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The formula would become, "metric_health * 90 + metric_availability * 90 + metric_reachability * 100", resulting in "0.4 * 90 + 0.2 * 90 + 0.4 * 100 = 94", So a metric of 94 for this node, which is averaged with all the other nodes in this group, or the whole network to result in the metric for each group and the entire network.

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Interface Availability Reporting

How NMIS reports interface availability can be a little confusing for some people, as some people see that it should be 0 when the node is unreachable or Undefined when the node is unreachable.  NMIS introduced an option to give this control to the user of the system.  The configuration option is interface_availability_value_when_down, it is U (undefined) by default.

The reason that U is used by default, is because when the node is down, is is not possible to observe the metrics from the node, the scientific method states that you should record "unobservable" or nothing when you do not have a valid observation for that time period.

How this works is that when a node is DOWN (unreachable) and interface_availability_value_when_down = U, NMIS will save U to the overall interface availability, which will mean that the node could be down for 2 hours, and the interface availability metric for the node will be 100%.  In the same scenario if interface_availability_value_when_down = 0, the interface availability metric will be ( 1 - 2/48 ) * 100 = 95.83% available.

During normal operation and a node is UP, interfaces will be polled the the operational state (ifOperStatus) will change the availability of an interface, when ifOperStatus is up the result is 100, when down it is 0.

When a node is DOWN, NO interface specific data is processed so nothing is saved for the interface for that period of time, this is treated by default as U when a graph or calculation is made the result will be 100% available.