diff --git a/common/bpf.c b/common/bpf.c
index 1816496..91b12d1 100644
--- a/common/bpf.c
+++ b/common/bpf.c
@@ -198,11 +198,48 @@ struct bpf_insn dhcp_bpf_filter [] = {
 	BPF_STMT(BPF_RET+BPF_K, 0),
 };
 
+/*
+ * For relay port extension
+ */
+struct bpf_insn dhcp_bpf_relay_filter [] = {
+	/* Make sure this is an IP packet... */
+	BPF_STMT (BPF_LD + BPF_H + BPF_ABS, 12),
+	BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
+
+	/* Make sure it's a UDP packet... */
+	BPF_STMT (BPF_LD + BPF_B + BPF_ABS, 23),
+	BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
+
+	/* Make sure this isn't a fragment... */
+	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
+	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0),
+
+	/* Get the IP header length... */
+	BPF_STMT (BPF_LDX + BPF_B + BPF_MSH, 14),
+
+	/* Make sure it's to the right port... */
+	BPF_STMT (BPF_LD + BPF_H + BPF_IND, 16),
+	BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, 67, 2, 0),             /* patch */
+
+	/* relay can have an alternative port... */
+	BPF_STMT (BPF_LD + BPF_H + BPF_IND, 16),
+	BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),             /* patch */
+
+	/* If we passed all the tests, ask for the whole packet. */
+	BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
+
+	/* Otherwise, drop it. */
+	BPF_STMT(BPF_RET+BPF_K, 0),
+};
+
 #if defined (DEC_FDDI)
 struct bpf_insn *bpf_fddi_filter = NULL;
 #endif
 
 int dhcp_bpf_filter_len = sizeof dhcp_bpf_filter / sizeof (struct bpf_insn);
+
+int dhcp_bpf_relay_filter_len = sizeof dhcp_bpf_relay_filter / sizeof (struct bpf_insn);
+
 #if defined (HAVE_TR_SUPPORT)
 struct bpf_insn dhcp_bpf_tr_filter [] = {
         /* accept all token ring packets due to variable length header */
@@ -306,10 +343,22 @@ void if_register_receive (info)
 #endif /* DEC_FDDI */
 	p.bf_insns = dhcp_bpf_filter;
 
+	if (relay_port) {
+		/*
+		 * If user defined relay UDP port, we need to filter
+		 * on both port 67 and user UDP port.
+		 */
+		p.bf_len = dhcp_bpf_relay_filter_len;
+		p.bf_insns = dhcp_bpf_relay_filter;
+
+		dhcp_bpf_relay_filter [10].k = ntohs ((short)relay_port);
+	} else {
+
         /* Patch the server port into the BPF  program...
 	   XXX changes to filter program may require changes
 	   to the insn number(s) used below! XXX */
-	dhcp_bpf_filter [8].k = ntohs (local_port);
+		dhcp_bpf_filter [8].k = ntohs (local_port);
+	}
 
 	if (ioctl (info -> rfdesc, BIOCSETF, &p) < 0)
 		log_fatal ("Can't install packet filter program: %m");
diff --git a/common/discover.c b/common/discover.c
index 8e7f632..6c58190 100644
--- a/common/discover.c
+++ b/common/discover.c
@@ -44,6 +44,7 @@ int interfaces_invalidated;
 int quiet_interface_discovery;
 u_int16_t local_port;
 u_int16_t remote_port;
+u_int16_t relay_port = 0;
 int dhcpv4_over_dhcpv6 = 0;
 int (*dhcp_interface_setup_hook) (struct interface_info *, struct iaddr *);
 int (*dhcp_interface_discovery_hook) (struct interface_info *);
diff --git a/common/lpf.c b/common/lpf.c
index ee3820b..168b475 100644
--- a/common/lpf.c
+++ b/common/lpf.c
@@ -179,6 +179,9 @@ void if_deregister_send (info)
 extern struct sock_filter dhcp_bpf_filter [];
 extern int dhcp_bpf_filter_len;
 
+extern struct sock_filter dhcp_bpf_relay_filter [];
+extern int dhcp_bpf_relay_filter_len;
+
 #if defined (HAVE_TR_SUPPORT)
 extern struct sock_filter dhcp_bpf_tr_filter [];
 extern int dhcp_bpf_tr_filter_len;
@@ -252,13 +255,27 @@ static void lpf_gen_filter_setup (info)
 
