support loopback interface

Support managing the loopback interface through NM as the users want to
set the proper mtu for loopback interface when forwarding the packets.
Additionally, the IP addresses, DNS, route and routing rules are also
allowed to configure for the loopback connection profiles.

https://bugzilla.redhat.com/show_bug.cgi?id=2060905

44 files changed, 846 insertions, 50 deletions

diff --git a/Makefile.am b/Makefile.am
index e97e82b8db..9c6f0116d9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -965,6 +965,8 @@ introspection_sources = \
 	introspection/org.freedesktop.NetworkManager.Device.IPTunnel.h \
 	introspection/org.freedesktop.NetworkManager.Device.Infiniband.c \
 	introspection/org.freedesktop.NetworkManager.Device.Infiniband.h \
+	introspection/org.freedesktop.NetworkManager.Device.Loopback.c \
+	introspection/org.freedesktop.NetworkManager.Device.Loopback.h \
 	introspection/org.freedesktop.NetworkManager.Device.Lowpan.c \
 	introspection/org.freedesktop.NetworkManager.Device.Lowpan.h \
 	introspection/org.freedesktop.NetworkManager.Device.Macsec.c \
@@ -1052,6 +1054,7 @@ DBUS_INTERFACE_DOCS = \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.Generic.xml \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.IPTunnel.xml \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.Infiniband.xml \
+	docs/api/dbus-org.freedesktop.NetworkManager.Device.Loopback.xml \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.Lowpan.xml \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.Macsec.xml \
 	docs/api/dbus-org.freedesktop.NetworkManager.Device.Macvlan.xml \
@@ -1120,6 +1123,7 @@ dbusinterfaces_DATA = \
 	introspection/org.freedesktop.NetworkManager.Device.Generic.xml \
 	introspection/org.freedesktop.NetworkManager.Device.IPTunnel.xml \
 	introspection/org.freedesktop.NetworkManager.Device.Infiniband.xml \
+	introspection/org.freedesktop.NetworkManager.Device.Loopback.xml \
 	introspection/org.freedesktop.NetworkManager.Device.Lowpan.xml \
 	introspection/org.freedesktop.NetworkManager.Device.Macsec.xml \
 	introspection/org.freedesktop.NetworkManager.Device.Macvlan.xml \
@@ -1201,6 +1205,7 @@ src_libnm_core_impl_lib_h_pub_real = \
 	src/libnm-core-public/nm-setting-ip-tunnel.h \
 	src/libnm-core-public/nm-setting-ip4-config.h \
 	src/libnm-core-public/nm-setting-ip6-config.h \
+	src/libnm-core-public/nm-setting-loopback.h \
 	src/libnm-core-public/nm-setting-macsec.h \
 	src/libnm-core-public/nm-setting-macvlan.h \
 	src/libnm-core-public/nm-setting-match.h \
@@ -1280,6 +1285,7 @@ src_libnm_core_impl_lib_c_settings_real = \
 	src/libnm-core-impl/nm-setting-ip-tunnel.c \
 	src/libnm-core-impl/nm-setting-ip4-config.c \
 	src/libnm-core-impl/nm-setting-ip6-config.c \
+	src/libnm-core-impl/nm-setting-loopback.c \
 	src/libnm-core-impl/nm-setting-macsec.c \
 	src/libnm-core-impl/nm-setting-macvlan.c \
 	src/libnm-core-impl/nm-setting-match.c \
@@ -1674,6 +1680,7 @@ libnm_lib_h_pub_real = \
 	src/libnm-client-public/nm-device-generic.h \
 	src/libnm-client-public/nm-device-infiniband.h \
 	src/libnm-client-public/nm-device-ip-tunnel.h \
+	src/libnm-client-public/nm-device-loopback.h \
 	src/libnm-client-public/nm-device-macsec.h \
 	src/libnm-client-public/nm-device-macvlan.h \
 	src/libnm-client-public/nm-device-modem.h \
@@ -1744,6 +1751,7 @@ libnm_lib_c_real = \
 	src/libnm-client-impl/nm-device-generic.c \
 	src/libnm-client-impl/nm-device-infiniband.c \
 	src/libnm-client-impl/nm-device-ip-tunnel.c \
+	src/libnm-client-impl/nm-device-loopback.c \
 	src/libnm-client-impl/nm-device-macsec.c \
 	src/libnm-client-impl/nm-device-macvlan.c \
 	src/libnm-client-impl/nm-device-modem.c \
@@ -2503,6 +2511,8 @@ src_core_libNetworkManager_la_SOURCES = \
 	src/core/devices/nm-device-infiniband.h \
 	src/core/devices/nm-device-ip-tunnel.c \
 	src/core/devices/nm-device-ip-tunnel.h \
+	src/core/devices/nm-device-loopback.c \
+	src/core/devices/nm-device-loopback.h \
 	src/core/devices/nm-device-macsec.c \
 	src/core/devices/nm-device-macsec.h \
 	src/core/devices/nm-device-macvlan.c \
diff --git a/docs/api/Makefile.am b/docs/api/Makefile.am
index c89dbc4494..5553f06968 100644
--- a/docs/api/Makefile.am
+++ b/docs/api/Makefile.am
@@ -54,6 +54,7 @@ content_files = \
 	dbus-org.freedesktop.NetworkManager.Device.Generic.xml \
 	dbus-org.freedesktop.NetworkManager.Device.IPTunnel.xml \
 	dbus-org.freedesktop.NetworkManager.Device.Infiniband.xml \
+	dbus-org.freedesktop.NetworkManager.Device.Loopback.xml \
 	dbus-org.freedesktop.NetworkManager.Device.Macsec.xml \
 	dbus-org.freedesktop.NetworkManager.Device.Macvlan.xml \
 	dbus-org.freedesktop.NetworkManager.Device.Modem.xml \
diff --git a/docs/api/network-manager-docs.xml b/docs/api/network-manager-docs.xml
index 442b05aa7d..d8f4725cf6 100644
--- a/docs/api/network-manager-docs.xml
+++ b/docs/api/network-manager-docs.xml
@@ -193,6 +193,7 @@
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Generic.xml"/>
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.IPTunnel.xml"/>
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Infiniband.xml"/>
+      <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Loopback.xml"/>
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Lowpan.xml"/>
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Macsec.xml"/>
       <xi:include href="dbus-org.freedesktop.NetworkManager.Device.Macvlan.xml"/>
diff --git a/docs/libnm/libnm-docs.xml b/docs/libnm/libnm-docs.xml
index 11a1b73011..e54fda6c51 100644
--- a/docs/libnm/libnm-docs.xml
+++ b/docs/libnm/libnm-docs.xml
@@ -331,6 +331,7 @@ print ("NetworkManager version " + client.get_version())]]></programlisting></in
     <xi:include href="xml/nm-setting-ip-tunnel.xml"/>
     <xi:include href="xml/nm-setting-ip4-config.xml"/>
     <xi:include href="xml/nm-setting-ip6-config.xml"/>
+    <xi:include href="xml/nm-setting-loopback.xml"/>
     <xi:include href="xml/nm-setting-macsec.xml"/>
     <xi:include href="xml/nm-setting-macvlan.xml"/>
     <xi:include href="xml/nm-setting-match.xml"/>
@@ -380,6 +381,7 @@ print ("NetworkManager version " + client.get_version())]]></programlisting></in
     <xi:include href="xml/nm-device-generic.xml"/>
     <xi:include href="xml/nm-device-infiniband.xml"/>
     <xi:include href="xml/nm-device-ip-tunnel.xml"/>
+    <xi:include href="xml/nm-device-loopback.xml"/>
     <xi:include href="xml/nm-device-macsec.xml"/>
     <xi:include href="xml/nm-device-macvlan.xml"/>
     <xi:include href="xml/nm-device-modem.xml"/>
diff --git a/introspection/meson.build b/introspection/meson.build
index 7d495f7af3..9a35548842 100644
--- a/introspection/meson.build
+++ b/introspection/meson.build
@@ -17,6 +17,7 @@ ifaces = [
   'org.freedesktop.NetworkManager.Device.Generic',
   'org.freedesktop.NetworkManager.Device.IPTunnel',
   'org.freedesktop.NetworkManager.Device.Infiniband',
+  'org.freedesktop.NetworkManager.Device.Loopback',
   'org.freedesktop.NetworkManager.Device.Lowpan',
   'org.freedesktop.NetworkManager.Device.Macsec',
   'org.freedesktop.NetworkManager.Device.Macvlan',
diff --git a/introspection/org.freedesktop.NetworkManager.Device.Loopback.xml b/introspection/org.freedesktop.NetworkManager.Device.Loopback.xml
new file mode 100644
index 0000000000..059b5d7e14
--- /dev/null
+++ b/introspection/org.freedesktop.NetworkManager.Device.Loopback.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<node name="/">
+  <!--
+      org.freedesktop.NetworkManager.Device.Loopback:
+      @short_description: Loopback Device.
+
+  -->
+  <interface name="org.freedesktop.NetworkManager.Device.Loopback"/>
+</node>
diff --git a/man/NetworkManager.conf.xml b/man/NetworkManager.conf.xml
index 301172e4cc..2c1fc85217 100644
--- a/man/NetworkManager.conf.xml
+++ b/man/NetworkManager.conf.xml
@@ -1011,6 +1011,10 @@ ipv6.ip6-privacy=0
           </para></listitem>
         </varlistentry>
         <varlistentry>
+          <term><varname>loopback.mtu</varname></term>
+          <listitem><para>If configured explicitly to 0, the MTU is not reconfigured during device activation unless it is required due to IPv6 constraints. If left unspecified, a DHCP/IPv6 SLAAC provided value is used or the MTU is left unspecified on activation.</para></listitem>
+        </varlistentry>
+        <varlistentry>
           <term><varname>sriov.autoprobe-drivers</varname></term>
           <listitem><para>If left unspecified, drivers are autoprobed when the SR-IOV VF gets created.</para></listitem>
         </varlistentry>
diff --git a/po/POTFILES.in b/po/POTFILES.in
index 4f5ecb4496..e5c1f743a8 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -13,6 +13,7 @@ src/core/devices/nm-device-ethernet-utils.c
 src/core/devices/nm-device-ethernet.c
 src/core/devices/nm-device-infiniband.c
 src/core/devices/nm-device-ip-tunnel.c
+src/core/devices/nm-device-loopback.c
 src/core/devices/nm-device-macvlan.c
 src/core/devices/nm-device-tun.c
 src/core/devices/nm-device-veth.c
@@ -47,6 +48,7 @@ src/libnm-client-impl/nm-device-ethernet.c
 src/libnm-client-impl/nm-device-generic.c
 src/libnm-client-impl/nm-device-infiniband.c
 src/libnm-client-impl/nm-device-ip-tunnel.c
+src/libnm-client-impl/nm-device-loopback.c
 src/libnm-client-impl/nm-device-macvlan.c
 src/libnm-client-impl/nm-device-modem.c
 src/libnm-client-impl/nm-device-olpc-mesh.c
diff --git a/src/core/devices/nm-device-factory.c b/src/core/devices/nm-device-factory.c
index 41e9480fe5..2f0ae2e8e5 100644
--- a/src/core/devices/nm-device-factory.c
+++ b/src/core/devices/nm-device-factory.c
@@ -398,6 +398,7 @@ nm_device_factory_manager_load_factories(NMDeviceFactoryManagerFactoryFunc callb
     _ADD_INTERNAL(nm_ethernet_device_factory_get_type);
     _ADD_INTERNAL(nm_infiniband_device_factory_get_type);
     _ADD_INTERNAL(nm_ip_tunnel_device_factory_get_type);
+    _ADD_INTERNAL(nm_loopback_device_factory_get_type);
     _ADD_INTERNAL(nm_macsec_device_factory_get_type);
     _ADD_INTERNAL(nm_macvlan_device_factory_get_type);
     _ADD_INTERNAL(nm_ppp_device_factory_get_type);
diff --git a/src/core/devices/nm-device-loopback.c b/src/core/devices/nm-device-loopback.c
new file mode 100644
index 0000000000..129cbb8a85
--- /dev/null
+++ b/src/core/devices/nm-device-loopback.c
@@ -0,0 +1,163 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#include "src/core/nm-default-daemon.h"
+#include "nm-device-loopback.h"
+#include "nm-device-private.h"
+#include "libnm-platform/nm-platform.h"
+#include "nm-device-factory.h"
+#include "nm-setting-loopback.h"
+#include "libnm-core-aux-intern/nm-libnm-core-utils.h"
+
+#define _NMLOG_DEVICE_TYPE NMDeviceLoopback
+#include "nm-device-logging.h"
+
+/*****************************************************************************/
+
+struct _NMDeviceLoopback {
+    NMDevice parent;
+};
+
+struct _NMDeviceLoopbackClass {
+    NMDeviceClass parent;
+};
+
+G_DEFINE_TYPE(NMDeviceLoopback, nm_device_loopback, NM_TYPE_DEVICE)
+
+/*****************************************************************************/
+
+static NMDeviceCapabilities
+get_generic_capabilities(NMDevice *dev)
+{
+    /* In many aspects, loopback is a software device. Still, don't return
+     * NM_DEVICE_CAP_IS_SOFTWARE here, because we cannot delete nor create
+     * such an interface. */
+    return NM_DEVICE_CAP_NONE;
+}
+
+static guint32
+get_configured_mtu(NMDevice *device, NMDeviceMtuSource *out_source, gboolean *out_force)
+{
+    return nm_device_get_configured_mtu_from_connection(device,
+                                                        NM_TYPE_SETTING_LOOPBACK,
+                                                        out_source);
+}
+
+static const char *
+get_auto_ip_config_method(NMDevice *device, int addr_family)
+{
+    return NM_IS_IPv4(addr_family) ? NM_SETTING_IP4_CONFIG_METHOD_MANUAL
+                                   : NM_SETTING_IP6_CONFIG_METHOD_MANUAL;
+}
+
+static gboolean
+complete_connection(NMDevice            *device,
+                    NMConnection        *connection,
+                    const char          *specific_object,
+                    NMConnection *const *existing_connections,
+                    GError             **error)
+{
+    nm_utils_complete_generic_with_params(nm_device_get_platform(device),
+                                          connection,
+                                          NM_SETTING_LOOPBACK_SETTING_NAME,
+                                          existing_connections,
+                                          NULL,
+                                          _("Loopback connection"),
+                                          NULL,
+                                          nm_device_get_ip_iface(device));
+
+    _nm_connection_ensure_setting(connection, NM_TYPE_SETTING_LOOPBACK);
+
+    return TRUE;
+}
+
+static void
+update_connection(NMDevice *device, NMConnection *connection)
+{
+    _nm_connection_ensure_setting(connection, NM_TYPE_SETTING_LOOPBACK);
+}
+
+static gboolean
+can_reapply_change(NMDevice   *device,
+                   const char *setting_name,
+                   NMSetting  *s_old,
+                   NMSetting  *s_new,
+                   GHashTable *diffs,
+                   GError    **error)
+{
+    if (!nm_streq(setting_name, NM_SETTING_LOOPBACK_SETTING_NAME)) {
+        return NM_DEVICE_CLASS(nm_device_loopback_parent_class)
+            ->can_reapply_change(device, setting_name, s_old, s_new, diffs, error);
+    }
+
+    return nm_device_hash_check_invalid_keys(diffs,
+                                             NM_SETTING_LOOPBACK_SETTING_NAME,
+                                             error,
+                                             NM_SETTING_LOOPBACK_MTU);
+}
+
+/*****************************************************************************/
+
+static const NMDBusInterfaceInfoExtended interface_info_device_loopback = {
+    .parent = NM_DEFINE_GDBUS_INTERFACE_INFO_INIT(NM_DBUS_INTERFACE_DEVICE_LOOPBACK, ),
+};
+
+static void
+nm_device_loopback_init(NMDeviceLoopback *self)
+{}
+
+static void
+nm_device_loopback_class_init(NMDeviceLoopbackClass *klass)
+{
+    NMDeviceClass     *device_class      = NM_DEVICE_CLASS(klass);
+    NMDBusObjectClass *dbus_object_class = NM_DBUS_OBJECT_CLASS(klass);
+
+    dbus_object_class->interface_infos = NM_DBUS_INTERFACE_INFOS(&interface_info_device_loopback);
+
+    device_class->connection_type_supported        = NM_SETTING_LOOPBACK_SETTING_NAME;
+    device_class->connection_type_check_compatible = NM_SETTING_LOOPBACK_SETTING_NAME;
+    device_class->link_types = NM_DEVICE_DEFINE_LINK_TYPES(NM_LINK_TYPE_LOOPBACK);
+
+    device_class->complete_connection                    = complete_connection;
+    device_class->get_generic_capabilities               = get_generic_capabilities;
+    device_class->update_connection                      = update_connection;
+    device_class->act_stage1_prepare_set_hwaddr_ethernet = TRUE;
+    device_class->get_auto_ip_config_method              = get_auto_ip_config_method;
+    device_class->get_configured_mtu                     = get_configured_mtu;
+    device_class->can_reapply_change                     = can_reapply_change;
+}
+
+/*****************************************************************************/
+
+#define NM_TYPE_LOOPBACK_DEVICE_FACTORY (nm_loopback_device_factory_get_type())
+#define NM_LOOPBACK_DEVICE_FACTORY(obj) \
+    (G_TYPE_CHECK_INSTANCE_CAST((obj), NM_TYPE_LOOPBACK_DEVICE_FACTORY, NMLoopbackDeviceFactory))
+
+static NMDevice *
+create_device(NMDeviceFactory      *factory,
+              const char           *iface,
+              const NMPlatformLink *plink,
+              NMConnection         *connection,
+              gboolean             *out_ignore)
+{
+    return g_object_new(NM_TYPE_DEVICE_LOOPBACK,
+                        NM_DEVICE_IFACE,
+                        iface,
+                        NM_DEVICE_TYPE_DESC,
+                        "Loopback",
+                        NM_DEVICE_DEVICE_TYPE,
+                        NM_DEVICE_TYPE_LOOPBACK,
+                        NM_DEVICE_LINK_TYPE,
+                        NM_LINK_TYPE_LOOPBACK,
+                        NULL);
+}
+
+NM_DEVICE_FACTORY_DEFINE_INTERNAL(
+    LOOPBACK,
+    Loopback,
+    loopback,
+    NM_DEVICE_FACTORY_DECLARE_LINK_TYPES(NM_LINK_TYPE_LOOPBACK)
+        NM_DEVICE_FACTORY_DECLARE_SETTING_TYPES(NM_SETTING_LOOPBACK_SETTING_NAME),
+    factory_class->create_device = create_device;);
diff --git a/src/core/devices/nm-device-loopback.h b/src/core/devices/nm-device-loopback.h
new file mode 100644
index 0000000000..42db8ec050
--- /dev/null
+++ b/src/core/devices/nm-device-loopback.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#ifndef __NETWORKMANAGER_DEVICE_LOOPBACK_H__
+#define __NETWORKMANAGER_DEVICE_LOOPBACK_H__
+
+#include "nm-device-generic.h"
+
+#define NM_TYPE_DEVICE_LOOPBACK (nm_device_loopback_get_type())
+#define NM_DEVICE_LOOPBACK(obj) \
+    (G_TYPE_CHECK_INSTANCE_CAST((obj), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopback))
+#define NM_DEVICE_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_CAST((klass), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopbackClass))
+#define NM_IS_DEVICE_LOOPBACK(obj) (G_TYPE_CHECK_INSTANCE_TYPE((obj), NM_TYPE_DEVICE_LOOPBACK))
+#define NM_IS_DEVICE_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_TYPE((klass), NM_TYPE_DEVICE_LOOPBACK))
+#define NM_DEVICE_LOOPBACK_GET_CLASS(obj) \
+    (G_TYPE_INSTANCE_GET_CLASS((obj), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopbackClass))
+
+typedef struct _NMDeviceLoopback      NMDeviceLoopback;
+typedef struct _NMDeviceLoopbackClass NMDeviceLoopbackClass;
+
+GType nm_device_loopback_get_type(void);
+
+#endif /* __NETWORKMANAGER_DEVICE_LOOPBACK_H__ */
diff --git a/src/core/devices/nm-device.c b/src/core/devices/nm-device.c
index 132825af41..d3aa41b7cd 100644
--- a/src/core/devices/nm-device.c
+++ b/src/core/devices/nm-device.c
@@ -77,6 +77,7 @@
 
