Here are patches to add full multicast support to rwhod, and an updated man

page.  I tried all three modes (rwhod, rwhod -m, rwhod -m 32) on a machine
with 2 ethernet interfaces and they all worked.
Submitted by:	Bill Fenner <fenner@parc.xerox.com>

2 files changed, 196 insertions, 16 deletions

diff --git a/usr.sbin/rwhod/rwhod.8 b/usr.sbin/rwhod/rwhod.8
index 2922bcc..fc4b628 100644
--- a/usr.sbin/rwhod/rwhod.8
+++ b/usr.sbin/rwhod/rwhod.8
@@ -39,6 +39,7 @@
 .Nd system status server
 .Sh SYNOPSIS
 .Nm rwhod
+.Op Fl m Op Ar ttl
 .Sh DESCRIPTION
 .Nm Rwhod
 is the server which maintains the database used by the
@@ -47,19 +48,59 @@ and
 .Xr ruptime 1
 programs.  Its operation is predicated on the ability to
 .Em broadcast
+or
+.Em multicast
 messages on a network.
 .Pp
 .Nm Rwhod
 operates as both a producer and consumer of status information.
 As a producer of information it periodically
 queries the state of the system and constructs
-status messages which are broadcast on a network.
+status messages which are broadcasted or multicasted on a network.
 As a consumer of information, it listens for other
 .Nm rwhod
 servers' status messages, validating them, then recording
 them in a collection of files located in the directory
 .Pa /var/rwho .
 .Pp
+The
+.Fl m
+option causes rwhod to use IP multicast (instead of
+broadcast) on all interfaces that have
+the IFF_MULTICAST flag set in their "ifnet" structs
+(excluding the loopback interface).  The multicast
+reports are sent with a time-to-live of 1, to prevent
+forwarding beyond the directly-connected subnet(s).
+.Pp
+If the optional
+.Ar ttl
+argument is supplied with the
+.Fl m
+flag, rwhod will send IP multicast datagrams with a
+time-to-live of <ttl>, via a SINGLE interface rather
+than all interfaces.  <ttl> must be between 0 and
+32 (or MAX_MULTICAST_SCOPE).  Note that
+.Fl m Ar 1
+is different than
+.Fl m ,
+in that
+.Fl m Ar 1
+specifies transmission on one interface only.
+.Pp
+When
+.Fl m
+is used without a
+.Ar ttl
+argument, the program accepts multicast
+rwhod reports from all multicast-capable interfaces.  If a
+.Ar ttl
+argument is given, it accepts multicast reports from only one interface, the
+one on which reports are sent (which may be controlled via the host's routing
+table).  Regardless of the "-m" option, the program accepts broadcast or
+unicast reports from all interfaces.  Thus, this program will hear the
+reports of old, non-multicasting rwhods, but, if multicasting is used,
+those old rwhods won't hear the reports generated by this program.
+.Pp
 The server transmits and receives messages at the port indicated
 in the ``rwho'' service specification; see 
 .Xr services 5 .
@@ -134,7 +175,6 @@ image currently operating.
 .Xr rwho 1 ,
 .Xr ruptime 1
 .Sh BUGS
-There should be a way to relay status information between networks. 
 Status information should be sent only upon request rather than continuously.
 People often interpret the server dying
 or network communication failures
diff --git a/usr.sbin/rwhod/rwhod.c b/usr.sbin/rwhod/rwhod.c
index 75c02ff..66ead27 100644
--- a/usr.sbin/rwhod/rwhod.c
+++ b/usr.sbin/rwhod/rwhod.c
@@ -67,6 +67,49 @@ static char sccsid[] = "@(#)rwhod.c	8.1 (Berkeley) 6/6/93";
 #include <utmp.h>
 
