: head/sys/net/if_tap.c
===================================================================
--- head/sys/net/if_tap.c
+++ head/sys/net/if_tap.c
@@ -723,10 +723,12 @@
 static int
 tapioctl(struct cdev *dev, u_long cmd, caddr_t data, int flag, struct thread *td)
 {
+	struct ifreq		 ifr;
 	struct tap_softc	*tp = dev->si_drv1;
 	struct ifnet		*ifp = tp->tap_ifp;
 	struct tapinfo		*tapp = NULL;
 	int			 f;
+	int			 error;
 #if defined(COMPAT_FREEBSD6) || defined(COMPAT_FREEBSD5) || \
     defined(COMPAT_FREEBSD4)
 	int			 ival;
@@ -738,7 +740,18 @@
 			if (ifp->if_type != tapp->type)
 				return (EPROTOTYPE);
 			mtx_lock(&tp->tap_mtx);
-			ifp->if_mtu = tapp->mtu;
+			if (ifp->if_mtu != tapp->mtu) {
+				strncpy(ifr.ifr_name, if_name(ifp), IFNAMSIZ);
+				ifr.ifr_mtu = tapp->mtu;
+				CURVNET_SET(ifp->if_vnet);
+				error = ifhwioctl(SIOCSIFMTU, ifp,
+				    (caddr_t)&ifr, td);
+				CURVNET_RESTORE();
+				if (error) {
+					mtx_unlock(&tp->tap_mtx);
+					return (error);
+				}
+			}
 			ifp->if_baudrate = tapp->baudrate;
 			mtx_unlock(&tp->tap_mtx);
 			break;
Index: head/sys/net/if_tun.c
===================================================================
--- head/sys/net/if_tun.c
+++ head/sys/net/if_tun.c
@@ -662,24 +662,29 @@
 tunioctl(struct cdev *dev, u_long cmd, caddr_t data, int flag,
     struct thread *td)
 {
-	int		error;
+	struct ifreq ifr;
 	struct tun_softc *tp = dev->si_drv1;
 	struct tuninfo *tunp;
+	int error;
 
 	switch (cmd) {
 	case TUNSIFINFO:
 		tunp = (struct tuninfo *)data;
-		if (tunp->mtu < IF_MINMTU)
-			return (EINVAL);
-		if (TUN2IFP(tp)->if_mtu != tunp->mtu) {
-			error = priv_check(td, PRIV_NET_SETIFMTU);
-			if (error)
-				return (error);
-		}
 		if (TUN2IFP(tp)->if_type != tunp->type)
 			return (EPROTOTYPE);
 		mtx_lock(&tp->tun_mtx);
-		TUN2IFP(tp)->if_mtu = tunp->mtu;
+		if (TUN2IFP(tp)->if_mtu != tunp->mtu) {
+			strncpy(ifr.ifr_name, if_name(TUN2IFP(tp)), IFNAMSIZ);
+			ifr.ifr_mtu = tunp->mtu;
+			CURVNET_SET(TUN2IFP(tp)->if_vnet);
+			error = ifhwioctl(SIOCSIFMTU, TUN2IFP(tp),
+			    (caddr_t)&ifr, td);
+			CURVNET_RESTORE();
+			if (error) {
+				mtx_unlock(&tp->tun_mtx);
+				return (error);
+			}
+		}
 		TUN2IFP(tp)->if_baudrate = tunp->baudrate;
 		mtx_unlock(&tp->tun_mtx);
 		break;
Index: head/sys/net/if_var.h
===================================================================
--- head/sys/net/if_var.h
+++ head/sys/net/if_var.h
@@ -760,6 +760,8 @@
 /* accessors for struct ifreq */
 void *ifr_data_get_ptr(void *ifrp);
 
+int ifhwioctl(u_long, struct ifnet *, caddr_t, struct thread *);
+
 #ifdef DEVICE_POLLING
 enum poll_cmd { POLL_ONLY, POLL_AND_CHECK_STATUS };