diff --git a/tools/simwifi/sim_wifi.sh b/tools/simwifi/sim_wifi.sh
index 5b7c785ece..4088bbb160 100755
--- a/tools/simwifi/sim_wifi.sh
+++ b/tools/simwifi/sim_wifi.sh
@@ -520,11 +520,19 @@ init()
 
 clean()
 {
+  [ -z "$1" ] && {
+    echo "Missing the default wan interface."
+    exit -1
+  }
+
   recovery_to_init
 
   cur_mode=$(get_var mode $DEFCONF_FILE)
   [ "$cur_mode" = "hwsim" ] &&  modprobe -r mac80211_hwsim
 
+  echo "defwan:$1" > $DEFCONF_FILE
+  [ -n "$1" -a  -n "$(ifconfig | grep $1)" ] && stop_bridge $1
+
   rm -fr $RUN_DIR
   rm -f $UDHCPC_SCRIPT
 }
@@ -532,7 +540,7 @@ clean()
 usage()
 {
   echo "$(basename $SOURCE) (rename <old> <new> |"
-  echo -e "\t init <wan> <mode> |clean |"
+  echo -e "\t init <wan> <mode> |clean <wan> |"
   echo -e "\t start_wpa <wlan0> |stop_wpa |"
   echo -e "\t start_hostapd <wlan0> |stop_hostapd |"
   echo -e "\t start_udhcpc <wlan0> |stop_udhcpc |"
@@ -552,7 +560,7 @@ get_script_path $0
 
 case $1 in
   init) init $2 $3;;
-  clean) clean;;
+  clean) clean $2;;
   start_bridge) start_bridge $2;;
   stop_bridge) stop_bridge $2;;
   start_hwsim)  start_hwsim $2 $3;;