Interface or link speed and the interface bandwidth command: What NetFlow Analyzer reports

ManageEngine NetFlow Analyzer is the first NetFlow solution to offer one-minute granularity for speed, volume, and utilization reports. It even lets you drill down into any minute and find the conversations causing traffic, giving you sub-minute visibility.

In this blog, we’ll discuss how NetFlow Analyzer reports on speed and utilization, and what the purpose of the bandwidth command is on a router. First, let’s see how speed and utilization are calculated for a particular minute using the NetFlow exports.

Consider any report in NetFlow Analyzer with a reporting granularity of one minute. The speed value of any particular minute is calculated by adding the transmission volume of all the conversations happening in that particular minute from the interface, and the value is divided by 60 seconds to derive the speed.

Here’s an example:

Speed calculation

At 10:10, total IN traffic is 50MB (volume is always represented in bytes). The speed = 50MB x 8 / 60. The multiplication by eight is to convert the volume to bits, which is divided by 60 (seconds) to get the speed.

So, from the above calculation, the data rate at 10:10 is 6.67Mbps (speed is always represented in bits per second).

Utilization calculation

Now that we’ve identified the link usage at 10:10 is 6.67 Mbps, we can find the utilization, which is how much of the actual link capability was used for the transmission of traffic. Utilization = (Usage rate / Actual link speed) x 100. So, for an 8Mbps link, the utilization would be (6.67 Mbps / 8 Mbps) x 100 = 83%.

What is the router bandwidth command?

Users often complain about not getting the speed set on an interface or about incorrect utilization reports. User data rate depends on the operating link speed or bandwidth, not the bandwidth configured on the interface using the IOS bandwidth command. The bandwidth configured on the interface is to help routing protocols choose the best route to transmit the packets. We recommend that users set the link speed as the bandwidth on the interface for efficient routing.

NetFlow Analyzer reports are based on the actual data rate on the link, not on the bandwidth set on the interface. However, since NetFlow Analyzer fetches the link speed via SNMP from the router based on the bandwidth speed set, the utilization calculation will be effected. For this reason, it’s important to set the right speed using the bandwidth command to get better routing efficiency and correct reports in NetFlow Analyzer. It’s not possible to get faster throughput from any interface by configuring a faster speed using the bandwidth command.

With this information, users should be in a better position to see the right utilization reports in NetFlow Analyzer for real-time traffic and also route network traffic more efficiently.

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Reference: http://articles.techrepublic.com.com/5100-10878_11-6093972.html