GateScript: A Scripting Language for Generic Active Gateways

In this paper, we present GateScript, a scripting language for active applications to be executed on generic active gateways. Unlike other active networking platforms, it offers a simple scripting language for expressing custom processing of packets at different protocol layers without the need for interpretation of complex protocol data structures. In this way, the user writes statements in a script-like language while using protocol-specific variables and predefined function calls acting on the packet’s content. From a textual description, we automatically create a packet parser and reassembler for a given protocol. The parser decomposes PDUs arriving in an active application into protocol variables that can be used in the script language. After processing, outcoming packets are reconstructed from the protocol variables. GateScript also enables active applications to react to the state of the environment: they can receive events from monitors and test variables reflecting the state of the environment. We have designed an architecture for a generic active gateway (GAG) that supports GateScript. An active application can dynamically install/remove a packet filter that intercepts relevant packets and passes them to the application. We have implemented GAG on Linux: its packet forwarding part is implemented in the kernel and all other components as user space processes.