diff --git a/CHANGELOG b/CHANGELOG
index 60edb330..f39acfa3 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -499,6 +499,10 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-11-27 Simon Goldschmidt
+  * ip.c: fixed bug #21643 (udp_send/raw_send don't fail if netif is down) by
+    letting ip_route only use netifs that are up.
+
   2007-11-27 Simon Goldschmidt
   * err.h, api_lib.c, api_msg.c, sockets.c: Changed error handling: ERR_MEM, ERR_BUF
     and ERR_RTE are seen as non-fatal, all other errors are fatal. netconns and
diff --git a/src/core/ipv4/ip.c b/src/core/ipv4/ip.c
index 1b990ec8..dd316041 100644
--- a/src/core/ipv4/ip.c
+++ b/src/core/ipv4/ip.c
@@ -73,15 +73,18 @@ ip_route(struct ip_addr *dest)
   /* iterate through netifs */
   for(netif = netif_list; netif != NULL; netif = netif->next) {
     /* network mask matches? */
-    if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
-      /* return netif on which to forward IP packet */
-      return netif;
+    if (netif_is_up(netif)) {
+      if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
+        /* return netif on which to forward IP packet */
+        return netif;
+      }
     }
   }
-  if (netif_default == NULL) {
+  if ((netif_default == NULL) || (!netif_is_up(netif_default))) {
     LWIP_DEBUGF(IP_DEBUG | 2, ("ip_route: No route to 0x%"X32_F"\n", dest->addr));
     IP_STATS_INC(ip.rterr);
     snmp_inc_ipoutnoroutes();
+    return NULL;
   }
   /* no matching netif found, use default netif */
   return netif_default;