diff --git a/src/bacnet/bacenum.h b/src/bacnet/bacenum.h
index 9067c87b..e9c1afe8 100644
--- a/src/bacnet/bacenum.h
+++ b/src/bacnet/bacenum.h
@@ -1714,6 +1714,8 @@ typedef enum {
     NETWORK_MESSAGE_WHAT_IS_NETWORK_NUMBER = 18,
     NETWORK_MESSAGE_NETWORK_NUMBER_IS = 19,
     /* X'14' to X'7F': Reserved for use by ASHRAE, */
+    NETWORK_MESSAGE_ASHRAE_RESERVED_MIN = 20,
+    NETWORK_MESSAGE_ASHRAE_RESERVED_MAX = 127,
     /* X'80' to X'FF': Available for vendor proprietary messages */
     NETWORK_MESSAGE_INVALID = 0x100
 } BACNET_NETWORK_MESSAGE_TYPE;
diff --git a/src/bacnet/basic/npdu/h_npdu.c b/src/bacnet/basic/npdu/h_npdu.c
index dfaf863d..3b66144a 100644
--- a/src/bacnet/basic/npdu/h_npdu.c
+++ b/src/bacnet/basic/npdu/h_npdu.c
@@ -194,6 +194,13 @@ static void network_control_handler(BACNET_ADDRESS *src,
         default:
             break;
     }
+    if ((npdu_data->network_message_type >=
+         NETWORK_MESSAGE_ASHRAE_RESERVED_MIN) &&
+        (npdu_data->network_message_type <=
+         NETWORK_MESSAGE_ASHRAE_RESERVED_MAX)) {
+        npdu_send_reject_message_to_network(
+            src, dnet, status);
+    }
 }
 
 /** Handler for the NPDU portion of a received packet.
@@ -275,3 +282,37 @@ void npdu_handler(BACNET_ADDRESS *src, uint8_t *pdu, uint16_t pdu_len)
 
     return;
 }
+
+/**
+ * Send NPDU reject message to network
+ *
+ * @param dst - the destination address for the message
+ * @param net - local network number
+ * @param status - 0=learned, 1=assigned
+ * @return number of bytes sent
+ */
+int npdu_send_reject_message_to_network(
+    BACNET_ADDRESS *dst, uint16_t net, uint8_t status)
+{
+    uint16_t len = 0;
+    int pdu_len = 0;
+    int bytes_sent = 0;
+    bool data_expecting_reply = false;
+    BACNET_NPDU_DATA npdu_data;
+    BACNET_ADDRESS my_address = { 0 };
+    uint8_t pdu[MAX_NPDU + 2 + 1] = { 0 };
+
+    datalink_get_my_address(&my_address);
+    npdu_encode_npdu_network(&npdu_data,
+        NETWORK_MESSAGE_REJECT_MESSAGE_TO_NETWORK,
+        data_expecting_reply, MESSAGE_PRIORITY_NORMAL);
+    pdu_len = npdu_encode_pdu(pdu, dst, &my_address, &npdu_data);
+    pdu[pdu_len++] = NETWORK_REJECT_UNKNOWN_MESSAGE_TYPE;
+    if ((pdu_len > 0) && (pdu_len <= MAX_NPDU)) {
+        len = encode_unsigned16(&pdu[pdu_len], net);
+        pdu_len += len;
+        bytes_sent = datalink_send_pdu(dst, &npdu_data, pdu, pdu_len);
+    }
+
+    return bytes_sent;
+}
diff --git a/src/bacnet/basic/npdu/h_npdu.h b/src/bacnet/basic/npdu/h_npdu.h
index be14c94d..53ecc9e5 100644
--- a/src/bacnet/basic/npdu/h_npdu.h
+++ b/src/bacnet/basic/npdu/h_npdu.h
@@ -84,6 +84,11 @@ extern "C" {
     void npdu_router_get_my_address(
         uint16_t dnet,
         BACNET_ADDRESS * my_address);
+    BACNET_STACK_EXPORT
+    int npdu_send_reject_message_to_network(
+        BACNET_ADDRESS *dst,
+        uint16_t net,
+        uint8_t status);
 
 #ifdef __cplusplus
 }