This article applies as of PRTG 22

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

HTTP Advanced sensor and differing values

When requesting URLs, the HTTP Advanced sensor 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 Monitoring Engine, there are the following settings:

• Default
• Compatibility engine

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 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 Compatibility engine 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 GM'
'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 engine example has 10 bytes more because of 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.