device: merge branch 'th/device-mtu-bgo777251'

https://bugzilla.gnome.org/show_bug.cgi?id=777251

26 files changed, 465 insertions, 460 deletions

diff --git a/src/devices/adsl/nm-device-adsl.c b/src/devices/adsl/nm-device-adsl.c
index 9af6e69035..53841a7fc2 100644
--- a/src/devices/adsl/nm-device-adsl.c
+++ b/src/devices/adsl/nm-device-adsl.c
@@ -482,10 +482,10 @@ act_stage3_ip4_config_start (NMDevice *device,
 	    && nm_ppp_manager_start (priv->ppp_manager, req,
 	                             nm_setting_adsl_get_username (s_adsl),
 	                             30, 0, &err)) {
-		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_STATE_CHANGED,
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_STATE_CHANGED,
 		                  G_CALLBACK (ppp_state_changed),
 		                  self);
-		g_signal_connect (priv->ppp_manager, "ip4-config",
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_IP4_CONFIG,
 		                  G_CALLBACK (ppp_ip4_config),
 		                  self);
 		ret = NM_ACT_STAGE_RETURN_POSTPONE;
@@ -577,7 +577,7 @@ set_property (GObject *object, guint prop_id,
 {
 	switch (prop_id) {
 	case PROP_ATM_INDEX:
-		/* construct only */
+		/* construct-only */
 		NM_DEVICE_ADSL_GET_PRIVATE ((NMDeviceAdsl *) object)->atm_index = g_value_get_int (value);
 		break;
 	default:
diff --git a/src/devices/bluetooth/nm-bluez-device.c b/src/devices/bluetooth/nm-bluez-device.c
index 4d2e9b1d7e..92b2c91895 100644
--- a/src/devices/bluetooth/nm-bluez-device.c
+++ b/src/devices/bluetooth/nm-bluez-device.c
@@ -1077,7 +1077,7 @@ set_property (GObject *object, guint prop_id,
 
 	switch (prop_id) {
 	case PROP_PATH:
-		/* construct only */
+		/* construct-only */
 		priv->path = g_value_dup_string (value);
 		break;
 	default:
diff --git a/src/devices/bluetooth/nm-bluez4-adapter.c b/src/devices/bluetooth/nm-bluez4-adapter.c
index b781def3a7..c0c1be30b7 100644
--- a/src/devices/bluetooth/nm-bluez4-adapter.c
+++ b/src/devices/bluetooth/nm-bluez4-adapter.c
@@ -281,7 +281,7 @@ set_property (GObject *object, guint prop_id,
 
 	switch (prop_id) {
 	case PROP_PATH:
-		/* construct only */
+		/* construct-only */
 		priv->path = g_value_dup_string (value);
 		break;
 	default:
diff --git a/src/devices/nm-device-bond.c b/src/devices/nm-device-bond.c
index cca76bfed3..5dba19d91c 100644
--- a/src/devices/nm-device-bond.c
+++ b/src/devices/nm-device-bond.c
@@ -383,25 +383,6 @@ act_stage1_prepare (NMDevice *dev, NMDeviceStateReason *reason)
 	return ret;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *self, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (self);
-	g_assert (connection);
-	s_wired = nm_connection_get_setting_wired (connection);
-
-	if (s_wired) {
-		/* MTU override */
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
 static gboolean
 enslave_slave (NMDevice *device,
                NMDevice *slave,
@@ -523,7 +504,7 @@ nm_device_bond_class_init (NMDeviceBondClass *klass)
 
 	parent_class->create_and_realize = create_and_realize;
 	parent_class->act_stage1_prepare = act_stage1_prepare;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 	parent_class->enslave_slave = enslave_slave;
 	parent_class->release_slave = release_slave;
 
diff --git a/src/devices/nm-device-bridge.c b/src/devices/nm-device-bridge.c
index a610997c77..613d59cd76 100644
--- a/src/devices/nm-device-bridge.c
+++ b/src/devices/nm-device-bridge.c
@@ -445,6 +445,7 @@ nm_device_bridge_class_init (NMDeviceBridgeClass *klass)
 	parent_class->act_stage1_prepare = act_stage1_prepare;
 	parent_class->enslave_slave = enslave_slave;
 	parent_class->release_slave = release_slave;
+	parent_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 
 	nm_exported_object_class_add_interface (NM_EXPORTED_OBJECT_CLASS (klass),
 	                                        NMDBUS_TYPE_DEVICE_BRIDGE_SKELETON,
diff --git a/src/devices/nm-device-ethernet.c b/src/devices/nm-device-ethernet.c
index 07f60d05b8..0dc09762aa 100644
--- a/src/devices/nm-device-ethernet.c
+++ b/src/devices/nm-device-ethernet.c
@@ -1055,10 +1055,10 @@ pppoe_stage3_ip4_config_start (NMDeviceEthernet *self, NMDeviceStateReason *reas
 	    && nm_ppp_manager_start (priv->ppp_manager, req,
 	                             nm_setting_pppoe_get_username (s_pppoe),
 	                             30, 0, &err)) {
-		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_STATE_CHANGED,
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_STATE_CHANGED,
 		                  G_CALLBACK (ppp_state_changed),
 		                  self);
-		g_signal_connect (priv->ppp_manager, "ip4-config",
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_IP4_CONFIG,
 		                  G_CALLBACK (ppp_ip4_config),
 		                  self);
 		ret = NM_ACT_STAGE_RETURN_POSTPONE;
@@ -1391,26 +1391,14 @@ act_stage3_ip4_config_start (NMDevice *device,
 	return NM_DEVICE_CLASS (nm_device_ethernet_parent_class)->act_stage3_ip4_config_start (device, out_config, reason);
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
+static guint32
+get_configured_mtu (NMDevice *device, gboolean *out_is_user_config)
 {
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
 	/* MTU only set for plain ethernet */
 	if (NM_DEVICE_ETHERNET_GET_PRIVATE ((NMDeviceEthernet *) device)->ppp_manager)
-		return;
-
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-	s_wired = nm_connection_get_setting_wired (connection);
-	g_assert (s_wired);
+		return 0;
 
-	/* MTU override */
-	mtu = nm_setting_wired_get_mtu (s_wired);
-	if (mtu)
-		nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
+	return nm_device_get_configured_mtu_for_wired (device, out_is_user_config);
 }
 
 static void
@@ -1774,7 +1762,7 @@ nm_device_ethernet_class_init (NMDeviceEthernetClass *klass)
 	parent_class->act_stage1_prepare = act_stage1_prepare;
 	parent_class->act_stage2_config = act_stage2_config;
 	parent_class->act_stage3_ip4_config_start = act_stage3_ip4_config_start;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = get_configured_mtu;
 	parent_class->deactivate = deactivate;
 	parent_class->spec_match_list = spec_match_list;
 	parent_class->update_connection = update_connection;
diff --git a/src/devices/nm-device-infiniband.c b/src/devices/nm-device-infiniband.c
index b0871b0a95..4f07761aad 100644
--- a/src/devices/nm-device-infiniband.c
+++ b/src/devices/nm-device-infiniband.c
@@ -118,22 +118,22 @@ act_stage1_prepare (NMDevice *dev, NMDeviceStateReason *reason)
 	return NM_ACT_STAGE_RETURN_SUCCESS;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *self, NMIP4Config *config)
+static guint32
+get_configured_mtu (NMDevice *device, gboolean *out_is_user_config)
 {
-	NMConnection *connection;
-	NMSettingInfiniband *s_infiniband;
+	NMSettingInfiniband *setting;
 	guint32 mtu;
 
-	connection = nm_device_get_applied_connection (self);
-	g_assert (connection);
-	s_infiniband = nm_connection_get_setting_infiniband (connection);
-	g_assert (s_infiniband);
+	nm_assert (NM_IS_DEVICE (device));
+	nm_assert (out_is_user_config);
+
+	setting = NM_SETTING_INFINIBAND (nm_device_get_applied_setting (device, NM_TYPE_SETTING_INFINIBAND));
+	if (!setting)
+		g_return_val_if_reached (0);
 
-	/* MTU override */
-	mtu = nm_setting_infiniband_get_mtu (s_infiniband);
-	if (mtu)
-		nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
+	mtu = nm_setting_infiniband_get_mtu (setting);
+	*out_is_user_config = (mtu != 0);
+	return mtu ?: NM_DEVICE_DEFAULT_MTU_INFINIBAND;
 }
 
 static gboolean
@@ -381,7 +381,7 @@ nm_device_infiniband_class_init (NMDeviceInfinibandClass *klass)
 	parent_class->update_connection = update_connection;
 
 	parent_class->act_stage1_prepare = act_stage1_prepare;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = get_configured_mtu;
 
 	obj_properties[PROP_IS_PARTITION] =
 	     g_param_spec_boolean (NM_DEVICE_INFINIBAND_IS_PARTITION, "", "",
diff --git a/src/devices/nm-device-ip-tunnel.c b/src/devices/nm-device-ip-tunnel.c
index 718876086e..9220c75201 100644
--- a/src/devices/nm-device-ip-tunnel.c
+++ b/src/devices/nm-device-ip-tunnel.c
@@ -744,22 +744,22 @@ create_and_realize (NMDevice *device,
 	return TRUE;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
+static guint32
+get_configured_mtu (NMDevice *self, gboolean *out_is_user_config)
 {
-	NMConnection *connection;
-	NMSettingIPTunnel *s_ip_tunnel;
+	NMSettingIPTunnel *setting;
 	guint32 mtu;
 