 	/* Set up the bpf filter program structure.    This is defined in
 	   bpf.c */
-	p.len = dhcp_bpf_filter_len;
-	p.filter = dhcp_bpf_filter;
+	if (relay_port) {
+		/*
+		 * If user defined relay UDP port, we need to filter
+		 * on both port 67 and user UDP port.
+		 */
+		p.len = dhcp_bpf_relay_filter_len;
+		p.filter = dhcp_bpf_relay_filter;
+	} else {
+		p.len = dhcp_bpf_filter_len;
+		p.filter = dhcp_bpf_filter;
+	}
 
         /* Patch the server port into the LPF  program...
 	   XXX changes to filter program may require changes
 	   to the insn number(s) used below! XXX */
-	dhcp_bpf_filter [8].k = ntohs ((short)local_port);
+
+	if (relay_port) { /* DHCP relay port check */
+		dhcp_bpf_relay_filter [10].k = ntohs ((short)relay_port);
+	} else {
+		dhcp_bpf_filter [8].k = ntohs ((short)local_port);
+	}
 
 	if (setsockopt (info -> rfdesc, SOL_SOCKET, SO_ATTACH_FILTER, &p,
 			sizeof p) < 0) {
diff --git a/common/packet.c b/common/packet.c
index e600e37..e278edc 100644
--- a/common/packet.c
+++ b/common/packet.c
@@ -168,6 +168,11 @@ void assemble_udp_ip_header (interface, buf, bufix,
 	/* Fill out the UDP header */
 	udp.uh_sport = local_port;		/* XXX */
 	udp.uh_dport = port;			/* XXX */
+
+	/* Change to relay port defined if sending to server */
+	if (relay_port && (port == htons(67))) {
+		udp.uh_sport = relay_port;
+	}
 	udp.uh_ulen = htons(sizeof(udp) + len);
 	memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 
@@ -297,7 +302,8 @@ decode_udp_ip_header(struct interface_info *interface,
 	  return -1;
 
   /* Is it to the port we're serving? */
-  if (udp.uh_dport != local_port)
+  if ((udp.uh_dport != local_port) &&
+      ((relay_port == 0) || (udp.uh_dport != relay_port)))
 	  return -1;
 #endif /* USERLAND_FILTER */
 
diff --git a/common/raw.c b/common/raw.c
index a15f8ee..69a6af2 100644
--- a/common/raw.c
+++ b/common/raw.c
@@ -55,14 +55,14 @@ void if_register_send (info)
 
 	/* Set up the address we're going to connect to. */
 	name.sin_family = AF_INET;
-	name.sin_port = local_port;
+	name.sin_port = (relay_port) ? relay_port: local_port;
 	name.sin_addr.s_addr = htonl (INADDR_BROADCAST);
 	memset (name.sin_zero, 0, sizeof (name.sin_zero));
 
 	/* List addresses on which we're listening. */
         if (!quiet_interface_discovery)
 		log_info ("Sending on %s, port %d",
-		      piaddr (info -> address), htons (local_port));
+		      piaddr (info -> address), htons (name.sin_port));
 	if ((sock = socket (AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0)
 		log_fatal ("Can't create dhcp socket: %m");
 
diff --git a/common/socket.c b/common/socket.c
index e8851b4..3ab4391 100644
--- a/common/socket.c
+++ b/common/socket.c
@@ -177,7 +177,7 @@ if_register_socket(struct interface_info *info, int family,
 	default:
 		addr = (struct sockaddr_in *)&name; 
 		addr->sin_family = AF_INET;
-		addr->sin_port = local_port;
+		addr->sin_port = (relay_port) ? relay_port : local_port;
 		memcpy(&addr->sin_addr,
 		       &local_address,
 		       sizeof(addr->sin_addr));
diff --git a/includes/dhcp.h b/includes/dhcp.h
index f916468..60f4d96 100644
--- a/includes/dhcp.h
+++ b/includes/dhcp.h
@@ -184,6 +184,7 @@ struct dhcp_packet {
 #define RAI_REMOTE_ID	2
 #define RAI_AGENT_ID	3
 #define RAI_LINK_SELECT	5
+#define RAI_RELAY_PORT  19
 
