Protocol Complications with the IP Network Address Translator

Many internet applications can be adversely affected when end nodes are not in the same address realm and seek the assistance of NAT enroute to bridge the realms. NAT device alone cannot provide the necessary application/protocol transparency in all cases and seeks the assistance of Application Level Gateways (ALGs) where possible, to provide transparency. The purpose of this document is to identify the protocols and applications that break with NAT enroute. The document also attempts to identify any known workarounds. It is impossible to capture all the applications that break with NAT in a single document. This document attempts to capture as much information as possible, but by no means a comprehensive coverage. We hope this coverage provides clues for applications not covered here.