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-	s_ip_tunnel = nm_connection_get_setting_ip_tunnel (connection);
-	g_assert (s_ip_tunnel);
+	nm_assert (NM_IS_DEVICE (self));
+	nm_assert (out_is_user_config);
+
+	setting = NM_SETTING_IP_TUNNEL (nm_device_get_applied_setting (self, NM_TYPE_SETTING_IP_TUNNEL));
+	if (!setting)
+		g_return_val_if_reached (0);
 
-	/* MTU override */
-	mtu = nm_setting_ip_tunnel_get_mtu (s_ip_tunnel);
-	if (mtu)
-		nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
+	mtu = nm_setting_ip_tunnel_get_mtu (setting);
+	*out_is_user_config = (mtu != 0);
+	return mtu ?: NM_DEVICE_DEFAULT_MTU_WIRED;
 }
 
 static NMDeviceCapabilities
@@ -873,7 +873,7 @@ nm_device_ip_tunnel_class_init (NMDeviceIPTunnelClass *klass)
 	device_class->check_connection_compatible = check_connection_compatible;
 	device_class->create_and_realize = create_and_realize;
 	device_class->get_generic_capabilities = get_generic_capabilities;
-	device_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	device_class->get_configured_mtu = get_configured_mtu;
 	device_class->unrealize_notify = unrealize_notify;
 
 	NM_DEVICE_CLASS_DECLARE_TYPES (klass,
diff --git a/src/devices/nm-device-macvlan.c b/src/devices/nm-device-macvlan.c
index 9d3c3c370b..94206716b3 100644
--- a/src/devices/nm-device-macvlan.c
+++ b/src/devices/nm-device-macvlan.c
@@ -156,7 +156,7 @@ parent_changed_notify (NMDevice *device,
 
 	if (new_parent) {
 		priv->parent_state_id = g_signal_connect (new_parent,
-		                                          "state-changed",
+		                                          NM_DEVICE_STATE_CHANGED,
 		                                          G_CALLBACK (parent_state_changed),
 		                                          device);
 
@@ -489,24 +489,6 @@ act_stage1_prepare (NMDevice *dev, NMDeviceStateReason *reason)
 	return NM_ACT_STAGE_RETURN_SUCCESS;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-
-	s_wired = nm_connection_get_setting_wired (connection);
-	if (s_wired) {
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
 /*****************************************************************************/
 
 static void
@@ -570,7 +552,7 @@ nm_device_macvlan_class_init (NMDeviceMacvlanClass *klass)
 	device_class->connection_type = NM_SETTING_MACVLAN_SETTING_NAME;
 	device_class->create_and_realize = create_and_realize;
 	device_class->get_generic_capabilities = get_generic_capabilities;
-	device_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	device_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 	device_class->is_available = is_available;
 	device_class->link_changed = link_changed;
 	device_class->parent_changed_notify = parent_changed_notify;
diff --git a/src/devices/nm-device-private.h b/src/devices/nm-device-private.h
index c2ba98f387..7b36ba46f0 100644
--- a/src/devices/nm-device-private.h
+++ b/src/devices/nm-device-private.h
@@ -118,6 +118,16 @@ void nm_device_ip_method_failed (NMDevice *self, int family, NMDeviceStateReason
 
 gboolean nm_device_ipv6_sysctl_set (NMDevice *self, const char *property, const char *value);
 
+/*****************************************************************************/
+
+#define NM_DEVICE_DEFAULT_MTU_WIRED          ((guint32) 1500)
+#define NM_DEVICE_DEFAULT_MTU_WIRELESS       ((guint32) 1500)
+#define NM_DEVICE_DEFAULT_MTU_INFINIBAND     ((guint32) 0)
+
+guint32 nm_device_get_configured_mtu_for_wired (NMDevice *self, gboolean *out_is_user_config);
+
+/*****************************************************************************/
+
 #define NM_DEVICE_CLASS_DECLARE_TYPES(klass, conn_type, ...) \
 	NM_DEVICE_CLASS (klass)->connection_type = conn_type; \
 	{ \
diff --git a/src/devices/nm-device-tun.c b/src/devices/nm-device-tun.c
index bb66c50f80..2f42269234 100644
--- a/src/devices/nm-device-tun.c
+++ b/src/devices/nm-device-tun.c
@@ -314,24 +314,6 @@ act_stage1_prepare (NMDevice *device, NMDeviceStateReason *reason)
 }
 
 static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-
-	s_wired = nm_connection_get_setting_wired (connection);
-	if (s_wired) {
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
-static void
 unrealize_notify (NMDevice *device)
 {
 	NMDeviceTun *self = NM_DEVICE_TUN (device);
@@ -434,7 +416,7 @@ nm_device_tun_class_init (NMDeviceTunClass *klass)
 	device_class->unrealize_notify = unrealize_notify;
 	device_class->update_connection = update_connection;
 	device_class->act_stage1_prepare = act_stage1_prepare;
-	device_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	device_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 
 	obj_properties[PROP_OWNER] =
 	     g_param_spec_int64 (NM_DEVICE_TUN_OWNER, "", "",
diff --git a/src/devices/nm-device-vlan.c b/src/devices/nm-device-vlan.c
index d07e831850..3979c95d8d 100644
--- a/src/devices/nm-device-vlan.c
+++ b/src/devices/nm-device-vlan.c
@@ -572,24 +572,6 @@ act_stage1_prepare (NMDevice *device, NMDeviceStateReason *reason)
 	return ret;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-
-	s_wired = nm_connection_get_setting_wired (connection);
-	if (s_wired) {
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
 /*****************************************************************************/
 
 static void
@@ -630,7 +612,7 @@ nm_device_vlan_class_init (NMDeviceVlanClass *klass)
 	parent_class->unrealize_notify = unrealize_notify;
 	parent_class->get_generic_capabilities = get_generic_capabilities;
 	parent_class->act_stage1_prepare = act_stage1_prepare;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 	parent_class->is_available = is_available;
 	parent_class->parent_changed_notify = parent_changed_notify;
 
diff --git a/src/devices/nm-device-vxlan.c b/src/devices/nm-device-vxlan.c
index 63961ae5a6..b450813377 100644
--- a/src/devices/nm-device-vxlan.c
+++ b/src/devices/nm-device-vxlan.c
@@ -512,24 +512,6 @@ act_stage1_prepare (NMDevice *device, NMDeviceStateReason *reason)
 	return NM_ACT_STAGE_RETURN_SUCCESS;
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-
-	s_wired = nm_connection_get_setting_wired (connection);
-	if (s_wired) {
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
 /*****************************************************************************/
 
 static void
@@ -622,7 +604,7 @@ nm_device_vxlan_class_init (NMDeviceVxlanClass *klass)
 	device_class->get_generic_capabilities = get_generic_capabilities;
 	device_class->update_connection = update_connection;
 	device_class->act_stage1_prepare = act_stage1_prepare;
-	device_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	device_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 
 	obj_properties[PROP_ID] =
 	     g_param_spec_uint (NM_DEVICE_VXLAN_ID, "", "",
diff --git a/src/devices/nm-device.c b/src/devices/nm-device.c
index fe5e930e41..c236a85803 100644
--- a/src/devices/nm-device.c
+++ b/src/devices/nm-device.c
@@ -306,8 +306,13 @@ typedef struct _NMDevicePrivate {
 	bool            ignore_carrier;
 	gulong          ignore_carrier_id;
 	guint32         mtu;
-	guint32         ip_mtu;
-	bool            up;   /* IFF_UP */
+	guint32         ip6_mtu;
+	guint32 mtu_initial;
+	guint32 ip6_mtu_initial;
+
+	bool mtu_initialized:1;
+
+	bool            up:1;   /* IFF_UP */
 
 	/* Generic DHCP stuff */
 	guint32         dhcp_timeout;
@@ -383,7 +388,6 @@ typedef struct _NMDevicePrivate {
 	NMIP6Config *  ext_ip6_config_captured; /* Configuration captured from platform. */
 	GSList *       vpn6_configs;   /* VPNs which use this device */
 	bool           nm_ipv6ll; /* TRUE if NM handles the device's IPv6LL address */
-	guint32        ip6_mtu;
 	NMIP6Config *  dad6_ip6_config;
 
 	NMNDisc *      ndisc;
@@ -492,7 +496,7 @@ static NMActStageReturn dhcp4_start (NMDevice *self, NMConnection *connection, N
 static gboolean dhcp6_start (NMDevice *self, gboolean wait_for_ll, NMDeviceStateReason *reason);
 static void nm_device_start_ip_check (NMDevice *self);
 static void realize_start_setup (NMDevice *self, const NMPlatformLink *plink);
-static void nm_device_set_mtu (NMDevice *self, guint32 mtu);
+static void _commit_mtu (NMDevice *self, const NMIP4Config *config);
 static void dhcp_schedule_restart (NMDevice *self, int family, const char *reason);
 static void _cancel_activation (NMDevice *self);
 
