diff --git a/src/routing_layer/nat_detection.c b/src/routing_layer/nat_detection.c
index 6b9cc306..96c0bd38 100644
--- a/src/routing_layer/nat_detection.c
+++ b/src/routing_layer/nat_detection.c
@@ -1181,15 +1181,25 @@ uint64_t nat_detection_probe_delay(struct NAT_DETECTION *detector) {
     return delay > 10000 ? 10000 : delay;
 }
 
-int nat_detection_observe_allowed(struct NAT_DETECTION *detector, struct ETCP_SOCKET *socket,
-                                  const uint8_t peer_key[32], const uint8_t *tag, size_t length) {
-    if (!detector || !socket || socket->probe_only || !tag || length != ROUTE_OBSERVE_TAG_SIZE || memcmp(tag, "NAT3UDP!", 8)) return 1;
+int nat_detection_ping_allowed(struct NAT_DETECTION *detector, struct ETCP_SOCKET *socket,
+                               const uint8_t peer_key[32], const struct sockaddr_storage *source,
+                               uint8_t flags, const uint8_t *tag, size_t length) {
+    if (!detector || !socket || socket->probe_only || (flags & ETCP_PING_FLAG_ADDRESS_CHECK)) return 1;
     nat_detection_probe_delay(detector);
     struct nat_socket *state = socket_state(detector, socket, 0);
     if (!state || !state->reservation_fingerprint || state->cold_until <= get_time_tb() ||
         (!detector->automatic && !state->phase && !state->forced) ||
         (state->measured_profile.source == ADDRESS_SOURCE_ETCP && state->measured_profile.mapping && state->measured_profile.inbound)) return 1;
-    uint64_t peer = sc_derive_node_id_from_pubkey(peer_key), group_id = read64(tag + 25), round = read64(tag + 17), owner = peer;
+    uint64_t peer = sc_derive_node_id_from_pubkey(peer_key);
+    if (!(flags & ETCP_PING_FLAG_OBSERVE)) {
+        history_load(state);
+        if (contacted(state, source)) return 1;
+        DEBUG_DEBUG(DEBUG_CATEGORY_NAT, "NAT background PING reply deferred socket=%s peer=%016llx source=%s",
+                    socket->name, (unsigned long long)peer, sockaddr_storage_to_str(source).str);
+        return 0;
+    }
+    if (!tag || length != ROUTE_OBSERVE_TAG_SIZE || memcmp(tag, "NAT3UDP!", 8)) return 1;
+    uint64_t group_id = read64(tag + 25), round = read64(tag + 17), owner = peer;
     if (state->phase && state->group_id == group_id && state->round == round && (state->helper == peer || state->observer == peer)) return 1;
     for (struct nat_binding *binding = detector->bindings; binding; binding = binding->next)
         if (binding->group_id == group_id && binding->round == round && binding->helper == peer && binding->expires > get_time_tb()) {
diff --git a/src/routing_layer/nat_detection.h b/src/routing_layer/nat_detection.h
index b2387ce7..59733262 100644
--- a/src/routing_layer/nat_detection.h
+++ b/src/routing_layer/nat_detection.h
@@ -43,8 +43,9 @@ void nat_detection_cancel_group(struct NAT_DETECTION *detector, uint64_t group_i
 /* Короткий приоритет начального измерения перед фоновыми UDP-пробами достижимости; задержка в timebase. */
 uint64_t nat_detection_probe_delay(struct NAT_DETECTION *detector);
 /* Холодные измерения сериализуются по node_id; делегированные пробы более раннего owner пропускаются. */
-int nat_detection_observe_allowed(struct NAT_DETECTION *detector, struct ETCP_SOCKET *socket,
-                                  const uint8_t peer_key[32], const uint8_t *tag, size_t length);
+int nat_detection_ping_allowed(struct NAT_DETECTION *detector, struct ETCP_SOCKET *socket,
+                               const uint8_t peer_key[32], const struct sockaddr_storage *source,
+                               uint8_t flags, const uint8_t *tag, size_t length);
 void nat_detection_link_ready(struct NAT_DETECTION *detector, struct ETCP_LINK *link);
 void nat_detection_cancel_for_conn(struct NAT_DETECTION *detector, struct ETCP_CONN *connection);
 void nat_detection_socket_removed(struct NAT_DETECTION *detector, struct ETCP_SOCKET *socket);
diff --git a/src/transport_layer/etcp_connections.c b/src/transport_layer/etcp_connections.c
index 3f46de74..202ba4ea 100644
--- a/src/transport_layer/etcp_connections.c
+++ b/src/transport_layer/etcp_connections.c
@@ -1796,8 +1796,8 @@ static int handle_ping(struct ETCP_SOCKET* e_sock, struct ETCP_DGRAM* pkt, const
     if ((flags & ETCP_PING_FLAG_OBSERVE) && (flags & ETCP_PING_FLAG_ADDRESS_CHECK)) {
         DEBUG_WARN(DEBUG_CATEGORY_NAT, "UDP probe has incompatible flags=%02x", flags); return 7;
     }
+    if (!nat_detection_ping_allowed(e_sock->instance->nat_det, e_sock, decrypted_pubkey, addr, flags, udata, ulen)) return 0;
     if ((flags & ETCP_PING_FLAG_OBSERVE) && e_sock->instance->nat_det) {
-        if (!nat_detection_observe_allowed(e_sock->instance->nat_det, e_sock, decrypted_pubkey, udata, ulen)) return 0;
         nat_detection_record_observation(e_sock->instance->nat_det, e_sock, decrypted_pubkey, addr, udata, ulen);
     }
     if ((flags & ETCP_PING_FLAG_ADDRESS_CHECK) && e_sock->instance->nat_det)