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?
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.
It is that simple. Make the dns entry point to your vpn subnet 10.10.100.X. The way it works is anyone not on your vpn won’t be able to resolve the ip address and will get an error. Anyone on the vpn will be able to resolve the ip address and connect via the vpn connection.
The part people are talking about that is likely confusing you is that if your service is already available via your actual ip address 1.2.3.4 then you have a security concern since anyone can access 1.2.3.4 even without your domain name pointing there. They are encouraging you to make sure your 1.2.3.4 network doesn’t allow access but updating your firewall settings to make sure it blocks connections that are not made via your vpn subnet of 10.10.100.X
Thank you for the clarification. I’ll give that a shot. Cheers!
If there is a firewall between the client and the server (which there should be), then no, the server will not respond.
The VPN jumps the firewall. When you set up the VPN service, you created firewall rules to allow the VPN traffic. Then when you have the VPN connected, all traffic to the destination network is tunneled through that one connection.