Ethernet connection issues CM1150V

> Fairly snarky reply. [...]

   Fairly incomplete/uninformative problem description.

> [...] three ethernet ports that don't do what most people would assume
> they do [...]

   You're far ahead of me.  I haven't surveyed enough people to know
what "most people would assume".  When confronted with multiple Ethernet
ports on a _modem_ (not a router), my first reaction would be to get
some documentation which explained how to use them.  Which I did.

> [...] When the ad on Amazon states [...]

   _Whose_ "the ad on Amazon"?  Not my fault.

> [...] knowing Xfinity only has one IP per household and requires
> routing for additional devices, it isn't very clear that it cannot do
> this.

   Who's "knowing" this?  I know nothing, but I might guess that Xfinity
offers some level of service which involves a block of IP addresses.
I'd expect typical residential service to provide one IP address.  So
I'd expect a _modem_ not to be able to improve upon that.

> [...] Go to the link it points to for support and find something,
> ANYTHING, that explicitly says those ports cannot be used to connect to
> another device. [...]

   Go to that link and find _anything_ which supports your assumption?

> [...] where the cable comes into my house is a terrible place for a
> wifi router, [...]

   There are many ways to run (co-ax or Ethernet) cable from one place
to another, and many ways to disribute wireless-network signals in a
large building.

   I gather that you bought a device which does not meet your
expectations, and you are unhappy.  You seem to believe that those
expectations were reasonable, but they've proved to be wrong.  If you
believe that you were misled, then you might direct your complaint to
the folks who led you.  I'm not sure what you expect anyone in this
(mostly) user-to-user forum to do.