@@ -643,9 +647,14 @@ nm_device_ipv6_sysctl_set (NMDevice *self, const char *property, const char *val
 }
 
 static guint32
-nm_device_ipv6_sysctl_get_int32 (NMDevice *self, const char *property, gint32 fallback)
+nm_device_ipv6_sysctl_get_uint32 (NMDevice *self, const char *property, guint32 fallback)
 {
-	return nm_platform_sysctl_get_int32 (NM_PLATFORM_GET, NMP_SYSCTL_PATHID_ABSOLUTE (nm_utils_ip6_property_path (nm_device_get_ip_iface (self), property)), fallback);
+	return nm_platform_sysctl_get_int_checked (NM_PLATFORM_GET,
+	                                           NMP_SYSCTL_PATHID_ABSOLUTE (nm_utils_ip6_property_path (nm_device_get_ip_iface (self), property)),
+	                                           10,
+	                                           0,
+	                                           G_MAXUINT32,
+	                                           fallback);
 }
 
 gboolean
@@ -910,9 +919,6 @@ nm_device_set_ip_iface (NMDevice *self, const char *iface)
 	/* We don't care about any saved values from the old iface */
 	g_hash_table_remove_all (priv->ip6_saved_properties);
 
-	if (priv->ip_ifindex)
-		priv->ip_mtu = nm_platform_link_get_mtu (NM_PLATFORM_GET, priv->ip_ifindex);
-
 	_notify (self, PROP_IP_IFACE);
 	return TRUE;
 }
@@ -1631,38 +1637,6 @@ find_slave_info (NMDevice *self, NMDevice *slave)
 	return NULL;
 }
 
-static void
-apply_mtu_from_config (NMDevice *self)
-{
-	const char *method = NM_SETTING_IP4_CONFIG_METHOD_DISABLED;
-	NMSettingIPConfig *s_ip4;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	/* Devices having an IPv4 configuration will set MTU during the commit
-	 * stage, so it is an error to call this function if the IPv4 method is not
-	 * 'disabled'.
-	 */
-	s_ip4 = (NMSettingIPConfig *)
-		nm_device_get_applied_setting (self, NM_TYPE_SETTING_IP4_CONFIG);
-	if (s_ip4)
-		method = nm_setting_ip_config_get_method (s_ip4);
-	g_return_if_fail (nm_streq (method, NM_SETTING_IP4_CONFIG_METHOD_DISABLED));
-
-	s_wired  = (NMSettingWired *)
-		nm_device_get_applied_setting (self, NM_TYPE_SETTING_WIRED);
-
-	if (s_wired) {
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu) {
-			_LOGD (LOGD_DEVICE | LOGD_IP,
-			       "setting MTU of device without IP4 config to %u",
-			       mtu);
-			nm_device_set_mtu (self, mtu);
-		}
-	}
-}
-
 /**
  * nm_device_master_enslave_slave:
  * @self: the master device
@@ -1723,7 +1697,7 @@ nm_device_master_enslave_slave (NMDevice *self, NMDevice *slave, NMConnection *c
 	/* Since slave devices don't have their own IP configuration,
 	 * set the MTU here.
 	 */
-	apply_mtu_from_config (slave);
+	_commit_mtu (slave, NM_DEVICE_GET_PRIVATE (slave)->ip4_config);
 
 	return success;
 }
@@ -2171,7 +2145,6 @@ device_link_changed (NMDevice *self)
 		_notify (self, PROP_DRIVER);
 	}
 
-	/* Update MTU if it has changed. */
 	if (priv->mtu != info.mtu) {
 		priv->mtu = info.mtu;
 		_notify (self, PROP_MTU);
@@ -2318,9 +2291,6 @@ device_ip_link_changed (NMDevice *self)
 
 	_stats_update_counters_from_pllink (self, pllink);
 
-	if (priv->ip_mtu != pllink->mtu)
-		priv->ip_mtu = pllink->mtu;
-
 	if (_ip_iface_update (self, pllink->name))
 		nm_device_update_dynamic_ip_setup (self);
 
@@ -2584,6 +2554,7 @@ realize_start_setup (NMDevice *self, const NMPlatformLink *plink)
 	NMDeviceCapabilities capabilities = 0;
 	NMConfig *config;
 	guint real_rate;
+	guint32 mtu;
 
 	g_return_if_fail (NM_IS_DEVICE (self));
 
@@ -2604,6 +2575,15 @@ realize_start_setup (NMDevice *self, const NMPlatformLink *plink)
 	/* Balanced by a thaw in nm_device_realize_finish() */
 	g_object_freeze_notify (G_OBJECT (self));
 
+	priv->mtu_initialized = FALSE;
+	priv->mtu_initial = 0;
+	priv->ip6_mtu_initial = 0;
+	priv->ip6_mtu = 0;
+	if (priv->mtu) {
+		priv->mtu = 0;
+		_notify (self, PROP_MTU);
+	}
+
 	if (plink) {
 		g_return_if_fail (link_type_compatible (self, plink->type, NULL, NULL));
 		update_device_from_platform_link (self, plink);
@@ -2619,8 +2599,11 @@ realize_start_setup (NMDevice *self, const NMPlatformLink *plink)
 		if (nm_platform_link_is_software (NM_PLATFORM_GET, priv->ifindex))
 			capabilities |= NM_DEVICE_CAP_IS_SOFTWARE;
 
-		priv->mtu = nm_platform_link_get_mtu (NM_PLATFORM_GET, priv->ifindex);
-		_notify (self, PROP_MTU);
+		mtu = nm_platform_link_get_mtu (NM_PLATFORM_GET, priv->ifindex);
+		if (priv->mtu != mtu) {
+			priv->mtu = mtu;
+			_notify (self, PROP_MTU);
+		}
 
 		nm_platform_link_get_driver_info (NM_PLATFORM_GET,
 		                                  priv->ifindex,
@@ -2831,6 +2814,11 @@ nm_device_unrealize (NMDevice *self, gboolean remove_resources, GError **error)
 	if (nm_clear_g_free (&priv->ip_iface))
 		_notify (self, PROP_IP_IFACE);
 
+	if (priv->mtu != 0) {
+		priv->mtu = 0;
+		_notify (self, PROP_MTU);
+	}
+
 	if (priv->driver_version) {
 		g_clear_pointer (&priv->driver_version, g_free);
 		_notify (self, PROP_DRIVER_VERSION);
@@ -5175,7 +5163,6 @@ END_ADD_DEFAULT_ROUTE:
 		priv->default_route.v4_has = _device_get_default_route_from_platform (self, AF_INET, (NMPlatformIPRoute *) &priv->default_route.v4);
 	}
 
-	/* Allow setting MTU etc */
 	if (commit) {
 		if (NM_DEVICE_GET_CLASS (self)->ip4_config_pre_commit)
 			NM_DEVICE_GET_CLASS (self)->ip4_config_pre_commit (self, composite);
@@ -5710,7 +5697,7 @@ act_stage3_ip4_config_start (NMDevice *self,
 		} else
 			g_return_val_if_reached (NM_ACT_STAGE_RETURN_FAILURE);
 	} else if (strcmp (method, NM_SETTING_IP4_CONFIG_METHOD_DISABLED) == 0) {
-		apply_mtu_from_config (self);
+		_commit_mtu (self, priv->ip4_config);
 		ret = NM_ACT_STAGE_RETURN_SUCCESS;
 	} else
 		_LOGW (LOGD_IP4, "unhandled IPv4 config method '%s'; will fail", method);
@@ -5944,9 +5931,6 @@ END_ADD_DEFAULT_ROUTE:
 			                                 nm_device_get_ip_ifindex (self),
 			                                 iid);
 		}
-
-		if (NM_DEVICE_GET_CLASS (self)->ip6_config_pre_commit)
-			NM_DEVICE_GET_CLASS (self)->ip6_config_pre_commit (self, composite);
 	}
 
 	routes_full_sync =    commit
@@ -6587,82 +6571,172 @@ linklocal6_start (NMDevice *self)
 
 /*****************************************************************************/
 
-static void nm_device_ipv6_set_mtu (NMDevice *self, guint32 mtu);
-
-static void
-set_ip_mtu (NMDevice *self, guint32 mtu)
+guint32
+nm_device_get_configured_mtu_for_wired (NMDevice *self, gboolean *out_is_user_config)
 {
-	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
+	NMConnection *connection;
+	NMSettingWired *setting;
+	guint32 mtu;
 
-	if (priv->ip_ifindex)
-		priv->ip_mtu = mtu;
-	else
-		priv->mtu = mtu;
-}
+	nm_assert (NM_IS_DEVICE (self));
+	nm_assert (out_is_user_config);
 
-static guint32
-get_ip_mtu (NMDevice *self)
-{
-	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
+	connection = nm_device_get_applied_connection (self);
+	if (!connection)
+		g_return_val_if_reached (0);
 
