If your DSL is combo modem/router, it does not have WAN interface, so you cannot use it with your new broadband connection.
You need to buy a new router, and you better look for gigabit router if you want to fully utilize the fiber.
If your DSL is combo modem/router, it does not have WAN interface, so you cannot use it with your new broadband connection.
You need to buy a new router, and you better look for gigabit router if you want to fully utilize the fiber.