Method for controlling access operations on networks (NW, NW UKR, NW KR) based on IT systems, in particular automation networks, control networks or supervisory networks comprising embedded systems or distributed systems, in which at least one from at least one network (NW UKR) that is uncritical in regard to operation and/or safety, in particular referred to as a standard network, and at least one network (NW KR) that is critical in regard to operation and/or safety is accessed by a control unit to set up a network connectivity, characterized in that a) the respective set-up of the network connectivity prompts at least one network communication protocol used in the respective network (NW, NW UKR, NW KR) for network communication to be ascertained by the control unit, b) the respectively ascertained network communication protocol is collated by the control unit with a multiplicity of reference protocols, preferably stored in a list, that are usually used in the operation- and/or safety-critical networks (NW KR), c) if the collation of the ascertained network communication protocol with the reference protocols reveals that at least one ascertained network communication protocol is concordant with a dedicated reference protocol of the reference protocols, the respective set-up of the network connectivity then prompts at least one warning, in particular at least one "critical network signal <CNS>", to be provided by the control unit, in particular if an inadvertent or intentional but inadmissible attempt is made, e.g. in the course of diagnosis, service, start-up, maintenance, configuration, etc., to set up the connectivity to the operation- and/or safety-critical network (NW KR), otherwise the network connectivity is set up, in particular for network diagnosis, network service, network start-up, network maintenance, network configuration, etc., by the control unit without the provision of the warning. a) the respective set-up of the network connectivity prompts at least one network communication protocol used in the respective network (NW, NW UKR, NW KR) for network communication to be ascertained by the control unit, b) the respectively ascertained network communication protocol is collated by the control unit with a multiplicity of reference protocols, preferably stored in a list, that are usually used in the operation- and/or safety-critical networks (NW KR), c) if the collation of the ascertained network communication protocol with the reference protocols reveals that at least one ascertained network communication protocol is concordant with a dedicated reference protocol of the reference protocols, the respective set-up of the network connectivity then prompts at least one warning, in particular at least one "critical network signal <CNS>", to be provided by the control unit, in particular if an inadvertent or intentional but inadmissible attempt is made, e.g. in the course of diagnosis, service, start-up, maintenance, configuration, etc., to set up the connectivity to the operation- and/or safety-critical network (NW KR), otherwise the network connectivity is set up, in particular for network diagnosis, network service, network start-up, network maintenance, network configuration, etc., by the control unit without the provision of the warning.