 #include "nm-device-generic.h"
 #include "nm-device-bridge.h"
+#include "nm-device-loopback.h"
 #include "nm-device-vlan.h"
 #include "nm-device-vrf.h"
 #include "nm-device-wireguard.h"
@@ -1581,6 +1582,9 @@ _prop_get_ipv4_link_local(NMDevice *self)
     if (!s_ip4)
         return NM_SETTING_IP4_LL_DISABLED;
 
+    if (NM_IS_DEVICE_LOOPBACK(self))
+        return NM_SETTING_IP4_LL_DISABLED;
+
     link_local = nm_setting_ip4_config_get_link_local(s_ip4);
 
     if (link_local == NM_SETTING_IP4_LL_DEFAULT) {
@@ -2734,13 +2738,6 @@ _ethtool_state_set(NMDevice *self)
 
 /*****************************************************************************/
 
-static gboolean
-is_loopback(NMDevice *self)
-{
-    return NM_IS_DEVICE_GENERIC(self)
-           && NM_DEVICE_GET_PRIVATE(self)->ifindex == NM_LOOPBACK_IFINDEX;
-}
-
 gboolean
 nm_device_is_vpn(NMDevice *self)
 {
@@ -5000,6 +4997,9 @@ nm_device_get_route_metric_default(NMDeviceType device_type)
      */
 
     switch (device_type) {
+    case NM_DEVICE_TYPE_LOOPBACK:
+        return 30;
+
     /* 50 is also used for VPN plugins (NM_VPN_ROUTE_METRIC_DEFAULT).
      *
      * Note that returning 50 from this function means that this device-type is
@@ -5420,7 +5420,7 @@ concheck_is_possible(NMDevice *self)
 {
     NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE(self);
 
