Merged rt44535 (relay port)

27 files changed, 685 insertions, 57 deletions

diff --git a/RELNOTES b/RELNOTES
index 7d2d4927..6b11b787 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -312,6 +312,19 @@ dhcp-users@lists.isc.org.
   when building with --enable-use-sockets and --enable-ipv4-pktinfo.
   [ISC-Bugs #36118]
 
+(to be finalized before code freeze next year)
+- Added experimental support for relay port (draft-ietf-dhc-relay-port-10.txt)
+  feature for DHCPv4, DHCPv6 and DHCPv4-over-DHCPv6. As the code points
+  were not yet assigned by IANA temporary (next free) values are used.
+  Relay port had be enabled at compile time via --enable-relay-port and
+  is fully backward compatible, i.e. works with previous implementations
+  of servers and relays, of course in this case using legacy ports.
+  A new --rp <relay-port> command line option specifies to dhcrelay
+  an alternate source port for upstream (i.e. toward the server) messages.
+(update this)
+  Thanks to Naiming Shen and Enke Chen for submitting patches.
+  [ISC-Bugs #44535]
+
 			Changes since 4.3.6 (Bugs):
 
 - Corrected an issue where the server would return a client's previously
diff --git a/common/bpf.c b/common/bpf.c
index dc41f809..16076fea 100644
--- a/common/bpf.c
+++ b/common/bpf.c
@@ -192,12 +192,51 @@ struct bpf_insn dhcp_bpf_filter [] = {
 	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),
+	BPF_STMT (BPF_RET + BPF_K, (u_int)-1),
 
 	/* Otherwise, drop it. */
-	BPF_STMT(BPF_RET+BPF_K, 0),
+	BPF_STMT (BPF_RET + BPF_K, 0),
 };
 
+#if defined(RELAY_PORT)
+/*
+ * 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),
+};
+
+int dhcp_bpf_relay_filter_len =
+	sizeof dhcp_bpf_relay_filter / sizeof (struct bpf_insn);
+#endif
+
 #if defined (DEC_FDDI)
 struct bpf_insn *bpf_fddi_filter = NULL;
 #endif
@@ -309,7 +348,19 @@ void if_register_receive (info)
         /* 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);
+#if defined(RELAY_PORT)
+	if (relay_port) {
+		/*
+		 * If user defined relay UDP port, we need to filter
+		 * also on the 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 (relay_port);
+	}
+#endif
+	p.bf_insns [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 f81d63f7..6ef88529 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 *);
@@ -581,6 +582,10 @@ discover_interfaces(int state) {
 	int ir;
 	isc_result_t status;
 	int wifcount = 0;
+#ifdef RELAY_PORT
+	int updone = 0;
+	int downdone = 0;
+#endif
 
 	static int setup_fallback = 0;
 
@@ -946,9 +951,39 @@ discover_interfaces(int state) {
 		switch (local_family) {
 #ifdef DHCPv6 
 		case AF_INET6:
+#ifdef RELAY_PORT
+#define UPSTREAM(ifp) \
+	((ifp->flags & INTERFACE_STREAMS) == INTERFACE_UPSTREAM)
+#define DOWNSTREAM(ifp) \
+        ((ifp->flags & INTERFACE_STREAMS) == INTERFACE_DOWNSTREAM)
+
+			if (relay_port) {
+				/*
+				 * The normal IPv6 relay only needs one
+				 * socket as long as we find an interface.
+				 * When user relay port is defined, and we
+				 * have two different UDP ports. One to
+				 * receive from DHCP client with port 547,
+				 * and the other is user defined for sending
+				 * to the server or upstream relay agent.
+				 * Thus we need to register sockets for one
+				 * upstream and one downstream interfaces.
+				 */
+				if (updone && UPSTREAM(tmp))
+					    continue;
+				if (downdone && DOWNSTREAM(tmp))
+					    continue;
+			}
+#endif
 			status = omapi_register_io_object((omapi_object_t *)tmp,
 							  if_readsocket, 
 							  0, got_one_v6, 0, 0);
+#ifdef RELAY_PORT
+			if (UPSTREAM(tmp))
+				updone++;
+			else
+				downdone++;
+#endif
 			break;
 #endif /* DHCPv6 */
 		case AF_INET:
@@ -970,8 +1005,12 @@ discover_interfaces(int state) {
 		 * dynamically adding and removing interfaces, but
 		 * we're well beyond that point in terms of mess.
 		 */
-		if (((state == DISCOVER_SERVER) || (state == DISCOVER_RELAY)) &&
-		    (local_family == AF_INET6))
+		if (((state == DISCOVER_SERVER) || (state == DISCOVER_RELAY))
+		    && (local_family == AF_INET6)
+#if defined(RELAY_PORT)
+		    && ((relay_port == 0) || (updone && downdone))
+#endif
+		    )
 			break;
 #endif
 	} /* for (tmp = interfaces; ... */
diff --git a/common/dlpi.c b/common/dlpi.c
index b459dc6d..3990bf12 100644
--- a/common/dlpi.c
+++ b/common/dlpi.c
@@ -409,6 +409,10 @@ void if_deregister_send (info)
    XXX Changes to the filter program may require changes to the constant
    offsets used in if_register_send to patch the NIT program! XXX */
 
+#if defined(RELAY_PORT)
+#error "Relay port is not yet supported for DLPI"
+#endif
+
 void if_register_receive (info)
 	struct interface_info *info;
 {
diff --git a/common/lpf.c b/common/lpf.c
index 6e6ba014..82a279bb 100644
--- a/common/lpf.c
+++ b/common/lpf.c
@@ -177,6 +177,11 @@ void if_deregister_send (info)
 extern struct sock_filter dhcp_bpf_filter [];
 extern int dhcp_bpf_filter_len;
 
+#if defined(RELAY_PORT)
+extern struct sock_filter dhcp_bpf_relay_filter [];
+extern int dhcp_bpf_relay_filter_len;
+#endif
+
 #if defined (HAVE_TR_SUPPORT)
 extern struct sock_filter dhcp_bpf_tr_filter [];
 extern int dhcp_bpf_tr_filter_len;
@@ -256,7 +261,19 @@ static void lpf_gen_filter_setup (info)
         /* 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 defined(RELAY_PORT)
+	if (relay_port) {
+		/*
+		 * If user defined relay UDP port, we need to filter
+		 * also on the user UDP port.
+		 */
+		p.len = dhcp_bpf_relay_filter_len;
+		p.filter = dhcp_bpf_relay_filter;
+
+		dhcp_bpf_relay_filter [10].k = ntohs (relay_port);
+	}
+#endif
+	dhcp_bpf_filter [8].k = ntohs (local_port);
 
 	if (setsockopt (info -> rfdesc, SOL_SOCKET, SO_ATTACH_FILTER, &p,
 			sizeof p) < 0) {
diff --git a/common/nit.c b/common/nit.c
index 1e14ebb7..d822c151 100644
--- a/common/nit.c
+++ b/common/nit.c
@@ -172,6 +172,10 @@ void if_deregister_send (info)
    XXX Changes to the filter program may require changes to the constant
    offsets used in if_register_send to patch the NIT program! XXX */
 
+#if defined(RELAY_PORT)
+#error "Relay port is not yet supported for NIT"
+#endif
+
 void if_register_receive (info)
 	struct interface_info *info;
 {
diff --git a/common/packet.c b/common/packet.c
index d6907fe0..f3f62c19 100644
--- a/common/packet.c
+++ b/common/packet.c
@@ -167,6 +167,12 @@ void assemble_udp_ip_header (interface, buf, bufix,
 	/* Fill out the UDP header */
 	udp.uh_sport = local_port;		/* XXX */
 	udp.uh_dport = port;			/* XXX */
+#if defined(RELAY_PORT)
+	/* Change to relay port defined if sending to server */
+	if (relay_port && (port == htons(67))) {
+		udp.uh_sport = relay_port;
+	}
+#endif
 	udp.uh_ulen = htons(sizeof(udp) + len);
 	memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 
@@ -296,7 +302,12 @@ decode_udp_ip_header(struct interface_info *interface,
 	  return -1;
 