-	if (priv->ip_ifindex)
-		return priv->ip_mtu;
-	else
-		return priv->mtu;
+	setting = nm_connection_get_setting_wired (connection);
+
+	if (setting) {
+		mtu = nm_setting_wired_get_mtu (setting);
+		if (mtu) {
+			*out_is_user_config = TRUE;
+			return mtu;
+		}
+	}
+	*out_is_user_config = FALSE;
+	return NM_DEVICE_DEFAULT_MTU_WIRED;
 }
 
+/*****************************************************************************/
+
 static void
-nm_device_set_mtu (NMDevice *self, guint32 mtu)
+_commit_mtu (NMDevice *self, const NMIP4Config *config)
 {
 	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
-	int ifindex = nm_device_get_ip_ifindex (self);
-	guint32 ip_mtu;
+	guint32 ip6_mtu, ip6_mtu_orig;
+	guint32 mtu_desired, mtu_desired_orig;
+	guint32 mtu_plat;
+	struct {
+		gboolean initialized;
+		guint32 value;
+	} ip6_mtu_sysctl;
+	int ifindex;
+	char sbuf[64], sbuf1[64], sbuf2[64];
 
-	if (mtu)
-		set_ip_mtu (self, mtu);
+	ifindex = nm_device_get_ip_ifindex (self);
+	if (ifindex <= 0)
+		return;
 
-	/* Ensure the IPv6 MTU is still alright. */
-	if (priv->ip6_mtu)
-		nm_device_ipv6_set_mtu (self, priv->ip6_mtu);
+	if (nm_device_uses_assumed_connection (self)) {
+		/* for assumed connections we don't tamper with the MTU. This is
+		 * a bug and supposed to be fixed by the unmanaged/assumed rework. */
+		return;
+	}
 
-	ip_mtu = get_ip_mtu (self);
-	if (ip_mtu && ip_mtu != nm_platform_link_get_mtu (NM_PLATFORM_GET, ifindex))
-		nm_platform_link_set_mtu (NM_PLATFORM_GET, ifindex, ip_mtu);
-}
+	{
+		gboolean mtu_is_user_config = FALSE;
+		guint32 mtu = 0;
 
-static void
-nm_device_ipv6_set_mtu (NMDevice *self, guint32 mtu)
-{
-	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
-	guint32 ip_mtu = get_ip_mtu (self);
-	guint32 plat_mtu = nm_device_ipv6_sysctl_get_int32 (self, "mtu", ip_mtu);
+		/* preferably, get the MTU from explict user-configuration.
+		 * Only if that fails, look at the current @config (which contains
+		 * MTUs from DHCP/PPP) or maybe fallback to a device-specific MTU. */
+
+		if (NM_DEVICE_GET_CLASS (self)->get_configured_mtu)
+			mtu = NM_DEVICE_GET_CLASS (self)->get_configured_mtu (self, &mtu_is_user_config);
+
+		if (mtu && mtu_is_user_config)
+			mtu_desired = mtu;
+		else {
+			if (config)
+				mtu_desired = nm_ip4_config_get_mtu (config);
+			else
+				mtu_desired = 0;
+			if (!mtu_desired && !priv->mtu_initialized) {
+				/* there is no MTU specified, and this is the first commit of the MTU.
+				 * Reset a per-device MTU default, as returned from get_configured_mtu().
+				 *
+				 * The device might choose not to return a default MTU via get_configured_mtu()
+				 * to suppress this behavior. */
+				mtu_desired = mtu;
+			}
+		}
+	}
 
-	priv->ip6_mtu = mtu ?: plat_mtu;
+	if (mtu_desired && mtu_desired < 1280) {
+		NMSettingIPConfig *s_ip6;
 
-	if (priv->ip6_mtu && ip_mtu && ip_mtu < priv->ip6_mtu) {
-		_LOGI (LOGD_DEVICE | LOGD_IP6, "Lowering IPv6 MTU (%d) to match device MTU (%d)",
-		       priv->ip6_mtu, ip_mtu);
-		priv->ip6_mtu = ip_mtu;
+		s_ip6 = (NMSettingIPConfig *) nm_device_get_applied_setting (self, NM_TYPE_SETTING_IP6_CONFIG);
+		if (s_ip6 && nm_streq0 (nm_setting_ip_config_get_method (s_ip6),
+		                        NM_SETTING_IP6_CONFIG_METHOD_IGNORE)) {
+			/* the interface has IPv6 enabled. The MTU with IPv6 cannot be smaller
+			 * then 1280.
+			 *
+			 * For slave-devices (that don't have @s_ip6 we) don't do this fixup because
+			 * it's anyway an unsolved problem when the slave configures a conflicting
+			 * MTU. */
+			mtu_desired = 1280;
+		}
 	}
 
-	if (priv->ip6_mtu && priv->ip6_mtu < 1280) {
-		_LOGI (LOGD_DEVICE | LOGD_IP6, "IPv6 MTU (%d) smaller than 1280, adjusting",
-		       priv->ip6_mtu);
-		priv->ip6_mtu = 1280;
+	ip6_mtu = priv->ip6_mtu;
+	if (!ip6_mtu && !priv->mtu_initialized) {
+		/* initially, if the IPv6 MTU is not specified, grow it as large as the
+		 * link MTU @mtu_desired. Only exception is, if @mtu_desired is so small
+		 * to disable IPv6. */
+		if (mtu_desired >= 1280)
+			ip6_mtu = mtu_desired;
 	}
 
-	if (priv->ip6_mtu && ip_mtu && ip_mtu < priv->ip6_mtu) {
-		_LOGI (LOGD_DEVICE | LOGD_IP6, "Raising device MTU (%d) to match IPv6 MTU (%d)",
-		       ip_mtu, priv->ip6_mtu);
-		nm_device_set_mtu (self, priv->ip6_mtu);
+	priv->mtu_initialized = TRUE;
+
+	if (!ip6_mtu && !mtu_desired)
+		return;
+
+	mtu_desired_orig = mtu_desired;
+	ip6_mtu_orig = ip6_mtu;
+
+	mtu_plat = nm_platform_link_get_mtu (NM_PLATFORM_GET, ifindex);
+
+	if (ip6_mtu) {
+		ip6_mtu = NM_MAX (1280, ip6_mtu);
+
+		if (!mtu_desired)
+			mtu_desired = mtu_plat;
+
+		if (mtu_desired) {
+			mtu_desired = NM_MAX (1280, mtu_desired);
+
+			if (mtu_desired < ip6_mtu)
+				ip6_mtu = mtu_desired;
+		}
 	}
 
-	if (priv->ip6_mtu != plat_mtu) {
-		char val[64];
+	_LOGT (LOGD_DEVICE, "mtu: device-mtu: %u%s, ipv6-mtu: %u%s, ifindex: %d",
+	       (guint) mtu_desired,
+	       mtu_desired == mtu_desired_orig ? "" : nm_sprintf_buf (sbuf1, " (was %u)", (guint) mtu_desired_orig),
+	       (guint) ip6_mtu,
+	       ip6_mtu == ip6_mtu_orig ? "" : nm_sprintf_buf (sbuf2, " (was %u)", (guint) ip6_mtu_orig),
+	       ifindex);
+
+	ip6_mtu_sysctl.initialized = FALSE;
+#define _IP6_MTU_SYS() \
+	({ \
+		if (!ip6_mtu_sysctl.initialized) { \
+			ip6_mtu_sysctl.value = nm_device_ipv6_sysctl_get_uint32 (self, "mtu", 0); \
+			ip6_mtu_sysctl.initialized = TRUE; \
+		} \
+		ip6_mtu_sysctl.value; \
+	})
+	if (   (mtu_desired && mtu_desired != mtu_plat)
+	    || (ip6_mtu && ip6_mtu != _IP6_MTU_SYS ())) {
+
+		if (!priv->mtu_initial && !priv->ip6_mtu_initial) {
+			/* before touching any of the MTU paramters, record the
+			 * original setting to restore on deactivation. */
+			priv->mtu_initial = mtu_plat;
+			priv->ip6_mtu_initial = _IP6_MTU_SYS ();
+		}
+
+		if (mtu_desired && mtu_desired != mtu_plat)
+			nm_platform_link_set_mtu (NM_PLATFORM_GET, ifindex, mtu_desired);
 
-		nm_device_ipv6_sysctl_set (self, "mtu",
-		                           nm_sprintf_buf (val, "%u", (unsigned) mtu));
+		if (ip6_mtu && ip6_mtu != _IP6_MTU_SYS ()) {
+			nm_device_ipv6_sysctl_set (self, "mtu",
+			                           nm_sprintf_buf (sbuf, "%u", (unsigned) ip6_mtu));
+		}
 	}
+#undef _IP6_MTU_SYS
 }
 
 static void
@@ -6788,8 +6862,12 @@ ndisc_config_changed (NMNDisc *ndisc, const NMNDiscData *rdata, guint changed_in
 	if (changed & NM_NDISC_CONFIG_HOP_LIMIT)
 		nm_platform_sysctl_set_ip6_hop_limit_safe (NM_PLATFORM_GET, nm_device_get_ip_iface (self), rdata->hop_limit);
 
