I'm thinking about installing a switch between my cable modem and router with my voip adapter plugging into the switch as well as the router plugging into the switch. The obvious questions are why and will the cable company then see two ip addresses.
The why relates to the voip company, Voip.com, telling me to install a RJ45 "splitter" between the modem and router (kind of scary tech recommendation). At least a switch would work.
The second question involves the ip address. For obvious reasons, I don't want the cable company to see two ip address behind my modem. Any thoughts.
A unmanaged switch does not have an IP address. It is a ethernet switch and it switches ethernet packets and on the level of ethernet packets there are no IP addresses.
If you plug in a switch to the modem and the voip adapter and the router to the switch then you have two devices directly connecting to the modem and the internet. Traffic just goes through the switch.
This will work, if 1) your modem allows multiple sessions at a time and b) your ISP allows you multiple sessions and multiple IP addresses at a time. Each device will require a unique public IP address from your ISP. There is nothing you can do about that if you connect two devices directly to the modem and the internet. The switch is only the mean to connect three or more devices.
If you don't want your ISP to give you the second IP you must use a router or alternate the use of the devices.