-    if (!nm_device_is_real(self) || is_loopback(self))
+    if (!nm_device_is_real(self) || NM_IS_DEVICE_LOOPBACK(self))
         return FALSE;
 
     /* we enable periodic checks for every device state (except UNKNOWN). Especially with
@@ -7462,11 +7462,6 @@ realize_start_setup(NMDevice             *self,
                                   NM_UNMANAGED_EXTERNAL_DOWN,
                                   _dev_unmanaged_is_external_down(self, TRUE));
 
-    /* Unmanaged the loopback device with an explicit NM_UNMANAGED_BY_TYPE flag.
-     * Later we might want to manage 'lo' too. Currently, that doesn't work because
-     * NetworkManager might down the interface or remove the 127.0.0.1 address. */
-    nm_device_set_unmanaged_flags(self, NM_UNMANAGED_BY_TYPE, is_loopback(self));
-
     nm_device_set_unmanaged_by_user_udev(self);
     nm_device_set_unmanaged_by_user_conf(self);
 
@@ -7656,9 +7651,9 @@ nm_device_unrealize(NMDevice *self, gboolean remove_resources, GError **error)
     nm_device_set_unmanaged_flags(self, NM_UNMANAGED_PLATFORM_INIT, TRUE);
 
     nm_device_set_unmanaged_flags(self,
-                                  NM_UNMANAGED_PARENT | NM_UNMANAGED_BY_TYPE
-                                      | NM_UNMANAGED_USER_UDEV | NM_UNMANAGED_USER_EXPLICIT
-                                      | NM_UNMANAGED_EXTERNAL_DOWN | NM_UNMANAGED_IS_SLAVE,
+                                  NM_UNMANAGED_PARENT | NM_UNMANAGED_USER_UDEV
+                                      | NM_UNMANAGED_USER_EXPLICIT | NM_UNMANAGED_EXTERNAL_DOWN
+                                      | NM_UNMANAGED_IS_SLAVE,
                                   NM_UNMAN_FLAG_OP_FORGET);
 
     nm_device_state_changed(self,
@@ -10800,7 +10795,8 @@ _dev_ipll6_set_llstate(NMDevice *self, NML3IPv6LLState llstate, const struct in6
               || (!priv->ipll_data_6.v6.ipv6ll
                   && NM_IN_SET(priv->ipll_data_6.v6.llstate,
                                NM_L3_IPV6LL_STATE_NONE,
-                               NM_L3_IPV6LL_STATE_DEFUNCT)));
+                               NM_L3_IPV6LL_STATE_DEFUNCT,
+                               NM_L3_IPV6LL_STATE_READY)));
 
     switch (priv->ipll_data_6.v6.llstate) {
     case NM_L3_IPV6LL_STATE_NONE:
@@ -10883,6 +10879,11 @@ _dev_ipll6_start(NMDevice *self)
     if (priv->ipll_data_6.v6.ipv6ll)
         return;
 
+    if (NM_IS_DEVICE_LOOPBACK(self)) {
+        _dev_ipll6_set_llstate(self, NM_L3_IPV6LL_STATE_READY, NULL);
+        return;
+    }
+
     if (!priv->l3cfg) {
         _LOGD(LOGD_IP6, "linklocal6: no IP link for IPv6");
         goto out_fail;
@@ -10994,6 +10995,10 @@ nm_device_get_configured_mtu_from_connection(NMDevice          *self,
         if (setting)
             mtu = nm_setting_wireguard_get_mtu(NM_SETTING_WIREGUARD(setting));
         global_property_name = NM_CON_DEFAULT("wireguard.mtu");
+    } else if (setting_type == NM_TYPE_SETTING_LOOPBACK) {
+        if (setting)
+            mtu = nm_setting_loopback_get_mtu(NM_SETTING_LOOPBACK(setting));
+        global_property_name = NM_CON_DEFAULT("loopback.mtu");
     } else
         g_return_val_if_reached(0);
 
@@ -14129,7 +14134,6 @@ NM_UTILS_FLAGS2STR_DEFINE(nm_unmanaged_flags2str,
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_SLEEPING, "sleeping"),
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_QUITTING, "quitting"),
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_PARENT, "parent"),
-                          NM_UTILS_FLAGS2STR(NM_UNMANAGED_BY_TYPE, "by-type"),
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_PLATFORM_INIT, "platform-init"),
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_USER_EXPLICIT, "user-explicit"),
                           NM_UTILS_FLAGS2STR(NM_UNMANAGED_BY_DEFAULT, "by-default"),
@@ -17128,10 +17132,12 @@ get_address_for_hostname_dns_lookup(NMDevice *self, int addr_family)
 
     if (head_entry) {
         c_list_for_each_entry (iter, &head_entry->lst_entries_head, lst_entries) {
-            const NMPlatformIPAddress *addr = NMP_OBJECT_CAST_IP_ADDRESS(iter->obj);
+            const NMPlatformIPXAddress *addr = NMP_OBJECT_CAST_IPX_ADDRESS(iter->obj);
 
             if (IS_IPv4) {
-                return g_inet_address_new_from_bytes(addr->address_ptr, G_SOCKET_FAMILY_IPV4);
+                if (nm_ip4_addr_is_loopback(addr->a4.address))
+                    continue;
+                return g_inet_address_new_from_bytes(addr->ax.address_ptr, G_SOCKET_FAMILY_IPV4);
             }
 
             /* For IPv6 prefer, in order:
@@ -17140,15 +17146,19 @@ get_address_for_hostname_dns_lookup(NMDevice *self, int addr_family)
              * - link-local
              */
 
-            if (!IN6_IS_ADDR_LINKLOCAL(addr->address_ptr)) {
-                if (!(addr->n_ifa_flags & IFA_F_DEPRECATED)) {
-                    return g_inet_address_new_from_bytes(addr->address_ptr, G_SOCKET_FAMILY_IPV6);
+            if (IN6_ARE_ADDR_EQUAL(&addr->a6.address, &in6addr_loopback))
+                continue;
+
+            if (!IN6_IS_ADDR_LINKLOCAL(addr->ax.address_ptr)) {
+                if (!(addr->ax.n_ifa_flags & IFA_F_DEPRECATED)) {
+                    return g_inet_address_new_from_bytes(addr->ax.address_ptr,
+                                                         G_SOCKET_FAMILY_IPV6);
                 }
-                addr6_nonll = addr->address_ptr;
+                addr6_nonll = addr->ax.address_ptr;
                 continue;
             }
 
-            addr6_ll = addr->address_ptr;
+            addr6_ll = addr->ax.address_ptr;
         }
 
         if (addr6_nonll || addr6_ll)
@@ -17548,7 +17558,7 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
         nm_assert(priv->type == NM_DEVICE_TYPE_UNKNOWN);
         priv->type = g_value_get_uint(value);
         nm_assert(priv->type > NM_DEVICE_TYPE_UNKNOWN);
-        nm_assert(priv->type <= NM_DEVICE_TYPE_VRF);
+        nm_assert(priv->type <= NM_DEVICE_TYPE_LOOPBACK);
         break;
     case PROP_LINK_TYPE:
         /* construct-only */
diff --git a/src/core/devices/nm-device.h b/src/core/devices/nm-device.h
index de850e68f2..cbf5929f54 100644
--- a/src/core/devices/nm-device.h
+++ b/src/core/devices/nm-device.h
@@ -562,7 +562,6 @@ void nm_device_copy_ip6_dns_config(NMDevice *self, NMDevice *from_device);
  * @NM_UNMANAGED_SLEEPING: %TRUE when unmanaged because NM is sleeping.
  * @NM_UNMANAGED_QUITTING: %TRUE when unmanaged because NM is shutting down.
  * @NM_UNMANAGED_PARENT: %TRUE when unmanaged due to parent device being unmanaged
- * @NM_UNMANAGED_BY_TYPE: %TRUE for unmanaging device by type, like loopback.
  * @NM_UNMANAGED_PLATFORM_INIT: %TRUE when unmanaged because platform link not
  *   yet initialized. Unrealized device are also unmanaged for this reason.
  * @NM_UNMANAGED_USER_EXPLICIT: %TRUE when unmanaged by explicit user decision
@@ -593,20 +592,19 @@ typedef enum {
     NM_UNMANAGED_SLEEPING      = (1LL << 0),
     NM_UNMANAGED_QUITTING      = (1LL << 1),
     NM_UNMANAGED_PARENT        = (1LL << 2),
-    NM_UNMANAGED_BY_TYPE       = (1LL << 3),
-    NM_UNMANAGED_PLATFORM_INIT = (1LL << 4),
-    NM_UNMANAGED_USER_EXPLICIT = (1LL << 5),
-    NM_UNMANAGED_USER_SETTINGS = (1LL << 6),
+    NM_UNMANAGED_PLATFORM_INIT = (1LL << 3),
+    NM_UNMANAGED_USER_EXPLICIT = (1LL << 4),
+    NM_UNMANAGED_USER_SETTINGS = (1LL << 5),
 
     /* These flags can be non-effective and be overwritten
      * by other flags. */
-    NM_UNMANAGED_BY_DEFAULT    = (1LL << 7),
-    NM_UNMANAGED_USER_CONF     = (1LL << 8),
-    NM_UNMANAGED_USER_UDEV     = (1LL << 9),
-    NM_UNMANAGED_EXTERNAL_DOWN = (1LL << 10),
-    NM_UNMANAGED_IS_SLAVE      = (1LL << 11),
+    NM_UNMANAGED_BY_DEFAULT    = (1LL << 6),
+    NM_UNMANAGED_USER_CONF     = (1LL << 7),
+    NM_UNMANAGED_USER_UDEV     = (1LL << 8),
+    NM_UNMANAGED_EXTERNAL_DOWN = (1LL << 9),
+    NM_UNMANAGED_IS_SLAVE      = (1LL << 10),
 
-    NM_UNMANAGED_ALL = ((1LL << 12) - 1),
+    NM_UNMANAGED_ALL = ((1LL << 11) - 1),
 } NMUnmanagedFlags;
 
 typedef enum {
diff --git a/src/core/dns/nm-dns-systemd-resolved.c b/src/core/dns/nm-dns-systemd-resolved.c
index 5a22fa25ca..9608106141 100644
--- a/src/core/dns/nm-dns-systemd-resolved.c
+++ b/src/core/dns/nm-dns-systemd-resolved.c
@@ -418,6 +418,8 @@ prepare_one_interface(NMDnsSystemdResolved *self, const InterfaceConfig *ic)
     gboolean                      has_default_route = FALSE;
     guint                         i;
 
