PromethOS: A dynamically extensible router architecture supporting explicit routing. Commercially available routers typically have a monolithic operating system that cannot be easily tailored and upgraded and support new network protocols. PromethOS is a modular router architecture based on Linux 2.4 which can be dynamically extended by plugin modules that are installed in the networking kernel. To install and configure plugins we present a novel signaling protocol that establishes explicitly routed paths transiting selected nodes in a predefined order. Such paths can be non-simple, where a given node is being visited more than once.