This article applies to PRTG Network Monitor 18 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, you have 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 example for the compatibility mode has 10 bytes more due to the second X-Refresh entry, so the bytes received value differs from the bytes received value in the example for the default mode.

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