How to address the NAT traversal problem

NAT traversal problem, in simple terms, refers to the difficulty of establishing direct communication between devices located behind routers or firewalls. NAT modifies private IP addresses to public IP addresses to enable multiple devices to share a single public IP address. NAT traversal can create issues for certain network applications that allow direct communication between host devices, including peer-to-peer applications, video conferencing, online gaming, or real-time communication protocols like voice over IP (VoIP).

Solutions for NAT traversal problem

Several techniques can be used to address the NAT traversal problem. Some of them are as follows:

Port forwarding: It allows to connect computer on the internet with any specific computer on a local area network (LAN). It involves configuring the NAT device to forward incoming traffic on a specific port to a specific device on the private network. Consider we have a web server running on a device in our local network with the IP address 192.168.1.100. We want to access this server from the public network. To do this, we can configure our NAT device to forward incoming traffic on the default HTTP port 80 to 192.168.1.100:80. When someone accesses our public address from the internet, the NAT device will forward the incoming traffic to the web server as shown in the figure below:

Universal plug and play (UPnP): A special protocol that allows devices to configure NAT traversal automatically. Whenever a device on a private network shows interest in connecting with another device, it advertises its description and actions it can support by utilizing the protocols like TCP/IP, HTTP, XML, etc. This allows other devices to discover its presence on the network. It is an easy way to enable NAT traversal for devices that don't support manual port forwarding or other NAT traversal techniques.

Hole punching: It involves a third-party server as a mediator to establish a direct connection between two hosts located behind the NAT devices. The steps involved in the hole punching are as follows:

• First, each host sends a request message to the mediation server to form a connection to the other host.

• In response, the mediator server sends a message to each host with the opposite host's IP address and port number.

• Now, each host sends a message directly to the other host's IP address and port number using the information provided by the meditation server.

This technique is only suitable for a few cases because it is less efficient and increases the cost of accumulating additional resources in a more complex network environment.

Virtual private network (VPN): VPN creates a secure and encrypted connection between two devices. It allows both devices to communicate with each other like they are on the same local network, but physically they are separated by public internet. VPN allows private and secure communication between devices without manual port forwarding or other NAT traversal techniques. This technique is very useful when employees need to securely access resources on a company's private network from outside the office.

NAT serves as a fundamental component of modern networking. Still, its limitations in certain applications highlight the need for innovative solutions and protocols to ensure smooth communication in increasingly complex network environments.