+    nm_assert(ic->ifindex != NM_LOOPBACK_IFINDEX);
+
     g_variant_builder_init(&dns, G_VARIANT_TYPE("(ia(iay))"));
     g_variant_builder_add(&dns, "i", ic->ifindex);
     g_variant_builder_open(&dns, G_VARIANT_TYPE("a(iay)"));
@@ -708,6 +710,13 @@ update(NMDnsPlugin             *plugin,
 
         nm_assert(ifindex == nm_l3_config_data_get_ifindex(ip_data->l3cd));
 
+        if (ifindex == NM_LOOPBACK_IFINDEX) {
+            /* systemd-resolved API is per-link, and loopback is not supported.
+             * Unclear what to do about DNS configuration on loopback. Just skip
+             * it here. */
+            continue;
+        }
+
         ic = g_hash_table_lookup(interfaces, GINT_TO_POINTER(ifindex));
         if (!ic) {
             ic  = g_slice_new(InterfaceConfig);
diff --git a/src/core/meson.build b/src/core/meson.build
index f3359ad0f5..d830fbdd89 100644
--- a/src/core/meson.build
+++ b/src/core/meson.build
@@ -103,6 +103,7 @@ libNetworkManager = static_library(
     'devices/nm-device-generic.c',
     'devices/nm-device-infiniband.c',
     'devices/nm-device-ip-tunnel.c',
+    'devices/nm-device-loopback.c',
     'devices/nm-device-macsec.c',
     'devices/nm-device-macvlan.c',
     'devices/nm-device-ppp.c',
diff --git a/src/core/nm-l3cfg.c b/src/core/nm-l3cfg.c
index f2ed0f63fb..56c40579c5 100644
--- a/src/core/nm-l3cfg.c
+++ b/src/core/nm-l3cfg.c
@@ -1430,7 +1430,8 @@ _acd_data_free(AcdData *acd_data)
 }
 
 static guint
-_acd_data_collect_tracks_data(const AcdData     *acd_data,
+_acd_data_collect_tracks_data(NML3Cfg           *self,
+                              const AcdData     *acd_data,
                               NMTernary          dirty_selector,
                               guint32           *out_best_acd_timeout_msec,
                               NML3AcdDefendType *out_best_acd_defend_type)
@@ -1466,6 +1467,12 @@ _acd_data_collect_tracks_data(const AcdData     *acd_data,
     nm_assert(n == 0 || best_acd_defend_type > _NM_L3_ACD_DEFEND_TYPE_NONE);
     nm_assert(best_acd_defend_type <= NM_L3_ACD_DEFEND_TYPE_ALWAYS);
 
+    if (self->priv.ifindex == NM_LOOPBACK_IFINDEX) {
+        /* On loopback interface, ACD makes no sense. We always force the
+         * timeout to zero, which means no ACD. */
+        best_acd_timeout_msec = 0;
+    }
+
     NM_SET_OUT(out_best_acd_timeout_msec, n > 0 ? best_acd_timeout_msec : 0u);
     NM_SET_OUT(out_best_acd_defend_type, best_acd_defend_type);
     return n;
@@ -2313,7 +2320,8 @@ _l3_acd_data_state_change(NML3Cfg           *self,
         return;
 
 handle_init:
-        if (_acd_data_collect_tracks_data(acd_data,
+        if (_acd_data_collect_tracks_data(self,
+                                          acd_data,
                                           NM_TERNARY_FALSE,
                                           &acd_timeout_msec,
                                           &acd_defend_type)
@@ -2362,7 +2370,8 @@ handle_init:
 
         /* we just did a commit of the IP configuration and now visit all ACD states
          * and kick off the necessary actions... */
-        if (_acd_data_collect_tracks_data(acd_data,
+        if (_acd_data_collect_tracks_data(self,
+                                          acd_data,
                                           NM_TERNARY_TRUE,
                                           &acd_timeout_msec,
                                           &acd_defend_type)
@@ -2465,7 +2474,8 @@ handle_init:
             /* after a timeout, re-probe the address. This only happens if the caller
              * does not deconfigure the address after USED/CONFLICT. But in that case,
              * we eventually want to retry. */
-            if (_acd_data_collect_tracks_data(acd_data,
+            if (_acd_data_collect_tracks_data(self,
+                                              acd_data,
                                               NM_TERNARY_TRUE,
                                               &acd_timeout_msec,
                                               &acd_defend_type)
@@ -3713,6 +3723,42 @@ _l3cfg_update_combined_config(NML3Cfg               *self,
                                     &hook_data);
         }
 
+        if (self->priv.ifindex == NM_LOOPBACK_IFINDEX) {
+            NMPlatformIPXRoute rx;
+
+            if (!nm_l3_config_data_lookup_address_4(l3cd, NM_IPV4LO_ADDR1, 8, NM_IPV4LO_ADDR1)) {
+                const NMPlatformIP4Address ip4_address = (NMPlatformIP4Address){
+                    .address      = NM_IPV4LO_ADDR1,
+                    .peer_address = NM_IPV4LO_ADDR1,
+                    .ifindex      = NM_LOOPBACK_IFINDEX,
+                    .plen         = 8,
+                };
+                nm_l3_config_data_add_address_4(l3cd, &ip4_address);
+            }
+            if (!nm_l3_config_data_lookup_address_6(l3cd, &in6addr_loopback)) {
+                const NMPlatformIP6Address ip6_address = (NMPlatformIP6Address){
+                    .address = IN6ADDR_LOOPBACK_INIT,
+                    .ifindex = NM_LOOPBACK_IFINDEX,
+                    .plen    = 128,
+                };
+                nm_l3_config_data_add_address_6(l3cd, &ip6_address);
+            }
+
+            rx.r4 = (NMPlatformIP4Route){
+                .ifindex       = NM_LOOPBACK_IFINDEX,
+                .rt_source     = NM_IP_CONFIG_SOURCE_KERNEL,
+                .network       = NM_IPV4LO_ADDR1,
+                .plen          = 8,
+                .table_coerced = nm_platform_route_table_coerce(RT_TABLE_LOCAL),
+                .scope_inv     = nm_platform_route_scope_inv(RT_SCOPE_HOST),
+                .type_coerced  = nm_platform_route_type_coerce(RTN_LOCAL),
+                .pref_src      = NM_IPV4LO_ADDR1,
+            };
+            nm_platform_ip_route_normalize(AF_INET, &rx.rx);
+            if (!nm_l3_config_data_lookup_route(l3cd, AF_INET, &rx.rx)) {
+                nm_l3_config_data_add_route_4(l3cd, &rx.r4);
+            }
+        }
         for (i = 0; i < l3_config_datas_len; i++) {
             const L3ConfigData *l3cd_data = l3_config_datas_arr[i];
             int                 IS_IPv4;
@@ -4552,6 +4598,29 @@ _l3_commit_one(NML3Cfg              *self,
         }
     }
 
+    if (self->priv.ifindex == NM_LOOPBACK_IFINDEX) {
+        if (!addresses) {
+            addresses = g_ptr_array_new_with_free_func((GDestroyNotify) nmp_object_unref);
+            if (IS_IPv4) {
+                g_ptr_array_add(addresses,
+                                nmp_object_new(NMP_OBJECT_TYPE_IP4_ADDRESS,
+                                               &((const NMPlatformIP4Address){
+                                                   .address      = NM_IPV4LO_ADDR1,
+                                                   .peer_address = NM_IPV4LO_ADDR1,
+                                                   .ifindex      = NM_LOOPBACK_IFINDEX,
+                                                   .plen         = 8,
+                                               })));
+            } else {
+                g_ptr_array_add(addresses,
+                                nmp_object_new(NMP_OBJECT_TYPE_IP6_ADDRESS,
+                                               &((const NMPlatformIP6Address){
+                                                   .address = IN6ADDR_LOOPBACK_INIT,
+                                                   .ifindex = NM_LOOPBACK_IFINDEX,
+                                                   .plen    = 128,
+                                               })));
+            }
+        }
+    }
     /* FIXME(l3cfg): need to honor and set nm_l3_config_data_get_ndisc_*(). */
     /* FIXME(l3cfg): need to honor and set nm_l3_config_data_get_mtu(). */
 
@@ -4560,7 +4629,9 @@ _l3_commit_one(NML3Cfg              *self,
                                 self->priv.ifindex,
                                 addresses,
                                 addresses_prune,
-                                NMP_IP_ADDRESS_SYNC_FLAGS_WITH_NOPREFIXROUTE);
+                                self->priv.ifindex == NM_LOOPBACK_IFINDEX
+                                    ? NMP_IP_ADDRESS_SYNC_FLAGS_NONE
+                                    : NMP_IP_ADDRESS_SYNC_FLAGS_WITH_NOPREFIXROUTE);
 
     _nodev_routes_sync(self, addr_family, commit_type, routes_nodev);
 
diff --git a/src/core/nm-manager.c b/src/core/nm-manager.c
index df890cdb6f..f9e8c65e8d 100644
--- a/src/core/nm-manager.c
+++ b/src/core/nm-manager.c
@@ -19,6 +19,7 @@
 #include "NetworkManagerUtils.h"
 #include "devices/nm-device-factory.h"
 #include "devices/nm-device-generic.h"
+#include "devices/nm-device-loopback.h"
 #include "devices/nm-device.h"
 #include "dns/nm-dns-manager.h"
 #include "dhcp/nm-dhcp-manager.h"
@@ -1464,8 +1465,11 @@ find_best_device_state(NMManager *manager)
     NMActiveConnection *ac;
 
     c_list_for_each_entry (ac, &priv->active_connections_lst_head, active_connections_lst) {
-        NMActiveConnectionState ac_state = nm_active_connection_get_state(ac);
+        NMActiveConnectionState ac_state;
 
