Fault Tolerance for Flexible Time-Triggered Ethernet-based systems (FT4FTT) is a project to devise an architecture for distributed embedded systems that provides both flexibility to changing real-time requirements and high reliability through fault tolerance. One of the key parts of such an architecture is the communication subsystem. When designing such a subsystem many decisions have to be made. To understand how such decisions impact the reliability of the final design, in this paper we present a framework to evaluate the reliability of a large number of potential designs. The approach is based on storing a finite subset of the design space for the communication subsystem of FT4FTT in an undirected graph and then generating a continuous-time Markov chain from the graph to evaluate the reliability of each design belonging to the subset.