How Does a Website Know

[BobH]

How does a website determine that your browser is connecting through a VPN? Is there something in a TCP/IP packet that identifies the source as using a VPN? If so, what? If not, how is it that websites can respond that you must turn your VPN off to access their pages?

I thought the purpose of a VPN was to provide some degree of anonymity.

[HansV]

From How can your VPN be traced?:

The IP addresses of VPN servers aren't difficult to recognize — there are even databases specializing in VPN detection, that try to determine whether an IP belongs to a particular provider. When you access a website with a VPN on, it may be able to identify that you're using a VPN using your IP. However, this doesn't mean the website will know the identity of the person behind the IP address — just that they are using a VPN.

[BobH]

I learned something new today.

Thanks, Hans!