this post was submitted on 13 Aug 2023
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How can I restrict visiting a service through a domain to VPN-connected devices? (self.selfhosted)
submitted 1 year ago by TheQuantumPhysicist to c/selfhosted
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Say I have a public server with a service (email, web server, etc) that's accessible through https://myservice.example.com, and I would like to restrict that service with a VPN. How do I do that?

I know how to setup a VPN. I know how to use some of the services through that VPN. But see, if I want to use that VPN, I connect my client to that VPN, then I get the subnet of that VPN, say 10.10.100.0, through which I can access the devices by address.

But I see some services offer things like https://myservice.example.com, and they only work when that VPN is connected. How does that work? Is it just some DNS setting at the domain level or there's more to it?

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[–] TheQuantumPhysicist 1 points 1 year ago* (last edited 1 year ago) (1 children)

Please see this comment to understand my frustrations with the answers in this thread (copy/pasted from another comment):

I’ve been managing servers for over 10 years, and I never have felt stupider, and I still don’t understand how to do this. Everyone is making a comment that I don’t understand.

Let’s talk internet 101, and please tell me where I’m wrong.

You make a request to https://myservice.example.com. The DNS responds to a query giving you an IP address, say 1.2.3.4. Now the client software makes another request to 1.2.3.4:433 (say if we’re attempting to access an https server, binding the SNI address to the SSL/TLS header). The request will be sent to that server, and the server will respond. In what part of all this process can the VPN can do anything?

Normally if you want to access a device through VPN, you make a request to a WHOLE other ip address in another subnet on another (virtual) device locally. It has absolutely nothing to do with 1.2.3.4. It’s something like 10.10.100.X… or similar. How will my domain, myservice.example.com, route to that address, 10.10.100.X? Is it as dumb and simple as routing there? Or is there more to it? It doesn’t sound right to make the DNS server record point to 10.10.100.X.

[–] elbarto777 1 points 1 year ago

I'm sorry. I don't know enough about the subject. I'm sure there are firewall daemons, or IPTABLES configuration that can do what you want, but that's beyond my area of expertise. Good luck.