Index: sys/net/route.c
===================================================================
--- sys/net/route.c	(revision 194233)
+++ sys/net/route.c	(working copy)
@@ -61,6 +61,8 @@ static void rtable_init(void **);
 /* compare two sockaddr structures */
 #define	sa_equal(a1, a2) (bcmp((a1), (a2), (a1)->sa_len) == 0)
 
+#define	_SOCKADDR_TMPSIZE 128 /* Not too big.. kernel stack size is limited */
+
 /*
  * Convert a 'struct radix_node *' to a 'struct rtentry *'.
  * The operation can be done safely (in this code) because a
@@ -1139,6 +1141,7 @@ rtinit(struct ifaddr *ifa, int cmd, int flags)
 	struct rtentry *rt = NULL;
 	struct rt_addrinfo info;
 	int error;
+	char tempbuf[_SOCKADDR_TMPSIZE];
 
 	if (flags & RTF_HOST) {
 		dst = ifa->ifa_dstaddr;
@@ -1189,6 +1192,14 @@ bad:
 			return (flags & RTF_HOST ? EHOSTUNREACH : ENETUNREACH);
 		}
 	}
+
+	if (cmd == RTM_ADD) {
+		if (netmask != NULL) {
+			rt_maskedcopy(dst, (struct sockaddr *)tempbuf, netmask);
+			dst = (struct sockaddr *)tempbuf;
+ 		}
+	}
+
 	/*
 	 * Do the actual request
 	 */
@@ -1198,6 +1209,18 @@ bad:
 	info.rti_info[RTAX_DST] = dst;
 	info.rti_info[RTAX_GATEWAY] = ifa->ifa_addr;
 	info.rti_info[RTAX_NETMASK] = netmask;
+	/*
+	 * When adding an interface route - using 'ifconfig up',
+	 * for example - overwrite the route that was already there
+	 * for that subnet.  This fixes a scenario where we take
+	 * an interface down, routing daemon installs new route
+	 * for the subnet formerly reachable through that interface,
+	 * then we bring the interface up, but it remains
+	 * unusable - the routing daemon can't send advertisements
+	 * through it, as there is no route.
+	 */
+	if (cmd == RTM_ADD)
+		rtrequest1(RTM_DELETE, &info, NULL);
 	error = rtrequest1(cmd, &info, &rt);
 	if (error == 0 && rt != NULL) {
 		/*