+        if (NM_IS_DEVICE_LOOPBACK(nm_active_connection_get_device(ac)))
+            continue;
+        ac_state = nm_active_connection_get_state(ac);
         switch (ac_state) {
         case NM_ACTIVE_CONNECTION_STATE_ACTIVATED:
             if (nm_active_connection_get_default(ac, AF_UNSPEC)) {
@@ -7087,10 +7091,6 @@ nm_manager_write_device_state(NMManager *self, NMDevice *device, int *out_ifinde
     ifindex = nm_device_get_ip_ifindex(device);
     if (ifindex <= 0)
         return FALSE;
-    if (ifindex == NM_LOOPBACK_IFINDEX) {
-        /* ignore loopback */
-        return FALSE;
-    }
 
     if (!nm_platform_link_get(priv->platform, ifindex))
         return FALSE;
diff --git a/src/libnm-client-impl/libnm.ver b/src/libnm-client-impl/libnm.ver
index 4a5455ede0..a48eacbb53 100644
--- a/src/libnm-client-impl/libnm.ver
+++ b/src/libnm-client-impl/libnm.ver
@@ -1847,5 +1847,8 @@ global:
 
 libnm_1_42_0 {
 global:
+	nm_device_loopback_get_type;
+	nm_setting_loopback_get_mtu;
+	nm_setting_loopback_get_type;
 	nm_setting_ovs_interface_get_ofport_request;
 } libnm_1_40_0;
diff --git a/src/libnm-client-impl/meson.build b/src/libnm-client-impl/meson.build
index 46464a6328..72f1be9d0c 100644
--- a/src/libnm-client-impl/meson.build
+++ b/src/libnm-client-impl/meson.build
@@ -17,6 +17,7 @@ libnm_client_impl_sources = files(
   'nm-device-generic.c',
   'nm-device-infiniband.c',
   'nm-device-ip-tunnel.c',
+  'nm-device-loopback.c',
   'nm-device-macsec.c',
   'nm-device-macvlan.c',
   'nm-device-modem.c',
diff --git a/src/libnm-client-impl/nm-client.c b/src/libnm-client-impl/nm-client.c
index a2ca833336..de8fb7d4cc 100644
--- a/src/libnm-client-impl/nm-client.c
+++ b/src/libnm-client-impl/nm-client.c
@@ -31,6 +31,7 @@
 #include "nm-device-generic.h"
 #include "nm-device-infiniband.h"
 #include "nm-device-ip-tunnel.h"
+#include "nm-device-loopback.h"
 #include "nm-device-macsec.h"
 #include "nm-device-macvlan.h"
 #include "nm-device-modem.h"
diff --git a/src/libnm-client-impl/nm-device-loopback.c b/src/libnm-client-impl/nm-device-loopback.c
new file mode 100644
index 0000000000..24ebcc126f
--- /dev/null
+++ b/src/libnm-client-impl/nm-device-loopback.c
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#include "libnm-client-impl/nm-default-libnm.h"
+
+#include "nm-device-loopback.h"
+
+#include "nm-object-private.h"
+#include "nm-setting-loopback.h"
+#include "nm-setting-connection.h"
+
+/*****************************************************************************/
+
+struct _NMDeviceLoopback {
+    NMDevice parent;
+};
+
+struct _NMDeviceLoopbackClass {
+    NMDeviceClass parent;
+};
+
+G_DEFINE_TYPE(NMDeviceLoopback, nm_device_loopback, NM_TYPE_DEVICE)
+
+#define NM_DEVICE_LOOPBACK_GET_PRIVATE(self) \
+    _NM_GET_PRIVATE(self, NMDeviceLoopback, NM_IS_DEVICE_LOOPBACK, NMObject, NMDevice)
+
+/*****************************************************************************/
+
+static gboolean
+connection_compatible(NMDevice *device, NMConnection *connection, GError **error)
+{
+    const char *iface_name;
+
+    if (!NM_DEVICE_CLASS(nm_device_loopback_parent_class)
+             ->connection_compatible(device, connection, error))
+        return FALSE;
+
+    if (!nm_connection_is_type(connection, NM_SETTING_LOOPBACK_SETTING_NAME)) {
+        g_set_error_literal(error,
+                            NM_DEVICE_ERROR,
+                            NM_DEVICE_ERROR_INCOMPATIBLE_CONNECTION,
+                            _("The connection was not a loopback connection."));
+        return FALSE;
+    }
+
+    iface_name = nm_connection_get_interface_name(connection);
+    if (!iface_name) {
+        g_set_error_literal(error,
+                            NM_DEVICE_ERROR,
+                            NM_DEVICE_ERROR_INVALID_CONNECTION,
+                            _("The connection did not specify an interface name."));
+        return FALSE;
+    }
+
+    return TRUE;
+}
+
+static GType
+get_setting_type(NMDevice *device)
+{
+    return NM_TYPE_SETTING_LOOPBACK;
+}
+
+/*****************************************************************************/
+
+static void
+nm_device_loopback_init(NMDeviceLoopback *device)
+{}
+
+const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_loopback =
+    NML_DBUS_META_IFACE_INIT(NM_DBUS_INTERFACE_DEVICE_LOOPBACK,
+                             nm_device_loopback_get_type,
+                             NML_DBUS_META_INTERFACE_PRIO_INSTANTIATE_30, );
+
+static void
+nm_device_loopback_class_init(NMDeviceLoopbackClass *loopback_class)
+{
+    NMDeviceClass *device_class = NM_DEVICE_CLASS(loopback_class);
+
+    device_class->connection_compatible = connection_compatible;
+    device_class->get_setting_type      = get_setting_type;
+}
diff --git a/src/libnm-client-impl/nm-device.c b/src/libnm-client-impl/nm-device.c
index 238e7c1709..fcf07a6b52 100644
--- a/src/libnm-client-impl/nm-device.c
+++ b/src/libnm-client-impl/nm-device.c
@@ -312,6 +312,7 @@ coerce_type(NMDeviceType type)
     case NM_DEVICE_TYPE_WIREGUARD:
     case NM_DEVICE_TYPE_WIFI_P2P:
     case NM_DEVICE_TYPE_VRF:
+    case NM_DEVICE_TYPE_LOOPBACK:
         return type;
     }
     return NM_DEVICE_TYPE_UNKNOWN;
@@ -1811,6 +1812,8 @@ get_type_name(NMDevice *device)
         return _("Wi-Fi P2P");
     case NM_DEVICE_TYPE_VRF:
         return _("VRF");
+    case NM_DEVICE_TYPE_LOOPBACK:
+        return _("Loopback");
     case NM_DEVICE_TYPE_GENERIC:
     case NM_DEVICE_TYPE_UNUSED1:
     case NM_DEVICE_TYPE_UNUSED2:
diff --git a/src/libnm-client-impl/nm-libnm-utils.c b/src/libnm-client-impl/nm-libnm-utils.c
index 6a7c155e76..8064fd775f 100644
--- a/src/libnm-client-impl/nm-libnm-utils.c
+++ b/src/libnm-client-impl/nm-libnm-utils.c
@@ -693,6 +693,7 @@ const NMLDBusMetaIface *const _nml_dbus_meta_ifaces[] = {
     &_nml_dbus_meta_iface_nm_device_generic,
     &_nml_dbus_meta_iface_nm_device_iptunnel,
     &_nml_dbus_meta_iface_nm_device_infiniband,
+    &_nml_dbus_meta_iface_nm_device_loopback,
     &_nml_dbus_meta_iface_nm_device_lowpan,
     &_nml_dbus_meta_iface_nm_device_macsec,
     &_nml_dbus_meta_iface_nm_device_macvlan,
diff --git a/src/libnm-client-impl/nm-libnm-utils.h b/src/libnm-client-impl/nm-libnm-utils.h
index 9d9cfa2530..69754c6a09 100644
--- a/src/libnm-client-impl/nm-libnm-utils.h
+++ b/src/libnm-client-impl/nm-libnm-utils.h
@@ -556,7 +556,7 @@ struct _NMLDBusMetaIface {
                              NML_DBUS_META_IFACE_OBJ_PROPERTIES(),                              \
                              ##__VA_ARGS__)
 
-extern const NMLDBusMetaIface *const _nml_dbus_meta_ifaces[44];
+extern const NMLDBusMetaIface *const _nml_dbus_meta_ifaces[45];
 
