Index: dhcpd.8
===================================================================
RCS file: /cvs/src/usr.sbin/dhcpd/dhcpd.8,v
diff -u -p -r1.36 dhcpd.8
--- dhcpd.8	27 Jun 2024 16:39:31 -0000	1.36
+++ dhcpd.8	7 Jun 2025 04:29:40 -0000
@@ -132,15 +132,8 @@ on systems where
 is unable to identify non-broadcast interfaces.
 .Pp
 .Nm
-normally runs in routing domain 0.
-In order to run in another
-.Xr rdomain 4 ,
-.Nm
-needs to be started with a list of interfaces
-which share the same routing domain,
-which allows
-.Nm
-to set its own routing domain accordingly.
+will skip interfaces configured in a different routing domain to
+the one it was executed in.
 .Pp
 DHCP traffic always bypasses IPsec.
 Otherwise there could be situations when a server has an IPsec SA for the
Index: dhcpd.c
===================================================================
RCS file: /cvs/src/usr.sbin/dhcpd/dhcpd.c,v
diff -u -p -r1.61 dhcpd.c
--- dhcpd.c	4 Jun 2025 21:16:25 -0000	1.61
+++ dhcpd.c	7 Jun 2025 04:29:40 -0000
@@ -71,6 +71,7 @@ struct group root_group;
 u_int16_t server_port;
 u_int16_t client_port;
 
+int rdomain;
 struct passwd *pw;
 int log_priority;
 int pfpipe[2];
@@ -87,7 +88,7 @@ char *leased_tab = NULL;
 int
 main(int argc, char *argv[])
 {
-	int ch, cftest = 0, rdomain = -1, udpsockmode = 0;
+	int ch, cftest = 0, udpsockmode = 0;
 	int debug = 0, verbose = 0;
 	char *sync_iface = NULL;
 	char *sync_baddr = NULL;
@@ -98,6 +99,8 @@ main(int argc, char *argv[])
 	log_init(1, LOG_DAEMON);	/* log to stderr until daemonized */
 	log_setverbose(1);
 
+	rdomain = getrtable();
+
 	opterr = 0;
 	while ((ch = getopt(argc, argv, "A:C:L:c:dfl:nu::vY:y:")) != -1)
 		switch (ch) {
@@ -197,11 +200,7 @@ main(int argc, char *argv[])
 
 	db_startup();
 	if (!udpsockmode || argc > 0)
-		discover_interfaces(&rdomain);
-
-	if (rdomain != -1)
-		if (setrtable(rdomain) == -1)
-			fatal("setrtable");
+		discover_interfaces();
 
 	if (syncsend || syncrecv) {
 		if (sync_init(sync_iface, sync_baddr, sync_port) == -1)
Index: dhcpd.h
===================================================================
RCS file: /cvs/src/usr.sbin/dhcpd/dhcpd.h,v
diff -u -p -r1.72 dhcpd.h
--- dhcpd.h	31 May 2025 07:47:45 -0000	1.72
+++ dhcpd.h	7 Jun 2025 04:29:40 -0000
@@ -443,7 +443,7 @@ ssize_t receive_packet(struct interface_
 extern struct interface_info *interfaces;
 extern struct protocol *protocols;
 extern struct dhcpd_timeout *timeouts;
-void discover_interfaces(int *);
+void discover_interfaces(void);
 void dispatch(void);
 int locate_network(struct packet *);
 void got_one(struct protocol *);
Index: dispatch.c
===================================================================
RCS file: /cvs/src/usr.sbin/dhcpd/dispatch.c,v
diff -u -p -r1.49 dispatch.c
--- dispatch.c	4 Jun 2025 21:16:25 -0000	1.49
+++ dispatch.c	7 Jun 2025 04:29:40 -0000
@@ -67,6 +67,8 @@
 #include "log.h"
 #include "sync.h"
 
+extern int rdomain;
+
 struct interface_info *interfaces;
 struct protocol *protocols;
 struct dhcpd_timeout *timeouts;
@@ -81,14 +83,14 @@ int get_rdomain(char *);
    subnet it's on, and add it to the list of interfaces. */
 
 void
-discover_interfaces(int *rdomain)
+discover_interfaces(void)
 {
 	struct interface_info *tmp;
 	struct interface_info *last, *next;
 	struct subnet *subnet;
 	struct shared_network *share;
 	struct sockaddr_in foo;
-	int ir = 0, ird;
+	int ir;
 	struct ifreq *tif;
 	struct ifaddrs *ifap, *ifa;
 
@@ -99,11 +101,7 @@ discover_interfaces(int *rdomain)
 	 * If we already have a list of interfaces, the interfaces were
 	 * requested.
 	 */
-	if (interfaces != NULL)
-		ir = 1;
-	else
-		/* must specify an interface when rdomains are used */
-		*rdomain = 0;
+	ir = (interfaces != NULL);
 
 	/* Cycle through the list of interfaces looking for IP addresses. */
 	for (ifa = ifap; ifa != NULL; ifa = ifa->ifa_next) {
@@ -125,15 +123,6 @@ discover_interfaces(int *rdomain)
 		if (tmp == NULL && ir)
 			continue;
 