-	if (changed & NM_NDISC_CONFIG_MTU)
-		priv->ip6_mtu = rdata->mtu;
+	if (changed & NM_NDISC_CONFIG_MTU) {
+		if (priv->ip6_mtu != rdata->mtu) {
+			_LOGD (LOGD_DEVICE, "mtu: set IPv6 MTU to %u", (guint) rdata->mtu);
+			priv->ip6_mtu = rdata->mtu;
+		}
+	}
 
 	nm_device_activate_schedule_ip6_config_result (self);
 }
@@ -7204,8 +7282,7 @@ act_stage3_ip6_config_start (NMDevice *self,
 	 * expose any ipv6 sysctls or allow presence of any addresses on the interface,
 	 * including LL, which * would make it impossible to autoconfigure MTU to a
 	 * correct value. */
-	if (!nm_device_uses_assumed_connection (self))
-		nm_device_ipv6_set_mtu (self, priv->ip6_mtu);
+	_commit_mtu (self, priv->ip4_config);
 
 	/* Any method past this point requires an IPv6LL address. Use NM-controlled
 	 * IPv6LL if this is not an assumed connection, since assumed connections
@@ -9081,8 +9158,7 @@ nm_device_set_ip4_config (NMDevice *self,
 	if (commit && new_config) {
 		gboolean assumed = nm_device_uses_assumed_connection (self);
 
-		nm_device_set_mtu (self, nm_ip4_config_get_mtu (new_config));
-
+		_commit_mtu (self, new_config);
 		/* For assumed devices we must not touch the kernel-routes, such as the device-route.
 		 * FIXME: this is wrong in case where "assumed" means "take-over-seamlessly". In this
 		 * case, we should manage the device route, for example on new DHCP lease. */
@@ -9250,7 +9326,7 @@ nm_device_set_ip6_config (NMDevice *self,
 
 	/* Always commit to nm-platform to update lifetimes */
 	if (commit && new_config) {
-		nm_device_ipv6_set_mtu (self, priv->ip6_mtu);
+		_commit_mtu (self, priv->ip4_config);
 		success = nm_ip6_config_commit (new_config,
 		                                ip_ifindex,
 		                                routes_full_sync);
@@ -11414,6 +11490,27 @@ nm_device_cleanup (NMDevice *self, NMDeviceStateReason reason, CleanupType clean
 		NM_DEVICE_GET_CLASS (self)->deactivate_reset_hw_addr (self);
 	}
 
+	priv->mtu_initialized = FALSE;
+	if (priv->mtu_initial || priv->ip6_mtu_initial) {
+		ifindex = nm_device_get_ip_ifindex (self);
+
+		if (   ifindex > 0
+		    && cleanup_type == CLEANUP_TYPE_DECONFIGURE) {
+			_LOGT (LOGD_DEVICE, "mtu: reset device-mtu: %u, ipv6-mtu: %u, ifindex: %d",
+			       (guint) priv->mtu_initial, (guint) priv->ip6_mtu_initial, ifindex);
+			if (priv->mtu_initial)
+				nm_platform_link_set_mtu (NM_PLATFORM_GET, ifindex, priv->mtu_initial);
+			if (priv->ip6_mtu_initial) {
+				char sbuf[64];
+
+				nm_device_ipv6_sysctl_set (self, "mtu",
+				                           nm_sprintf_buf (sbuf, "%u", (unsigned) priv->ip6_mtu_initial));
+			}
+		}
+		priv->mtu_initial = 0;
+		priv->ip6_mtu_initial = 0;
+	}
+
 	_cleanup_generic_post (self, cleanup_type);
 }
 
@@ -13082,9 +13179,6 @@ set_property (GObject *object, guint prop_id,
 		g_free (priv->firmware_version);
 		priv->firmware_version = g_value_dup_string (value);
 		break;
-	case PROP_MTU:
-		priv->mtu = g_value_get_uint (value);
-		break;
 	case PROP_IP4_ADDRESS:
 		priv->ip4_address = g_value_get_uint (value);
 		break;
diff --git a/src/devices/nm-device.h b/src/devices/nm-device.h
index 904c7d2390..52a74d268a 100644
--- a/src/devices/nm-device.h
+++ b/src/devices/nm-device.h
@@ -232,6 +232,8 @@ typedef struct {
 	                                  NMConnection *connection,
 	                                  char **specific_object);
 
+	guint32     (*get_configured_mtu) (NMDevice *self, gboolean *out_is_user_config);
+
 	/* Checks whether the connection is compatible with the device using
 	 * only the devices type and characteristics.  Does not use any live
 	 * network information like WiFi scan lists etc.
@@ -275,9 +277,7 @@ typedef struct {
 	NMActStageReturn    (* act_stage4_ip6_config_timeout)   (NMDevice *self,
 	                                                         NMDeviceStateReason *reason);
 
-	/* Called right before IP config is set; use for setting MTU etc */
 	void                (* ip4_config_pre_commit) (NMDevice *self, NMIP4Config *config);
-	void                (* ip6_config_pre_commit) (NMDevice *self, NMIP6Config *config);
 
 	/* Async deactivating (in the DEACTIVATING phase) */
 	void            (* deactivate_async)        (NMDevice *self,
diff --git a/src/devices/team/nm-device-team.c b/src/devices/team/nm-device-team.c
index d67fb6b23e..28d91ab33c 100644
--- a/src/devices/team/nm-device-team.c
+++ b/src/devices/team/nm-device-team.c
@@ -628,25 +628,6 @@ act_stage1_prepare (NMDevice *device, NMDeviceStateReason *reason)
 }
 
 static void
-ip4_config_pre_commit (NMDevice *self, NMIP4Config *config)
-{
-	NMConnection *connection;
-	NMSettingWired *s_wired;
-	guint32 mtu;
-
-	connection = nm_device_get_applied_connection (self);
-	g_assert (connection);
-	s_wired = nm_connection_get_setting_wired (connection);
-
-	if (s_wired) {
-		/* MTU override */
-		mtu = nm_setting_wired_get_mtu (s_wired);
-		if (mtu)
-			nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
-	}
-}
-
-static void
 deactivate (NMDevice *device)
 {
 	NMDeviceTeam *self = NM_DEVICE_TEAM (device);
@@ -876,7 +857,7 @@ nm_device_team_class_init (NMDeviceTeamClass *klass)
 	parent_class->master_update_slave_connection = master_update_slave_connection;
 
 	parent_class->act_stage1_prepare = act_stage1_prepare;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = nm_device_get_configured_mtu_for_wired;
 	parent_class->deactivate = deactivate;
 	parent_class->enslave_slave = enslave_slave;
 	parent_class->release_slave = release_slave;
diff --git a/src/devices/wifi/nm-device-wifi.c b/src/devices/wifi/nm-device-wifi.c
index 9556adfc2d..9d002e8362 100644
--- a/src/devices/wifi/nm-device-wifi.c
+++ b/src/devices/wifi/nm-device-wifi.c
@@ -2741,22 +2741,22 @@ act_stage3_ip6_config_start (NMDevice *device,
 	return NM_DEVICE_CLASS (nm_device_wifi_parent_class)->act_stage3_ip6_config_start (device, out_config, reason);
 }
 
-static void
-ip4_config_pre_commit (NMDevice *device, NMIP4Config *config)
+static guint32
+get_configured_mtu (NMDevice *device, gboolean *out_is_user_config)
 {
-	NMConnection *connection;
-	NMSettingWireless *s_wifi;
+	NMSettingWireless *setting;
 	guint32 mtu;
 
-	connection = nm_device_get_applied_connection (device);
-	g_assert (connection);
-	s_wifi = nm_connection_get_setting_wireless (connection);
-	g_assert (s_wifi);
+	nm_assert (NM_IS_DEVICE (device));
+	nm_assert (out_is_user_config);
+
+	setting = NM_SETTING_WIRELESS (nm_device_get_applied_setting (device, NM_TYPE_SETTING_WIRELESS));
+	if (!setting)
+		g_return_val_if_reached (0);
 