   /* Is it to the port we're serving? */
+#if defined(RELAY_PORT)
+  if ((udp.uh_dport != local_port) &&
+      ((relay_port == 0) || (udp.uh_dport != relay_port)))
+#else
   if (udp.uh_dport != local_port)
+#endif
 	  return -1;
 #endif /* USERLAND_FILTER */
 
diff --git a/common/raw.c b/common/raw.c
index 3ad0bfd2..5c88b25e 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 8879bc20..483eb9c3 100644
--- a/common/socket.c
+++ b/common/socket.c
@@ -65,6 +65,10 @@
 static int no_global_v6_socket = 0;
 static unsigned int global_v6_socket_references = 0;
 static int global_v6_socket = -1;
+#if defined(RELAY_PORT)
+static unsigned int relay_port_v6_socket_references = 0;
+static int relay_port_v6_socket = -1;
+#endif
 
 static void if_register_multicast(struct interface_info *info);
 #endif
@@ -157,6 +161,11 @@ if_register_socket(struct interface_info *info, int family,
 		addr6 = (struct sockaddr_in6 *)&name; 
 		addr6->sin6_family = AF_INET6;
 		addr6->sin6_port = local_port;
+#if defined(RELAY_PORT)
+		if (relay_port &&
+		    ((info->flags & INTERFACE_STREAMS) == INTERFACE_UPSTREAM))
+			addr6->sin6_port = relay_port;
+#endif
 		/* A server feature */
 		if (bind_local_address6) {
 			memcpy(&addr6->sin6_addr,
@@ -187,7 +196,7 @@ 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));
@@ -496,6 +505,10 @@ if_register6(struct interface_info *info, int do_multicast) {
 		log_fatal("Impossible condition at %s:%d", MDL);
 	}
 
+#if defined(RELAY_PORT)
+	if (!relay_port ||
+	    ((info->flags & INTERFACE_STREAMS) == INTERFACE_DOWNSTREAM)) {
+#endif
 	if (global_v6_socket_references == 0) {
 		global_v6_socket = if_register_socket(info, AF_INET6,
 						      &req_multi, NULL);
@@ -527,6 +540,30 @@ if_register6(struct interface_info *info, int do_multicast) {
 	info->wfdesc = global_v6_socket;
 	global_v6_socket_references++;
 
+#if defined(RELAY_PORT)
+	} else {
+	/*
+	 * If relay port is defined, we need to register one
+	 * IPv6 UPD socket to handle upstream server or relay agent
+	 * with a non-547 UDP local port.
+	 */
+	if ((relay_port_v6_socket_references == 0) &&
+	    ((info->flags & INTERFACE_STREAMS) == INTERFACE_UPSTREAM)) {
+		relay_port_v6_socket = if_register_socket(info, AF_INET6,
+							  &req_multi, NULL);
+		if (relay_port_v6_socket < 0) {
+			log_fatal("Impossible condition at %s:%d", MDL);
+		} else {
+			log_info("Bound to relay port *:%d",
+				 (int) ntohs(relay_port));
+		}
+	}
+	info->rfdesc = relay_port_v6_socket;
+	info->wfdesc = relay_port_v6_socket;
+	relay_port_v6_socket_references++;
+	}
+#endif
+
 	if (req_multi)
 		if_register_multicast(info);
 
@@ -617,6 +654,16 @@ if_deregister6(struct interface_info *info) {
 		global_v6_socket_references--;
 		info->rfdesc = -1;
 		info->wfdesc = -1;
+#if defined(RELAY_PORT)
+	} else if (relay_port &&
+		   (info->rfdesc == relay_port_v6_socket) &&
+		   (info->wfdesc == relay_port_v6_socket) &&
+		   (relay_port_v6_socket_references > 0)) {
+		/* Dereference the relay port v6 socket. */
+		relay_port_v6_socket_references--;
+		info->rfdesc = -1;
+		info->wfdesc = -1;
+#endif
 	} else {
 		log_fatal("Impossible condition at %s:%d", MDL);
 	}
@@ -633,12 +680,23 @@ if_deregister6(struct interface_info *info) {
 		}
 	}
 
-	if (!no_global_v6_socket &&
-	    (global_v6_socket_references == 0)) {
-		close(global_v6_socket);
-		global_v6_socket = -1;
+	if (!no_global_v6_socket) {
+		if (global_v6_socket_references == 0) {
+			close(global_v6_socket);
+			global_v6_socket = -1;
 
-		log_info("Unbound from *:%d", ntohs(local_port));
+			log_info("Unbound from *:%d",
+				 (int) ntohs(local_port));
+		}
+#if defined(RELAY_PORT)
+		if (relay_port && (relay_port_v6_socket_references == 0)) {
+			close(relay_port_v6_socket);
+			relay_port_v6_socket = -1;
+
+			log_info("Unbound from relay port *:%d",
+				 (int) ntohs(relay_port));
+		}
+#endif
 	}
 }
 #endif /* DHCPv6 */
diff --git a/common/tables.c b/common/tables.c
index 2350e803..b3d5ae66 100644
--- a/common/tables.c
+++ b/common/tables.c
@@ -557,12 +557,6 @@ static struct option dhcpv6_options[] = {
 	{ "solmax-rt", "L",			&dhcpv6_universe, 82, 1 },
 	{ "inf-max-rt", "L",			&dhcpv6_universe, 83, 1 },
 #endif
-#if defined(RFC7710_OPTIONS)
-	{ "v6-captive-portal", "t",		&dhcpv6_universe, 103, 1 },
-#endif
-#if defined(RFC6153_OPTIONS)
-	{ "ipv6-address-andsf", "6A",		&dhcpv6_universe, 143, 1 },
-#endif
 
 			/* RFC7341 OPTIONS */
 #if defined(RFC7341_OPTIONS)
@@ -570,6 +564,16 @@ static struct option dhcpv6_options[] = {
 	{ "dhcp4-o-dhcp6-server", "6A",		&dhcpv6_universe, 88, 1 },
 #endif
 
+#if defined(RFC7710_OPTIONS)
+	{ "v6-captive-portal", "t",		&dhcpv6_universe, 103, 1 },
+#endif
+
+	{ "relay-source-port", "S",		&dhcpv6_universe, 135, 1 },
+
+#if defined(RFC6153_OPTIONS)
+	{ "ipv6-address-andsf", "6A",		&dhcpv6_universe, 143, 1 },
+#endif
+
 	{ NULL, NULL, NULL, 0, 0 }
 };
 
diff --git a/common/upf.c b/common/upf.c
index 1b49301e..9785879a 100644
--- a/common/upf.c
+++ b/common/upf.c
@@ -156,6 +156,9 @@ void if_deregister_send (info)
    XXX Changes to the filter program may require changes to the constant
    offsets used in if_register_send to patch the UPF program! XXX */
 
+#if defined(RELAY_PORT)
+#error "Relay port is not yet supported for UPF"
+#endif
 
 void if_register_receive (info)
 	struct interface_info *info;
diff --git a/configure b/configure
index 5d12223e..e76404a8 100755
--- a/configure
+++ b/configure
@@ -768,6 +768,7 @@ enable_tracing
 enable_delayed_ack
 enable_dhcpv6
 enable_dhcpv4o6
+enable_relay_port
 enable_paranoia
 enable_early_chroot
 enable_ipv4_pktinfo
@@ -1446,6 +1447,7 @@ Optional Features:
   --enable-dhcpv6         enable support for DHCPv6 (default is yes)
   --enable-dhcpv4o6       enable support for DHCPv4-over-DHCPv6 (default is
                           no)
+  --enable-relay-port     enable support for relay port (default is no)
   --enable-paranoia       enable support for chroot/setuid (default is no)
   --enable-early-chroot   enable chrooting prior to configuration (default is
                           no)
@@ -5487,6 +5489,19 @@ else
     enable_dhcpv4o6="no"
 fi
 
+# Relay port (draft-ietf-dhc-relay-port-10.txt) optional compile-time feature.
+# Check whether --enable-relay-port was given.
+if test "${enable_relay_port+set}" = set; then :
+  enableval=$enable_relay_port;
+fi
+
+# Relay port is off by default (for now)
+if test "$enable_relay_port" = "yes"; then
+
+$as_echo "#define RELAY_PORT 1" >>confdefs.h
+
+fi
+
 # PARANOIA is off by default (until we can test it with all features)
 # Check whether --enable-paranoia was given.
 if test "${enable_paranoia+set}" = set; then :
@@ -6207,6 +6222,7 @@ fi
 done
   # needed for linux/filter.h on old systems
 
