Index: usr.sbin/rtadvd/if.c
===================================================================
--- usr.sbin/rtadvd/if.c	(revision 274720)
+++ usr.sbin/rtadvd/if.c	(working copy)
@@ -404,6 +404,7 @@ update_ifinfo_nd_flags(struct ifinfo *ifi)
 	return (0);
 }
 
+#define MAX_SYSCTL_TRY 5
 struct ifinfo *
 update_ifinfo(struct ifilist_head_t *ifi_head, int ifindex)
 {
@@ -416,26 +417,45 @@ update_ifinfo(struct ifilist_head_t *ifi_head, int
 	char *lim;
 	int mib[] = { CTL_NET, PF_ROUTE, 0, AF_INET6, NET_RT_IFLIST, 0 };
 	int error;
+	int ntry = 0;
 
 	syslog(LOG_DEBUG, "<%s> enter", __func__);
 
-	if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), NULL, &len, NULL, 0) <
-	    0) {
-		syslog(LOG_ERR,
-		    "<%s> sysctl: NET_RT_IFLIST size get failed", __func__);
-		exit(1);
-	}
-	if ((msg = malloc(len)) == NULL) {
-		syslog(LOG_ERR, "<%s> malloc failed", __func__);
-		exit(1);
-	}
-	if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), msg, &len, NULL, 0) <
-	    0) {
-		syslog(LOG_ERR,
-		    "<%s> sysctl: NET_RT_IFLIST get failed", __func__);
-		exit(1);
-	}
+	do {
+		/*
+		 * We'll try to get addresses several times in case that
+		 * the number of addresses is unexpectedly increased during
+		 * the two sysctl calls.  This should rarely happen.
+		 * Portability note: since FreeBSD does not add margin of
+		 * memory at the first sysctl, the possibility of failure on
+		 * the second sysctl call is a bit higher.
+		 */
 
+		if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), NULL, &len, NULL,
+		    0) < 0) {
+			syslog(LOG_ERR,
+			    "<%s> sysctl: NET_RT_IFLIST size get failed",
+			    __func__);
+			exit(1);
+		}
+		if ((msg = malloc(len)) == NULL) {
+			syslog(LOG_ERR, "<%s> malloc failed", __func__);
+			exit(1);
+		}
+		if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), msg, &len, NULL,
+		    0) < 0) {
+			if (errno != ENOMEM || ++ntry >= MAX_SYSCTL_TRY) {
+				free(msg);
+				syslog(LOG_ERR,
+				    "<%s> sysctl: NET_RT_IFLIST get failed",
+				    __func__);
+				exit(1);
+			}
+			free(msg);
+			msg = NULL;
+		}
+	} while (msg == NULL);
+
 	lim = msg + len;
 	for (ifm = (struct if_msghdr *)msg;
 	     ifm != NULL && ifm < (struct if_msghdr *)lim;