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_accesspoint;
@@ -572,6 +572,7 @@ extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_dummy;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_generic;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_infiniband;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_iptunnel;
+extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_loopback;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_lowpan;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_macsec;
 extern const NMLDBusMetaIface _nml_dbus_meta_iface_nm_device_macvlan;
diff --git a/src/libnm-client-public/NetworkManager.h b/src/libnm-client-public/NetworkManager.h
index 1cd94d1110..6d8a643b30 100644
--- a/src/libnm-client-public/NetworkManager.h
+++ b/src/libnm-client-public/NetworkManager.h
@@ -42,6 +42,7 @@
 #include "nm-setting-ip6-config.h"
 #include "nm-setting-ip-config.h"
 #include "nm-setting-ip-tunnel.h"
+#include "nm-setting-loopback.h"
 #include "nm-setting-macsec.h"
 #include "nm-setting-macvlan.h"
 #include "nm-setting-match.h"
@@ -109,6 +110,7 @@
 #include "nm-device-generic.h"
 #include "nm-device-infiniband.h"
 #include "nm-device-ip-tunnel.h"
+#include "nm-device-loopback.h"
 #include "nm-device-macsec.h"
 #include "nm-device-macvlan.h"
 #include "nm-device-modem.h"
diff --git a/src/libnm-client-public/meson.build b/src/libnm-client-public/meson.build
index 5232bcb486..bac7e4574b 100644
--- a/src/libnm-client-public/meson.build
+++ b/src/libnm-client-public/meson.build
@@ -20,6 +20,7 @@ libnm_client_headers = files(
   'nm-device-generic.h',
   'nm-device-infiniband.h',
   'nm-device-ip-tunnel.h',
+  'nm-device-loopback.h',
   'nm-device-macsec.h',
   'nm-device-macvlan.h',
   'nm-device-modem.h',
diff --git a/src/libnm-client-public/nm-autoptr.h b/src/libnm-client-public/nm-autoptr.h
index 6c34946ca7..31ae2cce26 100644
--- a/src/libnm-client-public/nm-autoptr.h
+++ b/src/libnm-client-public/nm-autoptr.h
@@ -43,6 +43,7 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceEthernet, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceGeneric, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceIPTunnel, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceInfiniband, g_object_unref)
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceLoopback, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceMacsec, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceMacvlan, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMDeviceModem, g_object_unref)
@@ -82,6 +83,7 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingIP6Config, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingIPConfig, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingIPTunnel, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingInfiniband, g_object_unref)
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingLoopback, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingMacsec, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingMacvlan, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(NMSettingMatch, g_object_unref)
diff --git a/src/libnm-client-public/nm-device-loopback.h b/src/libnm-client-public/nm-device-loopback.h
new file mode 100644
index 0000000000..67e58417ba
--- /dev/null
+++ b/src/libnm-client-public/nm-device-loopback.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#ifndef __NM_DEVICE_LOOPBACK_H__
+#define __NM_DEVICE_LOOPBACK_H__
+
+#if !defined(__NETWORKMANAGER_H_INSIDE__) && !defined(NETWORKMANAGER_COMPILATION)
+#error "Only <NetworkManager.h> can be included directly."
+#endif
+
+#include "nm-device.h"
+
+G_BEGIN_DECLS
+
+#define NM_TYPE_DEVICE_LOOPBACK (nm_device_loopback_get_type())
+#define NM_DEVICE_LOOPBACK(obj) \
+    (G_TYPE_CHECK_INSTANCE_CAST((obj), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopback))
+#define NM_DEVICE_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_CAST((klass), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopbackClass))
+#define NM_IS_DEVICE_LOOPBACK(obj) (G_TYPE_CHECK_INSTANCE_TYPE((obj), NM_TYPE_DEVICE_LOOPBACK))
+#define NM_IS_DEVICE_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_TYPE((klass), NM_TYPE_DEVICE_LOOPBACK))
+#define NM_DEVICE_LOOPBACK_GET_CLASS(obj) \
+    (G_TYPE_INSTANCE_GET_CLASS((obj), NM_TYPE_DEVICE_LOOPBACK, NMDeviceLoopbackClass))
+
+#define NM_DEVICE_LOOPBACK_HW_ADDRESS "hw-address"
+
+/**
+ * NMDeviceLoopback:
+ */
+typedef struct _NMDeviceLoopback      NMDeviceLoopback;
+typedef struct _NMDeviceLoopbackClass NMDeviceLoopbackClass;
+
+GType nm_device_loopback_get_type(void);
+
+G_END_DECLS
+
+#endif /* __NM_DEVICE_LOOPBACK_H__ */
diff --git a/src/libnm-core-impl/meson.build b/src/libnm-core-impl/meson.build
index 83c290857c..d779236ea1 100644
--- a/src/libnm-core-impl/meson.build
+++ b/src/libnm-core-impl/meson.build
@@ -24,6 +24,7 @@ libnm_core_settings_sources = files(
   'nm-setting-ip-tunnel.c',
   'nm-setting-ip4-config.c',
   'nm-setting-ip6-config.c',
+  'nm-setting-loopback.c',
   'nm-setting-macsec.c',
   'nm-setting-macvlan.c',
   'nm-setting-match.c',
diff --git a/src/libnm-core-impl/nm-meta-setting-base-impl.c b/src/libnm-core-impl/nm-meta-setting-base-impl.c
index 69daa76c9d..49d94e5cb6 100644
--- a/src/libnm-core-impl/nm-meta-setting-base-impl.c
+++ b/src/libnm-core-impl/nm-meta-setting-base-impl.c
@@ -32,6 +32,7 @@
 #include "nm-setting-ip-tunnel.h"
 #include "nm-setting-ip4-config.h"
 #include "nm-setting-ip6-config.h"
+#include "nm-setting-loopback.h"
 #include "nm-setting-macsec.h"
 #include "nm-setting-macvlan.h"
 #include "nm-setting-match.h"
@@ -358,6 +359,13 @@ const NMMetaSettingInfo nm_meta_setting_infos[] = {
             .setting_name      = NM_SETTING_IP_TUNNEL_SETTING_NAME,
             .get_setting_gtype = nm_setting_ip_tunnel_get_type,
         },
+    [NM_META_SETTING_TYPE_LOOPBACK] =
+        {
+            .meta_type         = NM_META_SETTING_TYPE_LOOPBACK,
+            .setting_priority  = NM_SETTING_PRIORITY_HW_BASE,
+            .setting_name      = NM_SETTING_LOOPBACK_SETTING_NAME,
+            .get_setting_gtype = nm_setting_loopback_get_type,
+        },
     [NM_META_SETTING_TYPE_MACSEC] =
         {
             .meta_type         = NM_META_SETTING_TYPE_MACSEC,
@@ -608,6 +616,7 @@ const NMMetaSettingType nm_meta_setting_types_by_priority[] = {
     NM_META_SETTING_TYPE_GSM,
     NM_META_SETTING_TYPE_INFINIBAND,
     NM_META_SETTING_TYPE_IP_TUNNEL,
+    NM_META_SETTING_TYPE_LOOPBACK,
     NM_META_SETTING_TYPE_MACSEC,
     NM_META_SETTING_TYPE_MACVLAN,
     NM_META_SETTING_TYPE_OVS_BRIDGE,
diff --git a/src/libnm-core-impl/nm-setting-loopback.c b/src/libnm-core-impl/nm-setting-loopback.c
new file mode 100644
index 0000000000..ea2dc005f8
--- /dev/null
+++ b/src/libnm-core-impl/nm-setting-loopback.c
@@ -0,0 +1,192 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#include "libnm-core-impl/nm-default-libnm-core.h"
+
+#include "nm-setting-loopback.h"
+
+#include "nm-connection-private.h"
+#include "nm-setting-connection.h"
+#include "nm-setting-private.h"
+
+/**
+ * SECTION:nm-setting-loopback
+ * @short_description: Describes connection properties for loopback interfaces
+ *
+ * The #NMSettingLoopback object is a #NMSetting subclass that describes properties
+ * necessary for connection to loopback devices
+ **/
+
+/*****************************************************************************/
+
+NM_GOBJECT_PROPERTIES_DEFINE(NMSettingLoopback, PROP_MTU, );
+
+typedef struct {
+    guint32 mtu;
+} NMSettingLoopbackPrivate;
+
+/**
+ * NMSettingLoopback:
+ *
+ * Loopback Link Settings
+ */
+struct _NMSettingLoopback {
+    NMSetting parent;
+};
+
+struct _NMSettingLoopbackClass {
+    NMSettingClass parent;
+    gpointer       padding[4];
+};
+
+#define NM_SETTING_LOOPBACK_GET_PRIVATE(o) \
+    (G_TYPE_INSTANCE_GET_PRIVATE((o), NM_TYPE_SETTING_LOOPBACK, NMSettingLoopbackPrivate))
+
+G_DEFINE_TYPE(NMSettingLoopback, nm_setting_loopback, NM_TYPE_SETTING)
+
+/*****************************************************************************/
+
+/**
+ * nm_setting_loopback_get_mtu:
+ * @setting: the #NMSettingLoopback
+ *
+ * Returns: the #NMSettingLoopback:mtu property of the setting
+ **/
+guint32
+nm_setting_loopback_get_mtu(NMSettingLoopback *setting)
+{
+    g_return_val_if_fail(NM_IS_SETTING_LOOPBACK(setting), 0);
+
+    return NM_SETTING_LOOPBACK_GET_PRIVATE(setting)->mtu;
+}
+
+static gboolean
+verify(NMSetting *setting, NMConnection *connection, GError **error)
+{
+    if (connection) {
+        NMSettingIPConfig *s_ip4;
+        NMSettingIPConfig *s_ip6;
+        const char        *method;
+
+        if ((s_ip4 = nm_connection_get_setting_ip4_config(connection))) {
+            if ((method = nm_setting_ip_config_get_method(s_ip4))
+                && !NM_IN_STRSET(method,
+                                 NM_SETTING_IP4_CONFIG_METHOD_AUTO,
+                                 NM_SETTING_IP4_CONFIG_METHOD_MANUAL)) {
+                g_set_error(error,
+                            NM_CONNECTION_ERROR,
+                            NM_CONNECTION_ERROR_INVALID_PROPERTY,
+                            _("ipv4 method \"%s\" is not supported for loopback"),
+                            method);
+                g_prefix_error(error,
+                               "%s.%s: ",
+                               NM_SETTING_IP4_CONFIG_SETTING_NAME,
+                               NM_SETTING_IP_CONFIG_METHOD);
+                return FALSE;
+            }
+            if (!NM_IN_SET(nm_setting_ip4_config_get_link_local(NM_SETTING_IP4_CONFIG(s_ip4)),
+                           NM_SETTING_IP4_LL_DEFAULT,
+                           NM_SETTING_IP4_LL_AUTO,
+                           NM_SETTING_IP4_LL_DISABLED)) {
+                g_set_error(error,
+                            NM_CONNECTION_ERROR,
+                            NM_CONNECTION_ERROR_INVALID_PROPERTY,
+                            _("ipv4.link-local cannot be enabled for loopback"));
+                g_prefix_error(error,
+                               "%s.%s: ",
+                               NM_SETTING_IP4_CONFIG_SETTING_NAME,
+                               NM_SETTING_IP4_CONFIG_LINK_LOCAL);
+                return FALSE;
+            }
+        }
+        if ((s_ip6 = nm_connection_get_setting_ip6_config(connection))) {
+            if ((method = nm_setting_ip_config_get_method(s_ip6))
+                && !NM_IN_STRSET(method,
+                                 NM_SETTING_IP6_CONFIG_METHOD_AUTO,
+                                 NM_SETTING_IP6_CONFIG_METHOD_MANUAL)) {
+                g_set_error(error,
+                            NM_CONNECTION_ERROR,
+                            NM_CONNECTION_ERROR_INVALID_PROPERTY,
+                            _("ipv6 method \"%s\" is not supported for loopback"),
+                            method);
+                g_prefix_error(error,
+                               "%s.%s: ",
+                               NM_SETTING_IP6_CONFIG_SETTING_NAME,
+                               NM_SETTING_IP_CONFIG_METHOD);
+                return FALSE;
+            }
+        }
+    }
+    return TRUE;
+}
+
+/*****************************************************************************/
+
+static void
+nm_setting_loopback_init(NMSettingLoopback *setting)
+{}
+
+/**
+ * nm_setting_loopback_new:
+ *
+ * Creates a new #NMSettingLoopback object with default values.
+ *
+ * Returns: (transfer full): the new empty #NMSettingLoopback object
+ *
+ * Since: 1.42
+ **/
+NMSetting *
+nm_setting_loopback_new(void)
+{
+    return g_object_new(NM_TYPE_SETTING_LOOPBACK, NULL);
+}
+
+static void
+nm_setting_loopback_class_init(NMSettingLoopbackClass *klass)
+{
+    GObjectClass   *object_class        = G_OBJECT_CLASS(klass);
+    NMSettingClass *setting_class       = NM_SETTING_CLASS(klass);
+    GArray         *properties_override = _nm_sett_info_property_override_create_array();
+
+    g_type_class_add_private(klass, sizeof(NMSettingLoopbackPrivate));
+
+    object_class->get_property = _nm_setting_property_get_property_direct;
+    object_class->set_property = _nm_setting_property_set_property_direct;
+
+    setting_class->verify = verify;
+
+    /**
+     * NMSettingLoopback:mtu:
+     *
+     * If non-zero, only transmit packets of the specified size or smaller,
+     * breaking larger packets up into multiple Ethernet frames.
+     *
+     * Since: 1.42
+     **/
+    /* ---ifcfg-rh---
+     * property: mtu
+     * variable: MTU
+     * description: MTU of the interface.
+     * ---end---
+     */
+    _nm_setting_property_define_direct_uint32(properties_override,
+                                              obj_properties,
+                                              NM_SETTING_LOOPBACK_MTU,
+                                              PROP_MTU,
+                                              0,
+                                              G_MAXUINT32,
+                                              0,
+                                              NM_SETTING_PARAM_FUZZY_IGNORE,
+                                              NMSettingLoopbackPrivate,
+                                              mtu);
+
+    g_object_class_install_properties(object_class, _PROPERTY_ENUMS_LAST, obj_properties);
+
+    _nm_setting_class_commit(setting_class,
+                             NM_META_SETTING_TYPE_LOOPBACK,
+                             NULL,
+                             properties_override,
+                             NM_SETT_INFO_PRIVATE_OFFSET_FROM_CLASS);
+}
diff --git a/src/libnm-core-impl/tests/test-setting.c b/src/libnm-core-impl/tests/test-setting.c
index 6306437118..fcff3de536 100644
--- a/src/libnm-core-impl/tests/test-setting.c
+++ b/src/libnm-core-impl/tests/test-setting.c
@@ -121,7 +121,7 @@ test_nm_meta_setting_types_by_priority(void)
     G_STATIC_ASSERT_EXPR(_NM_META_SETTING_TYPE_NUM
                          == G_N_ELEMENTS(nm_meta_setting_types_by_priority));
 
