ExtremeVPN Logo

What is a Deep Packet Inspection?

Last updated: April 17, 2024 13 min read
What is a Deep Packet Inspection

Deep Packet Inspection (DPI) serves as a vigilant guardian for your network, just like a team of Secret Service agents. But is protecting the network using the DPI technique worth it? This article will explore the importance of DPI, the techniques and tool DPI use, and its workings to determine whether its implementation is essential to preserve your digital network.

As the name suggests, Deep packet inspection (DPI) is a process that deeply analyzes and manages your internet traffic immediately when your data packet is delivered at the network checkpoint or firewall. 

When you send a query online, whether visiting a website, transfering a file, or emailing someone, it first gets divided into small fragments dubbed as packets. A packet comprises headers and payloads. Both contain all the information about its sender, destination, and actual data. 


Take your home’s router as an example. When you do something online, it performs a basic packet inspection in a pretext to protect your device. It first inspects the incoming packet’s header against a set of rules (Access Control List), such as its source/destinations and IP addresses/port numbers. When an incoming packet doesn’t fall under your predetermined rules, your router blocks them from entering the network. This process is called Conventional Packet Filtering.

Compared to Conventional Packet Filtering, which analyzes the headers only, a DPI performs the analysis on both the header and payload. In this way, one can prevent unwanted traffic, like spam, cyber intrusions, or viruses, from entering their network. Anyone who oversees your network can set these rules depending on their level of control. It could either be you, your ISP, or your network administrator. 

To counter the rapid increase of cyber attacks and malicious intrusions in recent times, various organizations worldwide employ the DPI technique as their defense to ensure the protection and security of their employees and networks. 

How Does DPI Operate?

Bypass Security Firewalls

There are various DPI-supported tools available over the web, such as next-gen firewalls, intrusion attempt detection tools, network monitoring devices, and even some brands of your home router. To understand the DPI technique comprehensively and how it helps you to perform a deep analysis of your network, using an appropriate DPI tool is also essential. 

Following is the detailed process of performing a deep packet inspection analysis:

  1. Packet Capture: The DPI tool utilizes several methods like port monitoring or network taps to ascertain the incoming packets.
  2. Packet Decoding: Once it captures the packet, it goes through the entire packet in line with the OSI model, commencing with the bottom physical layer towards the application layer at the top. 
  3. Protocol Analysis: Deep packet inspection tools embed a list of known protocols inside it to check which protocol the incoming packet used. These protocols list could range from SMTP for email, HTTP for web traffic, or FTP for file transfers.
  4. Content Analysis: As mentioned above, the main difference between DPI and conventional packet inspection is that it analyzes the packet’s entire content, including its payload. It looks for particular signatures and patterns that match the known malicious content or the pre-defined prohibited data. 
  5. Action: Based on its findings, the DPI tool will act as per the predetermined set of actions to either allow it to proceed further, reroute it, block it, or pause it for more investigation.
  6. Logging: At this stage, DPI tools usually log their analysis results for future review. This proves useful in recognizing patterns, documenting network activity, and troubleshooting problems.

DPI and Conventional Packet Filtering

Extensive Server Network

Unless you have a completely isolated network with no packet filtering plans, you’ll likely choose between deep packet inspection (DPI) and traditional packet filtering. DPI examines both the header and packet contents, while packet filtering only looks at the header for details like source/destination IP, protocol, and ports.

Initially, Packet filtering was a great solution as firewalls couldn’t efficiently analyze large data volumes. However, hackers found ways to bypass conventional packet filtering. Also, it can be an uphill task to set up its rules as inappropriate regulations could impact the router’s efficiency, keeping in mind that many routers need more processing power to protect your network from incoming threats.

Despite needing more processing power, DPI offers a more effective solution for threat blocking and traffic prioritization, which reduces the compulsion of dealing with numerous rules settings compared to traditional packet filtering.

Governments’ Inclination Towards DPI

Bypass Restrictions

Various authoritarian governments implement Internet restrictions on their residents. These restrictions range from accessing unbiased information, interacting with the international community freely, and the freedom to criticize their regime publicly. These countries include China, Russia, Egypt, Iran, and more. According to a survey conducted by Cloudflare, there was a rapid rise in internet blackouts recently. In fact, continuous internet blackouts around the globe have become a common trend. And the impact such blackouts pose on the global economy is immense. Last year alone, the global economy suffered a $24 billion loss due to 114 blackouts across 23 countries. 

