Some synchronization issues in OSPF routing

Abstract

A routing protocol such as OSPF has a cyclic behavior to regularly update its view of the network topology. Its behavior is divided into periods. Each period produces a flood of network information messages. We observe a regular activity in terms of messages exchanges and filling of receive buffers in routers. This article examines the consequences of possible overlap of activity between periods, leading to a buffer overflow. OSPF allows “out of sync” flows by considering an initial delay (phase). We study the optimum calculation of these offsets to reduce the load, while maintaining a short period to ensure a protocol reactive to topology changes. Such studies are conducted using a simulated Petri net model. A heuristic for determining initial delays is proposed. A core network in Germany serves as illustration.