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What is STUN?
Session Traversal Utilities for NAT (STUN) is a protocol used in computer networking to enable devices in a private network to communicate with servers or devices on the Internet. NAT (Network Address Translation) is commonly used in routers to map multiple private IP addresses to a single public IP address, allowing multiple devices to share the same Internet connection.
Understanding NAT Traversal
When a device behind a NAT wants to establish a communication session with a device on the Internet, it faces a challenge. Since the NAT router modifies the IP addresses and ports of outgoing network packets, the device on the Internet is unable to directly address those packets to the device behind the NAT.
This is where STUN comes into play. It allows devices behind a NAT to determine the public IP address and port mapping assigned to them by the NAT router. This information is essential for establishing direct peer-to-peer communication between two devices across the Internet.
How STUN Works
STUN works by employing a STUN server, which acts as an intermediary between the devices behind the NAT and the devices on the Internet. When a device wants to figure out its public IP address and port mapping, it sends a special STUN packet to the STUN server.
The STUN server then observes the source IP address and port of the packet and includes this information in a response. The device behind the NAT receives the response from the server and deduces its public IP address and port mapping from it. This information can then be exchanged with the devices it wants to communicate with, enabling direct peer-to-peer communication.
STUN vs. TURN
It’s important to note that STUN is not always sufficient for establishing direct communication between devices behind NATs due to various network configurations and restrictions. In such cases, a protocol called TURN (Traversal Using Relays around NAT) is used.
TURN involves using a relay server as an intermediary for data transmission between devices. This allows devices behind restrictive NATs to still establish communication, albeit with a slight increase in latency due to the relay server acting as a middleman.
In summary, STUN is a crucial protocol for enabling NAT traversal, allowing devices behind a NAT to establish direct peer-to-peer communication with devices on the Internet. It works by providing devices with their public IP address and port mapping, facilitating direct communication.
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