Only one computer connects to the internet thru wired xfinity exthernet ports

Just got connected with XFINITY, & renting their Arris TG1682 that comes with [x4] Ethernet connections on the back & x2 Phone jacks.

Using all WIRED connections, I connected two computers to two of the Ethernet connections on the back of the modem/router and only ONE computer will connect to the computer at a time?!!

I went to 10.0.0.1 and logged on to look at hardware connected and the two devices show the SAME MAC address, Is that correct?

Does Xfinity need to assign me an additional MAC Address so BOTH computers can connect to the internet at the same time, or is the router not work

on these modems if the 10.0.0.1 setup shows bridge mode for wired connections? I thought the ROUTER assigns new ip addresses so MULTIPLE computers can access the internet.

I know this is not an issue with WIRELESS, but its not the same for wired connections.

Thanks!