+relay_port_supported="no"
 ac_fn_c_check_header_compile "$LINENO" "linux/filter.h" "ac_cv_header_linux_filter_h" "
 #ifdef HAVE_LINUX_TYPES_H
 #include <linux/types.h>
@@ -6223,6 +6239,7 @@ then
 
 $as_echo "#define HAVE_LPF 1" >>confdefs.h
 
+	relay_port_supported="yes"
 else
 	ac_fn_c_check_header_mongrel "$LINENO" "sys/dlpi.h" "ac_cv_header_sys_dlpi_h" "$ac_includes_default"
 if test "x$ac_cv_header_sys_dlpi_h" = xyes; then :
@@ -6247,10 +6264,17 @@ fi
 
 $as_echo "#define HAVE_BPF 1" >>confdefs.h
 
+			relay_port_supported="yes"
 		fi
 	fi
 fi
 
+if test "$enable_relay_port" = "yes"; then
+	if test "$relay_port_supported" != "yes"; then
+		as_fn_error $? "--enable-relay-port requires BPF or LPF" "$LINENO" 5
+	fi
+fi
+
 # SIOCGLIFCONF uses some transport structures.  Trick is not all platforms
 # use the same structures.  We like to use 'struct lifconf' and 'struct
 # lifreq', but we'll use these other structures if they're present.  HPUX
@@ -9014,6 +9038,7 @@ Features:
   dhcpv6:        $enable_dhcpv6
   delayed-ack:   $enable_delayed_ack
   dhcpv4o6:      $enable_dhcpv4o6
+  relay-port:    $enable_relay_port
 
 Developer:
   ATF unittests : $atf_path
diff --git a/configure.ac b/configure.ac
index 52e7bb4e..62593d3f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -177,6 +177,15 @@ else
     enable_dhcpv4o6="no"
 fi
 
+# Relay port (draft-ietf-dhc-relay-port-10.txt) optional compile-time feature.
+AC_ARG_ENABLE(relay-port,
+	AS_HELP_STRING([--enable-relay-port],[enable support for relay port (default is no)]))
+# Relay port is off by default (for now)
+if test "$enable_relay_port" = "yes"; then
+	AC_DEFINE([RELAY_PORT], [1],
+		  [Define to 1 to include relay port support.])
+fi
+
 # PARANOIA is off by default (until we can test it with all features)
 AC_ARG_ENABLE(paranoia,
 	AS_HELP_STRING([--enable-paranoia],[enable support for chroot/setuid (default is no)]))
@@ -521,6 +530,7 @@ AC_CHECK_HEADERS(ifaddrs.h)
 # figure out what IPv4 interface code to use
 AC_CHECK_HEADERS(linux/types.h)  # needed for linux/filter.h on old systems
 
+relay_port_supported="no"
 AC_CHECK_HEADER(linux/filter.h, DO_LPF=1, ,
 [
 #ifdef HAVE_LINUX_TYPES_H
@@ -531,6 +541,7 @@ if test -n "$DO_LPF"
 then
 	AC_DEFINE([HAVE_LPF], [1],
 		  [Define to 1 to use the Linux Packet Filter interface code.])
+	relay_port_supported="yes"
 else
 	AC_CHECK_HEADER(sys/dlpi.h, DO_DLPI=1)
 	if test -n "$DO_DLPI"
@@ -544,10 +555,17 @@ else
 			AC_DEFINE([HAVE_BPF], [1],
 				   [Define to 1 to use the
 				   Berkeley Packet Filter interface code.])
+			relay_port_supported="yes"
 		fi
 	fi
 fi
 
+if test "$enable_relay_port" = "yes"; then
+	if test "$relay_port_supported" != "yes"; then
+		AC_MSG_ERROR([--enable-relay-port requires BPF or LPF])
+	fi
+fi
+
 # SIOCGLIFCONF uses some transport structures.  Trick is not all platforms
 # use the same structures.  We like to use 'struct lifconf' and 'struct
 # lifreq', but we'll use these other structures if they're present.  HPUX
@@ -1035,6 +1053,7 @@ Features:
   dhcpv6:        $enable_dhcpv6
   delayed-ack:   $enable_delayed_ack
   dhcpv4o6:      $enable_dhcpv4o6
+  relay-port:    $enable_relay_port
 
 Developer:
   ATF unittests : $atf_path
diff --git a/configure.ac+lt b/configure.ac+lt
index e8c0b16a..ede7ec04 100644
--- a/configure.ac+lt
+++ b/configure.ac+lt
@@ -178,6 +178,15 @@ else
     enable_dhcpv4o6="no"
 fi
 
+# Relay port (draft-ietf-dhc-relay-port-10.txt) optional compile-time feature.
+AC_ARG_ENABLE(relay-port,
+	AS_HELP_STRING([--enable-relay-port],[enable support for relay port (default is no)]))
+# Relay port is off by default (for now)
+if test "$enable_relay_port" = "yes"; then
+	AC_DEFINE([RELAY_PORT], [1],
+		  [Define to 1 to include relay port support.])
+fi
+
 # PARANOIA is off by default (until we can test it with all features)
 AC_ARG_ENABLE(paranoia,
 	AS_HELP_STRING([--enable-paranoia],[enable support for chroot/setuid (default is no)]))
@@ -522,6 +531,7 @@ AC_CHECK_HEADERS(ifaddrs.h)
 # figure out what IPv4 interface code to use
 AC_CHECK_HEADERS(linux/types.h)  # needed for linux/filter.h on old systems
 
+relay_port_supported="no"
 AC_CHECK_HEADER(linux/filter.h, DO_LPF=1, ,
 [
 #ifdef HAVE_LINUX_TYPES_H
@@ -532,6 +542,7 @@ if test -n "$DO_LPF"
 then
 	AC_DEFINE([HAVE_LPF], [1],
 		  [Define to 1 to use the Linux Packet Filter interface code.])
+	relay_port_supported="yes"
 else
 	AC_CHECK_HEADER(sys/dlpi.h, DO_DLPI=1)
 	if test -n "$DO_DLPI"
@@ -545,10 +556,17 @@ else
 			AC_DEFINE([HAVE_BPF], [1],
 				   [Define to 1 to use the
 				   Berkeley Packet Filter interface code.])
+			relay_port_supported="yes"
 		fi
 	fi
 fi
 
+if test "$enable_relay_port" = "yes"; then
+	if test "$relay_port_supported" != "yes"; then
+		AC_MSG_ERROR([--enable-relay-port requires BPF or LPF])
+	fi
+fi
+
 # SIOCGLIFCONF uses some transport structures.  Trick is not all platforms
 # use the same structures.  We like to use 'struct lifconf' and 'struct
 # lifreq', but we'll use these other structures if they're present.  HPUX
@@ -1040,6 +1058,7 @@ Features:
   dhcpv6:        $enable_dhcpv6
   delayed-ack:   $enable_delayed_ack
   dhcpv4o6:      $enable_dhcpv4o6
+  relay-port:    $enable_relay_port
 
 Developer:
   ATF unittests : $atf_path
diff --git a/configure.ac-base b/configure.ac-base
index 89d3fbff..c6136ca9 100644
--- a/configure.ac-base
+++ b/configure.ac-base
@@ -183,6 +183,15 @@ else
     enable_dhcpv4o6="no"
 fi
 
+# Relay port (draft-ietf-dhc-relay-port-10.txt) optional compile-time feature.
+AC_ARG_ENABLE(relay-port,
+	AS_HELP_STRING([--enable-relay-port],[enable support for relay port (default is no)]))
+# Relay port is off by default (for now)
+if test "$enable_relay_port" = "yes"; then
+	AC_DEFINE([RELAY_PORT], [1],
+		  [Define to 1 to include relay port support.])
+fi
+
 # PARANOIA is off by default (until we can test it with all features)
 AC_ARG_ENABLE(paranoia,
 	AS_HELP_STRING([--enable-paranoia],[enable support for chroot/setuid (default is no)]))
@@ -527,6 +536,7 @@ AC_CHECK_HEADERS(ifaddrs.h)
 # figure out what IPv4 interface code to use
 AC_CHECK_HEADERS(linux/types.h)  # needed for linux/filter.h on old systems
 
