OSPF Convergence Times

Abstract

Following the merger of telecom and IP networks, there has been a sharp rise in the number and types of multimedia applications such as interactive real-time Voice/Video over IP. This has put a new service requirement on IP networks and thus has required the IP network solution providers and telecom operators to device new techniques and optimizations to meet the needs of these business critical applications. One way to address these demands is to implement fast and efficient routing mechanism as the data packets are exchanged end to end. Open Shortest Path First (OSPF) is one of the widely deployed routing protocols responsible for this. Most of the important operations of OSPF that contribute to fast convergence such as fast failure detection, shortest path computation and flooding are controlled by timers. These timers, as specified in RFC2328 are fixed and too conservative for modern networks. Today, there has been an increasing effort to make these timers dynamic so that the values are determined based on the experienced network load and stability instead of a preset static value. This thesis is in part a thorough assessment of the state of the art on OSPF timers and fast convergence techniques. The other major contribution of this work is the implementation of the Link State Advertisement (LSA) throttling algorithm as an adaptive technique to control unwanted LSA generations at times of network instabilities. We used two simulators; OPNET Modeler (Academic Version) because of its advanced graphical user interface (GUI) and result analysis tools, and the open source OMNET++ for its open OSPFv2 source code. The outcome of this thesis therefore the work done on literature review which embraces a set of recommended techniques to achieve sub-second convergence, a simulation supported analysis of the associated stability issues in terms of convergence time and CPU load and also the introduction of our own pseudo code and implementation of the LSA throttling algorithm, originally introduced in CISCO 12.0(25) S. The simulation work has proved the LSA throttling algorithm indeed improves a network’s convergence speed and can be deployed on any size OSPF network including large ISP networks consisting of thousands of routers.