Understanding Chassis Cluster Redundancy Group Interface Monitoring

For a redundancy group to automatically fail over to another node, its interfaces must be monitored. When you configure a redundancy group, you can specify a set of interfaces that the redundancy group is to monitor for status (or “health”) to determine whether the interface is up or down. A monitored interface can be a child interface of any of its redundant Ethernet interfaces. When you configure an interface for a redundancy group to monitor, you give it a weight.

Every redundancy group has a threshold tolerance value initially set to 255. When an interface monitored by a redundancy group becomes unavailable, its weight is subtracted from the redundancy group's threshold. When a redundancy group's threshold reaches 0, it fails over to the other node. For example, if redundancy group 1 was primary on node 0, on the threshold-crossing event, redundancy group 1 becomes primary on node 1. In this case, all the child interfaces of redundancy group 1's redundant Ethernet interfaces begin handling traffic.

A redundancy group failover occurs because the cumulative weight of the redundancy group's monitored interfaces has brought its threshold value to 0. When the monitored interfaces of a redundancy group on both nodes reach their thresholds at the same time, the redundancy group is primary on the node with the lower node ID, in this case node 0.

Note: If you want to dampen the failovers occurring because of interface monitoring failures, use the hold-down-interval statement.

Understanding Chassis Cluster Redundancy Group Interface Monitoring

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