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Ubuntu WiFi hotspot with LAN access but no internet

in flag
sed1

Is it possible to create an Ubuntu 20.04 hotspot where the connected devices do not have access to the internet, but those devices can be accessed on specific ports from the Ubuntu machine?

For example, if I have a smart device such as a camera connected to the hotspot I might want to access it's settings page on port 80 or rtsp on port 554, but I don't want it to be able to access the internet (or access resources on the local LAN i.e. make unsolicited outgoing requests).

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in flag
matigo
If you are using a consumer-grade router, you can accomplish this by setting the DNS Server to something like 127.0.0.1, then configuring the devices that actually need Internet to use something else, such as a DNS server on the local network or 1.1.1.1
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in flag
sed1
If you mean changing the DNS for those devices on the router (or devices themselves), couldn't the devices change their MAC address (or the DNS setting) to something else to get around this, so they look like a different device - would it be robust? I did research whether using two routers (different subnets) and a static route between them (?) might be the right way to do this, but I found that totally confusing. I thought maybe doing it via Ubuntu hotspot might be more simple as I am using the machine as a server to access such devices anyway (and cheaper as I currently have only ISP router)
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in flag
matigo
I don’t know your network config, it’s hardware, it’s limitations. However, if something is on a network — regardless of the OS — then it can use what the network offers. If there is doubt about the honesty of the devices, then perhaps it’s best not to put them on the network at all. Do you plan on having a Ubuntu system act as a dedicated network switch for these dubious network devices? If so, custom firewall rules via `ufw` may be the way to go. VLANs or DNS sinks on the network switch/hub itself is generally simpler and easier to maintain long-term.
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