Patent N. 2596533. Publication in the B.O.P.I. the 10th of january of 2017. The present invention is applied in security systems in a redundant Ethernet ring in which a security header is encapsulated within a redundancy header. Although security is introduced within the redundancy, when a node receives a frame of which it is a recipient, it also authenticates the redundancy header, while the intermediate nodes may not authenticate the redundancy header to avoid delays in the network