[ -z "$MAC" ] || ifconfig $TAP | grep -q "ether $MAC" || \
ifconfig $TAP hw ether $MAC
[ -z "$IP" ] || ip addr show dev $TAP | grep -q $IP || \
[ -z "$MAC" ] || ifconfig $TAP | grep -q "ether $MAC" || \
ifconfig $TAP hw ether $MAC
[ -z "$IP" ] || ip addr show dev $TAP | grep -q $IP || \