About Packet Loss

Intermapper can 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 when 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.

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. You can reset this value using the Reset link in the Status window (which resets all the device's statistics) or by selecting one or more devices and selecting Monitor > Reset Short-term Packet Loss.

Packet Loss Notifiers

Intermapper can send alerts and notifications 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 turns the appropriate color and Intermapper sends the appropriate alert. These thresholds can be set in the following places:

• Server Settings - Device Thresholds apply to all devices on all maps.
• Map Settings - Device Thresholds apply to all 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 and 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 packet loss statistics from continuing to increase during an outage. (If Intermapper continued to count lost packets while a device was down, the statistics incorrectly indicate there was high packet loss when the problem was most likely something else.)

In addition, Intermapper ignores the packets lost when determining that a device is down. For example, the default is that three successive lost packets indicate that the device is down (no longer responding). However, these three dropped packets are incorrectly shown as a 3% packet loss. Consequently, Intermapper removes the 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.