Entuity uses two methods to indicate the availability of a device:
- A device is considered reachable when its management IP address responds to ICMP ping requests.
- It is measured as a percentage (e.g. 80%).
- Uptime is calculated by refining the reachability metric.
- It is calculated by identifying reachbility outages (i.e. periods when the device is not responding to ICMP ping) and then checking the value of sysUpTime at the start and end of eacah outage to determine whether the device rebooted during the outage.
- From this information, Entuity calculates the percentage of time during which the device was up during the reachability outage and the percentage of time that the exact status of the device was unknown during the outage.
- The Reachability value is then adjusted accordingly to take into account this additional information. Therefore, the Uptime value should be the same as or greater than Reachability, never smaller than Reachability.
In the below example, the device was operating continuously for 7 days. This is determined by polling for sysUptime, and therefore Uptime = 100%. However, during this time, the device responded to ICMP only 6% of the time.