the techniques they use to detect it and block you

Let’s explain to you How can websites know if you use a VPN to navigate through it. Because we can use the VPN to make our browsing more private or to make the websites think that we are browsing from another country. We can do this with the best vpn services as NordVPNand also with the free vpn. But web pages also have tools at their disposal to detect when we are doing it.

Many websites use these VPN detection technologies as part of their fraud prevention strategies. Services use them for things as varied as enforcing internal pricing policies, protecting content with a copyright that establishes where it can be consumed, or even in some cases complying with strict requirements that force them to detect and restrict the use of VPNs.

Be that as it may, VPN detection technologies exist, and although not all pages use them, it is always interesting to know about them. This way, if you ever come across a page that asks you to disable the VPN or blocks your access, you can know how they managed to know that you are using it.

In addition to VPN use detection techniques, at the end of the article we will also tell you a couple of them that are used to identify yourself even if you use a VPN. Thus, it will not matter if you have this privacy layer active, because they will still be able to know that it is you.

IP address blacklists

One of the most popular VPN detection techniques is to look up the IP address you are using in databases of addresses that these services are known to use, something like a blacklist of IP addresses that are attributed to VPNs. These databases are typically maintained and managed by specialized commercial discovery services.

All VPN services have their own servers in dozens of countries around the world, and These servers have specific IP addresses. There are companies that detect these addresses and put them in a database that they then offer to other companies that need to verify if there are connections of this type.

To detect these addresses, they can look for those that are used by a very large number of users, or because they are addresses from data center ranges and not residential ISPs.

ASN analysis and network type

In addition to this, you should know which IP address in the world belongs to a block managed by a specific network operator, identified by what is known as the Autonomous System Number (ASN). From that data, a web server can easily determine which internet provider the user is connecting to.

This opens the door to something called ASN fingerprint, with which commercial VPNs can be identified. They do this by crossing the information with databases that distinguish between IPs of residential operators and IPs of data centers. If your IP address is registered to a hosting or cloud infrastructure provider instead of a home ISP, red flags go off immediately.

DNS, WebRTC and IPv6 leaks

Despite having an active VPN, sometimes a glitch can cause queries to translate domain names into their IPs don’t go through the encryption tunnelbut rather they go to the DNS server of your ISP or operating system. If when this happens a website detects that your apparent IP is from one country but your browser’s DNS queries are from an ISP in another, the inconsistency makes it obvious that you are using a VPN.

Leaks due to failures in WebRTC They are more subtle and browser-specific. It is the technology that allows real-time communications between browsers, and to establish that connection you need to know your real IP. Sometimes, to achieve this, you can bypass the VPN tunnel with queries to STUN servers, and if the filtered IP does not match the public one, you can also deduce the use of a VPN. The particularity of this type of technique is that it does not require an active call: any page with JavaScript can launch a STUN request silently without the user knowing.

IPv6 leaks are one of the most common and least known techniques to detect VPN usage. Many VPNs only tunnel IPv4 traffic but leave IPv6 uncovered, exposing your IP address.

Discrepancies between latency and time zone

Some platforms may look for temporal patterns that do not fit typical user behavior. For example, a website may detect a higher latency than normal for the country you are connecting from, which would indicate that you are routing your connection from a distant location. Although It is not a completely reliable verificationas latency spikes can be due to legitimate reasons.

I could also compare the browser’s time zone with that of the associated region to your IP address. Thus, if you connect from China but your browser uses the Spanish time zone, it can be deduced that you use a VPN. Although it is not a reliable method either, because it is easy to change the time zone when you browse and you are going to use a VPN.

VPN protocol detection

Each VPN protocol has unique and recognizable characteristics. OpenVPN, WireGuard or IKEv2 They have a different behavior when establishing a connection, as well as a different structure of the headers and byte sequences. They also use specific ports to establish connection.

And with this data, it can also be detected if you use a VPN. ISPs and network administrators can monitor the ports that VPNs usually use and detect if there is a lot of encrypted traffic on them, and they can also look for the rest of the characteristics of each VPN protocol to detect that you are using one.

Cookies, logged sessions and cross-platform tracking

The VPN protects your connection, but not your identity. If you are connected to an account, such as Google or Netflix, the platform will recognize you even if you change your IP using persistent cookies that were already stored on your computer before activating the VPN. With this, websites can recognize you even if you use a VPN.

Analysis of your online behavior

Finally, some platforms can also analyze other features of your online behavior when you go online and look for features that point to the use of a VPN. For example, they could detect simultaneous sessions from different regions or rapid changes between countries.

They could also compare your current activity with historical data from previous sessions you have had on that website, and identify behaviors that do not match. For example, if you interact with country-specific content while logged in through an IP address from a different region.

They don’t detect a VPN, but they detect you

Let’s now go with other techniques that They will not detect if you use a VPN. However, we add them because they are used to detect and identify you even if you are using a VPN.

Browser fingerprinting

This is not a technique to identify a VPNbut it can identify you as a user even if you use it. Although the VPN hides your IP, it doesn’t change anything your browser says about you when you visit a website. This opens the door to “Browser fingerprinting”, which is what it is called to build a unique profile based on the characteristics of your browser and device.

Data such as your screen resolution, the extensions you have, your operating system, the fonts you have installed and other similar things can create a profile that makes you perfectly recognizable. And with this, you can be recognized even if you change your IP using a VPN.

Deep data packet inspection

When you use a VPN, both ISPs and network administrators cannot decrypt your traffic, but They can recognize if you use a VPN by the patterns characteristics of a VPN. To do this, they can use modern firewalls that support deep packet inspection (DPI), a method of analyzing network traffic in real time.

DPI will look for patterns that do not match normal Internet activity, such as constant data packet sizes, uniform transmission intervals, or especially long encrypted sessions between endpoints. These are characteristics that can point to the use of a VPN connection.

In Xataka Basics | Guide to configure your router in depth: where to place it, how to configure it and its main functions