+relay_port_supported="no"
 AC_CHECK_HEADER(linux/filter.h, DO_LPF=1, ,
 [
 #ifdef HAVE_LINUX_TYPES_H
@@ -537,6 +547,7 @@ if test -n "$DO_LPF"
 then
 	AC_DEFINE([HAVE_LPF], [1],
 		  [Define to 1 to use the Linux Packet Filter interface code.])
+	relay_port_supported="yes"
 else
 	AC_CHECK_HEADER(sys/dlpi.h, DO_DLPI=1)
 	if test -n "$DO_DLPI"
@@ -550,10 +561,17 @@ else
 			AC_DEFINE([HAVE_BPF], [1],
 				   [Define to 1 to use the
 				   Berkeley Packet Filter interface code.])
+			relay_port_supported="yes"
 		fi
 	fi
 fi
 
+if test "$enable_relay_port" = "yes"; then
+	if test "$relay_port_supported" != "yes"; then
+		AC_MSG_ERROR([--enable-relay-port requires BPF or LPF])
+	fi
+fi
+
 # SIOCGLIFCONF uses some transport structures.  Trick is not all platforms
 # use the same structures.  We like to use 'struct lifconf' and 'struct
 # lifreq', but we'll use these other structures if they're present.  HPUX
@@ -1076,6 +1094,7 @@ Features:
   dhcpv6:        $enable_dhcpv6
   delayed-ack:   $enable_delayed_ack
   dhcpv4o6:      $enable_dhcpv4o6
+  relay-port:    $enable_relay_port
 
 Developer:
   ATF unittests : $atf_path
diff --git a/configure.ac-lt b/configure.ac-lt
index 52e7bb4e..62593d3f 100644
--- a/configure.ac-lt
+++ b/configure.ac-lt
@@ -177,6 +177,15 @@ else
     enable_dhcpv4o6="no"
 fi
 
+# Relay port (draft-ietf-dhc-relay-port-10.txt) optional compile-time feature.
+AC_ARG_ENABLE(relay-port,
+	AS_HELP_STRING([--enable-relay-port],[enable support for relay port (default is no)]))
+# Relay port is off by default (for now)
+if test "$enable_relay_port" = "yes"; then
+	AC_DEFINE([RELAY_PORT], [1],
+		  [Define to 1 to include relay port support.])
+fi
+
 # PARANOIA is off by default (until we can test it with all features)
 AC_ARG_ENABLE(paranoia,
 	AS_HELP_STRING([--enable-paranoia],[enable support for chroot/setuid (default is no)]))
@@ -521,6 +530,7 @@ AC_CHECK_HEADERS(ifaddrs.h)
 # figure out what IPv4 interface code to use
 AC_CHECK_HEADERS(linux/types.h)  # needed for linux/filter.h on old systems
 
+relay_port_supported="no"
 AC_CHECK_HEADER(linux/filter.h, DO_LPF=1, ,
 [
 #ifdef HAVE_LINUX_TYPES_H
@@ -531,6 +541,7 @@ if test -n "$DO_LPF"
 then
 	AC_DEFINE([HAVE_LPF], [1],
 		  [Define to 1 to use the Linux Packet Filter interface code.])
+	relay_port_supported="yes"
 else
 	AC_CHECK_HEADER(sys/dlpi.h, DO_DLPI=1)
 	if test -n "$DO_DLPI"
@@ -544,10 +555,17 @@ else
 			AC_DEFINE([HAVE_BPF], [1],
 				   [Define to 1 to use the
 				   Berkeley Packet Filter interface code.])
+			relay_port_supported="yes"
 		fi
 	fi
 fi
 
+if test "$enable_relay_port" = "yes"; then
+	if test "$relay_port_supported" != "yes"; then
+		AC_MSG_ERROR([--enable-relay-port requires BPF or LPF])
+	fi
+fi
+
 # SIOCGLIFCONF uses some transport structures.  Trick is not all platforms
 # use the same structures.  We like to use 'struct lifconf' and 'struct
 # lifreq', but we'll use these other structures if they're present.  HPUX
@@ -1035,6 +1053,7 @@ Features:
   dhcpv6:        $enable_dhcpv6
   delayed-ack:   $enable_delayed_ack
   dhcpv4o6:      $enable_dhcpv4o6
+  relay-port:    $enable_relay_port
 
 Developer:
   ATF unittests : $atf_path
diff --git a/doc/DHCPv4-over-DHCPv6 b/doc/DHCPv4-over-DHCPv6
index 2d82a057..415ea041 100644
--- a/doc/DHCPv4-over-DHCPv6
+++ b/doc/DHCPv4-over-DHCPv6
@@ -219,3 +219,10 @@ to start the server.
 
 Finally note in the configuration file the use of the shared-network to
 connect the DHCPv4 and  DHCPv6 subnets.
+
+USE WITH DHCPv6 RELAY(s)
+If the DHCPv6 infrastructure uses one (or more) relay because the client
+and the server are not on the same link the best choice is to put the
+first (closest to client) relay address in the dhcp4-o-dhcp6-server
+option so the same path between the DHCPv6 client part and server part
+will be used for DHCPv6 and DHCPv4-over-DHCPv6 traffic.
diff --git a/includes/config.h.in b/includes/config.h.in
index 28a4cfa9..1608f671 100644
--- a/includes/config.h.in
+++ b/includes/config.h.in
@@ -157,6 +157,9 @@
 /* Define to any value to include Ari's PARANOIA patch. */
 #undef PARANOIA
 
+/* Define to 1 to include relay port support. */
+#undef RELAY_PORT
+
 /* The size of `struct iaddr *', as computed by sizeof. */
 #undef SIZEOF_STRUCT_IADDR_P
 
diff --git a/includes/dhcp.h b/includes/dhcp.h
index c9c482d0..0a74137e 100644
--- a/includes/dhcp.h
+++ b/includes/dhcp.h
@@ -183,6 +183,8 @@ struct dhcp_packet {
 #define RAI_REMOTE_ID	2
 #define RAI_AGENT_ID	3
 #define RAI_LINK_SELECT	5
+/* not yet assigned but next free value */
+#define RAI_RELAY_PORT  19
 
 /* FQDN suboptions: */
 #define FQDN_NO_CLIENT_UPDATE		1
diff --git a/includes/dhcp6.h b/includes/dhcp6.h
index b51bac26..c78501c6 100644
--- a/includes/dhcp6.h
+++ b/includes/dhcp6.h
@@ -115,6 +115,8 @@
 #define D6O_V6_PCP_SERVER			86 /* RFC7291 */
 #define D6O_DHCPV4_MSG				87 /* RFC7341 */
 #define D6O_DHCP4_O_DHCP6_SERVER		88 /* RFC7341 */
+/* not yet assigned but next free value */
+#define D6O_RELAY_SOURCE_PORT			135 /* I-D */
 
 /*
  * Status Codes, from RFC 3315 section 24.4, and RFC 3633, 5007, 5460.
diff --git a/includes/dhcpd.h b/includes/dhcpd.h
index 044aca93..90456b76 100644
--- a/includes/dhcpd.h
+++ b/includes/dhcpd.h
@@ -469,9 +469,12 @@ struct packet {
 	 */
 	isc_boolean_t unicast;
 
-	/* Propogates server value SV_ECHO_CLIENT_ID so it is available
+	/* Propagates server value SV_ECHO_CLIENT_ID so it is available
          * in cons_options() */
 	int sv_echo_client_id;
+
+	/* Relay port check */
+	isc_boolean_t relay_source_port;
 };
 
 /*
@@ -2440,6 +2443,8 @@ void eval_network_statements(struct option_state **options,
 			    struct packet *packet,
 			    struct group *network_group);
 
+u_int16_t dhcp_check_relayport(struct packet *packet);
+
 /* dhcpleasequery.c */
 void dhcpleasequery (struct packet *, int);
 void dhcpv6_leasequery (struct data_string *, struct packet *);
@@ -2833,6 +2838,7 @@ extern int bind_local_address6;
 
