by RealNC » Mon Aug 10, 2015 8:58 am
Wait, I didn't explain why that was a problem with running a web server...
The issue is that a computer tries to connect to your web server by using your IP and the appropriate port. Say, 1.1.1.1:80. That step works just fine. The bytes are sent by that remote computer to 1.1.1.1, and they are received by your modem. The router then takes them and sends them to your desktop computer (because you forwarded port 80). The web server sees those bytes, and replies back. That reply, however, is taken by OpenVPN and send to the VPN server. The VPN server, which has a different IP, say 2.2.2.2, then forwards them to the remote computer that initiated the connection.
So what the remote computer sees, is that some bytes arrived from IP 2.2.2.2, even though it tried to connect to 1.1.1.1. It expects an answer from 1.1.1.1, but the answer came from 2.2.2.2. That doesn't work. The remote computer ignores that reply, because it came from a different place.
Wait, I didn't explain why that was a problem with running a web server...
The issue is that a computer tries to connect to your web server by using your IP and the appropriate port. Say, 1.1.1.1:80. That step works just fine. The bytes are sent by that remote computer to 1.1.1.1, and they are received by your modem. The router then takes them and sends them to your desktop computer (because you forwarded port 80). The web server sees those bytes, and replies back. That reply, however, is taken by OpenVPN and send to the VPN server. The VPN server, which has a different IP, say 2.2.2.2, then forwards them to the remote computer that initiated the connection.
So what the remote computer sees, is that some bytes arrived from IP 2.2.2.2, even though it tried to connect to 1.1.1.1. It expects an answer from 1.1.1.1, but the answer came from 2.2.2.2. That doesn't work. The remote computer ignores that reply, because it came from a different place.