Well unlike desktops gaming systems tend to need some static or simi-static port forwarding.
And while at first thought you'd think oh so ports x, y, and z are needed to be forwarded to xbox1, then what about xbox2.
Well when the xbox is able to use UPNP to configure the router there are additional ports it can use instead of the widely know ports.
so the 2nd xbox is then able to use UPnP to config your UPnP enabled router to forward some ports to it. all dynamically.--
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