TCP/IP Fingerprint Checker

Description of Fingerprinting Sections

To interpret these results, it's crucial to understand how different fields in the IP header and TCP header correlate with operating systems. The scores and details provided can help identify the operating system your device is using based on the header values and configuration. For example, specific TCP/IP characteristics commonly found in Windows systems will result in a high score for Windows, etc.

Section

avg_score_os_class

details

Purpose

Provides an average score for different operating systems based on the fingerprint. This score helps estimate which OS you’re using.

Provides additional content, including your IP address and indicates if an OS mismatch is present. It also shows a perfect score for reference.

Provides detailed information about the TCP/IP packet, including fields from the IP header and TCP header (source and destination IP address, port numbers, checksums, and more).

What Is TCP/IP Fingerprinting?

TCP/IP fingerprinting technique helps identify the operating system of a device connected to the internet by analyzing the characteristics of its TCP/IP headers. Since each OS sets specific values in the initial TCP SYN packet that initiates the TCP protocol handshake, this information can be used to create a fingerprint that is unique for an OS or its specific version. 
This fingerprinting method is often used in network security to identify devices and detect unauthorized access. IT professionals also rely on it for troubleshooting network issues, ensuring that all devices on the network use approved software, and more.

How Does TCP/IP Fingerprinting Work?

Simply put, TCP/IP fingerprinting analyzes specific fields in the TCP header and the IP header of a device's network packets. Here's a brief breakdown of how it works:

Analyzing Packet Headers

This checker examines the TCP and IP header to collect certain information, including the internet header length, TCP header size, window scale value, and maximum segment size. These values are important because different operating systems customize them in specific ways.
IP Header

Certain fields in this header, including IHL (internet header length), Total length, Identification, Flags, TTL (time to live), Protocol, and Header checksum, provide entropy that helps distinguish between operating systems.

TCP Header

The key fields in this header include Sequence number, Acknowledgement number, Data offset, Flags, Window size, Checksum, and Urgent pointer. The header size and options data are crucial as their value varies across different OSes. Furthermore, examining the congestion control mechanism used by the TCP protocol provides additional insights since certain algorithms are more commonly associated with specific operating systems.

Analyzing Responses to Specific Probes

By analyzing network packets, the checker can provide details about your operating system and how it's configured. Certain OSes may set specific flags in the TCP header or use certain initial TTL values, which can be indicative.
Entropy From TCP Options Data

Furthermore, the checker examines TCP options data, which is variable and often unique to specific operating systems. The presence and order of TCP options, such as MSS (maximum segment size) and window scaling, provide valuable hints about the OS used.
Comparing With Known Patterns

Finally, the data gets compared against a database of patterns for different operating systems. By matching these patterns, the checker can make an educated guess about the OS your device is using.

Use Cases and Importance of TCP/IP Fingerprinting

This fingerprinting method has critical use cases across several domains:

Web scraping

Masking your OS can be crucial to avoiding detection, as web servers can throttle or block traffic coming from devices using a specific OS or known automation tools (such as web scrapers).
Network security and troubleshooting

Network administrators can use TCP/IP fingerprinting to identify devices that should not be on the network, including intruders, unauthorized personal devices, and more. It can also help with identifying misconfigured devices which may cause issues due to incompatible software.
Online privacy

Understanding and modifying your TCP/IP fingerprint can help preserve your privacy online. By modifying your fingerprint, you can make your activity significantly harder to track and protect yourself from profiling and targeted attacks.

How to Change a TCP/IP Fingerprint

Changing certain aspects of your fingerprint offers several benefits. Primarily, it's useful for web scraping or accessing restricted content as it can help bypass security measures designed to block certain types of traffic. 

Here are a few common ways to modify a TCP/IP fingerprint:

Using proxy servers

By simply connecting to the internet through a proxy server, you can mask your IP address and alter your fingerprint. Aside from a new IP address, proxies can also present different TCP protocol characteristics to the destination server.
Adjusting network settings

Certain OSes have elaborate configuration options, so it's worth checking if there's a chance to adjust your device's TCP and IP headers, window scale, and other parameters.
Using specialized tools and scripts

Tools like Nmap can help you modify your TCP/IP fingerprint by altering TCP header size and other data. You can get similar results with scripts which modify network stack parameters, and specialized spoofing tools which automate the process of altering this fingerprint on different operating systems.