diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index f884c039b52..c40928f75af 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -135,6 +135,14 @@ __FBSDID("$FreeBSD$");
 
 #include <net/route.h>
 
+#ifdef INET6
+/*
+ * XXX: declare here to avoid to include many inet6 related files..
+ * should be more generalized?
+ */
+extern void	nd6_setmtu(struct ifnet *);
+#endif
+
 /*
  * Size of the route hash table.  Must be a power of two.
  */
@@ -772,7 +780,7 @@ bridge_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	} args;
 	struct ifdrv *ifd = (struct ifdrv *) data;
 	const struct bridge_control *bc;
-	int error = 0;
+	int error = 0, oldmtu;
 
 	switch (cmd) {
 
@@ -818,12 +826,24 @@ bridge_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 				break;
 		}
 
+		oldmtu = ifp->if_mtu;
 		BRIDGE_LOCK(sc);
 		error = (*bc->bc_func)(sc, &args);
 		BRIDGE_UNLOCK(sc);
 		if (error)
 			break;
 
+		/*
+		 * Bridge MTU may change during addition of the first port.
+		 * If it did, do network layer specific procedure.
+		 */
+		if (ifp->if_mtu != oldmtu) {
+#ifdef INET6
+			nd6_setmtu(ifp);
+#endif
+			rt_updatemtu(ifp);
+		}
+
 		if (bc->bc_flags & BC_F_COPYOUT)
 			error = copyout(&args, ifd->ifd_data, ifd->ifd_len);
 
diff --git a/sys/net/if_lagg.c b/sys/net/if_lagg.c
index 174fd4479d8..d38f772f689 100644
--- a/sys/net/if_lagg.c
+++ b/sys/net/if_lagg.c
@@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
 #include <net/if_types.h>
 #include <net/if_var.h>
 #include <net/bpf.h>
+#include <net/route.h>
 #include <net/vnet.h>
 
 #if defined(INET) || defined(INET6)
@@ -74,6 +75,14 @@ __FBSDID("$FreeBSD$");
 #include <net/if_lagg.h>
 #include <net/ieee8023ad_lacp.h>
 
+#ifdef INET6
+/*
+ * XXX: declare here to avoid to include many inet6 related files..
+ * should be more generalized?
+ */
+extern void	nd6_setmtu(struct ifnet *);
+#endif
+
 #define	LAGG_RLOCK()	struct epoch_tracker lagg_et; epoch_enter_preempt(net_epoch_preempt, &lagg_et)
 #define	LAGG_RUNLOCK()	epoch_exit_preempt(net_epoch_preempt, &lagg_et)
 #define	LAGG_RLOCK_ASSERT()	NET_EPOCH_ASSERT()
@@ -1178,7 +1187,7 @@ lagg_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	struct ifnet *tpif;
 	struct thread *td = curthread;
 	char *buf, *outbuf;
-	int count, buflen, len, error = 0;
+	int count, buflen, len, error = 0, oldmtu;
 
 	bzero(&rpbuf, sizeof(rpbuf));
 
@@ -1453,10 +1462,23 @@ lagg_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 				    tpif->if_xname);
 		}
 #endif
+		oldmtu = ifp->if_mtu;
 		LAGG_XLOCK(sc);
 		error = lagg_port_create(sc, tpif);
 		LAGG_XUNLOCK(sc);
 		if_rele(tpif);
+
+		/*
+		 * LAGG MTU may change during addition of the first port.
+		 * If it did, do network layer specific procedure.
+		 */
+		if (ifp->if_mtu != oldmtu) {
+#ifdef INET6
+			nd6_setmtu(ifp);
+#endif
+			rt_updatemtu(ifp);
+		}
+
 		VLAN_CAPABILITIES(ifp);
 		break;
 	case SIOCSLAGGDELPORT:
diff --git a/sys/net/if_vlan.c b/sys/net/if_vlan.c
index 88844b0e848..a9ab3f85018 100644
--- a/sys/net/if_vlan.c
+++ b/sys/net/if_vlan.c
@@ -46,6 +46,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_inet.h"
+#include "opt_inet6.h"
 #include "opt_kern_tls.h"
 #include "opt_vlan.h"
 #include "opt_ratelimit.h"
@@ -75,6 +76,7 @@ __FBSDID("$FreeBSD$");
 #include <net/if_dl.h>
 #include <net/if_types.h>
 #include <net/if_vlan_var.h>
+#include <net/route.h>
 #include <net/vnet.h>
 
 #ifdef INET
@@ -82,6 +84,14 @@ __FBSDID("$FreeBSD$");
 #include <netinet/if_ether.h>
 #endif
 
+#ifdef INET6
+/*
+ * XXX: declare here to avoid to include many inet6 related files..
+ * should be more generalized?
+ */
+extern void	nd6_setmtu(struct ifnet *);
+#endif
+
 #define	VLAN_DEF_HWIDTH	4
 #define	VLAN_IFFLAGS	(IFF_BROADCAST | IFF_MULTICAST)
 
@@ -1807,7 +1817,7 @@ vlan_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	struct ifvlan *ifv;
 	struct ifvlantrunk *trunk;
 	struct vlanreq vlr;
-	int error = 0;
+	int error = 0, oldmtu;
 
 	ifr = (struct ifreq *)data;
 	ifa = (struct ifaddr *) data;
@@ -1901,8 +1911,20 @@ vlan_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 			error = ENOENT;
 			break;
 		}
+		oldmtu = ifp->if_mtu;
 		error = vlan_config(ifv, p, vlr.vlr_tag);
 		if_rele(p);
+
+		/*
+		 * VLAN MTU may change during addition of the vlandev.
+		 * If it did, do network layer specific procedure.
+		 */
+		if (ifp->if_mtu != oldmtu) {
+#ifdef INET6
+			nd6_setmtu(ifp);
+#endif
+			rt_updatemtu(ifp);
+		}
 		break;
 
 	case SIOCGETVLAN: