This paper presents a performability estimation approach which measures the ability of a network to deliver its services in the presence of component failures. The measurement is based on two important network service parameters, the end-to-end delay and the packet loss. To evaluate the approach, different network topologies are studied using the OPNET Modeler. The results of simulations for four random topologies and two routing protocols, the RIP and the OSPF are presented and compared. The OSPF protocol with different delay timer values is also evaluated.