-	/* MTU override */
-	mtu = nm_setting_wireless_get_mtu (s_wifi);
-	if (mtu)
-		nm_ip4_config_set_mtu (config, mtu, NM_IP_CONFIG_SOURCE_USER);
+	mtu = nm_setting_wireless_get_mtu (setting);
+	*out_is_user_config = (mtu != 0);
+	return mtu ?: NM_DEVICE_DEFAULT_MTU_WIRELESS;
 }
 
 static gboolean
@@ -3215,7 +3215,7 @@ nm_device_wifi_class_init (NMDeviceWifiClass *klass)
 
 	parent_class->act_stage1_prepare = act_stage1_prepare;
 	parent_class->act_stage2_config = act_stage2_config;
-	parent_class->ip4_config_pre_commit = ip4_config_pre_commit;
+	parent_class->get_configured_mtu = get_configured_mtu;
 	parent_class->act_stage3_ip4_config_start = act_stage3_ip4_config_start;
 	parent_class->act_stage3_ip6_config_start = act_stage3_ip6_config_start;
 	parent_class->act_stage4_ip4_config_timeout = act_stage4_ip4_config_timeout;
diff --git a/src/devices/wwan/nm-modem.c b/src/devices/wwan/nm-modem.c
index 4a8e9094ad..04c95a2bed 100644
--- a/src/devices/wwan/nm-modem.c
+++ b/src/devices/wwan/nm-modem.c
@@ -563,16 +563,16 @@ ppp_stage3_ip_config_start (NMModem *self,
 	if (   priv->ppp_manager
 	    && nm_ppp_manager_start (priv->ppp_manager, req, ppp_name,
 	                             ip_timeout, baud_override, &error)) {
-		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_STATE_CHANGED,
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_STATE_CHANGED,
 		                  G_CALLBACK (ppp_state_changed),
 		                  self);
-		g_signal_connect (priv->ppp_manager, "ip4-config",
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_IP4_CONFIG,
 		                  G_CALLBACK (ppp_ip4_config),
 		                  self);
-		g_signal_connect (priv->ppp_manager, "ip6-config",
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_IP6_CONFIG,
 		                  G_CALLBACK (ppp_ip6_config),
 		                  self);
-		g_signal_connect (priv->ppp_manager, "stats",
+		g_signal_connect (priv->ppp_manager, NM_PPP_MANAGER_SIGNAL_STATS,
 		                  G_CALLBACK (ppp_stats),
 		                  self);
 
diff --git a/src/dhcp/nm-dhcp-client.c b/src/dhcp/nm-dhcp-client.c
index 31eb8276c5..ba7c6dbf0e 100644
--- a/src/dhcp/nm-dhcp-client.c
+++ b/src/dhcp/nm-dhcp-client.c
@@ -851,7 +851,7 @@ set_property (GObject *object, guint prop_id,
 		g_warn_if_fail (priv->ifindex > 0);
 		break;
 	case PROP_HWADDR:
-		/* construct only */
+		/* construct-only */
 		priv->hwaddr = g_value_dup_boxed (value);
 		break;
 	case PROP_IPV6:
diff --git a/src/nm-auth-manager.c b/src/nm-auth-manager.c
index 73063b9b92..4359d8f187 100644
--- a/src/nm-auth-manager.c
+++ b/src/nm-auth-manager.c
@@ -509,7 +509,7 @@ set_property (GObject *object, guint prop_id, const GValue *value, GParamSpec *p
 
 	switch (prop_id) {
 	case PROP_POLKIT_ENABLED:
-		/* construct only */
+		/* construct-only */
 		priv->polkit_enabled = !!g_value_get_boolean (value);
 		break;
 	default:
diff --git a/src/nm-config.c b/src/nm-config.c
index 2d61b92961..87d0c8a7b9 100644
--- a/src/nm-config.c
+++ b/src/nm-config.c
@@ -2232,7 +2232,7 @@ set_property (GObject *object, guint prop_id,
 
 	switch (prop_id) {
 	case PROP_CMD_LINE_OPTIONS:
-		/* construct only */
+		/* construct-only */
 		cli = g_value_get_pointer (value);
 		if (!cli)
 			_nm_config_cmd_line_options_clear (&priv->cli);
@@ -2240,7 +2240,7 @@ set_property (GObject *object, guint prop_id,
 			_nm_config_cmd_line_options_copy (cli, &priv->cli);
 		break;
 	case PROP_ATOMIC_SECTION_PREFIXES:
-		/* construct only */
+		/* construct-only */
 		priv->atomic_section_prefixes = g_strdupv (g_value_get_boxed (value));
 		break;
 	default:
diff --git a/src/nm-ip4-config.c b/src/nm-ip4-config.c
index 2bd0d36cb3..1486edccc7 100644
--- a/src/nm-ip4-config.c
+++ b/src/nm-ip4-config.c
@@ -35,26 +35,49 @@
 
 #include "introspection/org.freedesktop.NetworkManager.IP4Config.h"
 
+/*****************************************************************************/
+
+/* internal guint32 are assigned to gobject properties of type uint. Ensure, that uint is large enough */
+G_STATIC_ASSERT (sizeof (uint) >= sizeof (guint32));
+G_STATIC_ASSERT (G_MAXUINT >= 0xFFFFFFFF);
+
+/*****************************************************************************/
+
+NM_GOBJECT_PROPERTIES_DEFINE (NMIP4Config,
+	PROP_IFINDEX,
+	PROP_ADDRESS_DATA,
+	PROP_ADDRESSES,
+	PROP_ROUTE_DATA,
+	PROP_ROUTES,
+	PROP_GATEWAY,
+	PROP_NAMESERVERS,
+	PROP_DOMAINS,
+	PROP_SEARCHES,
+	PROP_DNS_OPTIONS,
+	PROP_WINS_SERVERS,
+	PROP_DNS_PRIORITY,
+);
+
 typedef struct {
-	gboolean never_default;
+	bool never_default:1;
+	bool metered:1;
+	bool has_gateway:1;
 	guint32 gateway;
-	gboolean has_gateway;
+	guint32 mss;
+	guint32 mtu;
+	int ifindex;
+	NMIPConfigSource mtu_source;
+	gint dns_priority;
+	gint64 route_metric;
 	GArray *addresses;
 	GArray *routes;
 	GArray *nameservers;
 	GPtrArray *domains;
 	GPtrArray *searches;
 	GPtrArray *dns_options;
-	guint32 mss;
 	GArray *nis;
 	char *nis_domain;
 	GArray *wins;
-	guint32 mtu;
-	NMIPConfigSource mtu_source;
-	int ifindex;
-	gint64 route_metric;
-	gboolean metered;
-	gint dns_priority;
 	GVariant *address_data_variant;
 	GVariant *addresses_variant;
 } NMIP4ConfigPrivate;
@@ -72,33 +95,7 @@ G_DEFINE_TYPE (NMIP4Config, nm_ip4_config, NM_TYPE_EXPORTED_OBJECT)
 
 #define NM_IP4_CONFIG_GET_PRIVATE(self) _NM_GET_PRIVATE(self, NMIP4Config, NM_IS_IP4_CONFIG)
 
-/* internal guint32 are assigned to gobject properties of type uint. Ensure, that uint is large enough */
-G_STATIC_ASSERT (sizeof (uint) >= sizeof (guint32));
-G_STATIC_ASSERT (G_MAXUINT >= 0xFFFFFFFF);
-
-NM_GOBJECT_PROPERTIES_DEFINE (NMIP4Config,
-	PROP_IFINDEX,
-	PROP_ADDRESS_DATA,
-	PROP_ADDRESSES,
-	PROP_ROUTE_DATA,
-	PROP_ROUTES,
-	PROP_GATEWAY,
-	PROP_NAMESERVERS,
-	PROP_DOMAINS,
-	PROP_SEARCHES,
-	PROP_DNS_OPTIONS,
-	PROP_WINS_SERVERS,
-	PROP_DNS_PRIORITY,
-);
-
-NMIP4Config *
-nm_ip4_config_new (int ifindex)
-{
-	g_return_val_if_fail (ifindex >= -1, NULL);
-	return (NMIP4Config *) g_object_new (NM_TYPE_IP4_CONFIG,
-	                                     NM_IP4_CONFIG_IFINDEX, ifindex,
-	                                     NULL);
-}
+/*****************************************************************************/
 
 int
 nm_ip4_config_get_ifindex (const NMIP4Config *config)
@@ -705,9 +702,11 @@ nm_ip4_config_merge (NMIP4Config *dst, const NMIP4Config *src, NMIPConfigMergeFl
 		nm_ip4_config_set_mss (dst, nm_ip4_config_get_mss (src));
 
 	/* MTU */
-	if (nm_ip4_config_get_mtu (src))
-		nm_ip4_config_set_mtu (dst, nm_ip4_config_get_mtu (src),
-		                       nm_ip4_config_get_mtu_source (src));
+	if (   src_priv->mtu_source > dst_priv->mtu_source
+	    || (   src_priv->mtu_source == dst_priv->mtu_source
+	        && (   (!dst_priv->mtu && src_priv->mtu)
+	            || (dst_priv->mtu && src_priv->mtu < dst_priv->mtu))))
+		nm_ip4_config_set_mtu (dst, src_priv->mtu, src_priv->mtu_source);
 
 	/* NIS */
 	if (!NM_FLAGS_HAS (merge_flags, NM_IP_CONFIG_MERGE_NO_DNS)) {
@@ -935,7 +934,8 @@ nm_ip4_config_subtract (NMIP4Config *dst, const NMIP4Config *src)
 		nm_ip4_config_set_mss (dst, 0);
 
 	/* MTU */
-	if (nm_ip4_config_get_mtu (src) == nm_ip4_config_get_mtu (dst))
+	if (   nm_ip4_config_get_mtu (src) == nm_ip4_config_get_mtu (dst)
+	    && nm_ip4_config_get_mtu_source (src) == nm_ip4_config_get_mtu_source (dst))
 		nm_ip4_config_set_mtu (dst, 0, NM_IP_CONFIG_SOURCE_UNKNOWN);
 
 	/* NIS */
@@ -1255,7 +1255,8 @@ nm_ip4_config_replace (NMIP4Config *dst, const NMIP4Config *src, gboolean *relev
 	}
 
