diff --git a/src/core/devices/nm-device-private.h b/src/core/devices/nm-device-private.h
index eb37b14ffb..b55e8b4380 100644
--- a/src/core/devices/nm-device-private.h
+++ b/src/core/devices/nm-device-private.h
@@ -143,7 +143,7 @@ NMIP6Config *nm_device_ip6_config_new(NMDevice *self);
 
 NMIPConfig *nm_device_ip_config_new(NMDevice *self, int addr_family);
 
-NML3ConfigData *nm_device_create_l3_config_data(NMDevice *self);
+NML3ConfigData *nm_device_create_l3_config_data(NMDevice *self, NMIPConfigSource source);
 
 /*****************************************************************************/
 
diff --git a/src/core/devices/nm-device.c b/src/core/devices/nm-device.c
index 1fd6ba61da..3c1db20c42 100644
--- a/src/core/devices/nm-device.c
+++ b/src/core/devices/nm-device.c
@@ -2407,7 +2407,7 @@ nm_device_ip_config_new(NMDevice *self, int addr_family)
 }
 
 NML3ConfigData *
-nm_device_create_l3_config_data(NMDevice *self)
+nm_device_create_l3_config_data(NMDevice *self, NMIPConfigSource source)
 {
     int ifindex;
 
@@ -2417,7 +2417,7 @@ nm_device_create_l3_config_data(NMDevice *self)
     if (ifindex <= 0)
         g_return_val_if_reached(NULL);
 
-    return nm_l3_config_data_new(nm_device_get_multi_index(self), ifindex);
+    return nm_l3_config_data_new(nm_device_get_multi_index(self), ifindex, source);
 }
 
 static void
diff --git a/src/core/ndisc/nm-ndisc.c b/src/core/ndisc/nm-ndisc.c
index cf1b58ecf4..655a2523ad 100644
--- a/src/core/ndisc/nm-ndisc.c
+++ b/src/core/ndisc/nm-ndisc.c
@@ -112,9 +112,7 @@ nm_ndisc_data_to_l3cd(NMDedupMultiIndex *       multi_idx,
     guint                                   i;
     const gint32                            now_sec = nm_utils_get_monotonic_timestamp_sec();
 
-    l3cd = nm_l3_config_data_new(multi_idx, ifindex);
-
-    nm_l3_config_data_set_source(l3cd, NM_IP_CONFIG_SOURCE_NDISC);
+    l3cd = nm_l3_config_data_new(multi_idx, ifindex, NM_IP_CONFIG_SOURCE_NDISC);
 
     nm_l3_config_data_set_ip6_privacy(l3cd, ip6_privacy);
 
diff --git a/src/core/nm-l3-config-data.c b/src/core/nm-l3-config-data.c
index 407295e569..51ea92f634 100644
--- a/src/core/nm-l3-config-data.c
+++ b/src/core/nm-l3-config-data.c
@@ -639,12 +639,14 @@ _idx_type_init(DedupMultiIdxType *idx_type, NMPObjectType obj_type)
 }
 
 NML3ConfigData *
-nm_l3_config_data_new(NMDedupMultiIndex *multi_idx, int ifindex)
+nm_l3_config_data_new(NMDedupMultiIndex *multi_idx, int ifindex, NMIPConfigSource source)
 {
     NML3ConfigData *self;
 
     nm_assert(multi_idx);
     nm_assert(ifindex > 0);
+    nm_assert(source == NM_IP_CONFIG_SOURCE_UNKNOWN
+              || (source >= NM_IP_CONFIG_SOURCE_KERNEL && source <= NM_IP_CONFIG_SOURCE_USER));
 
     self  = g_slice_new(NML3ConfigData);
     *self = (NML3ConfigData){
@@ -659,7 +661,7 @@ nm_l3_config_data_new(NMDedupMultiIndex *multi_idx, int ifindex)
         .proxy_method                  = NM_PROXY_CONFIG_METHOD_UNKNOWN,
         .route_table_sync_4            = NM_IP_ROUTE_TABLE_SYNC_MODE_NONE,
         .route_table_sync_6            = NM_IP_ROUTE_TABLE_SYNC_MODE_NONE,
-        .source                        = NM_IP_CONFIG_SOURCE_UNKNOWN,
+        .source                        = source,
         .ip6_privacy                   = NM_SETTING_IP6_CONFIG_PRIVACY_UNKNOWN,
         .ndisc_hop_limit_set           = FALSE,
         .ndisc_reachable_time_msec_set = FALSE,
@@ -1678,18 +1680,6 @@ nm_l3_config_data_set_ip6_mtu(NML3ConfigData *self, guint32 ip6_mtu)
     return TRUE;
 }
 
-gboolean
-nm_l3_config_data_set_source(NML3ConfigData *self, NMIPConfigSource source)
-{
-    nm_assert(_NM_IS_L3_CONFIG_DATA(self, FALSE));
-
-    if (self->source == source)
-        return FALSE;
-
-    self->source = source;
-    return TRUE;
-}
-
 NMSettingIP6ConfigPrivacy
 nm_l3_config_data_get_ip6_privacy(const NML3ConfigData *self)
 {
@@ -2570,7 +2560,7 @@ nm_l3_config_data_new_from_connection(NMDedupMultiIndex *multi_idx,
     NML3ConfigData *self;
     NMSettingProxy *s_proxy;
 
-    self = nm_l3_config_data_new(multi_idx, ifindex);
+    self = nm_l3_config_data_new(multi_idx, ifindex, NM_IP_CONFIG_SOURCE_USER);
 
