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Why do my HTTP Advanced sensors differ in the bytes received value?

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My HTTP Advanced sensors are showing different values in the Bytes received channel. What is causing this?

http http-advanced-sensor prtg

Created on Mar 29, 2018 7:59:20 AM by  Brandy Greger [Paessler Support]



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This article applies to PRTG Network Monitor 19 or later

HTTP Advanced Sensors and Differing Values

When requesting URLs, the HTTP Advanced sensors may show different values for the Bytes received channel. This is because of the two different Monitoring Engine implementations.

Monitoring Engine Settings

In the sensor's settings under section HTTP Engine, there are the following Monitoring Engine settings:

  • Default/High Performance (recommended)
  • Alternate/Compatibility Mode

Both implementations receive the same header, but in different formats. Some websites, for example, return set-cookie with only one line, others with two or three lines.

The Default/High Performance (recommended) setting receives the HTTP header like this, for example: X-Refresh: s=6n|h=0|c=G|rd=Fri, 23 Mar 2018 08:35:36 GMT|dd=Fri, 23 Mar 2018 08:35:36 GMT,s=5f|h=2|c=G|rd=Fri, 23 Mar 2018 08:35:36 GMT|dd=Fri, 23 Mar 2018 08:35:37 GMT

The Alternate/Compatibility Mode setting receives the HTTP header like this, for example:

'X-Refresh: s=6n|h=0|c=G|rd=Fri, 23 Mar 2018 08:33:47 GMT|dd=Fri, 23 Mar 2018 08:33:47 GMT' 'X-Refresh: s=2n|h=1|c=G|rd=Fri, 23 Mar 2018 08:33:47 GMT|dd=Fri, 23 Mar 2018 08:33:48 GMT'

The header in the compatibility mode example has 10 bytes more due to the second X-Refresh entry, so the bytes received value differs from the bytes received value in the default mode example.

Because of the format differences, it is possible that your sensors show differing values in the Bytes received channel.

Created on Mar 29, 2018 8:48:22 AM by  Brandy Greger [Paessler Support]

Last change on May 22, 2019 9:58:17 AM by  Maike Behnsen [Paessler Support]



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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.