-    G_STATIC_ASSERT_EXPR(_NM_META_SETTING_TYPE_NUM == 52);
+    G_STATIC_ASSERT_EXPR(_NM_META_SETTING_TYPE_NUM == 53);
 
     arr = g_ptr_array_new_with_free_func(g_object_unref);
 
diff --git a/src/libnm-core-intern/nm-core-internal.h b/src/libnm-core-intern/nm-core-internal.h
index ee4cc25b42..e2f2690276 100644
--- a/src/libnm-core-intern/nm-core-internal.h
+++ b/src/libnm-core-intern/nm-core-internal.h
@@ -43,6 +43,7 @@
 #include "nm-setting-ip-tunnel.h"
 #include "nm-setting-ip4-config.h"
 #include "nm-setting-ip6-config.h"
+#include "nm-setting-loopback.h"
 #include "nm-setting-macsec.h"
 #include "nm-setting-macvlan.h"
 #include "nm-setting-match.h"
diff --git a/src/libnm-core-intern/nm-meta-setting-base-impl.h b/src/libnm-core-intern/nm-meta-setting-base-impl.h
index 1268865954..ea2175f84c 100644
--- a/src/libnm-core-intern/nm-meta-setting-base-impl.h
+++ b/src/libnm-core-intern/nm-meta-setting-base-impl.h
@@ -127,6 +127,7 @@ typedef enum _nm_packed {
     NM_META_SETTING_TYPE_IP_TUNNEL,
     NM_META_SETTING_TYPE_IP4_CONFIG,
     NM_META_SETTING_TYPE_IP6_CONFIG,
+    NM_META_SETTING_TYPE_LOOPBACK,
     NM_META_SETTING_TYPE_MACSEC,
     NM_META_SETTING_TYPE_MACVLAN,
     NM_META_SETTING_TYPE_MATCH,
diff --git a/src/libnm-core-public/meson.build b/src/libnm-core-public/meson.build
index f1da4d023d..beeeaedd47 100644
--- a/src/libnm-core-public/meson.build
+++ b/src/libnm-core-public/meson.build
@@ -29,6 +29,7 @@ libnm_core_headers = files(
   'nm-setting-ip-tunnel.h',
   'nm-setting-ip4-config.h',
   'nm-setting-ip6-config.h',
+  'nm-setting-loopback.h',
   'nm-setting-macsec.h',
   'nm-setting-macvlan.h',
   'nm-setting-match.h',
diff --git a/src/libnm-core-public/nm-core-types.h b/src/libnm-core-public/nm-core-types.h
index c86c28fa47..4db0c86e3d 100644
--- a/src/libnm-core-public/nm-core-types.h
+++ b/src/libnm-core-public/nm-core-types.h
@@ -35,6 +35,7 @@ typedef struct _NMSettingIP6Config        NMSettingIP6Config;
 typedef struct _NMSettingIPConfig         NMSettingIPConfig;
 typedef struct _NMSettingIPTunnel         NMSettingIPTunnel;
 typedef struct _NMSettingInfiniband       NMSettingInfiniband;
+typedef struct _NMSettingLoopback         NMSettingLoopback;
 typedef struct _NMSettingMacsec           NMSettingMacsec;
 typedef struct _NMSettingMacvlan          NMSettingMacvlan;
 typedef struct _NMSettingMatch            NMSettingMatch;
diff --git a/src/libnm-core-public/nm-dbus-interface.h b/src/libnm-core-public/nm-dbus-interface.h
index 4557dde0fb..3960b198a7 100644
--- a/src/libnm-core-public/nm-dbus-interface.h
+++ b/src/libnm-core-public/nm-dbus-interface.h
@@ -39,6 +39,7 @@
 #define NM_DBUS_INTERFACE_DEVICE_GRE           NM_DBUS_INTERFACE_DEVICE ".Gre"
 #define NM_DBUS_INTERFACE_DEVICE_INFINIBAND    NM_DBUS_INTERFACE_DEVICE ".Infiniband"
 #define NM_DBUS_INTERFACE_DEVICE_IP_TUNNEL     NM_DBUS_INTERFACE_DEVICE ".IPTunnel"
+#define NM_DBUS_INTERFACE_DEVICE_LOOPBACK      NM_DBUS_INTERFACE_DEVICE ".Loopback"
 #define NM_DBUS_INTERFACE_DEVICE_MACSEC        NM_DBUS_INTERFACE_DEVICE ".Macsec"
 #define NM_DBUS_INTERFACE_DEVICE_MACVLAN       NM_DBUS_INTERFACE_DEVICE ".Macvlan"
 #define NM_DBUS_INTERFACE_DEVICE_MODEM         NM_DBUS_INTERFACE_DEVICE ".Modem"
@@ -216,6 +217,7 @@ typedef enum {
  * @NM_DEVICE_TYPE_WIREGUARD: a WireGuard interface
  * @NM_DEVICE_TYPE_WIFI_P2P: an 802.11 Wi-Fi P2P device. Since: 1.16.
  * @NM_DEVICE_TYPE_VRF: A VRF (Virtual Routing and Forwarding) interface. Since: 1.24.
+ * @NM_DEVICE_TYPE_LOOPBACK: a loopback interface. Since: 1.40.
  *
  * #NMDeviceType values indicate the type of hardware represented by a
  * device object.
@@ -253,6 +255,7 @@ typedef enum {
     NM_DEVICE_TYPE_WIREGUARD     = 29,
     NM_DEVICE_TYPE_WIFI_P2P      = 30,
     NM_DEVICE_TYPE_VRF           = 31,
+    NM_DEVICE_TYPE_LOOPBACK      = 32,
 } NMDeviceType;
 
 /**
diff --git a/src/libnm-core-public/nm-setting-loopback.h b/src/libnm-core-public/nm-setting-loopback.h
new file mode 100644
index 0000000000..16bff60514
--- /dev/null
+++ b/src/libnm-core-public/nm-setting-loopback.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2022 Red Hat, Inc.
+ */
+
+#ifndef __NM_SETTING_LOOPBACK_H__
+#define __NM_SETTING_LOOPBACK_H__
+
+#if !defined(__NETWORKMANAGER_H_INSIDE__) && !defined(NETWORKMANAGER_COMPILATION)
+#error "Only <NetworkManager.h> can be included directly."
+#endif
+
+#include "nm-setting.h"
+
+G_BEGIN_DECLS
+
+#define NM_TYPE_SETTING_LOOPBACK (nm_setting_loopback_get_type())
+#define NM_SETTING_LOOPBACK(obj) \
+    (G_TYPE_CHECK_INSTANCE_CAST((obj), NM_TYPE_SETTING_LOOPBACK, NMSettingLoopback))
+#define NM_SETTING_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_CAST((klass), NM_TYPE_SETTING_LOOPBACKCONFIG, NMSettingLoopbackClass))
+#define NM_IS_SETTING_LOOPBACK(obj) (G_TYPE_CHECK_INSTANCE_TYPE((obj), NM_TYPE_SETTING_LOOPBACK))
+#define NM_IS_SETTING_LOOPBACK_CLASS(klass) \
+    (G_TYPE_CHECK_CLASS_TYPE((klass), NM_TYPE_SETTING_LOOPBACK))
+#define NM_SETTING_LOOPBACK_GET_CLASS(obj) \
+    (G_TYPE_INSTANCE_GET_CLASS((obj), NM_TYPE_SETTING_LOOPBACK, NMSettingLoopbackClass))
+
+#define NM_SETTING_LOOPBACK_SETTING_NAME "loopback"
+
+#define NM_SETTING_LOOPBACK_MTU "mtu"
+
+typedef struct _NMSettingLoopbackClass NMSettingLoopbackClass;
+
+NM_AVAILABLE_IN_1_42
+GType nm_setting_loopback_get_type(void);
+NM_AVAILABLE_IN_1_42
+NMSetting *nm_setting_loopback_new(void);
+
+guint32 nm_setting_loopback_get_mtu(NMSettingLoopback *setting);
+
+G_END_DECLS
+
+#endif /* __NM_SETTING_LOOPBACK_H__ */
diff --git a/src/libnm-platform/nm-platform.c b/src/libnm-platform/nm-platform.c
index 3dfe3404d4..792aa68349 100644
--- a/src/libnm-platform/nm-platform.c
+++ b/src/libnm-platform/nm-platform.c
@@ -4665,7 +4665,26 @@ nm_platform_ip_address_get_prune_list(NMPlatform            *self,
     c_list_for_each (iter, &head_entry->lst_entries_head) {
         const NMPObject *obj = c_list_entry(iter, NMDedupMultiEntry, lst_entries)->obj;
 
-        if (!IS_IPv4) {
+        if (IS_IPv4) {
+            const NMPlatformIP4Address *a4 = NMP_OBJECT_CAST_IP4_ADDRESS(obj);
+
+            if (a4->address == NM_IPV4LO_ADDR1 && a4->plen == NM_IPV4LO_PREFIXLEN) {
+                const NMPlatformIP4Address addr = (NMPlatformIP4Address){
+                    .ifindex                   = NM_LOOPBACK_IFINDEX,
+                    .address                   = NM_IPV4LO_ADDR1,
+                    .peer_address              = NM_IPV4LO_ADDR1,
+                    .plen                      = NM_IPV4LO_PREFIXLEN,
+                    .use_ip4_broadcast_address = TRUE,
+                };
+
+                if (nm_platform_ip4_address_cmp(a4,
+                                                &addr,
+                                                NM_PLATFORM_IP_ADDRESS_CMP_TYPE_SEMANTICALLY)
+                    == 0) {
+                    continue;
+                }
+            }
+        } else {
             const NMPlatformIP6Address *a6 = NMP_OBJECT_CAST_IP6_ADDRESS(obj);
 
             if (NM_FLAGS_HAS(a6->n_ifa_flags, IFA_F_SECONDARY)
@@ -4766,6 +4785,44 @@ nm_platform_ip_route_get_prune_list(NMPlatform            *self,
              * pruning them. */
 