 /* FQDN suboptions: */
 #define FQDN_NO_CLIENT_UPDATE		1
diff --git a/includes/dhcpd.h b/includes/dhcpd.h
index 261714d..38fd61a 100644
--- a/includes/dhcpd.h
+++ b/includes/dhcpd.h
@@ -2788,6 +2788,7 @@ extern struct in_addr local_address;
 
 extern u_int16_t local_port;
 extern u_int16_t remote_port;
+extern u_int16_t relay_port;
 extern int dhcpv4_over_dhcpv6;
 extern int (*dhcp_interface_setup_hook) (struct interface_info *,
 					 struct iaddr *);
diff --git a/relay/dhcrelay.c b/relay/dhcrelay.c
index 344cee7..11c7696 100644
--- a/relay/dhcrelay.c
+++ b/relay/dhcrelay.c
@@ -151,7 +151,8 @@ char *progname;
 #ifdef DHCPv6
 #define DHCRELAY_USAGE \
 "Usage: %s [-4] [-d] [-q] [-a] [-D]\n"\
-"                     [-A <length>] [-c <hops>] [-p <port>]\n" \
+"                     [-A <length>] [-c <hops>]\n" \
+"                     [-p <port> | -rp <relay-port>\n" \
 "                     [-pf <pid-file>] [--no-pid]\n"\
 "                     [-m append|replace|forward|discard]\n" \
 "                     [-i interface0 [ ... -i interfaceN]\n" \
@@ -168,7 +169,8 @@ char *progname;
 "       upper (server link): [address%%]interface"
 #else
 #define DHCRELAY_USAGE \
-"Usage: %s [-d] [-q] [-a] [-D] [-A <length>] [-c <hops>] [-p <port>]\n" \
+"Usage: %s [-d] [-q] [-a] [-D] [-A <length>] [-c <hops>]\n" \
+"                [-p <port> | -rp <relay-port>\n" \
 "                [-pf <pid-file>] [--no-pid]\n" \
 "                [-m append|replace|forward|discard]\n" \
 "                [-i interface0 [ ... -i interfaceN]\n" \
@@ -194,6 +196,8 @@ char *progname;
  * \return Nothing
  */
 static const char use_noarg[] = "No argument for command: %s";
+static const char use_port_defined[] = "Port already set, %s inappropriate";
+static const char lpf_sock_support[] = "Only LPF and BPF are supported: %s";
 #ifdef DHCPv6
 static const char use_badproto[] = "Protocol already set, %s inappropriate";
 static const char use_v4command[] = "Command not used for DHCPv6: %s";
@@ -226,6 +230,7 @@ main(int argc, char **argv) {
 	int no_daemon = 0, quiet = 0;
 	int fd;
 	int i;
+	int port_defined = 0;
 #ifdef DHCPv6
 	struct stream_list *sl = NULL;
 	int local_family_set = 0;
@@ -295,9 +300,22 @@ main(int argc, char **argv) {
 		} else if (!strcmp(argv[i], "-p")) {
 			if (++i == argc)
 				usage(use_noarg, argv[i-1]);
+			if (port_defined)
+				usage(use_port_defined, argv[i-1]);
 			local_port = validate_port(argv[i]);
 			log_debug("binding to user-specified port %d",
 				  ntohs(local_port));
+			port_defined = ISC_TRUE;
+		} else if (!strcmp(argv[i], "-rp")) {
+			if (++i == argc)
+				usage(use_noarg, argv[i-1]);
+			if (port_defined)
+			    usage(use_port_defined, argv[i-1]);
+		    relay_port = validate_port(argv[i]);
+		    log_debug("binding to user-defined relay port %d",
+			      ntohs(relay_port));
+		    add_agent_options = 1;
+		    port_defined = ISC_TRUE;
 		} else if (!strcmp(argv[i], "-c")) {
 			int hcount;
 			if (++i == argc)
@@ -529,6 +547,11 @@ main(int argc, char **argv) {
  		}
 	}
 
+#if !defined (USE_BPF_RECEIVE) && !defined (USE_LPF_RECEIVE)
+	if (relay_port && (local_family == AF_INET))
+		usage(lpf_sock_support, "-rp");
+# endif
+
 	/*
 	 * If the user didn't specify a pid file directly
 	 * find one from environment variables or defaults
@@ -1212,6 +1235,10 @@ add_relay_agent_options(struct interface_info *ip, struct dhcp_packet *packet,
 		optlen += 6;
 	}
 
+	if (relay_port) {
+		optlen += 2;
+	}
+
 	/* We do not support relay option fragmenting(multiple options to
 	 * support an option data exceeding 255 bytes).
 	 */
@@ -1256,6 +1283,16 @@ add_relay_agent_options(struct interface_info *ip, struct dhcp_packet *packet,
 			log_debug ("Adding link selection suboption"
 				   " with addr: %s", inet_ntoa(giaddr));
 		}
+
+		/*
+		 * Draft-ietf-dhc-relay-port, the relay operation select
+		 * to use a different relay UDP source port when sending
+		 * and receiving to/from DHCP server.
+		 */
+		if (relay_port) {
+			*sp++ = RAI_RELAY_PORT;
+			*sp++ = 0u;
+		}
 	} else {
 		++agent_option_errors;
 		log_error("No room in packet (used %d of %d) "