-		ird = get_rdomain(ifa->ifa_name);
-		if (*rdomain == -1)
-			*rdomain = ird;
-		else if (*rdomain != ird && ir)
-			fatalx("Interface %s is not in rdomain %d",
-			    tmp->name, *rdomain);
-		else if (*rdomain != ird && !ir)
-			continue;
-
 		/* If there isn't already an interface by this name,
 		   allocate one. */
 		if (tmp == NULL) {
@@ -150,16 +139,19 @@ discover_interfaces(int *rdomain)
 		/* If we have the capability, extract link information
 		   and record it in a linked list. */
 		if (ifa->ifa_addr->sa_family == AF_LINK) {
-			struct sockaddr_dl *sdl =
-			    ((struct sockaddr_dl *)(ifa->ifa_addr));
+			struct if_data *ifi = ifa->ifa_data;
+			struct sockaddr_dl *sdl;
+
+			if (rdomain != ifi->ifi_rdomain)
+				continue;
+
+			sdl = (struct sockaddr_dl *)ifa->ifa_addr;
 			tmp->index = sdl->sdl_index;
 			tmp->hw_address.hlen = sdl->sdl_alen;
 			tmp->hw_address.htype = HTYPE_ETHER; /* XXX */
 			memcpy(tmp->hw_address.haddr,
 			    LLADDR(sdl), sdl->sdl_alen);
 		} else if (ifa->ifa_addr->sa_family == AF_INET) {
-			struct iaddr addr;
-
 			/* Get a pointer to the address... */
 			memcpy(&foo, ifa->ifa_addr, sizeof(foo));
 
@@ -182,55 +174,27 @@ discover_interfaces(int *rdomain)
 				tmp->ifp = tif;
 				tmp->primary_address = foo.sin_addr;
 			}
-
-			/* Grab the address... */
-			addr.len = 4;
-			memcpy(addr.iabuf, &foo.sin_addr.s_addr, addr.len);
-
-			/* If there's a registered subnet for this address,
-			   connect it together... */
-			if ((subnet = find_subnet(addr))) {
-				/* If this interface has multiple aliases
-				   on the same subnet, ignore all but the
-				   first we encounter. */
-				if (!subnet->interface) {
-					subnet->interface = tmp;
-					subnet->interface_address = addr;
-				} else if (subnet->interface != tmp) {
-					log_warnx("Multiple %s %s: %s %s",
-					    "interfaces match the",
-					    "same subnet",
-					    subnet->interface->name,
-					    tmp->name);
-				}
-				share = subnet->shared_network;
-				if (tmp->shared_network &&
-				    tmp->shared_network != share) {
-					log_warnx("Interface %s matches %s",
-					    tmp->name,
-					    "multiple shared networks");
-				} else {
-					tmp->shared_network = share;
-				}
-
-				if (!share->interface) {
-					share->interface = tmp;
-				} else if (share->interface != tmp) {
-					log_warnx("Multiple %s %s: %s %s",
-					    "interfaces match the",
-					    "same shared network",
-					    share->interface->name,
-					    tmp->name);
-				}
-			}
 		}
 	}
 
 	/* Discard interfaces we can't listen on. */
 	last = NULL;
 	for (tmp = interfaces; tmp; tmp = next) {
+		struct iaddr addr;
+
 		next = tmp->next;
 
+		if (tmp->index == 0) {
+			log_warnx("Can't listen on %s - wrong rdomain",
+			    tmp->name);
+			/* Remove tmp from the list of interfaces. */
+			if (!last)
+				interfaces = interfaces->next;
+			else
+				last->next = tmp->next;
+			continue;
+		}
+
 		if (!tmp->ifp) {
 			log_warnx("Can't listen on %s - it has no IP address.",
 			    tmp->name);
@@ -244,6 +208,47 @@ discover_interfaces(int *rdomain)
 
 		memcpy(&foo, &tmp->ifp->ifr_addr, sizeof tmp->ifp->ifr_addr);
 
+		/* Grab the address... */
+		addr.len = 4;
+		memcpy(addr.iabuf, &foo.sin_addr.s_addr, addr.len);
+
+		/* If there's a registered subnet for this address,
+		   connect it together... */
+		if ((subnet = find_subnet(addr))) {
+			/* If this interface has multiple aliases
+			   on the same subnet, ignore all but the
+			   first we encounter. */
+			if (!subnet->interface) {
+				subnet->interface = tmp;
+				subnet->interface_address = addr;
+			} else if (subnet->interface != tmp) {
+				log_warnx("Multiple %s %s: %s %s",
+				    "interfaces match the",
+				    "same subnet",
+				    subnet->interface->name,
+				    tmp->name);
+			}
+			share = subnet->shared_network;
+			if (tmp->shared_network &&
+			    tmp->shared_network != share) {
+				log_warnx("Interface %s matches %s",
+				    tmp->name,
+				    "multiple shared networks");
+			} else {
+				tmp->shared_network = share;
+			}
+
+			if (!share->interface) {
+				share->interface = tmp;
+			} else if (share->interface != tmp) {
+				log_warnx("Multiple %s %s: %s %s",
+				    "interfaces match the",
+				    "same shared network",
+				    share->interface->name,
+				    tmp->name);
+			}
+		}
+
 		if (!tmp->shared_network) {
 			log_warnx("Can't listen on %s - dhcpd.conf has no "
 			    "subnet declaration for %s.", tmp->name,
@@ -616,22 +621,4 @@ remove_protocol(struct protocol *proto)
 			free(p);
 		}
 	}
-}
-
-int
-get_rdomain(char *name)
-{
-	int rv = 0, s;
-	struct  ifreq ifr;
-
-	if ((s = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
-		fatal("get_rdomain socket");
-
-	memset(&ifr, 0, sizeof(ifr));
-	strlcpy(ifr.ifr_name, name, sizeof(ifr.ifr_name));
-	if (ioctl(s, SIOCGIFRDOMAIN, (caddr_t)&ifr) != -1)
-		rv = ifr.ifr_rdomainid;
-
-	close(s);
-	return rv;
 }