diff --git a/scripts/vm/network/ovs-pvlan-vm.sh b/scripts/vm/network/ovs-pvlan-vm.sh
index fd384814cc4..06e41fe4219 100755
--- a/scripts/vm/network/ovs-pvlan-vm.sh
+++ b/scripts/vm/network/ovs-pvlan-vm.sh
@@ -86,7 +86,8 @@ then
     exit 1
 fi
 
-trunk_port=1
+# try to find the physical link to outside, only supports eth and em prefix now
+trunk_port=`ovs-ofctl show $br | egrep "\((eth|em)[0-9]" | cut -d '(' -f 1|tr -d ' '`
 
 if [ "$op" == "add" ]
 then