 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.8 b/relay/dhcrelay.8
index 22567ee5..53cd28bf 100644
--- a/relay/dhcrelay.8
+++ b/relay/dhcrelay.8
@@ -43,6 +43,9 @@ dhcrelay - Dynamic Host Configuration Protocol Relay Agent
 [
 .B -p
 .I port
+|
+.B -rp
+.I relay-port
 ]
 [
 .B -c
@@ -112,6 +115,9 @@ dhcrelay - Dynamic Host Configuration Protocol Relay Agent
 [
 .B -p
 .I port
+|
+.B -rp
+.I relay-port
 ]
 [
 .B -c
@@ -174,7 +180,7 @@ the command line, to which DHCP/BOOTP queries should be relayed.
 .PP
 \fIOptions available for both DHCPv4 and DHCPv6:\fR
 .TP
--c COUNT
+-c \fIcount\fR
 Maximum hop count.  When forwarding packets, dhcrelay discards packets
 which have reached a hop count of COUNT.  Default is 10.  Maximum is 255.
 .TP
@@ -182,9 +188,17 @@ which have reached a hop count of COUNT.  Default is 10.  Maximum is 255.
 Force dhcrelay to run as a foreground process.  Useful when running
 dhcrelay under a debugger, or running out of inittab on System V systems.
 .TP
--p PORT
+-p \fIport\fR
 Listen and transmit on port PORT.  This is mostly useful for debugging
 purposes.  Default is port 67 for DHCPv4/BOOTP, or port 547 for DHCPv6.
+Incompatible with \fB-rp\fR.
+.TP
+-rp \fIrelay-port\fR
+Alternative source port for upstream (i.e toward the server) messages
+with DHCPv4 RAI relay-port sub-option or DHCPv6 relay-source-port
+option. Relay port support is only available if the code was compiled
+with (./configure --enable-relay-port) and requires LPF or BPF link
+layer access.
 .TP
 -q
 Quiet mode.  Prevents dhcrelay6 from printing its network configuration
@@ -209,7 +223,7 @@ be the printable name of the interface on which the client request was
 received.  The client supports inclusion of a Remote ID suboption as well,
 but this is not used by default.
 .TP
--A LENGTH
+-A \fIlength\fR
 Specify the maximum packet size to send to a DHCPv4/BOOTP server.  This
 might be done to allow sufficient space for addition of relay agent
 options while still fitting into the Ethernet MTU size.
diff --git a/relay/dhcrelay.c b/relay/dhcrelay.c
index 897a7766..aaedd8ff 100644
--- a/relay/dhcrelay.c
+++ b/relay/dhcrelay.c
@@ -152,8 +152,30 @@ static const char url[] =
 char *progname;
 
 #ifdef DHCPv6
+#ifdef RELAY_PORT
 #define DHCRELAY_USAGE \
-"Usage: %s [-4] [-d] [-q] [-a] [-D]\n"\
+"Usage: %s [-4] [-d] [-q] [-a] [-D]\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" \
+"                     [-iu interface0 [ ... -iu interfaceN]\n" \
+"                     [-id interface0 [ ... -id interfaceN]\n" \
+"                     [-U interface]\n" \
+"                     server0 [ ... serverN]\n\n" \
+"       %s -6   [-d] [-q] [-I] [-c <hops>]\n" \
+"                     [-p <port> | -rp <relay-port>]\n" \
+"                     [-pf <pid-file>] [--no-pid]\n" \
+"                     [-s <subscriber-id>]\n" \
+"                     -l lower0 [ ... -l lowerN]\n" \
+"                     -u upper0 [ ... -u upperN]\n" \
+"           lower (client link): [address%%]interface[#index]\n" \
+"           upper (server link): [address%%]interface\n\n" \
+"       %s {--version|--help|-h}"
+#else
+#define DHCRELAY_USAGE \
+"Usage: %s [-4] [-d] [-q] [-a] [-D]\n" \
 "                     [-A <length>] [-c <hops>] [-p <port>]\n" \
 "                     [-pf <pid-file>] [--no-pid]\n"\
 "                     [-m append|replace|forward|discard]\n" \
@@ -170,6 +192,20 @@ char *progname;
 "           lower (client link): [address%%]interface[#index]\n" \
 "           upper (server link): [address%%]interface\n\n" \
 "       %s {--version|--help|-h}"
+#endif
+#else /* !DHCPv6 */
+#ifdef RELAY_PORT
+#define DHCRELAY_USAGE \
+"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" \
+"                [-iu interface0 [ ... -iu interfaceN]\n" \
+"                [-id interface0 [ ... -id interfaceN]\n" \
+"                [-U interface]\n" \
+"                server0 [ ... serverN]\n\n" \
+"       %s {--version|--help|-h}"
 #else
 #define DHCRELAY_USAGE \
 "Usage: %s [-d] [-q] [-a] [-D] [-A <length>] [-c <hops>] [-p <port>]\n" \
@@ -182,6 +218,7 @@ char *progname;
 "                server0 [ ... serverN]\n\n" \
 "       %s {--version|--help|-h}"
 #endif
+#endif
 
 /*!
  *
@@ -199,6 +236,12 @@ char *progname;
  * \return Nothing
  */
 static const char use_noarg[] = "No argument for command: %s";
+#ifdef RELAY_PORT
+static const char use_port_defined[] = "Port already set, %s inappropriate";
+#if !defined (USE_BPF_RECEIVE) && !defined (USE_LPF_RECEIVE)
+static const char bpf_sock_support[] = "Only LPF and BPF are supported: %s";
+#endif
+#endif
 #ifdef DHCPv6
 static const char use_badproto[] = "Protocol already set, %s inappropriate";
 static const char use_v4command[] = "Command not used for DHCPv6: %s";
@@ -236,6 +279,9 @@ main(int argc, char **argv) {
 	int quiet = 0;
 	int fd;
 	int i;
+#ifdef RELAY_PORT
+	int port_defined = 0;
+#endif
 #ifdef DHCPv6
 	struct stream_list *sl = NULL;
 	int local_family_set = 0;
@@ -349,9 +395,26 @@ main(int argc, char **argv) {
 		} else if (!strcmp(argv[i], "-p")) {
 			if (++i == argc)
 				usage(use_noarg, argv[i-1]);
+#ifdef RELAY_PORT
+			if (port_defined)
+				usage(use_port_defined, argv[i-1]);
+			port_defined = 1;
+#endif
 			local_port = validate_port(argv[i]);
 			log_debug("binding to user-specified port %d",
 				  ntohs(local_port));
+#ifdef RELAY_PORT
+		} 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]);
+			port_defined = 1;
+			relay_port = validate_port(argv[i]);
+			log_debug("binding to user-specified relay port %d",
+				  ntohs(relay_port));
+			add_agent_options = 1;
+#endif
 		} else if (!strcmp(argv[i], "-c")) {
 			int hcount;
 			if (++i == argc)
@@ -572,6 +635,12 @@ main(int argc, char **argv) {
  		}
 	}
 
+#if defined(RELAY_PORT) && \
+    !defined (USE_BPF_RECEIVE) && !defined (USE_LPF_RECEIVE)
+	if (relay_port && (local_family == AF_INET))
+		usage(bpf_sock_support, "-rp");
+#endif
+
 	/*
 	 * If the user didn't specify a pid file directly
 	 * find one from environment variables or defaults
@@ -1259,6 +1328,12 @@ add_relay_agent_options(struct interface_info *ip, struct dhcp_packet *packet,
 		optlen += 6;
 	}
 
+#ifdef RELAY_PORT
+	if (relay_port) {
+		optlen += 2;
+	}
+#endif
+
 	/* We do not support relay option fragmenting(multiple options to
 	 * support an option data exceeding 255 bytes).
 	 */
@@ -1303,6 +1378,14 @@ add_relay_agent_options(struct interface_info *ip, struct dhcp_packet *packet,
 			log_debug ("Adding link selection suboption"
 				   " with addr: %s", inet_ntoa(giaddr));
 		}
+
+#ifdef RELAY_PORT
+		/* draft-ietf-dhc-relay-port-10.txt section 5.1 */
+		if (relay_port) {
+			*sp++ = RAI_RELAY_PORT;
+			*sp++ = 0u;
+		}
+#endif
 	} else {
 		++agent_option_errors;
 		log_error("No room in packet (used %d of %d) "
@@ -1548,6 +1631,9 @@ setup_streams(void) {
 static const int required_forw_opts[] = {
 	D6O_INTERFACE_ID,
 	D6O_SUBSCRIBER_ID,
+#if defined(RELAY_PORT)
+	D6O_RELAY_SOURCE_PORT,
+#endif
 	D6O_RELAY_MSG,
 	0
 };
@@ -1562,6 +1648,7 @@ process_up6(struct packet *packet, struct stream_list *dp) {
 	struct dhcpv6_relay_packet *relay;
 	struct option_state *opts;
 	struct stream_list *up;
+	u_int16_t relay_client_port = 0;
 
