How to use the command 'stun' (with examples)

The stun command refers to a classic STUN (Session Traversal Utilities for NAT) client, which assists in the traversal of network address translators (NAT) and firewalls by discovering the public IP address and type of NAT a client is behind. This functionality is crucial in peer-to-peer communication, such as Voice over IP (VoIP) and streaming applications, where knowing the external IP and NAT details helps establish a connection with another peer.

Use case 1: Making a STUN request

Code:

stun stun.1und1.de

Motivation:

The primary motivation for this example is to determine the public-facing IP address of your device when it is behind a NAT or firewall. By sending a STUN request, the client communicates with a STUN server to understand its IP address as visible to the outside world, and the type of NAT it is behind. This is especially useful when you need to establish direct connections for applications like video conferencing or online gaming, where knowing your public IP address can enhance connectivity.

Explanation:

• stun: This command initiates the STUN client functionality.
• stun.1und1.de: This argument specifies the STUN server being queried. The server stun.1und1.de provides information back to the client about its public-facing IP address and NAT type. Different servers could be used based on reliability and speed, but stun.1und1.de is a popular and frequently used source.

Example output:

STUN client version 0.97
Primary: Open
Return value is 0x0001
Public IP address: 93.184.216.34

The example output shows the version of the STUN client, the type of NAT encountered (if any), and most importantly, the public IP address visible on the internet: 93.184.216.34.

Use case 2: Making a STUN request and specifying the source port

Code:

stun stun.1und1.de -p 4302

Motivation:

The motivation behind specifying a source port for the STUN request is to test how your network and NAT handle connections from a specific port number. This is important in scenarios where fine-grained control over port usage is needed, such as when configuring network devices, setting up port forwarding, or troubleshooting connectivity issues. Specifying a source port also allows you to see if certain port ranges are being blocked or modified by the NAT, which is critical information for network administrators and developers of network-based applications.

Explanation:

• stun: Again, this part of the command launches the STUN client.
• stun.1und1.de: Indicates the STUN server to be queried, which provides the necessary external IP and NAT mapping information.
• -p 4302: The -p flag allows the user to specify a source port for the STUN request. The port number 4302 is an example, and users can specify any valid port number to test how their NAT processes connections on that specific port.

Example output:

STUN client version 0.97
Primary: Symmetric NAT
Return value is 0x0000
Mapped public address: 93.184.216.34:53210
Source port: 4302

The example output provides insights into the NAT behavior: the public IP address and the dynamically assigned mapped port. It shows that the device is behind a “Symmetric NAT,” which often poses challenges in establishing peer-to-peer connections. The source port of 4302 was requested by the client but was modified by the NAT to 53210, demonstrating how source ports can be managed by NAT.

Conclusion:

Understanding how the stun command works is vital for network diagnostics and effective connectivity management, especially in environments utilizing peer-to-peer communication. These examples showcase how you can retrieve your public IP address and evaluate NAT behavior, offering insights necessary for troubleshooting and optimizing network configurations. Using STUN commands with different options, such as specifying the source port, further refines this diagnostic process, aiding in the seamless configuration of networking applications.