diff -up dhcp-4.3.1/common/options.c.option97 dhcp-4.3.1/common/options.c
--- dhcp-4.3.1/common/options.c.option97	2014-12-17 10:49:23.364257702 +0100
+++ dhcp-4.3.1/common/options.c	2014-12-17 10:49:23.458256518 +0100
@@ -4270,13 +4270,26 @@ int validate_packet(struct packet *packe
 				"a future version of ISC DHCP will reject this");
 		}
 	} else {
-		/* 
-		 * If hlen is 0 we don't have any identifier, we warn the user
-		 * but continue processing the packet as we can.
-		 */
-		if (packet->raw->hlen == 0) {
-			log_debug("Received DHCPv4 packet without client-id"
-				  " option and empty hlen field.");
+		oc = lookup_option (&dhcp_universe, packet->options,
+				    DHO_PXE_CLIENT_ID);
+		if (oc) {
+			/* Let's check if pxe-client-id is sane */
+			if ((oc->data.len < 2) ||
+			    (oc->data.data[0] == '\0' &&
+			     oc->data.len != 17)) {
+				log_debug("Dropped DHCPv4 packet with wrong "
+				    "(len == %d) pxe-client-id", oc->data.len);
+				return (0);
+			}
+		} else {
+			/*
+			 * If hlen is 0 we don't have any identifier, we warn the user
+			 * but continue processing the packet as we can.
+			 */
+			if (packet->raw->hlen == 0) {
+				log_debug("Received DHCPv4 packet without client-id"
+						" option and empty hlen field.");
+			}
 		}
 	}
 
diff -up dhcp-4.3.1/common/tables.c.option97 dhcp-4.3.1/common/tables.c
--- dhcp-4.3.1/common/tables.c.option97	2014-12-17 10:49:23.365257689 +0100
+++ dhcp-4.3.1/common/tables.c	2014-12-17 10:49:23.459256505 +0100
@@ -197,8 +197,9 @@ static struct option dhcp_options[] = {
 	/* Defined by RFC 4578 */
 	{ "pxe-system-type", "S",		&dhcp_universe,  93, 1 },
 	{ "pxe-interface-id", "BBB",		&dhcp_universe,  94, 1 },
-	{ "pxe-client-id", "BX",		&dhcp_universe,  97, 1 },
 #endif
+	{ "pxe-client-id", "BX",		&dhcp_universe,  97, 1 },
+
 	{ "uap-servers", "t",			&dhcp_universe,  98, 1 },
 #if defined(RFC4776_OPTIONS)
         { "geoconf-civic", "X",                 &dhcp_universe, 99, 1 },
diff -up dhcp-4.3.1/includes/dhcp.h.option97 dhcp-4.3.1/includes/dhcp.h
--- dhcp-4.3.1/includes/dhcp.h.option97	2014-12-17 10:49:23.377257538 +0100
+++ dhcp-4.3.1/includes/dhcp.h	2014-12-17 10:49:23.459256505 +0100
@@ -159,6 +159,7 @@ struct dhcp_packet {
 #define DHO_AUTHENTICATE			90  /* RFC3118, was 210 */
 #define DHO_CLIENT_LAST_TRANSACTION_TIME	91
 #define DHO_ASSOCIATED_IP			92
+#define DHO_PXE_CLIENT_ID			97  /* RFC4578 */
 #define DHO_SUBNET_SELECTION			118 /* RFC3011! */
 #define DHO_DOMAIN_SEARCH			119 /* RFC3397 */
 #define DHO_CLASSLESS_STATIC_ROUTES		121 /* RFC3442 */
diff -up dhcp-4.3.1/server/dhcp.c.option97 dhcp-4.3.1/server/dhcp.c
--- dhcp-4.3.1/server/dhcp.c.option97	2014-12-17 10:49:23.409257135 +0100
+++ dhcp-4.3.1/server/dhcp.c	2014-12-17 10:49:23.460256492 +0100
@@ -196,6 +196,10 @@ dhcp (struct packet *packet) {
 			oc = lookup_option (&dhcp_universe, packet -> options,
 					    DHO_DHCP_CLIENT_IDENTIFIER);
 			if (!oc)
+				oc = lookup_option (&dhcp_universe,
+						    packet -> options,
+						    DHO_PXE_CLIENT_ID);
+			if (!oc)
 				goto nolease;
 