 	/* Check if the message should be relayed to the server. */
 	switch (packet->dhcpv6_msg_type) {
@@ -1622,6 +1709,10 @@ process_up6(struct packet *packet, struct stream_list *dp) {
 			}
 			memset(&relay->link_address, 0, 16);
 		}
+
+		if (packet->client_port != htons(547)) {
+			relay_client_port = packet->client_port;
+		}
 	} else {
 		relay->hop_count = 0;
 		if (!dp)
@@ -1674,6 +1765,30 @@ process_up6(struct packet *packet, struct stream_list *dp) {
 	}
 		
 
+#if defined(RELAY_PORT)
+	/*
+	 * If we use a non-547 UDP source port or if we have received
+	 * from a downstream relay agent uses a non-547 port, we need
+	 * to include the RELAY-SOURCE-PORT option. The "Downstream
+	 * UDP Port" field value in the option allow us to send
+	 * relay-reply message back to the downstream relay agent
+	 * with the correct UDP source port.
+        */
+	if (relay_port || relay_client_port) {
+		if (!save_option_buffer(&dhcpv6_universe, opts, NULL,
+					(unsigned char *) &relay_client_port,
+					sizeof(u_int16_t),
+					D6O_RELAY_SOURCE_PORT, 0)) {
+			log_error("Can't save relay-source-port.");
+			option_state_dereference(&opts, MDL);
+			return;
+		}
+	}
+#else
+	/* Avoid unused but set warning, */
+	(void)(relay_client_port);
+#endif
+
 	/* Add the relay-msg carrying the packet. */
 	if (!save_option_buffer(&dhcpv6_universe, opts,
 				NULL, (unsigned char *) packet->raw,
@@ -1708,6 +1823,9 @@ process_down6(struct packet *packet) {
 	struct data_string relay_msg;
 	const struct dhcpv6_packet *msg;
 	struct data_string if_id;
+#if defined(RELAY_PORT)
+	struct data_string down_port;
+#endif
 	struct sockaddr_in6 to;
 	struct iaddr peer;
 
@@ -1729,6 +1847,9 @@ process_down6(struct packet *packet) {
 	/* Inits. */
 	memset(&relay_msg, 0, sizeof(relay_msg));
 	memset(&if_id, 0, sizeof(if_id));
+#if defined(RELAY_PORT)
+	memset(&down_port, 0, sizeof(down_port));
+#endif
 	memset(&to, 0, sizeof(to));
 	to.sin6_family = AF_INET6;
 #ifdef HAVE_SA_LEN
@@ -1799,6 +1920,37 @@ process_down6(struct packet *packet) {
 		/* Relay-Reply of for another relay, not a client. */
 	      case DHCPV6_RELAY_REPL:
 		to.sin6_port = local_port;
+
+#if defined(RELAY_PORT)
+		oc = lookup_option(&dhcpv6_universe, packet->options,
+				   D6O_RELAY_SOURCE_PORT);
+		if (oc != NULL) {
+			u_int16_t down_relay_port;
+
+			memset(&down_port, 0, sizeof(down_port));
+			if (!evaluate_option_cache(&down_port, packet, NULL,
+						   NULL, packet->options, NULL,
+						   &global_scope, oc, MDL) ||
+			    (down_port.len != sizeof(u_int16_t))) {
+				log_info("Can't evaluate down "
+					 "relay-source-port.");
+				goto cleanup;
+			}
+			memcpy(&down_relay_port, down_port.data,
+			       sizeof(u_int16_t));
+			/*
+			 * If the down_relay_port value is non-zero,
+			 * that means our downstream relay agent uses
+			 * a non-547 UDP source port sending
+			 * relay-forw message to us. We need to use
+			 * the same UDP port sending reply back.
+			 */
+			if (down_relay_port) {
+				to.sin6_port = down_relay_port;
+			}
+		}
+#endif
+
 		/* Fall into: */
 
 	      case DHCPV6_ADVERTISE:
diff --git a/server/dhcp.c b/server/dhcp.c
index f16d001d..a0080e52 100644
--- a/server/dhcp.c
+++ b/server/dhcp.c
@@ -1063,6 +1063,20 @@ void dhcpdecline (packet, ms_nulltp)
 		lease_dereference (&lease, MDL);
 }
 
+#if defined(RELAY_PORT)
+u_int16_t dhcp_check_relayport(packet)
+	struct packet *packet;
+{
+	if (lookup_option(&agent_universe,
+			  packet->options,
+			  RAI_RELAY_PORT) != NULL) {
+		return (packet->client_port);
+	}
+
+	return (0);
+}
+#endif
+
 void dhcpinform (packet, ms_nulltp)
 	struct packet *packet;
 	int ms_nulltp;
@@ -1084,6 +1098,7 @@ void dhcpinform (packet, ms_nulltp)
 	struct interface_info *interface;
 	int result, h_m_client_ip = 0;
 	struct host_decl  *host = NULL, *hp = NULL, *h;
+	u_int16_t relay_port = 0;
 #if defined (DEBUG_INFORM_HOST)
 	int h_w_fixed_addr = 0;
 #endif
@@ -1146,6 +1161,10 @@ void dhcpinform (packet, ms_nulltp)
 		return;
 	}
 
+#if defined(RELAY_PORT)
+	relay_port = dhcp_check_relayport(packet);
+#endif
+
 	/* Find the subnet that the client is on. 
 	 * CC: Do the link selection / subnet selection
 	 */
@@ -1696,7 +1715,7 @@ void dhcpinform (packet, ms_nulltp)
 	 */
 	if (!raw.ciaddr.s_addr && gip.len) {
 		memcpy(&to.sin_addr, gip.iabuf, 4);
-		to.sin_port = local_port;
+		to.sin_port = relay_port ? relay_port : local_port;
 		raw.flags |= htons(BOOTP_BROADCAST);
 	} else {
 		gip.len = 0;
@@ -1753,6 +1772,7 @@ void nak_lease (packet, cip, network_group)
 	unsigned char nak = DHCPNAK;
 	struct packet outgoing;
 	unsigned i;
+	u_int16_t relay_port = 0;
 	struct option_state *options = (struct option_state *)0;
 	struct option_cache *oc = (struct option_cache *)0;
 	struct option_state *eval_options = NULL;
@@ -1781,6 +1801,10 @@ void nak_lease (packet, cip, network_group)
 	save_option (&dhcp_universe, options, oc);
 	option_cache_dereference (&oc, MDL);
 		     
+#if defined(RELAY_PORT)
+	relay_port = dhcp_check_relayport(packet);
+#endif
+
 	/* Set DHCP_MESSAGE to whatever the message is */
 	if (!option_cache_allocate (&oc, MDL)) {
 		log_error ("No memory for DHCPNAK message type.");
@@ -1929,7 +1953,7 @@ void nak_lease (packet, cip, network_group)
 	if (raw.giaddr.s_addr) {
 		to.sin_addr = raw.giaddr;
 		if (raw.giaddr.s_addr != htonl (INADDR_LOOPBACK))
-			to.sin_port = local_port;
+			to.sin_port = relay_port ? relay_port : local_port;
 		else
 			to.sin_port = remote_port; /* for testing. */
 
@@ -3752,6 +3776,7 @@ void dhcp_reply (lease)
 	int result;
 	struct lease_state *state = lease -> state;
 	int nulltp, bootpp, unicastp = 1;
+	u_int16_t relay_port = 0;
 	struct data_string d1;
 	const char *s;
 
@@ -3921,11 +3946,15 @@ void dhcp_reply (lease)
 #endif
 	memset (to.sin_zero, 0, sizeof to.sin_zero);
 