 	/* mtu */
-	if (src_priv->mtu != dst_priv->mtu) {
+	if (   src_priv->mtu != dst_priv->mtu
+	    || src_priv->mtu_source != dst_priv->mtu_source) {
 		nm_ip4_config_set_mtu (dst, src_priv->mtu, src_priv->mtu_source);
 		has_minor_changes = TRUE;
 	}
@@ -1332,7 +1333,7 @@ nm_ip4_config_dump (const NMIP4Config *config, const char *detail)
 	g_message (" dnspri: %d", nm_ip4_config_get_dns_priority (config));
 
 	g_message ("    mss: %"G_GUINT32_FORMAT, nm_ip4_config_get_mss (config));
-	g_message ("    mtu: %"G_GUINT32_FORMAT, nm_ip4_config_get_mtu (config));
+	g_message ("    mtu: %"G_GUINT32_FORMAT" (source: %d)", nm_ip4_config_get_mtu (config), (int) nm_ip4_config_get_mtu_source (config));
 
 	/* NIS */
 	for (i = 0; i < nm_ip4_config_get_num_nis_servers (config); i++) {
@@ -1385,7 +1386,7 @@ nm_ip4_config_set_never_default (NMIP4Config *config, gboolean never_default)
 {
 	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (config);
 
-	priv->never_default = !!never_default;
+	priv->never_default = never_default;
 }
 
 gboolean
@@ -2083,11 +2084,11 @@ nm_ip4_config_set_mtu (NMIP4Config *config, guint32 mtu, NMIPConfigSource source
 {
 	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (config);
 
-	if (source > priv->mtu_source) {
-		priv->mtu = mtu;
-		priv->mtu_source = source;
-	} else if (source == priv->mtu_source && (!priv->mtu || priv->mtu > mtu))
-		priv->mtu = mtu;
+	if (!mtu)
+		source = NM_IP_CONFIG_SOURCE_UNKNOWN;
+
+	priv->mtu = mtu;
+	priv->mtu_source = source;
 }
 
 guint32
@@ -2113,7 +2114,7 @@ nm_ip4_config_set_metered (NMIP4Config *config, gboolean metered)
 {
 	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (config);
 
-	priv->metered = !!metered;
+	priv->metered = metered;
 }
 
 gboolean
@@ -2234,43 +2235,6 @@ nm_ip4_config_equal (const NMIP4Config *a, const NMIP4Config *b)
 /*****************************************************************************/
 
 static void
-nm_ip4_config_init (NMIP4Config *config)
-{
-	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (config);
-
-	priv->addresses = g_array_new (FALSE, FALSE, sizeof (NMPlatformIP4Address));
-	priv->routes = g_array_new (FALSE, FALSE, sizeof (NMPlatformIP4Route));
-	priv->nameservers = g_array_new (FALSE, FALSE, sizeof (guint32));
-	priv->domains = g_ptr_array_new_with_free_func (g_free);
-	priv->searches = g_ptr_array_new_with_free_func (g_free);
-	priv->dns_options = g_ptr_array_new_with_free_func (g_free);
-	priv->nis = g_array_new (FALSE, TRUE, sizeof (guint32));
-	priv->wins = g_array_new (FALSE, TRUE, sizeof (guint32));
-	priv->route_metric = -1;
-}
-
-static void
-finalize (GObject *object)
-{
-	NMIP4Config *self = NM_IP4_CONFIG (object);
-	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (self);
-
-	nm_clear_g_variant (&priv->address_data_variant);
-	nm_clear_g_variant (&priv->addresses_variant);
-	g_array_unref (priv->addresses);
-	g_array_unref (priv->routes);
-	g_array_unref (priv->nameservers);
-	g_ptr_array_unref (priv->domains);
-	g_ptr_array_unref (priv->searches);
-	g_ptr_array_unref (priv->dns_options);
-	g_array_unref (priv->nis);
-	g_free (priv->nis_domain);
-	g_array_unref (priv->wins);
-
-	G_OBJECT_CLASS (nm_ip4_config_parent_class)->finalize (object);
-}
-
-static void
 get_property (GObject *object, guint prop_id,
               GValue *value, GParamSpec *pspec)
 {
@@ -2459,6 +2423,7 @@ set_property (GObject *object,
 
 	switch (prop_id) {
 	case PROP_IFINDEX:
+		/* construct-only */
 		priv->ifindex = g_value_get_int (value);
 		break;
 	default:
@@ -2467,6 +2432,54 @@ set_property (GObject *object,
 	}
 }
 
+/*****************************************************************************/
+
+static void
+nm_ip4_config_init (NMIP4Config *config)
+{
+	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (config);
+
+	priv->addresses = g_array_new (FALSE, FALSE, sizeof (NMPlatformIP4Address));
+	priv->routes = g_array_new (FALSE, FALSE, sizeof (NMPlatformIP4Route));
+	priv->nameservers = g_array_new (FALSE, FALSE, sizeof (guint32));
+	priv->domains = g_ptr_array_new_with_free_func (g_free);
+	priv->searches = g_ptr_array_new_with_free_func (g_free);
+	priv->dns_options = g_ptr_array_new_with_free_func (g_free);
+	priv->nis = g_array_new (FALSE, TRUE, sizeof (guint32));
+	priv->wins = g_array_new (FALSE, TRUE, sizeof (guint32));
+	priv->route_metric = -1;
+}
+
+NMIP4Config *
+nm_ip4_config_new (int ifindex)
+{
+	g_return_val_if_fail (ifindex >= -1, NULL);
+	return (NMIP4Config *) g_object_new (NM_TYPE_IP4_CONFIG,
+	                                     NM_IP4_CONFIG_IFINDEX, ifindex,
+	                                     NULL);
+}
+
+static void
+finalize (GObject *object)
+{
+	NMIP4Config *self = NM_IP4_CONFIG (object);
+	NMIP4ConfigPrivate *priv = NM_IP4_CONFIG_GET_PRIVATE (self);
+
+	nm_clear_g_variant (&priv->address_data_variant);
+	nm_clear_g_variant (&priv->addresses_variant);
+	g_array_unref (priv->addresses);
+	g_array_unref (priv->routes);
+	g_array_unref (priv->nameservers);
+	g_ptr_array_unref (priv->domains);
+	g_ptr_array_unref (priv->searches);
+	g_ptr_array_unref (priv->dns_options);
+	g_array_unref (priv->nis);
+	g_free (priv->nis_domain);
+	g_array_unref (priv->wins);
+
+	G_OBJECT_CLASS (nm_ip4_config_parent_class)->finalize (object);
+}
+
 static void
 nm_ip4_config_class_init (NMIP4ConfigClass *config_class)
 {
diff --git a/src/nm-ip6-config.c b/src/nm-ip6-config.c
index 713e2c12a0..c90d04aa5e 100644
--- a/src/nm-ip6-config.c
+++ b/src/nm-ip6-config.c
@@ -35,8 +35,15 @@
 
 #include "introspection/org.freedesktop.NetworkManager.IP6Config.h"
 
+/*****************************************************************************/
+
 typedef struct {
-	gboolean never_default;
+	bool never_default:1;
+	guint32 mss;
+	int ifindex;
+	int dns_priority;
+	NMSettingIP6ConfigPrivacy privacy;
+	gint64 route_metric;
 	struct in6_addr gateway;
 	GArray *addresses;
 	GArray *routes;
@@ -44,13 +51,8 @@ typedef struct {
 	GPtrArray *domains;
 	GPtrArray *searches;
 	GPtrArray *dns_options;
-	guint32 mss;
-	int ifindex;
-	gint64 route_metric;
-	gint dns_priority;
 	GVariant *address_data_variant;
 	GVariant *addresses_variant;
-	NMSettingIP6ConfigPrivacy privacy;
 } NMIP6ConfigPrivate;
 
 struct _NMIP6Config {
@@ -80,26 +82,7 @@ NM_GOBJECT_PROPERTIES_DEFINE (NMIP6Config,
 	PROP_DNS_PRIORITY,
 );
 
-NMIP6Config *
-nm_ip6_config_new (int ifindex)
-{
-	g_return_val_if_fail (ifindex >= -1, NULL);
-	return (NMIP6Config *) g_object_new (NM_TYPE_IP6_CONFIG,
-	                                     NM_IP6_CONFIG_IFINDEX, ifindex,
-	                                     NULL);
-}
-
-NMIP6Config *
-nm_ip6_config_new_cloned (const NMIP6Config *src)
-{
-	NMIP6Config *new;
-
-	g_return_val_if_fail (NM_IS_IP6_CONFIG (src), NULL);
-
-	new = nm_ip6_config_new (nm_ip6_config_get_ifindex (src));
-	nm_ip6_config_replace (new, src, NULL);
-	return new;
-}
+/*****************************************************************************/
 
 int
 nm_ip6_config_get_ifindex (const NMIP6Config *config)
@@ -1256,7 +1239,7 @@ nm_ip6_config_set_never_default (NMIP6Config *config, gboolean never_default)
 {
 	NMIP6ConfigPrivate *priv = NM_IP6_CONFIG_GET_PRIVATE (config);
 
