Your cable modem has two different interfaces, but only one can be used at a time. When the modem boots up it looks for equipment on both ports and whichever one it sees first gets the connection. To share your service between your PC and your SPA you will need to install a router. You will connect the WAN connection of your router to the modem and plug your PC and your SPA into the LAN connections of the router.

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Eric Chamberlain