One effective solution for such countries to deal more appropriately with this scale of loss could be by making the internet free for their residents. At the same time, they impose bans on the content or websites they don’t want to be accessible inside their borders by working with local ISPs. It is exactly as simple a solution as it seems. 

But there’s one catch: savvy internet geeks can bypass such government blocks using VPN services. In such cases, the governments must implement DPI monitoring to detect and restrict VPN usage inside the country.

Essential DPI Use Cases

What is a Deep Packet Inspection

Besides providing other major benefits, DPI is greatly helpful in improving system performance, preventing data leaks, and blocking malicious attacks on the network. Let’s briefly look at all of DPI’s important use cases below:

Malware Protection

DPI works greatly with antivirus tools in identifying incoming cyber threats such as viruses, ransomware, and spyware. It not only helps in having a closer look into all the incoming network traffic but also aids in pinpointing unusual traffic patterns, if any, to prepare security experts to deal with them directly. 

Avoiding Data Leaks

Deep packet inspection analyzes data packets regardless of their direction, incoming or outgoing, from your network. A handy tool for companies to ensure their data remains protected from any kind of data leaks, either intently or accidentally.

Enforcing Content Compliance

Companies also employ deep packet inspection technology to enforce their content policy while keeping employees from accessing potentially malicious and threatening applications such as P2P platforms. 

Network Optimization

By analyzing each packet’s content, DPI enables network administrators to take control of the data flowing through their networks. In this way, they can influence particular data flow through their network over others for better optimization.

Regulatory Policy

With the DPI technique, organizations worldwide can enforce their data privacy regulations. It helps them to oversee the data transmitted through the network to manage and implement their regulatory policy. 

Implementing Parental Control

Even though the DPI is more popularly known for companies’ utilization, parents can also use it at home to monitor their kids’ online activities. As DPI helps filter internet content, you can restrict access to certain websites on your network. It’s a more advanced approach than the conventional URL-dependent filters. 

Improving Streaming and VoIP Quality

With the DPI technique, you can also put a higher priority on particular VoiP and streaming platforms. This way, you can enjoy voice calls and streaming online with minimum latency.  

DPI Techniques and Tools


DPI implements several techniques and tools to identify and block certain packets that don’t fall under its pre-defined guidelines. 

  • Pattern Matching: DPI compares the incoming packets with its extensive library of known threats and instantly recognizes malicious patterns when they arise. Despite all this, this approach does not provide iron-clad protection to your network from undiscovered or yet-to-be-known attacks such as new malware and viruses. 
  • Protocol Anamoly: This protocol works on a “default deny” method to block all the incoming traffic unless your predetermined rules allow it. This technique protects your device from unknown attacks but is usually very restrictive as it will enable limited data packets to enter your network. 
  • Intrusion Prevention System (IPS): IPS also works well with DPI network techniques as both operate similarly while detecting threats in real-time. But contrary to DPI, IPS can sometimes err in picking up threats. It’s best to create a conservative set of rules and regulations to optimize the DPI’s functionality. 

How Does DPI Detect VPNs? 


Since the beginning of the internet revolution, there has been continuous tension between the internet geeks and the online censor authorities. To fight against the ISPs’ and repressive governments’ tactics to block certain ports by utilizing DPI techniques, using non-standard ports and VPNs became prominent. As a result, the governments started developing more advanced DPI techniques. In a nutshell, it is hard to defeat DPI as it adopts several ways to examine the entire packets’ content to identify VPN traffic. Some of these methods are as follows:

Protocol Analysis

In this process, the DPI technique helps identify the packets’ protocol, like whether they are using a VPN protocol, by analyzing their entire formats and structures more deeply. Usually, VPN protocols comprise OpenVPN, L2TP, PPTP, or IKEv2. 

Analyzing the Packet’s Size 

DPI also helps you gauge the packets’ whole size; if you find some irregularity in their size, there is a high chance of VPN utilization. 

Behavioral Analysis

The DPI technique makes deep analysis of a particular network behavior possible. Through this, we can identify if it’s VPN traffic or normal traffic. For instance, an unusual amount of internet traffic originating from a single server or an instant change of a particular packet’s IP address. In both these scenarios, one can easily suspect the usage of a VPN.

How Does Technology Implement DPI?

