What is this?

This knowledgebase contains questions and answers about PRTG Network Monitor and network monitoring in general.

Learn more

PRTG Network Monitor

Intuitive to Use. Easy to manage.
More than 500,000 users rely on Paessler PRTG every day. Find out how you can reduce cost, increase QoS and ease planning, as well.

Free Download

Top Tags

View all Tags

HTTPS Bad Request



Since the update to PRTG version all http sensors which monitor a website via https get "HTTP/1.1 400 Bad Request" failure although the sites are up & running. The http sensors using regular http still work.

Only in one of the failing sensors I found this (might not be related to the https issue): Failed to establish secure connection [Step 4] Socket Error # 10060 Connection timed out. [Step 0] Socket Error # 11004 [Step 1] Socket Error # 11004 [Step 2] Socket Error # 11004 [Step 3] Socket Error # 11004 [Step 4] Socket Error # 11004 [Unsecure] IOHandler value is not valid

PRTG is running on Windows Server 2008 R2 (6.1.1 Build 7601 Service Pack 1) with only one local probe. .NET Framework Support: .NET 4 Framework ist installiert (Installiert: v2.0.50727 (2.0.50727.5420), v4\Client (4.5.51209), v4\Full (4.5.51209), v4.0\Client (

Unfortunately I don't know much about debugging sensors in PRTG. Is there a way, besides sniffing, to display the request the http sensor is generating? How can I check SSL handling is working properly?

https httpsensor prtg

Created on Feb 2, 2016 8:56:22 AM

1 Reply

Accepted Answer



This is most probably related to the sensors now supporting SNI, please see this article for details.

Kind regards.

Created on Feb 3, 2016 2:48:15 PM by  Erhard Mikulik [Paessler Support]

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.