This article applies to PRTG Network Monitor 12 through 13.2.3.1986

Changing the HTTP KeepAlive Flag Value for PRTG

This information is deprecated—The function is not supported anymore in current PRTG versions!

The HTTP KeepAlive Flag Value function was removed from PRTG 13.2.3.1986 and all later versions.

Constantly rising threads of the PRTG Core.exe often hint on HTTP connections to the PRTG webserver which are not properly dropped. This can be caused by tools accessing the PRTG API, or potentially by a malfunctioning router.

Closing an HTTP connection is determined by the KeepAlive Flag in an HTTP request. PRTG will keep a connection open and alive if the flag is set. Usually it is set with a browser sending the requests. However, the number of requests should not rise. Though, in some cases, certain network hardware does not properly close the connection—the requests start to rise.

When encountering this issue, you can try to set the usehttpkeepalive value in the registry to 0 for PRTG. With this option set, PRTG will ignore clients' "keep alive" requests.

Caution: Please back up your system before manipulating the Windows registry!

Steps to Go

1. Open the registry editor and navigate to the right key:
   1. On a 64-bit Windows system, go to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Paessler\PRTG Network Monitor\Server\Webserver
   2. On a 32-bit Windows system, go to HKEY_LOCAL_MACHINE\SOFTWARE\Paessler\PRTG Network Monitor\Server\Webserver
2. Check if there is an entry usehttpkeepalive. If it exists, you can skip the next step.
3. Create a new DWORD : in the current path, right-click > New > DWORD Value and enter usehttpkeepalive as name.
4. Set resp. change the value for usehttpkeepalive from 1 to 0: right-click on usehttpkeepalive and select Modify…. In the value field, enter 0. Confirm with Ok.
5. Reboot the server to activate the settings.