 /*
+ * This version of Berkeley's rwhod has been modified to use IP multicast
+ * datagrams, under control of a new command-line option:
+ *
+ *	rwhod -m	causes rwhod to use IP multicast (instead of
+ *			broadcast or unicast) on all interfaces that have
+ *			the IFF_MULTICAST flag set in their "ifnet" structs
+ *			(excluding the loopback interface).  The multicast
+ *			reports are sent with a time-to-live of 1, to prevent
+ *			forwarding beyond the directly-connected subnet(s).
+ *
+ *	rwhod -m <ttl>	causes rwhod to send IP multicast datagrams with a
+ *			time-to-live of <ttl>, via a SINGLE interface rather
+ *			than all interfaces.  <ttl> must be between 0 and
+ *			MAX_MULTICAST_SCOPE, defined below.  Note that "-m 1"
+ *			is different than "-m", in that "-m 1" specifies
+ *			transmission on one interface only.
+ *
+ * When "-m" is used without a <ttl> argument, the program accepts multicast
+ * rwhod reports from all multicast-capable interfaces.  If a <ttl> argument
+ * is given, it accepts multicast reports from only one interface, the one
+ * on which reports are sent (which may be controlled via the host's routing
+ * table).  Regardless of the "-m" option, the program accepts broadcast or
+ * unicast reports from all interfaces.  Thus, this program will hear the
+ * reports of old, non-multicasting rwhods, but, if multicasting is used,
+ * those old rwhods won't hear the reports generated by this program.
+ *
+ *                  -- Steve Deering, Stanford University, February 1989
+ */
+
+#define NO_MULTICAST		0	  /* multicast modes */
+#define PER_INTERFACE_MULTICAST	1
+#define SCOPED_MULTICAST	2
+
+#define MAX_MULTICAST_SCOPE	32	  /* "site-wide", by convention */
+
+#define INADDR_WHOD_GROUP (u_long)0xe0000103      /* 224.0.1.3 */
+					  /* (belongs in protocols/rwhod.h) */
+
+int			multicast_mode  = NO_MULTICAST;
+int			multicast_scope;
+struct sockaddr_in	multicast_addr  = { sizeof multicast_addr, AF_INET };
+
+/*
  * Alarm interval. Don't forget to change the down time check in ruptime
  * if this is changed.
  */
@@ -109,7 +152,7 @@ void	 Sendto __P((int, char *, int, int, char *, int));
 int
 main(argc, argv)
 	int argc;
-	char argv[];
+	char *argv[];
 {
 	struct sockaddr_in from;
 	struct stat st;
@@ -122,21 +165,43 @@ main(argc, argv)
 		fprintf(stderr, "rwhod: not super user\n");
 		exit(1);
 	}
-	sp = getservbyname("who", "udp");
-	if (sp == NULL) {
-		fprintf(stderr, "rwhod: udp/who: unknown service\n");
+	argv++; argc--;
+	while (argc > 0 && *argv[0] == '-') {
+		if (strcmp(*argv, "-m") == 0) {
+			if (argc > 1 && isdigit(*(argv + 1)[0])) {
+				argv++, argc--;
+				multicast_mode  = SCOPED_MULTICAST;
+				multicast_scope = atoi(*argv);
+				if (multicast_scope > MAX_MULTICAST_SCOPE) {
+					fprintf(stderr,
+					"rwhod: ttl must not exceed %u\n",
+					MAX_MULTICAST_SCOPE);
+					exit(1);
+				}
+			}
+			else multicast_mode = PER_INTERFACE_MULTICAST;
+		}
+		else goto usage;
+		argv++, argc--;
+	}
+	if (argc > 0) {
+usage:		fprintf(stderr, "usage: rwhod [ -m [ ttl ] ]\n");
 		exit(1);
 	}
 #ifndef DEBUG
 	daemon(1, 0);
 #endif
+	(void) signal(SIGHUP, getboottime);
+	openlog("rwhod", LOG_PID, LOG_DAEMON);
+	sp = getservbyname("who", "udp");
+	if (sp == NULL) {
+		syslog(LOG_ERR, "rwhod: udp/who: unknown service\n");
+		exit(1);
+	}
 	if (chdir(_PATH_RWHODIR) < 0) {
-		(void)fprintf(stderr, "rwhod: %s: %s\n",
-		    _PATH_RWHODIR, strerror(errno));
+		syslog(LOG_ERR, "rwhod: %s: %m\n", _PATH_RWHODIR);
 		exit(1);
 	}
-	(void) signal(SIGHUP, getboottime);
-	openlog("rwhod", LOG_PID, LOG_DAEMON);
 	/*
 	 * Establish host name as returned by system.
 	 */
@@ -162,6 +227,7 @@ main(argc, argv)
 		exit(1);
 	}
 	memset(&sin, 0, sizeof(sin));
+	sin.sin_len = sizeof(sin);
 	sin.sin_family = AF_INET;
 	sin.sin_port = sp->s_port;
 	if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
@@ -335,9 +401,30 @@ onalrm(signo)
 	mywd.wd_sendtime = htonl(time(0));
 	mywd.wd_vers = WHODVERSION;
 	mywd.wd_type = WHODTYPE_STATUS;
-	for (np = neighbors; np != NULL; np = np->n_next)
-		(void)sendto(s, (char *)&mywd, cc, 0,
-				np->n_addr, np->n_addrlen);
+	if (multicast_mode == SCOPED_MULTICAST) {
+		(void) sendto(s, (char *)&mywd, cc, 0,
+				(struct sockaddr *)&multicast_addr,
+				sizeof(multicast_addr));
+	}
+	else for (np = neighbors; np != NULL; np = np->n_next) {
+		if (multicast_mode == PER_INTERFACE_MULTICAST &&
+		    np->n_flags & IFF_MULTICAST) {
+			/*
+			 * Select the outgoing interface for the multicast.
+			 */
+			if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
+			    &(((struct sockaddr_in *)np->n_addr)->sin_addr),
+			    sizeof(struct in_addr)) < 0) {
+				syslog(LOG_ERR,
+					"setsockopt IP_MULTICAST_IF: %m");
+				exit(1);
+			}
+			(void) sendto(s, (char *)&mywd, cc, 0,
+				(struct sockaddr *)&multicast_addr,
+				sizeof(multicast_addr));
+		} else (void) sendto(s, (char *)&mywd, cc, 0,
+					np->n_addr, np->n_addrlen);
+	}
 	if (utmpent && chdir(_PATH_RWHODIR)) {
 		syslog(LOG_ERR, "chdir(%s): %m", _PATH_RWHODIR);
 		exit(1);
@@ -410,6 +497,33 @@ configure(s)
 	char *buf, *lim, *next;
 	struct rt_addrinfo info;
 