-	priv->never_default = !!never_default;
+	priv->never_default = never_default;
 }
 
 gboolean
@@ -2000,38 +1983,6 @@ nm_ip6_config_equal (const NMIP6Config *a, const NMIP6Config *b)
 /*****************************************************************************/
 
 static void
-nm_ip6_config_init (NMIP6Config *config)
-{
-	NMIP6ConfigPrivate *priv = NM_IP6_CONFIG_GET_PRIVATE (config);
-
-	priv->addresses = g_array_new (FALSE, TRUE, sizeof (NMPlatformIP6Address));
-	priv->routes = g_array_new (FALSE, TRUE, sizeof (NMPlatformIP6Route));
-	priv->nameservers = g_array_new (FALSE, TRUE, sizeof (struct in6_addr));
-	priv->domains = g_ptr_array_new_with_free_func (g_free);
-	priv->searches = g_ptr_array_new_with_free_func (g_free);
-	priv->dns_options = g_ptr_array_new_with_free_func (g_free);
-	priv->route_metric = -1;
-}
-
-static void
-finalize (GObject *object)
-{
-	NMIP6Config *self = NM_IP6_CONFIG (object);
-	NMIP6ConfigPrivate *priv = NM_IP6_CONFIG_GET_PRIVATE (self);
-
-	g_array_unref (priv->addresses);
-	g_array_unref (priv->routes);
-	g_array_unref (priv->nameservers);
-	g_ptr_array_unref (priv->domains);
-	g_ptr_array_unref (priv->searches);
-	g_ptr_array_unref (priv->dns_options);
-	nm_clear_g_variant (&priv->address_data_variant);
-	nm_clear_g_variant (&priv->addresses_variant);
-
-	G_OBJECT_CLASS (nm_ip6_config_parent_class)->finalize (object);
-}
-
-static void
 nameservers_to_gvalue (GArray *array, GValue *value)
 {
 	GVariantBuilder builder;
@@ -2223,6 +2174,7 @@ set_property (GObject *object,
 
 	switch (prop_id) {
 	case PROP_IFINDEX:
+		/* construct-only */
 		priv->ifindex = g_value_get_int (value);
 		break;
 	default:
@@ -2231,6 +2183,61 @@ set_property (GObject *object,
 	}
 }
 
+/*****************************************************************************/
+
+static void
+nm_ip6_config_init (NMIP6Config *config)
+{
+	NMIP6ConfigPrivate *priv = NM_IP6_CONFIG_GET_PRIVATE (config);
+
+	priv->addresses = g_array_new (FALSE, TRUE, sizeof (NMPlatformIP6Address));
+	priv->routes = g_array_new (FALSE, TRUE, sizeof (NMPlatformIP6Route));
+	priv->nameservers = g_array_new (FALSE, TRUE, sizeof (struct in6_addr));
+	priv->domains = g_ptr_array_new_with_free_func (g_free);
+	priv->searches = g_ptr_array_new_with_free_func (g_free);
+	priv->dns_options = g_ptr_array_new_with_free_func (g_free);
+	priv->route_metric = -1;
+}
+
+NMIP6Config *
+nm_ip6_config_new (int ifindex)
+{
+	g_return_val_if_fail (ifindex >= -1, NULL);
+	return (NMIP6Config *) g_object_new (NM_TYPE_IP6_CONFIG,
+	                                     NM_IP6_CONFIG_IFINDEX, ifindex,
+	                                     NULL);
+}
+
+NMIP6Config *
+nm_ip6_config_new_cloned (const NMIP6Config *src)
+{
+	NMIP6Config *new;
+
+	g_return_val_if_fail (NM_IS_IP6_CONFIG (src), NULL);
+
+	new = nm_ip6_config_new (nm_ip6_config_get_ifindex (src));
+	nm_ip6_config_replace (new, src, NULL);
+	return new;
+}
+
+static void
+finalize (GObject *object)
+{
+	NMIP6Config *self = NM_IP6_CONFIG (object);
+	NMIP6ConfigPrivate *priv = NM_IP6_CONFIG_GET_PRIVATE (self);
+
+	g_array_unref (priv->addresses);
+	g_array_unref (priv->routes);
+	g_array_unref (priv->nameservers);
+	g_ptr_array_unref (priv->domains);
+	g_ptr_array_unref (priv->searches);
+	g_ptr_array_unref (priv->dns_options);
+	nm_clear_g_variant (&priv->address_data_variant);
+	nm_clear_g_variant (&priv->addresses_variant);
+
+	G_OBJECT_CLASS (nm_ip6_config_parent_class)->finalize (object);
+}
+
 static void
 nm_ip6_config_class_init (NMIP6ConfigClass *config_class)
 {
@@ -2239,12 +2246,10 @@ nm_ip6_config_class_init (NMIP6ConfigClass *config_class)
 
 	exported_object_class->export_path = NM_EXPORT_PATH_NUMBERED (NM_DBUS_PATH"/IP6Config");
 
-	/* virtual methods */
 	object_class->get_property = get_property;
 	object_class->set_property = set_property;
 	object_class->finalize = finalize;
 
-	/* properties */
 	obj_properties[PROP_IFINDEX] =
 	    g_param_spec_int (NM_IP6_CONFIG_IFINDEX, "", "",
 	                      -1, G_MAXINT, -1,
diff --git a/src/platform/nmp-netns.c b/src/platform/nmp-netns.c
index 232c6efc9e..c9c6850d54 100644
--- a/src/platform/nmp-netns.c
+++ b/src/platform/nmp-netns.c
@@ -676,12 +676,12 @@ set_property (GObject *object, guint prop_id,
 
 	switch (prop_id) {
 	case PROP_FD_NET:
-		/* construct only */
+		/* construct-only */
 		priv->fd_net = g_value_get_int (value);
 		g_return_if_fail (priv->fd_net > 0);
 		break;
 	case PROP_FD_MNT:
-		/* construct only */
+		/* construct-only */
 		priv->fd_mnt = g_value_get_int (value);
 		g_return_if_fail (priv->fd_mnt > 0);
 		break;
diff --git a/src/ppp/nm-ppp-manager.c b/src/ppp/nm-ppp-manager.c
index cc7451c97b..1bbe29d46b 100644
--- a/src/ppp/nm-ppp-manager.c
+++ b/src/ppp/nm-ppp-manager.c
@@ -1243,7 +1243,7 @@ nm_ppp_manager_class_init (NMPPPManagerClass *manager_class)
 	g_object_class_install_properties (object_class, _PROPERTY_ENUMS_LAST, obj_properties);
 
 	signals[STATE_CHANGED] =
-	    g_signal_new (NM_PPP_MANAGER_STATE_CHANGED,
+	    g_signal_new (NM_PPP_MANAGER_SIGNAL_STATE_CHANGED,
 	                  G_OBJECT_CLASS_TYPE (object_class),
 	                  G_SIGNAL_RUN_FIRST,
 	                  0,
@@ -1252,7 +1252,7 @@ nm_ppp_manager_class_init (NMPPPManagerClass *manager_class)
 	                  G_TYPE_UINT);
 
 	signals[IP4_CONFIG] =
-	    g_signal_new ("ip4-config",
+	    g_signal_new (NM_PPP_MANAGER_SIGNAL_IP4_CONFIG,
 	                  G_OBJECT_CLASS_TYPE (object_class),
 	                  G_SIGNAL_RUN_FIRST,
 	                  0,
@@ -1262,7 +1262,7 @@ nm_ppp_manager_class_init (NMPPPManagerClass *manager_class)
 	                  G_TYPE_OBJECT);
 
 	signals[IP6_CONFIG] =
-	    g_signal_new ("ip6-config",
+	    g_signal_new (NM_PPP_MANAGER_SIGNAL_IP6_CONFIG,
 	                  G_OBJECT_CLASS_TYPE (object_class),
 	                  G_SIGNAL_RUN_FIRST,
 	                  0,
@@ -1270,7 +1270,7 @@ nm_ppp_manager_class_init (NMPPPManagerClass *manager_class)
 	                  G_TYPE_NONE, 3, G_TYPE_STRING, G_TYPE_POINTER, G_TYPE_OBJECT);
 
 	signals[STATS] =
-	    g_signal_new ("stats",
+	    g_signal_new (NM_PPP_MANAGER_SIGNAL_STATS,
 	                  G_OBJECT_CLASS_TYPE (object_class),
 	                  G_SIGNAL_RUN_FIRST,
 	                  0,
diff --git a/src/ppp/nm-ppp-manager.h b/src/ppp/nm-ppp-manager.h
index a86fe26ae5..b1a7bb609a 100644
--- a/src/ppp/nm-ppp-manager.h
+++ b/src/ppp/nm-ppp-manager.h
@@ -23,7 +23,11 @@
 #define __NM_PPP_MANAGER_H__
 
 #define NM_PPP_MANAGER_PARENT_IFACE "parent-iface"
-#define NM_PPP_MANAGER_STATE_CHANGED "state-changed"
+
+#define NM_PPP_MANAGER_SIGNAL_STATE_CHANGED "state-changed"
+#define NM_PPP_MANAGER_SIGNAL_IP4_CONFIG    "ip4-config"
+#define NM_PPP_MANAGER_SIGNAL_IP6_CONFIG    "ip6-config"
+#define NM_PPP_MANAGER_SIGNAL_STATS         "stats"
 
 typedef struct _NMPPPManager NMPPPManager;