             if (NM_IS_IPv4(addr_family)) {
+                if (ifindex == NM_LOOPBACK_IFINDEX
+                    && NM_IN_SET(rt->r4.network, NM_IPV4LO_ADDR1, NM_IPV4LO_NETWORK)) {
+                    NMPlatformIP4Route r;
+
+                    if (rt->r4.network == NM_IPV4LO_ADDR1) {
+                        r = (NMPlatformIP4Route){
+                            .ifindex       = NM_LOOPBACK_IFINDEX,
+                            .type_coerced  = nm_platform_route_type_coerce(RTN_LOCAL),
+                            .table_coerced = nm_platform_route_table_coerce(local_table),
+                            .network       = NM_IPV4LO_ADDR1,
+                            .plen          = 32,
+                            .metric        = 0,
+                            .rt_source     = NM_IPV4LO_ADDR1,
+                            .scope_inv     = nm_platform_route_scope_inv(RT_SCOPE_HOST),
+                            .pref_src      = NM_IPV4LO_ADDR1,
+                        };
+                    } else {
+                        r = (NMPlatformIP4Route){
+                            .ifindex       = NM_LOOPBACK_IFINDEX,
+                            .type_coerced  = nm_platform_route_type_coerce(RTN_LOCAL),
+                            .table_coerced = nm_platform_route_table_coerce(local_table),
+                            .network       = NM_IPV4LO_NETWORK,
+                            .plen          = NM_IPV4LO_PREFIXLEN,
+                            .metric        = 0,
+                            .rt_source     = NM_IPV4LO_ADDR1,
+                            .scope_inv     = nm_platform_route_scope_inv(RT_SCOPE_HOST),
+                            .pref_src      = NM_IPV4LO_ADDR1,
+                        };
+                    }
+
+                    if (nm_platform_ip4_route_cmp(&rt->r4,
+                                                  &r,
+                                                  NM_PLATFORM_IP_ROUTE_CMP_TYPE_SEMANTICALLY)
+                        == 0) {
+                        continue;
+                    }
+                }
+
                 /* for each IPv4 address kernel adds a route like
                  *
                  *  local $ADDR dev $IFACE table local proto kernel scope host src $PRIMARY_ADDR
diff --git a/src/libnmc-setting/nm-meta-setting-base-impl.c b/src/libnmc-setting/nm-meta-setting-base-impl.c
index 69daa76c9d..49d94e5cb6 100644
--- a/src/libnmc-setting/nm-meta-setting-base-impl.c
+++ b/src/libnmc-setting/nm-meta-setting-base-impl.c
@@ -32,6 +32,7 @@
 #include "nm-setting-ip-tunnel.h"
 #include "nm-setting-ip4-config.h"
 #include "nm-setting-ip6-config.h"
+#include "nm-setting-loopback.h"
 #include "nm-setting-macsec.h"
 #include "nm-setting-macvlan.h"
 #include "nm-setting-match.h"
@@ -358,6 +359,13 @@ const NMMetaSettingInfo nm_meta_setting_infos[] = {
             .setting_name      = NM_SETTING_IP_TUNNEL_SETTING_NAME,
             .get_setting_gtype = nm_setting_ip_tunnel_get_type,
         },
+    [NM_META_SETTING_TYPE_LOOPBACK] =
+        {
+            .meta_type         = NM_META_SETTING_TYPE_LOOPBACK,
+            .setting_priority  = NM_SETTING_PRIORITY_HW_BASE,
+            .setting_name      = NM_SETTING_LOOPBACK_SETTING_NAME,
+            .get_setting_gtype = nm_setting_loopback_get_type,
+        },
     [NM_META_SETTING_TYPE_MACSEC] =
         {
             .meta_type         = NM_META_SETTING_TYPE_MACSEC,
@@ -608,6 +616,7 @@ const NMMetaSettingType nm_meta_setting_types_by_priority[] = {
     NM_META_SETTING_TYPE_GSM,
     NM_META_SETTING_TYPE_INFINIBAND,
     NM_META_SETTING_TYPE_IP_TUNNEL,
+    NM_META_SETTING_TYPE_LOOPBACK,
     NM_META_SETTING_TYPE_MACSEC,
     NM_META_SETTING_TYPE_MACVLAN,
     NM_META_SETTING_TYPE_OVS_BRIDGE,
diff --git a/src/libnmc-setting/nm-meta-setting-base-impl.h b/src/libnmc-setting/nm-meta-setting-base-impl.h
index 1268865954..ea2175f84c 100644
--- a/src/libnmc-setting/nm-meta-setting-base-impl.h
+++ b/src/libnmc-setting/nm-meta-setting-base-impl.h
@@ -127,6 +127,7 @@ typedef enum _nm_packed {
     NM_META_SETTING_TYPE_IP_TUNNEL,
     NM_META_SETTING_TYPE_IP4_CONFIG,
     NM_META_SETTING_TYPE_IP6_CONFIG,
+    NM_META_SETTING_TYPE_LOOPBACK,
     NM_META_SETTING_TYPE_MACSEC,
     NM_META_SETTING_TYPE_MACVLAN,
     NM_META_SETTING_TYPE_MATCH,
diff --git a/src/libnmc-setting/nm-meta-setting-desc.c b/src/libnmc-setting/nm-meta-setting-desc.c
index 45475ec405..abf7b7723d 100644
--- a/src/libnmc-setting/nm-meta-setting-desc.c
+++ b/src/libnmc-setting/nm-meta-setting-desc.c
@@ -6585,6 +6585,21 @@ static const NMMetaPropertyInfo *const property_infos_IP_TUNNEL[] = {
 };
 
 #undef  _CURRENT_NM_META_SETTING_TYPE
+#define _CURRENT_NM_META_SETTING_TYPE NM_META_SETTING_TYPE_LOOPBACK
+static const NMMetaPropertyInfo *const property_infos_LOOPBACK[] = {
+    PROPERTY_INFO_WITH_DESC (NM_SETTING_LOOPBACK_MTU,
+        .is_cli_option =                TRUE,
+        .property_alias =               "mtu",
+        .prompt =                       N_("MTU"),
+        .property_type =                &_pt_gobject_mtu,
+        .property_typ_data = DEFINE_PROPERTY_TYP_DATA_SUBTYPE (mtu,
+            .get_fcn =                  MTU_GET_FCN (NMSettingLoopback, nm_setting_loopback_get_mtu),
+        ),
+    ),
+    NULL
+};
+
+#undef  _CURRENT_NM_META_SETTING_TYPE
 #define _CURRENT_NM_META_SETTING_TYPE NM_META_SETTING_TYPE_MACSEC
 static const NMMetaPropertyInfo *const property_infos_MACSEC[] = {
     PROPERTY_INFO_WITH_DESC (NM_SETTING_MACSEC_PARENT,
@@ -8340,6 +8355,7 @@ _setting_init_fcn_wireless (ARGS_SETTING_INIT_FCN)
 #define SETTING_PRETTY_NAME_IP4_CONFIG          N_("IPv4 protocol")
 #define SETTING_PRETTY_NAME_IP6_CONFIG          N_("IPv6 protocol")
 #define SETTING_PRETTY_NAME_IP_TUNNEL           N_("IP-tunnel settings")
+#define SETTING_PRETTY_NAME_LOOPBACK            N_("Loopback settings")
 #define SETTING_PRETTY_NAME_MACSEC              N_("MACsec connection")
 #define SETTING_PRETTY_NAME_MACVLAN             N_("macvlan connection")
 #define SETTING_PRETTY_NAME_MATCH               N_("Match")
@@ -8499,6 +8515,12 @@ const NMMetaSettingInfoEditor nm_meta_setting_infos_editor[] = {
             NM_META_SETTING_VALID_PART_ITEM (ETHTOOL,               FALSE),
         ),
     ),
+    SETTING_INFO (LOOPBACK,
+        .valid_parts = NM_META_SETTING_VALID_PARTS (
+            NM_META_SETTING_VALID_PART_ITEM (CONNECTION,            TRUE),
+            NM_META_SETTING_VALID_PART_ITEM (LOOPBACK,              TRUE),
+        ),
+    ),
     SETTING_INFO (MACSEC,
         .valid_parts = NM_META_SETTING_VALID_PARTS (
             NM_META_SETTING_VALID_PART_ITEM (CONNECTION,            TRUE),
diff --git a/src/libnmc-setting/settings-docs.h.in b/src/libnmc-setting/settings-docs.h.in
index 4fdafed5db..0606d56366 100644
--- a/src/libnmc-setting/settings-docs.h.in
+++ b/src/libnmc-setting/settings-docs.h.in
@@ -432,5 +432,6 @@
 #define DESCRIBE_DOC_NM_SETTING_HOSTNAME_FROM_DNS_LOOKUP N_("Whether the system hostname can be determined from reverse DNS lookup of addresses on this device. When set to NM_TERNARY_DEFAULT (-1), the value from global configuration is used. If the property doesn't have a value in the global configuration, NetworkManager assumes the value to be NM_TERNARY_TRUE (1).")
 #define DESCRIBE_DOC_NM_SETTING_HOSTNAME_ONLY_FROM_DEFAULT N_("If set to NM_TERNARY_TRUE (1), NetworkManager attempts to get the hostname via DHCPv4/DHCPv6 or reverse DNS lookup on this device only when the device has the default route for the given address family (IPv4/IPv6). If set to NM_TERNARY_FALSE (0), the hostname can be set from this device even if it doesn't have the default route. When set to NM_TERNARY_DEFAULT (-1), the value from global configuration is used. If the property doesn't have a value in the global configuration, NetworkManager assumes the value to be NM_TERNARY_FALSE (0).")
 #define DESCRIBE_DOC_NM_SETTING_HOSTNAME_PRIORITY N_("The relative priority of this connection to determine the system hostname. A lower numerical value is better (higher priority).  A connection with higher priority is considered before connections with lower priority. If the value is zero, it can be overridden by a global value from NetworkManager configuration. If the property doesn't have a value in the global configuration, the value is assumed to be 100. Negative values have the special effect of excluding other connections with a greater numerical priority value; so in presence of at least one negative priority, only connections with the lowest priority value will be used to determine the hostname.")
+#define DESCRIBE_DOC_NM_SETTING_LOOPBACK_MTU N_("If non-zero, only transmit packets of the specified size or smaller, breaking larger packets up into multiple Ethernet frames.")
 #define DESCRIBE_DOC_NM_SETTING_OVS_EXTERNAL_IDS_DATA N_("A dictionary of key/value pairs with exernal-ids for OVS.")
 #define DESCRIBE_DOC_NM_SETTING_VETH_PEER N_("This property specifies the peer interface name of the veth. This property is mandatory.")
diff --git a/src/nmcli/generate-docs-nm-settings-nmcli.xml.in b/src/nmcli/generate-docs-nm-settings-nmcli.xml.in
index a9bde03d9b..7afb4c6eb9 100644
--- a/src/nmcli/generate-docs-nm-settings-nmcli.xml.in
+++ b/src/nmcli/generate-docs-nm-settings-nmcli.xml.in
@@ -762,6 +762,11 @@
         <property name="token"
                   description="Configure the token for draft-chown-6man-tokenised-ipv6-identifiers-02 IPv6 tokenized interface identifiers. Useful with eui64 addr-gen-mode." />
     </setting>
+    <setting name="loopback" >
+        <property name="mtu"
+                  alias="mtu"
+                  description="If non-zero, only transmit packets of the specified size or smaller, breaking larger packets up into multiple Ethernet frames." />
+    </setting>
     <setting name="macsec" >
         <property name="parent"
                   alias="dev"