Does a VPN Protect You Against Deep Packet Inspection by ISPs?

By SB •  Updated: 03/19/21 •  9 min read

A VPN can protect against deep packet inspection by ISPs by encrypting the data that is sent between your device and the VPN server, making it difficult for an ISP or other third party to examine the contents of the data packets, as they are securely encrypted — but it isn’t a failsafe and a VPN may not necessarily protect against other forms of surveillance or data collection by ISPs.

Imagine a cheap technology that can stop spam and malware, identify and block illegal downloads, and allow ISPs to prioritize the data they transmit by content as well as by type.

Now imagine a technology that gives network managers and governments the ability to monitor everything you do on the Internet, including reading and recording your e-mail and other digital communications, and tracking your every move on the Web.

The technology called Deep Packet Inspection (DPI) is used by ISPs and other government network providers around the world to monitor all the data transmitted to and from computers; a VPN is great as a layer of protection to prevent ISP snooping, but deep packet inspection technology can beat VPN encryption and can sniff and identify a lot of information from VPN packets.

If your Internet Service Provider utilizes Deep Packet Inspection (aka complete packet inspection), they are analyzing all of your traffic as opposed to basic network connection data such as to which IP addresses you are connecting, what port number, what protocol, and possibly a few other details about the network connection.

You may think you have secured your Internet data from abuse by ISPs and hackers (by using HTTPS and a VPN service) but DPI can still read your Internet traffic, identify patterns and create a fingerprint of you based on those patterns. Sometimes, the pattern-identifying abilities of DPI renders a VPN largely useless, and even though the data itself is encrypted, the VPN traffic has a header that identifies the packet as coming from a VPN client machine.

What Can My ISP See If They Use Deep Packet Inspection (DPI)?

Deep Packet Inspection (DPI) is a technology that allows a service provider to analyze network traffic in real time using the payload (IP packet content). DPI gives your internet service provider a lot of information about your connections and internet usage habits. In some cases, the full content of things like SMTP e-mails will be captured.

DPI is a method used by network administrators and ISPs to inspect and analyze the contents of network traffic at the packet level; it allows for the examination of both the header and the payload of network packets, rather than just looking at the header information that is typically used for routing and addressing.

DPI has a variety of functions:

So, DPI can be both a powerful tool for network management and a potential threat to privacy and freedom of speech, especially if the DPI capabilities are used to block or restrict access to certain websites or services.

Your internet service provider is likely hijacking your DNS traffic or running DPI on their network. Most ISPs use DPI to some extent for various reasons, and if they are inspecting your DNS traffic, they can also easily see everything else your computer requests, unless the data or connection is encrypted.

Can Your ISP See the Contents of HTTPS Connections?

The short answer is that your ISP does not necessarily know the contents of your browsing, but they do see from where you are downloading and the size of the download, and they can draw a lot of conclusions from these metadata.

Deep Packet Inspection and User Privacy Rights

With the (potential) change in US law about ISP and data privacy, combined with the (potential) loss of net neutrality, ISPs might be able to not only see 100% of your data, they could modify that data, slow or block sites they want, and might be able to sell any or all of your data to a third party.

The larger concern for most people is about data aggregation. By collecting user web browsing information, a data scientist (or your ISP) could create a personalized fingerprint for your Internet usage, and later associate this identity of behaviors with past activities, future activities, or activities from other locations (when you are at work, or are on vacation).

Likewise, your ISP may choose to sell this profile or data to organizations or marketers, where it could then be used against you in many ways. People have an expectation that their communications are private, and collecting this personal data very much goes against that privacy expectation.

So, whom do you trust more — your ISP or the VPN provider?

With DPI, your ISP would be able to see:

With that information, they can then use DNS filtering and firewalls to block the sites you’re trying to access.

HTTPS & VPN to Protect Against Invasive DPI

  1. HTTPS would prevent your ISP from being able to read data, but not all services use HTTPS.
  2. Keep in mind that your ISP can read metadata whether the connection is encrypted or not.
  3. A VPN would protect you against DPI performed by the ISP (but not by the VPN provider).
  4. VPNs use an encrypted tunnel to connect you to the ‘exit node’ — all of your traffic within this tunnel is encrypted, and all of the metadata will show packets leaving your computer and going to the VPN server (the actual server you are accessing remains undisclosed).

What Can DPI See, Even When You Utilize HTTPS Connections?

What Do VPNs Fail to Protect Against

While a VPN can protect against deep packet inspection by encrypting the data that is sent between your device and the VPN server, it may not necessarily protect against other forms of surveillance or data collection by ISPs, including:

  1. Metadata collection: ISPs can still collect information about the websites you visit, the IP addresses you connect to, and the amount of data you send and receive, even if you use a VPN.
  2. DNS Leak: Some VPNs might not protect the DNS queries which are made to the DNS resolver of your internet service provider. This could reveal the websites you visit to your ISP, even if the data itself is encrypted.
  3. Browser Fingerprinting: Browser Fingerprinting is a technique used to track your online activity by creating a unique fingerprint of your browser and device. Some VPNs may not be able to protect against this.
  4. Malicious VPN provider: if the VPN provider is malicious it could use their logs or sell them to third parties, which would allow others to see your internet activity.
  5. Legal Requests : some countries and ISP’s has laws that require VPN providers to cooperate with them and turn over logs of user’s activity. This would also reveal your internet activity despite you using VPN.

It’s important to keep in mind that while a VPN can provide a level of privacy and security, it is not a complete solution and other measures should be taken to protect your privacy, like practicing good OpSec.


I've been practicing OSINT and utilizing Linux as my daily operating system for over twenty years. The tools are always changing and so I'm always learning, but helping you understand the value of protecting your own data remains at the forefront of everything I do.