+#if defined(RELAY_PORT)
+	relay_port = dhcp_check_relayport(state->packet);
+#endif
+
 	/* If this was gatewayed, send it back to the gateway... */
 	if (raw.giaddr.s_addr) {
 		to.sin_addr = raw.giaddr;
 		if (raw.giaddr.s_addr != htonl (INADDR_LOOPBACK))
-			to.sin_port = local_port;
+			to.sin_port = relay_port ? relay_port : local_port;
 		else
 			to.sin_port = remote_port; /* For debugging. */
 
diff --git a/server/dhcpleasequery.c b/server/dhcpleasequery.c
index e16de0fe..40de910d 100644
--- a/server/dhcpleasequery.c
+++ b/server/dhcpleasequery.c
@@ -152,6 +152,7 @@ dhcpleasequery(struct packet *packet, int ms_nulltp) {
 	u_int32_t time_rebinding;
 	u_int32_t time_expiry;
 	u_int32_t client_last_transaction_time;
+	u_int16_t relay_port = 0;
 	struct sockaddr_in to;
 	struct in_addr siaddr;
 	struct data_string prl;
@@ -660,12 +661,16 @@ dhcpleasequery(struct packet *packet, int ms_nulltp) {
 #endif
 	memset(to.sin_zero, 0, sizeof(to.sin_zero));
 
+#if defined(RELAY_PORT)
+	relay_port = dhcp_check_relayport(packet);
+#endif
+
 	/* 
 	 * Leasequery packets are be sent to the gateway address.
 	 */
 	to.sin_addr = packet->raw->giaddr;
 	if (packet->raw->giaddr.s_addr != htonl(INADDR_LOOPBACK)) {
-		to.sin_port = local_port;
+		to.sin_port = relay_port ? relay_port : local_port;
 	} else {
 		to.sin_port = remote_port; /* XXXSK: For debugging. */
 	}
diff --git a/server/dhcpv6.c b/server/dhcpv6.c
index f4bdbf81..a7110f98 100644
--- a/server/dhcpv6.c
+++ b/server/dhcpv6.c
@@ -27,6 +27,14 @@ static void send_dhcpv4_response(struct data_string *raw);
 static void recv_dhcpv4_query(struct data_string *raw);
 static void dhcp4o6_dhcpv4_query(struct data_string *reply_ret,
 				 struct packet *packet);
+
+struct udp_data4o6 {
+	u_int16_t src_port;
+	u_int8_t  rsp_opt_exist;
+	u_int8_t  reserved;
+};
+
+static int offset_data4o6 = 36; /* 16+16+4 */
 #endif
 
 /*
@@ -211,7 +219,7 @@ isc_result_t dhcpv4o6_handler(omapi_object_t *h) {
 
 	cc = recv(dhcp4o6_fd, buf, sizeof(buf), 0);
 
-	if (cc < DHCP_FIXED_NON_UDP + 32)
+	if (cc < DHCP_FIXED_NON_UDP + offset_data4o6)
 		return ISC_R_UNEXPECTED;
 	memset(&raw, 0, sizeof(raw));
 	if (!buffer_allocate(&raw.buffer, cc, MDL)) {
@@ -237,7 +245,7 @@ isc_result_t dhcpv4o6_handler(omapi_object_t *h) {
  * \brief Send the DHCPv4-response back to the DHCPv6 side
  *  (DHCPv6 server function)
  *
- * Format: interface:16 + address:16 + DHCPv6 DHCPv4-response message
+ * Format: interface:16 + address:16 + udp:4 + DHCPv6 DHCPv4-response message
  *
  * \param raw the IPC message content
  */
@@ -246,6 +254,7 @@ static void send_dhcpv4_response(struct data_string *raw) {
 	char name[16 + 1];
 	struct sockaddr_in6 to_addr;
 	char pbuf[sizeof("ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255")];
+	struct udp_data4o6 udp_data;
 	int send_ret;
 
 	memset(name, 0, sizeof(name));
@@ -263,26 +272,32 @@ static void send_dhcpv4_response(struct data_string *raw) {
 	memset(&to_addr, 0, sizeof(to_addr));
 	to_addr.sin6_family = AF_INET6;
 	memcpy(&to_addr.sin6_addr, raw->data + 16, 16);
-	if ((raw->data[32] == DHCPV6_RELAY_FORW) ||
-	    (raw->data[32] == DHCPV6_RELAY_REPL)) {
-		to_addr.sin6_port = local_port;
+	memset(&udp_data, 0, sizeof(udp_data));
+	memcpy(&udp_data, raw->data + 32, 4);
+	if ((raw->data[36] == DHCPV6_RELAY_FORW) ||
+	    (raw->data[36] == DHCPV6_RELAY_REPL)) {
+		if (udp_data.rsp_opt_exist) {
+			to_addr.sin6_port = udp_data.src_port;
+		} else {
+			to_addr.sin6_port = local_port;
+		}
 	} else {
 		to_addr.sin6_port = remote_port;
 	}
 
 	log_info("send_dhcpv4_response(): sending %s on %s to %s port %d",
-		 dhcpv6_type_names[raw->data[32]],
+		 dhcpv6_type_names[raw->data[36]],
 		 name,
 		 inet_ntop(AF_INET6, raw->data + 16, pbuf, sizeof(pbuf)),
 		 ntohs(to_addr.sin6_port));
 
-	send_ret = send_packet6(ip, raw->data + 32, raw->len - 32, &to_addr);
+	send_ret = send_packet6(ip, raw->data + 36, raw->len - 36, &to_addr);
 	if (send_ret < 0) {
 		log_error("send_dhcpv4_response: send_packet6(): %m");
-	} else if (send_ret != raw->len - 32) {
+	} else if (send_ret != raw->len - 36) {
 		log_error("send_dhcpv4_response: send_packet6() "
 			  "sent %d of %d bytes",
-			  send_ret, raw->len - 32);
+			  send_ret, raw->len - 36);
 	}
 }
 #endif /* DHCP4o6 */
@@ -857,6 +872,9 @@ static const int required_opts_solicit[] = {
 };
 static const int required_opts_agent[] = {
 	D6O_INTERFACE_ID,
+#if defined(RELAY_PORT)
+	D6O_RELAY_SOURCE_PORT,
+#endif
 	D6O_RELAY_MSG,
 	0
 };
@@ -6854,6 +6872,35 @@ dhcpv6_relay_forw(struct data_string *reply_ret, struct packet *packet) {
 		data_string_forget(&a_opt, MDL);
 	}
 
+#if defined(RELAY_PORT)
+	/*
+	 * Append the relay_source_port option if present.
+	 */
+	oc = lookup_option(&dhcpv6_universe, packet->options,
+			   D6O_RELAY_SOURCE_PORT);
+	if (oc != NULL) {
+		if (!evaluate_option_cache(&a_opt, packet,
+					   NULL, NULL,
+					   packet->options, NULL,
+					   &global_scope, oc, MDL)) {
+			log_error("dhcpv6_relay_forw: error evaluating "
+				  "Relay Source Port.");
+			goto exit;
+		}
+		if (!save_option_buffer(&dhcpv6_universe, opt_state, NULL,
+					(unsigned char *)a_opt.data,
+					a_opt.len,
+					D6O_RELAY_SOURCE_PORT, 0)) {
+			log_error("dhcpv6_relay_forw: error saving "
+				  "Relay Source Port.");
+			goto exit;
+		}
+		data_string_forget(&a_opt, MDL);
+
+		packet->relay_source_port = ISC_TRUE;
+	}
+#endif
+
 	/*
 	 * Append our encapsulated stuff for caller.
 	 */
@@ -7147,6 +7194,35 @@ dhcp4o6_relay_forw(struct data_string *reply_ret, struct packet *packet) {
 		data_string_forget(&a_opt, MDL);
 	}
 
+#if defined(RELAY_PORT)
+	/*
+	 * Append the relay_source_port option if present.
+	 */
+	oc = lookup_option(&dhcpv6_universe, packet->options,
+			   D6O_RELAY_SOURCE_PORT);
+	if (oc != NULL) {
+		if (!evaluate_option_cache(&a_opt, packet,
+					   NULL, NULL,
+					   packet->options, NULL,
+					   &global_scope, oc, MDL)) {
+			log_error("dhcpv4o6_relay_forw: error evaluating "
+				  "Relay Source Port.");
+			goto exit;
+		}
+		if (!save_option_buffer(&dhcpv6_universe, opt_state, NULL,
+					(unsigned char *)a_opt.data,
+					a_opt.len,
+					D6O_RELAY_SOURCE_PORT, 0)) {
+			log_error("dhcpv4o6_relay_forw: error saving "
+				  "Relay Source Port.");
+			goto exit;
+		}
+		data_string_forget(&a_opt, MDL);
+
+		packet->relay_source_port = ISC_TRUE;
+	}
+#endif
+
 	/*
 	 * Append our encapsulated stuff for caller.
 	 */
@@ -7436,12 +7512,13 @@ exit:
  * \brief Forward a DHCPv4-query message to the DHCPv4 side
  *  (DHCPv6 server function)
  *
- * Format: interface:16 + address:16 + DHCPv6 DHCPv4-query message
+ * Format: interface:16 + address:16 + udp:4 + DHCPv6 DHCPv4-query message
  *
  * \brief packet the DHCPv6 DHCPv4-query message
  */
 static void forw_dhcpv4_query(struct packet *packet) {
 	struct data_string ds;
+	struct udp_data4o6 udp_data;
 	unsigned len;
 	int cc;
 
