About Packet Loss

InterMapper has the ability to monitor both long-term and short-term packet loss. These are useful for detecting problems in your network.
Long term Packet Loss is measured from the time InterMapper starts testing a device. InterMapper computes this from the total number of pings or SNMP queries sent, and the fraction of those that fail to respond.

Long-term Packet Loss

The Long-term Packet Loss is displayed in the device's Status Window, along with the total number of packets sent and responses received. It is possible to reset this value using the Reset link in the device's Status Window.

Short-term Packet Loss

InterMapper measures Short-term Packet Loss by counting the number of lost packets in the last 100 sent. To do this, each device retains the history of the last 100 packets sent/received.

The short-term packet loss is displayed in the device's Status Window as a percentage of the number of dropped packets in the last 100. This value can be reset via the Reset link in the Status Window(which resets all the device's statistics), or by selecting one or more devices and choosing Monitor -> Reset Short-term Packet Loss.

Packet Loss Notifiers

InterMapper can send alerts/notifiers when the short term packet loss statistics exceed certain thresholds. That is, when short term packet loss exceeds a warning, alarm, or critical threshold, the device will turn to the appropriate color and InterMapper will send the appropriate alert. These thresholds can be set in several places:

• Server Settings - Device Thresholds apply to all devices on all maps
• Map Settings - Device Thresholds apply to all the devices on a particular map, overriding the Server Settings value.
• Individual device - Set Thresholds... sets the thresholds for that particular device, overriding the map-wide or server-wide settings.

To disable alerts/notifications for high packet loss, set the packet loss thresholds to 100%.

Ignoring lost packets during outages

When a device goes down, InterMapper stops updating the packet loss history (both short and long term) for the duration of the outage. This prevents the packet loss statistics from continuing to increase during an outage. (If InterMapper continued to count lost packets while a device was down, the statistics would incorrectly indicate there was high packet loss when it was likely the problem was something else.)

In addition, InterMapper ignores the packets lost when determining that a device has gone down. For example, the default is that three successive lost packets will indicate that the device is down (no longer responding). However, these three dropped packets would be shown (incorrectly) as a 3% packet loss. Consequently, InterMapper removes those dropped packets from the history, so that it shows an accurate accounting.

When the device subsequently responds (after the problem has been corrected), InterMapper begins counting successful and lost packet responses again.