     _init_from_connection_ip(self, AF_INET, connection, route_table_4, route_metric_4);
     _init_from_connection_ip(self, AF_INET6, connection, route_table_6, route_metric_6);
@@ -2689,7 +2679,7 @@ nm_l3_config_data_new_from_platform(NMDedupMultiIndex *       multi_idx,
     if (nm_platform_link_get_master(platform, ifindex) > 0)
         return NULL;
 
-    self = nm_l3_config_data_new(multi_idx, ifindex);
+    self = nm_l3_config_data_new(multi_idx, ifindex, NM_IP_CONFIG_SOURCE_KERNEL);
 
     _init_from_platform(self, AF_INET, platform, ipv6_privacy_rfc4941);
     _init_from_platform(self, AF_INET6, platform, ipv6_privacy_rfc4941);
@@ -2929,7 +2919,7 @@ nm_l3_config_data_new_clone(const NML3ConfigData *src, int ifindex)
     if (ifindex <= 0)
         ifindex = src->ifindex;
 
-    self = nm_l3_config_data_new(src->multi_idx, ifindex);
+    self = nm_l3_config_data_new(src->multi_idx, ifindex, NM_IP_CONFIG_SOURCE_UNKNOWN);
     nm_l3_config_data_merge(self,
                             src,
                             NM_L3_CONFIG_MERGE_FLAGS_CLONE,
diff --git a/src/core/nm-l3-config-data.h b/src/core/nm-l3-config-data.h
index 9bed47e0f4..9274d8896d 100644
--- a/src/core/nm-l3-config-data.h
+++ b/src/core/nm-l3-config-data.h
@@ -82,7 +82,8 @@ typedef enum _nm_packed {
 
 static inline gboolean NM_IS_L3_CONFIG_DATA(const NML3ConfigData *self);
 
-NML3ConfigData *      nm_l3_config_data_new(NMDedupMultiIndex *multi_idx, int ifindex);
+NML3ConfigData *
+nm_l3_config_data_new(NMDedupMultiIndex *multi_idx, int ifindex, NMIPConfigSource source);
 const NML3ConfigData *nm_l3_config_data_ref(const NML3ConfigData *self);
 const NML3ConfigData *nm_l3_config_data_ref_and_seal(const NML3ConfigData *self);
 const NML3ConfigData *nm_l3_config_data_seal(const NML3ConfigData *self);
@@ -363,8 +364,6 @@ nm_l3_config_data_unset_flags(NML3ConfigData *self, NML3ConfigDatFlags flags)
 
 /*****************************************************************************/
 
-gboolean nm_l3_config_data_set_source(NML3ConfigData *self, NMIPConfigSource source);
-
 const NMPObject *nm_l3_config_data_get_first_obj(const NML3ConfigData *self,
                                                  NMPObjectType         obj_type,
                                                  gboolean (*predicate)(const NMPObject *obj));
diff --git a/src/core/nm-l3-ipv4ll.c b/src/core/nm-l3-ipv4ll.c
index 28ceb39e91..fcec44baf3 100644
--- a/src/core/nm-l3-ipv4ll.c
+++ b/src/core/nm-l3-ipv4ll.c
@@ -357,8 +357,7 @@ _l3cd_config_create(int ifindex, in_addr_t addr, NMDedupMultiIndex *multi_idx)
     nm_assert(ifindex > 0);
     nm_assert(multi_idx);
 
-    l3cd = nm_l3_config_data_new(multi_idx, ifindex);
-    nm_l3_config_data_set_source(l3cd, NM_IP_CONFIG_SOURCE_IP4LL);
+    l3cd = nm_l3_config_data_new(multi_idx, ifindex, NM_IP_CONFIG_SOURCE_IP4LL);
 
     nm_l3_config_data_add_address_4(l3cd, _l3cd_config_plat_init_addr(&a, ifindex, addr));
     nm_l3_config_data_add_route_4(l3cd, _l3cd_config_plat_init_route(&r, ifindex));
diff --git a/src/core/nm-l3cfg.c b/src/core/nm-l3cfg.c
index 340938fbc3..46bdac234b 100644
--- a/src/core/nm-l3cfg.c
+++ b/src/core/nm-l3cfg.c
@@ -3009,7 +3009,8 @@ _l3cfg_update_combined_config(NML3Cfg *              self,
         };
 
         l3cd = nm_l3_config_data_new(nm_platform_get_multi_idx(self->priv.platform),
-                                     self->priv.ifindex);
+                                     self->priv.ifindex,
+                                     NM_IP_CONFIG_SOURCE_UNKNOWN);
 
         for (i = 0; i < l3_config_datas_len; i++) {
             const L3ConfigData *l3cd_data = l3_config_datas_arr[i];
diff --git a/src/core/tests/test-l3cfg.c b/src/core/tests/test-l3cfg.c
index ba065c09b1..d877b5dc5a 100644
--- a/src/core/tests/test-l3cfg.c
+++ b/src/core/tests/test-l3cfg.c
@@ -389,7 +389,7 @@ test_l3cfg(gconstpointer test_data)
     {
         nm_auto_unref_l3cd_init NML3ConfigData *l3cd = NULL;
 
-        l3cd = nm_l3_config_data_new(f->multiidx, f->ifindex0);
+        l3cd = nm_l3_config_data_new(f->multiidx, f->ifindex0, NM_IP_CONFIG_SOURCE_UNKNOWN);
 
         nm_l3_config_data_add_address_4(
             l3cd,