Enhancing Simulation Mode Operation of ospfd

Abstract

In this paper, we describe our modifications to ospfd, a popular open-source implementation of OSPF routing protocol. The ospfd software can also be run in simulation mode, where processes, representing individual routers, communicate with each other over UDP sockets. Even though ospfd provides a fine-granularity implementation of OSPF protocol, its simulation mode operation leaves a lot to be desired. The main weakness of ospfd’s simulation mode operation is its lack of distinction between the real time and simulated time. The simulated time is represented in terms of ticks and increases at the same rate as the real time, i.e. the duration of an individual tick is fixed (e.g. 50ms). Consequently, the amount of work done by a router process in a given tick depends on how long this process has access to CPU during this tick. In our modifications, we introduced separation between the real time and simulated time by assigning specific (simulated) time durations with individual protocol tasks such as routing calculations and processing of OSPF packets (Hello, LSUpdate etc.). In modified ospfd, a tick gets over only when all router processes have completed the work they are supposed to do during the current tick. Additionally, we introduced several other modifications such as event based advancement of simulated time, script-based specification of topology change events and allowing router processes to run on multiple machines.