Interaction of firewalls and network address translators with internet applications

This document provides an overview of the impact of NATs and Firewalls on Internet applications and then describes state-of-the-art solutions and current research initiatives that allow applications to work in the presence of NATs and Firewalls. Firewalls and Network Address Translators are inevitable in modern Internet as they play a very important role in protecting and managing network resources but these middleboxes are obstacles for multimedia traffic that use dynamic ephemeral ports. There is a need for a signaling protocol, which can request a change of policy rules in a firewall or creation of a binding in the NAT. To develop a protocol or to design a network architecture, it is necessary to understand the implication of middleboxes such as NATs and Firewalls with respect to the deployment of services like Voice over IP. Different solutions for middlebox traversal have been developed over the past years with different constraints and limitations. This document compares these approaches against common criteria.