Method for controlling failover between redundant network interface

Abstract

A method by which redundant network interface modules (NIMs) interconnecting the communication buses of two local area networks communicate with one another at predetermined time intervals over the communication buses of both networks. A first NIM of a redundant pair of NIMs is designated as the primary and a second NIM of the redundant pair is designated as the secondary. Contents of the information communicated between the NIMs over the communication bus of the first network includes the status of the transmitting NIMs ability to communicate with the second network and the information communicated between the NIMs over the communication bus of the second network includes the status of the transmitting NIM's ability to communicate with the first network. Based on the information exchanged, the failure of the NIMs to communicate as scheduled, and the internal status of each NIM as understood by that NIM, the NIMs decide when failover from the primary NIM to the secondary NIM occurs.