T25 is just a cable modem. This is the situation , even though you have 2 Ethernet ports on the back of the modem , you will be able to connect one device at the time and the reason why its because the modem is getting just 1 valid IP address. If you want to use both ports at the same time you will need to contact your ISP and request a secondary IP Address

The majority of ISP’s only assign 1 public ip address unless you have a business account or pay for extra IP address. So for the majority of ISP’s only 1 device can be connected to a modem