The file is a configuration or firmware file used to "openline" (unlock) the Zhi Ling Tong (ZLT) P21 4G LTE router
: Some versions can be unlocked without files using a "14-14-14 seconds" reset trick performed on the physical reset button.
via LAN or Wi-Fi. Log in to the web-based management page (typically 192.168.254.254 or 192.168.8.1 ).