Method for planning a communication network of an industrial automation system, in which - failure rates of network components are captured using a modelling unit, - a network topology is captured using the modelling unit, - an availability of the communication network is checked on the basis of a stochastic communication network model, - if a predefinable minimum availability is undershot, the availability of the communication network is iteratively determined on the basis of the stochastic communication network model using first additional and/or alternative network components, - if the predefinable minimum availability is undershot despite using the additional and/or alternative network components, the availability of the communication network is determined again using second or further additional and/or alternative network components, - if the predefinable minimum availability is complied with, a checked network configuration is released for operation, characterized in that - the communication network is stochastically modelled with respect to a probable transmission duration of messages inside the communication network, an expected failure rate of the communication network being able to be derived from the resulting stochastic communication network model, - required maximum response times are predefined for successful message transmission inside the communication network of the industrial automation system, - the communication network model represents network components with regard to their failure rate and communication connections with regard to a probability of successful message transmission within the predefined maximum response time. - failure rates of network components are captured using a modelling unit, - a network topology is captured using the modelling unit, - an availability of the communication network is checked on the basis of a stochastic communication network model, - if a predefinable minimum availability is undershot, the availability of the communication network is iteratively determined on the basis of the stochastic communication network model using first additional and/or alternative network components, - if the predefinable minimum availability is undershot despite using the additional and/or alternative network components, the availability of the communication network is determined again using second or further additional and/or alternative network components, - if the predefinable minimum availability is complied with, a checked network configuration is released for operation, - the communication network is stochastically modelled with respect to a probable transmission duration of messages inside the communication network, an expected failure rate of the communication network being able to be derived from the resulting stochastic communication network model, - required maximum response times are predefined for successful message transmission inside the communication network of the industrial automation system, - the communication network model represents network components with regard to their failure rate and communication connections with regard to a probability of successful message transmission within the predefined maximum response time.