I want to add an isolated network to my current home network

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Hello. Segment 1 defines my current home network. A WiFi router provided by the ISP, its your basic home setup. I want to setup an additional isolated network.
(marked as Segment 2 on the diagram) I'm using my own spare wifi router for segment 2. I have 4 clients on this network for the purpose of converting and
transfering large video, graphics, and audio files between each other. I'm using this setup because I don't want to bog down my main network.

However, There will be times that I need to access the internet from segment 2. I need the router from Segment 2 to access the one in Segment 1.
What is the best way to do this? I've searched the forums and unsure of exactly what I have to do.

Can I connect both routers wirelessly?
Do I need to convert the second wifi router to an access point?
Do I need to change the firmware of the second router?



Thanks

 

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what kind of router is Segment2 using?
Depending on make, model, and version you might be able to use 3rd party firmware to wirelessly connect the two segments.

does Segment2 need to be isolated from Segment1, or are devices on Segment1+2 allowed to see each other?

are the four devices on Segment2 wired or wireless?