I see two separate issues:
- Extending service to a metal barn over 100 ft. from the house.
- Sharing "only internet access" to the barn.
Metal buildings are difficult in terms of WiFi, unless the WiFi access point can be mounted on the exterior or in a window. Metal blocks WiFi signals and over that distance a typical WiFi signal will be dramatically lower to begin with. The typical solutions to this are:
- #1 - Install an Ethernet cable. This provides full duplex gigabit capacity, but may be impractical to install. (It's not the cost of the cable, but the installation can be physically challenging and expensive.)
Connect a switch, WiFi access point, or router to this cable.
- #2 - Use a WiFi point to point bridge. Costing under $150, these units concentrate the WiFi signal in a narrow beam which provides higher signal strength. They are rated in terms of kilometers. Often one unit can be mounted inside the house, which removes the cost of penetrating the building wall. The far end will probably need to be mounted on the outside of the barn. The Ethernet cable from the barn unit goes inside and then anything can be connected to it.
"Only internet access" is more of an issue. Orbi residential products are not designed to create separate LANs. If the only connections in the barn are WiFi, then an 850 satellite located in the barn could be used to connect those devices to the guest WiFi network, which means they have no access to the primary network. But, nothing in the barn can be connected using Ethernet, which be definition is on the primary network.