Deep packet inspection also presents various benefits in the tech sphere, which include:

Protecting Infrastructure from Cyber Threats
  • Network Security Tool: DPI uses several techniques to detect upcoming threats. This alerts organizations about potential dangers and helps them make the amendments required to deal with them.
  • Network Traffic Management: DPI prioritizes data packets, which means you can manage the network traffic by setting the priority of data critical for your business.
  • Prevent P2P Downloading: Packets can be analyzed according to their recipients and contents so that you can stop P2P downloading.
  • Managing Remote Computers: DPI helps organizations to track remotely working individuals using a VPN. It also helps to prevent the spreading of spyware from one member’s personal computer to others. Moreover, DPI can help the firms decide which apps or services the members should access and which they shouldn’t.
  • Integration with Alerting Software: If DPI detects a threat or danger, it instantly notifies the team members using various tools so that they can respond accordingly. 

Advantages of the DPI Technique 


The deep packet inspection method presents the various benefits noted below:

  1. Network Security: DPI, when integrated with an intrusion prevention system (IPS) and intrusion detection, helps to handle distributed denial of service (DDOS) attacks and other harmful threats originated by ransomware, viruses, or worms that other preventive measures might lack in identifying. DPI operates the same as an antivirus but differs from it by identifying the threats before even impacting the end-user. For instance, with the help of DPI, organizations can stop malware or viruses before they enter the network. Additionally, it helps to control the usage of your proprietary applications in certain regions. 
  2. Preventing Data Loss. By employing the DPI technique, companies can also keep control of their data. For instance, anyone within the company would require a clearance before sending an email containing confidential data outside its network. 
  3. Internet Traffic Management: Using the DPI method, one can filter web traffic and information flow to optimize their network. This way, DPI can be configured to receive important messages immediately or to put their P2P downloads in priority mode. In this way, ISPs usually impact the user traffic by throttling. Content providers can also request ISPs to block their content’s accessibility in certain regions from being downloaded illegally. 
  4. Online Censorship: Various countries with lower internet freedom ratings employ DPI to monitor and control the accessibility of particular types of content, like social media platforms, and unethical content providing webpages such as porn, and political opposition or religious opposition. 
  5. Target Advertising: As with DPI, ISPs can monitor and collect their users’ personal preferences, likes and dislikes, and the whole data packet content; various advertising agencies can use such information to target their audience with the type of content they prefer.

Drawbacks of DPI

Worldwide Server Network

While DPI serves as a network management tool, it is not without its imperfections. It presents various challenges which require careful consideration before trusting in its capabilities.

DPI may hinder performance as it demands significant processing power. Considering the already allotted responsibilities of routers, such as NAT firewall and stateful inspection, using DPI adds complexity to the entire network infrastructure.

Privacy concerns emerge with using DPI, as its usage can be both beneficial and detrimental. Even though DPI helps block malware and thwart hackers. ISPs and government watchdogs can also misuse its functionality to restrict specific content or monitor their citizens online. 

While inspecting the encrypted traffic using DPI, the complexity of the whole process increases as the end-to-end encryption of traffic makes it challenging to check the contents of packets. However, the situation is easier to handle than it may seem. Despite the wider use of encrypted internet traffic (including VPN or HTTPS traffic and certain messaging or email platforms), various companies are turning to DPI due to its diminishing processing power requirements.


Deep Packet Inspection is a technique used to analyze and manage network traffic. It offers advantages not only to network administrators and ISPs but also to cybersecurity professionals and organizations seeking advanced network traffic analysis and control. Moreover, the technique has significantly contributed to the technology sphere. While DPI offers so many benefits, it also has drawbacks—excessive use may impact the overall network efficiency.


How does deep packet inspection work? Up
Deep packet inspection analyzes the incoming and outgoing data packets using various techniques and tools. Some of these methods include behavioral and signature-based analysis. These techniques help them to track the patterns, protocols, and anomalies within the data.
What are some benefits of using DPI? Up
DPI offers great benefits for the tech spectrum, such as traffic management, preventing data loss, managing remote workers, integration with the alerting software, etc.
Are there any drawbacks to using DPI? Up
DPI raises several privacy concerns due to in-depth user data examination, potential latency affecting network performance, difficulty in encrypting traffic, demand for resourceful hardware, and impacting network speed.

Knowledge is Power, ExtremeVPN is Freedom

Stay secure anywhere, anytime without any hassle!

GET STARTED 30 days money back guarantee

Share this article

About the Author

Ellie George is an IT expert passionate about finding, utilizing, and managing software solutions fo...
More from Ellie

Related Posts


No comments.

ExtremeVPN Watermakr Icon

Protect and enjoy your digital life with ExtremeVPN

  • Safe and seamless streaming
  • Privacy on Wi-Fi networks
  • No DNS leaks
  • One account, ten devices
  • 6,500+ servers in 78 countries
Get ExtremeVPN