IPv4 UDP Flow with Latency Measurement - automatic UDP checksum disabled
Posted by Mathieu Strubbe, Last modified by Dries Decock on 03 April 2018 02:03 PM

You probably arrived at this page after clicking on an Info Item in a ByteBlower Report looking like this one:

This article explains what this means.

What happened ?

The test scenario you just executed contains a flow, sending IPv4 UDP Frames with the Automatic Checksum enabled on the Layer 4 tab in the Frame View.

On top of that, the Latency Measurement option was enabled for this flow. To be able to measure the latency, a timestamp value is inserted at the end of each Frame. Of course, this makes the UDP checksum invalid.

So, after setting the timestamp, the UDP checksum should be re-calculated automatically. But on some ByteBlower servers, this is not possible. Due to limitations of the hardware used inside the ByteBlower server, it is not possible to send Frames with a timestamp and a correct UDP checksum.

The workaround we came up with, is to set the checksum value automatically to zero, which means that the checksum is disabled.

This way, the frames sent out by the ByteBlower server are perfectly valid, and will not be dropped by any device in your test setup.

For more technical details about this issue, check out this article: Known Issue: 100% packetloss on latency measurements 2x00/4x00 series

So, should I be worried ?

No, this is no reason to be worried.  In most cases, this will not affect the value of your report.

Some UDP checksum values have been set to zero, which means that they were disabled.

So only when you are testing devices that actually use this checksum value, you should be aware of the possible consequences caused by this behavior.

 

 



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