 			memset (&data, 0, sizeof data);
@@ -764,6 +768,9 @@ void dhcprelease (packet, ms_nulltp)
 
 	oc = lookup_option (&dhcp_universe, packet -> options,
 			    DHO_DHCP_CLIENT_IDENTIFIER);
+	if (!oc)
+		oc = lookup_option (&dhcp_universe, packet -> options,
+				    DHO_PXE_CLIENT_ID);
 	memset (&data, 0, sizeof data);
 	if (oc &&
 	    evaluate_option_cache (&data, packet, (struct lease *)0,
@@ -1191,6 +1198,9 @@ void dhcpinform (packet, ms_nulltp)
          */
 	oc = lookup_option(&dhcp_universe, packet->options,
 			   DHO_DHCP_CLIENT_IDENTIFIER);
+	if (!oc)
+		oc = lookup_option (&dhcp_universe, packet -> options,
+				    DHO_PXE_CLIENT_ID);
 	memset(&d1, 0, sizeof(d1));
 	if (oc &&
 	    evaluate_option_cache(&d1, packet, NULL, NULL,
@@ -2144,6 +2154,9 @@ void ack_lease (packet, lease, offer, wh
 		   can be used. */
 		oc = lookup_option (&dhcp_universe, packet -> options,
 				    DHO_DHCP_CLIENT_IDENTIFIER);
+		if (!oc)
+			oc = lookup_option (&dhcp_universe, packet -> options,
+					    DHO_PXE_CLIENT_ID);
 		if (oc &&
 		    evaluate_option_cache (&d1, packet, lease,
 					   (struct client_state *)0,
@@ -2715,6 +2728,9 @@ void ack_lease (packet, lease, offer, wh
 		/* Record the uid, if given... */
 		oc = lookup_option (&dhcp_universe, packet -> options,
 				    DHO_DHCP_CLIENT_IDENTIFIER);
+		if (!oc)
+			oc = lookup_option (&dhcp_universe, packet -> options,
+					    DHO_PXE_CLIENT_ID);
 		if (oc &&
 		    evaluate_option_cache(&d1, packet, lease, NULL,
 					  packet->options, state->options,
@@ -3812,6 +3828,9 @@ int find_lease (struct lease **lp,
 	   specified unique client identifier. */
 	oc = lookup_option (&dhcp_universe, packet -> options,
 			    DHO_DHCP_CLIENT_IDENTIFIER);
+	if (!oc)
+		oc = lookup_option (&dhcp_universe, packet -> options,
+				    DHO_PXE_CLIENT_ID);
 	memset (&client_identifier, 0, sizeof client_identifier);
 	if (oc &&
 	    evaluate_option_cache (&client_identifier,
diff -up dhcp-4.3.1/server/dhcpd.conf.5.option97 dhcp-4.3.1/server/dhcpd.conf.5
--- dhcp-4.3.1/server/dhcpd.conf.5.option97	2014-12-17 10:49:23.325258193 +0100
+++ dhcp-4.3.1/server/dhcpd.conf.5	2014-12-17 10:49:23.461256480 +0100
@@ -1559,10 +1559,12 @@ should be a name identifying the host.
 not specified for the host, \fIhostname\fR is used.
 .PP
 \fIHost\fR declarations are matched to actual DHCP or BOOTP clients
-by matching the \fRdhcp-client-identifier\fR option specified in the
+by matching the \fIdhcp-client-identifier\fR or \fIpxe-client-id\fR
+options specified in the
 \fIhost\fR declaration to the one supplied by the client, or, if the
 \fIhost\fR declaration or the client does not provide a
-\fRdhcp-client-identifier\fR option, by matching the \fIhardware\fR
+\fIdhcp-client-identifier\fR or \fIpxe-client-id\fR options,
+by matching the \fIhardware\fR
 parameter in the \fIhost\fR declaration to the network hardware
 address supplied by the client.  BOOTP clients do not normally
 provide a \fIdhcp-client-identifier\fR, so the hardware address must
@@ -1574,7 +1576,8 @@ to identify hosts.
 .PP
 Please be aware that
 .B only
-the \fIdhcp-client-identifier\fR option and the hardware address can be
+the \fIdhcp-client-identifier\fR and \fIpxe-client-id\fR
+options and the hardware address can be
 used to match a host declaration, or the \fIhost-identifier option\fR
 parameter for DHCPv6 servers.  For example, it is not possible to
 match a host declaration to a \fIhost-name\fR option.  This is
diff -up dhcp-4.3.1/server/dhcpleasequery.c.option97 dhcp-4.3.1/server/dhcpleasequery.c
--- dhcp-4.3.1/server/dhcpleasequery.c.option97	2014-08-07 00:35:02.000000000 +0200
+++ dhcp-4.3.1/server/dhcpleasequery.c	2014-12-17 10:49:23.457256530 +0100
@@ -269,7 +269,7 @@ dhcpleasequery(struct packet *packet, in
 		 */
 
