Modular Components for Network Address Translation

We present a general-purpose toolkit for network address translation in a modular, component-based networking system. Network address translation is a powerful, general technique for building network applications, such as allowing disparate address realms to communicate, load balancing among servers, and changing ordinary proxies into transparent proxies. The components of our toolkit can be combined in a variety of ways to implement these applications and others. The context of this work, the Click modular networking system, makes the NAT components simpler and more understandable. For example, the NAT components concern themselves solely with address translation; related functions, such as classification, are implemented by separate components. This design is more flexible than most existing NAT implementations. The user can choose where network address translation takes place in relation to other router functions, and can use multiple translators in a single configuration. These components have been in use in a production environment for several months. We describe our design approach, demonstrate its flexibility by presenting a range of examples of its use, and evaluate its performance