Deep Packet Inspection, often abbreviated as DPI, is a technique used in computer networks to achieve higher visibility and it is becoming an essential part of network traffic monitoring and management. Simply, packet inspection is the process of extracting details from data packets at some point in a network and using those details for analytical purposes such as identifying trends, categorizing traffic into applications, usage reporting, anomaly detection, and attack detection.
When it comes to DPI, it is a more sophisticated technology than normal or conventional packet filtering which we will discuss later. DPI plays a crucial role in understanding, analyzing, and managing the complex flow of data across networks. In the vast landscape of network security and traffic management, one term that frequently surfaces is DPI. Since today’s computer networks are rising in volume and getting more and more complex with digitalization, network engineers and network administrators understand and welcome DPI technologies to their organizations.
This blog post aims to dive into the depths of Deep Packet Inspection, exploring its definition, methods, and diverse applications it offers to the ever-evolving landscape of cybersecurity.
Conventional Packet Filtering vs. Deep Packet Inspection
Conventional Packet Filtering
Conventional packet filtering or Shallow Packet Inspection is a process of extracting basic flow details of individual packets and determine whether they should be allowed or deny. This is usually used in firewalls to block or allow data packets. In this method, it primarily examines the header information of packets including IP header and transport layer header, making decisions based on source and destination addresses, ports, and protocols.
Using the above 5 details, we can categorize all the packets travessing trough a network into sessions. A session is a packet exchange between two entities having above five-touple fixed during the session.
Five Touple :
- Source IP address
- Destination IP address
- Source Port
- Destination Port
- IP protocol
The packet filtering process operates at the network layer and tranport layer of the Open Systems Interconnection(OSI) model and it is an effective method for basic traffic categorization for the purposes of session analytics and basic control but lacks the depth required for detailed analysis.
Deep Packet Inspection
DPI goes beyond header information; dig into the payload or content of data packets. This granular inspection provides a wealth of information about the nature and purpose of the data and allows for a thorough understanding of the data being transmitted.
By operating at the application layer of the OSI model, DPI provides insights into the specific applications and services generating the traffic. In the following sections, we’ll explore the key techniques used in DPI, highlighting their roles in maintaining secure and efficient networks.
Methods of Deep Packet Inspection
1. Signature-Based Inspection
This is one of the basic methods identifies that known patterns or signatures within packet payloads, enabling the detection of specific applications, protocols, or threats.
Here, the content of the packets is compared against a database of predefined signatures. These signatures represent patterns associated with known applications, threats, viruses, malware, or other undesirable content.
Basically, this acts as mapping a set of bytes against a known byte pattern. Those signatures need to be updated regularly by network engineers according to new applications, updates of applications or new threats.
2. String Matching Analysis
Many applications have textual identifiers that are contained within the payload part of the IP packets. We can use those specific words or phrases to identify the applications and even extract more sophisticated details of the users as well. Usually thses texts can be URLs, keywords, malware patterns, policy violatioins(banned content).
(http request packets: user agent string contains Device info; Model, OS, Browser,..etc.)
3. Heuristic-Based Inspection
Uses algorithms and rules to identify deviations from normal patterns, allowing the detection of previously unknown threats or anomalies. Here we are defining a set of rules which can be used to clearly identify normal vs. abnormal behavior of sessions.
4. Behavioral Analysis
Monitors and analyzes the behavior of network traffic over time, establishing baselines for normal behavior and detecting unusual patterns. It analyzes how data flows, user actions, and network behaviors deviate from expected norms to detect anomalies, and identify threats.
This is helpful to identify possible threats within a network such as cyber attacks. Ex: Whenever a DoS(Denial of Service) or DDoS(Distributed Denial of Service) attack happens, it can cause an unusual behavior such as an abnormally high amount of DNS requests (DNS floods), so suspicious traffic originating from a single IP or a subnet and sudden increment in bandwidths.
5. Numerical Property Analysis
There are many other properties that we can track with the time related to the statistics of network sessions such as
- packet/payload sizes
- Packet Timing
- Throughput
- Connection Duration
By monitoring the trends of those properties over time, we can come up with analytic conclusions about the sessions. This can help identify patterns or anomalies associated with certain types of traffic.
Benefits of DPI
Improved Visibility
DPI offeres aplication and protocol awareness. A fiarly accurate DPI engine can identify specific applications and protocols regardless of the ports they use. Traditional filters may fail when applications use non-standard ports or encryption, but DPI can accurately classify traffic using the aforementioned methods.
Behavioral Analysis
DPI can analyze traffic patterns over time to identify anomalies or suspicious activities, providing a proactive approach to network security. Traditional methods typically rely on static rules, which may miss dynamic or evolving threats.
Traffic Prioritization
Improved Bandwidth Management: DPI enables traffic prioritization and throttling based on actual content, ensuring that critical applications get the bandwidth they need, whereas traditional filtering lacks such nuanced control.
By providing deep visibility, sophisticated analysis, and content-aware processing, DPI surpasses the basic functionality of traditional packet filtering to meet the demands of modern, complex network environments.
DPI plays a major role in industrial-level accurate network traffic monitoring and traffic management tools. Parqum Technologies offers a wide range of network monitoring tools(Paraqum Network Analyzer,Ceyanalyst,etc.) and a series of traffic optimization tools(Paraqum Wi-Di, Paraqum CeyMarshal,etc.) with powerful DPI engines that offer unparalleled visibility.