@@ -7458,7 +7535,7 @@ static void forw_dhcpv4_query(struct packet *packet) {
 	}
 
 	/* Get a buffer. */
-	len = packet->packet_length + 32;
+	len = packet->packet_length + 36;
 	memset(&ds, 0, sizeof(ds));
 	if (!buffer_allocate(&ds.buffer, len, MDL)) {
 		log_error("forw_dhcpv4_query: "
@@ -7472,7 +7549,10 @@ static void forw_dhcpv4_query(struct packet *packet) {
 	strncpy((char *)ds.buffer->data, packet->interface->name, 16);
 	memcpy(ds.buffer->data + 16,
 	       packet->client_addr.iabuf, 16);
-	memcpy(ds.buffer->data + 32,
+	memset(&udp_data, 0, sizeof(udp_data));
+	udp_data.src_port = packet->client_port;
+	memcpy(ds.buffer->data + 32, &udp_data, 4);
+	memcpy(ds.buffer->data + 36,
 	       (unsigned char *)packet->raw,
 	       packet->packet_length);
 
@@ -7690,6 +7770,15 @@ dhcpv6(struct packet *packet) {
 		to_addr.sin6_port = packet->client_port;
 #endif
 
+#if defined(RELAY_PORT)
+		/*
+		 * Check relay source port.
+		 */
+		if (packet->relay_source_port) {
+			to_addr.sin6_port = packet->client_port;
+		}
+#endif
+
 		memcpy(&to_addr.sin6_addr, packet->client_addr.iabuf,
 		       sizeof(to_addr.sin6_addr));
 
@@ -7716,7 +7805,7 @@ dhcpv6(struct packet *packet) {
  * Receive a message with a DHCPv4-query inside from the DHCPv6 server.
  * (code copied from \ref do_packet6() \ref and dhcpv6())
  *
- * Format: interface:16 + address:16 + DHCPv6 DHCPv4-query message
+ * Format: interface:16 + address:16 + udp:4 + DHCPv6 DHCPv4-query message
  *
  * \param raw the DHCPv6 DHCPv4-query message raw content
  */
@@ -7730,6 +7819,7 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 	const struct dhcpv4_over_dhcpv6_packet *msg;
 	struct data_string reply;
 	struct data_string ds;
+	struct udp_data4o6 udp_data;
 	unsigned len;
 	int cc;
 
@@ -7748,14 +7838,17 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 	iaddr.len = 16;
 	memcpy(iaddr.iabuf, raw->data + 16, 16);
 
+	memset(&udp_data, 0, sizeof(udp_data));
+	memcpy(&udp_data, raw->data + 32, 4);
+
 	/*
 	 * From do_packet6().
 	 */
 
-	if (!packet6_len_okay((char *)raw->data + 32, raw->len - 32)) {
+	if (!packet6_len_okay((char *)raw->data + 36, raw->len - 36)) {
 		log_error("recv_dhcpv4_query: "
 			 "short packet from %s, len %d, dropped",
-			 piaddr(iaddr), raw->len - 32);
+			 piaddr(iaddr), raw->len - 36);
 		return;
 	}
 
@@ -7774,18 +7867,18 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 		return;
 	}
 
-	packet->raw = (struct dhcp_packet *)(raw->data + 32);
-	packet->packet_length = raw->len - 32;
-	packet->client_port = remote_port;
+	packet->raw = (struct dhcp_packet *)(raw->data + 36);
+	packet->packet_length = raw->len - 36;
+	packet->client_port = udp_data.src_port;
 	packet->client_addr = iaddr;
 	interface_reference(&packet->interface, ip, MDL);
 
-	msg_type = raw->data[32];
+	msg_type = raw->data[36];
 	if ((msg_type == DHCPV6_RELAY_FORW) ||
 	    (msg_type == DHCPV6_RELAY_REPL)) {
 		int relaylen =
 		    (int)(offsetof(struct dhcpv6_relay_packet, options));
-		relay = (const struct dhcpv6_relay_packet *)(raw->data + 32);
+		relay = (const struct dhcpv6_relay_packet *)(raw->data + 36);
 		packet->dhcpv6_msg_type = relay->msg_type;
 
 		/* relay-specific data */
@@ -7797,7 +7890,7 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 
 		if (!parse_option_buffer(packet->options,
 					 relay->options,
-					 raw->len - 32 - relaylen,
+					 raw->len - 36 - relaylen,
 					 &dhcpv6_universe)) {
 			/* no logging here, as parse_option_buffer() logs all
 			   cases where it fails */
@@ -7808,7 +7901,7 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 		   (msg_type == DHCPV6_DHCPV4_RESPONSE)) {
 		int msglen =
 		    (int)(offsetof(struct dhcpv4_over_dhcpv6_packet, options));
-		msg = (struct dhcpv4_over_dhcpv6_packet *)(raw->data + 32);
+		msg = (struct dhcpv4_over_dhcpv6_packet *)(raw->data + 36);
 		packet->dhcpv6_msg_type = msg->msg_type;
 
 		/* message-specific data */
@@ -7817,7 +7910,7 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 
 		if (!parse_option_buffer(packet->options,
 					 msg->options,
-					 raw->len - 32 - msglen,
+					 raw->len - 36 - msglen,
 					 &dhcpv6_universe)) {
 			/* no logging here, as parse_option_buffer() logs all
 			   cases where it fails */
@@ -7878,18 +7971,19 @@ static void recv_dhcpv4_query(struct data_string *raw) {
          */
 	build_dhcpv6_reply(&reply, packet);
 
-	packet_dereference(&packet, MDL);
-
-	if (reply.data == NULL)
+	if (reply.data == NULL) {
+		packet_dereference(&packet, MDL);
 		return;
+	}
 
 	/*
 	 * Forward the response.
 	 */
-	len = reply.len + 32;
+	len = reply.len + 36;
 	memset(&ds, 0, sizeof(ds));
 	if (!buffer_allocate(&ds.buffer, len, MDL)) {
 		log_error("recv_dhcpv4_query: no memory.");
+		packet_dereference(&packet, MDL);
 		return;
 	}
 	ds.data = ds.buffer->data;
@@ -7897,7 +7991,15 @@ static void recv_dhcpv4_query(struct data_string *raw) {
 
 	memcpy(ds.buffer->data, name, 16);
 	memcpy(ds.buffer->data + 16, iaddr.iabuf, 16);
-	memcpy(ds.buffer->data + 32, reply.data, reply.len);
+	udp_data.rsp_opt_exist = packet->relay_source_port ? 1 : 0;
+	memcpy(ds.buffer->data + 32, &udp_data, 4);
+	memcpy(ds.buffer->data + 36, reply.data, reply.len);
+
+	/*
+	 * Now we can release the packet.
+	 */
+	packet_dereference(&packet, MDL);
+
 	cc = send(dhcp4o6_fd, ds.data, ds.len, 0);
 	if (cc < 0)
 		log_error("recv_dhcpv4_query: send(): %m");
diff --git a/server/stables.c b/server/stables.c
index f3424c92..170f6da3 100644
--- a/server/stables.c
+++ b/server/stables.c
@@ -169,6 +169,7 @@ static struct option agent_options[] = {
 	{ "agent-id", "I",			&agent_universe,   3, 1 },
 	{ "DOCSIS-device-class", "L",		&agent_universe,   4, 1 },
 	{ "link-selection", "I",		&agent_universe,   5, 1 },
+	{ "relay-port", "Z",			&agent_universe,  19, 1 },
 	{ NULL, NULL, NULL, 0, 0 }
 };