The availability and reachability metrics for routers and switches track two related–but very different–aspects of device connectivity.
Availability is a percentage of device uptime in a specific reporting period, such as 5 minutes. Uptime is defined as the amount of time the device is powered on and capable of processing data without considering whether it is reachable. A device that is up and capable of processing data can be unreachable because of a network or other communications failure by another device along its path.
If a device becomes unavailable, check its UPS and cables. Check the device for hardware issues. The Device Details pages let you compare the status of devices by the same manufacturer.
A device is either available (up) or unavailable (down), so the availability percentage is the reporting period (in seconds), divided by the average of the following two values:
Reachability refers to whether a device is reachable from the CA Performance Center data source. Typically a data source uses ICMP (ping testing) to communicate regularly with the target device. If communication fails for any reason (including the loss of the network path or routing), this communications failure is reported in the reachability statistics.
Reachability data comes from regular ping testing of all devices that support ICMP. The reachability value is the ping responses received from the device during each reporting interval. The value is expressed as a percentage of all ping tests attempted. For each reporting interval, the reachability is an average of the following two values:
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