Stability Analysis Of OSPF Protocol And Implementation In Access Convergence Router

With the increasing of time-sensitive services in Internet, network stability needs to satisfy more strictly demands. The important aspect of network stability is the stability of routing protocol. Based on the national 863 project "Research on system performance and key technologies of large-scale Access Convergence Router(ACR)", the thesis deeply and systematically studies the stability problem of OSPF protocol which we faced when it was implemented in ACR, points that network convergence time, route flap, congestion of protocol flow are three critical components of OSPF protocol stability, and proposes corresponding improvement mechanisms. Finally, OSPF and these improvement mechanisms are implemented in ACR. The main contribution of the thesis is as follows:1. Analyze the composition of convergence time in great detail, point that the detection time is the major part of convergence time and failure detection has more effect on stability, then deduce the probability distribution of failure detection time, build a stochastic process model, and calculate the averaging returning time of neighbor failure state. The time is determined by the loss rate of Hello packets and the parameter m (RouterDeadInterval= m·HelloInterval). At last, we come to a conclusion: it can lower the probability of false alarm by adjusting the parameter m along with the network state.2. A fast failure detection mechanism based network state was devised, which can dynamically adjust the parameter m along with the network state. Through simulation test, it shows that the mechanism not only reduces the detection time to milliseconds, but also lowers the probability of false alarm.3. For solving the route flap, an ASBR route summary mechanism and neighbor flap damping algorithm were devised. ASBR route summary mechanism can shield Autonomous System from unsteady AS-external-LSAs' effect. Neighbor flap damping algorithm gives a penalty to unsteady neighborship, for reducing the number of LSA originated by the flapping neighbor, and then simulated the algorithm.4. Analyzing the cause of forming protocol traffic congestion on OSPF network, it is pointed that the initial synchronization of link-state databases and periodic LSA refresh are primary factors of protocol flow congestion. We propose restraining the number of neighbor mechanism and enhancing randomized refresh mechanism for solving the problem.5. We devised the implementation frame and mechanism of OSPF that also included improvement mechanisms in ACR.