+	if (multicast_mode != NO_MULTICAST) {
+		multicast_addr.sin_addr.s_addr = htonl(INADDR_WHOD_GROUP);
+		multicast_addr.sin_port = sp->s_port;
+	}
+
+	if (multicast_mode == SCOPED_MULTICAST) {
+		struct ip_mreq mreq;
+		unsigned char ttl;
+
+		mreq.imr_multiaddr.s_addr = htonl(INADDR_WHOD_GROUP);
+		mreq.imr_interface.s_addr = htonl(INADDR_ANY);
+		if (setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP,
+					&mreq, sizeof(mreq)) < 0) {
+			syslog(LOG_ERR,
+				"setsockopt IP_ADD_MEMBERSHIP: %m");
+			return(0);
+		}
+		ttl = multicast_scope;
+		if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL,
+					&ttl, sizeof(ttl)) < 0) {
+			syslog(LOG_ERR,
+				"setsockopt IP_MULTICAST_TTL: %m");
+			return(0);
+		}
+		return(1);
+	}
+
 	mib[0] = CTL_NET;
 	mib[1] = PF_ROUTE;
 	mib[2] = 0;
@@ -433,7 +547,9 @@ configure(s)
 			continue;
 		}
 		if ((flags & IFF_UP) == 0 ||
-		    (flags & (IFF_BROADCAST|IFF_POINTOPOINT)) == 0)
+		    (flags & (((multicast_mode == PER_INTERFACE_MULTICAST) ?
+				IFF_MULTICAST : 0) |
+				IFF_BROADCAST|IFF_POINTOPOINT)) == 0)
 			continue;
 		if (ifm->ifm_type != RTM_NEWADDR)
 			quit("out of sync parsing NET_RT_IFLIST");
@@ -443,6 +559,7 @@ configure(s)
 			&info);
 		/* gag, wish we could get rid of Internet dependencies */
 #define dstaddr	info.rti_info[RTAX_BRD]
+#define ifaddr info.rti_info[RTAX_IFA]
 #define IPADDR_SA(x) ((struct sockaddr_in *)(x))->sin_addr.s_addr
 #define PORT_SA(x) ((struct sockaddr_in *)(x))->sin_port
 		if (dstaddr == 0 || dstaddr->sa_family != AF_INET)
@@ -464,10 +581,33 @@ configure(s)
 		np->n_addr = (struct sockaddr *)(np + 1);
 		np->n_addrlen = dstaddr->sa_len;
 		np->n_name = np->n_addrlen + (char *)np->n_addr;
-		np->n_next = neighbors;
-		neighbors = np;
 		memcpy((char *)np->n_addr, (char *)dstaddr, np->n_addrlen);
 		memcpy(np->n_name, sdl->sdl_data, sdl->sdl_nlen);
+		if (multicast_mode == PER_INTERFACE_MULTICAST &&
+		    (flags & IFF_MULTICAST) &&
+		   !(flags & IFF_LOOPBACK)) {
+			struct ip_mreq mreq;
+
+			memcpy((char *)np->n_addr, (char *)ifaddr,
+				np->n_addrlen);
+			mreq.imr_multiaddr.s_addr = htonl(INADDR_WHOD_GROUP);
+			mreq.imr_interface.s_addr =
+			  ((struct sockaddr_in *)np->n_addr)->sin_addr.s_addr;
+			if (setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP,
+						&mreq, sizeof(mreq)) < 0) {
+				syslog(LOG_ERR,
+				    "setsockopt IP_ADD_MEMBERSHIP: %m");
+#if 0
+				/* Fall back to broadcast on this if. */
+				np->n_flags &= ~IFF_MULTICAST;
+#else
+				free((char *)np);
+				continue;
+#endif
+			}
+		}
+		np->n_next = neighbors;
+		neighbors = np;
 	}
 	free(buf);
 	return (1);