 		memset(&uid, 0, sizeof(uid));
-		if (get_option(&uid, 
+		i = get_option(&uid,
 			       &dhcp_universe,
 			       packet,
 			       NULL,
@@ -279,8 +279,20 @@ dhcpleasequery(struct packet *packet, in
 			       packet->options, 
 			       &global_scope,
 			       DHO_DHCP_CLIENT_IDENTIFIER,
-			       MDL)) {
-
+			       MDL);
+		if (!i)
+			i = get_option(&uid,
+				       &dhcp_universe,
+				       packet,
+				       NULL,
+				       NULL,
+				       packet->options,
+				       NULL,
+				       packet->options,
+				       &global_scope,
+				       DHO_PXE_CLIENT_ID,
+				       MDL);
+		if (i) {
 			snprintf(dbg_info, 
 				 sizeof(dbg_info), 
 				 "client-id %s",
diff -up dhcp-4.3.1/server/failover.c.option97 dhcp-4.3.1/server/failover.c
--- dhcp-4.3.1/server/failover.c.option97	2014-12-17 10:49:23.413257085 +0100
+++ dhcp-4.3.1/server/failover.c	2014-12-17 10:49:23.462256467 +0100
@@ -5878,6 +5878,9 @@ int load_balance_mine (struct packet *pa
 
 	oc = lookup_option(&dhcp_universe, packet->options,
 			   DHO_DHCP_CLIENT_IDENTIFIER);
+	if (!oc)
+		oc = lookup_option(&dhcp_universe, packet -> options,
+				    DHO_PXE_CLIENT_ID);
 	memset(&ds, 0, sizeof ds);
 	if (oc &&
 	    evaluate_option_cache(&ds, packet, NULL, NULL,
diff -up dhcp-4.3.1/server/mdb.c.option97 dhcp-4.3.1/server/mdb.c
--- dhcp-4.3.1/server/mdb.c.option97	2014-08-07 00:35:03.000000000 +0200
+++ dhcp-4.3.1/server/mdb.c	2014-12-17 10:49:23.463256455 +0100
@@ -130,8 +130,9 @@ static int find_uid_statement (struct ex
 	    esp -> data.option &&
 	    (esp -> data.option -> option -> universe ==
 	     &dhcp_universe) &&
-	    (esp -> data.option -> option -> code ==
-	     DHO_DHCP_CLIENT_IDENTIFIER)) {
+	    ((esp -> data.option -> option -> code ==
+						DHO_DHCP_CLIENT_IDENTIFIER) ||
+	     (esp -> data.option -> option -> code == DHO_PXE_CLIENT_ID))) {
 		if (condp) {
 			log_error ("dhcp client identifier may not be %s",
 				   "specified conditionally.");