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

Auto-discovery adds disabled interface




On switches, auto-discovery adds interfaces that are administratively disabled and do not have an active link. Is this correct, can this unwanted behavior be changed?

What are the conditions for auto-discovery to add an interface? Can this be changed?

Kind regards, Bastiaan

add auto-discovery interfaces

Created on Jul 20, 2015 11:51:59 AM

Last change on May 23, 2019 4:59:13 AM by  Maike Guba [Paessler Support] (2,404) 2 1

5 Replies



Hello Bastiaan, thank you for your inquiry.

The auto-discovery always creates SNMP Traffic sensors for all interfaces whose SNMP Traffic Counters are above 0, regardless of their state. It behaves this way because the Interfaces Table is very volatile and there is no "definitive" way to approach this, as names change, indexes change and we want the auto-discovery to be consistent.

If a port has traffic or has had traffic since the previous restart, it will likely have an SNMP Traffic Counter above 0 and thus be added by auto-discovery. Ports that already have sensors will not be re-created.

This behavior is already described in some threads of the Knowledge Base:

For further questions, we are more than happy to help you.

Created on Jul 21, 2015 11:58:04 AM by  Luciano Lingnau [Paessler]

Last change on May 27, 2019 4:49:14 AM by  Maike Guba [Paessler Support] (2,404) 2 1



Hi Luciano,

Thank you for your indepth anwser.

We have cleared the interface counters of an disabled interface on a cisco 3950 switch with "clear counters 1/0/7". Run an "sh interface 1/0/7", the counters are all 0. Removed the interface sensor from the device and run an auto-discovery. The interface gets added again. Any idea why?

This interface auto-discovery algorithm can't be changed? As we are only interested in administratively enabled interfaces, much more logic, why measure disabled ones...., perhaps a PRTG sales thing :-)

Kind Regards, Bastiaan Bastiaan

Created on Jul 23, 2015 6:21:30 AM



Hello Bastiaan

Thank you for your efforts, unfortunately the SNMP Counters are not the same counters as the interface counters displayed within IOS and as Documented by Cisco those counters can't be forcedly cleared, the exception being rebooting the whole device.
It probably is that way because clearing those counters would affect all current SNMP Traffic measurements since the Traffic Counters are queried as Delta values. (Something like (currentvalue - previousvalue)/(previoustime - currenttime)) = ActualSpeed )

Currently we don't plan on changing that behavior because we don't consider that adding administratively disabled interfaces affects the product in any way, as they're SNMP Sensors and will unlikely adversely affect PRTG's performance, usability or storage consumption.

For any further questions, we're glad to help. Best Regards,

Created on Jul 23, 2015 12:01:27 PM by  Luciano Lingnau [Paessler]



Hi Luciano,

Again, thank you for your post.

We would like to monitor only interfaces that matter. I understand that it wont likely effect performance, but we have our reasons. We are using PRTG to monitor our IaaS cloud platform:

  • Cost, every sensor is a license slot (unneeded license use is not something customers like)
  • Not a blurry focus, only interfaces in view that matter in the sensor list
  • We can no longer enable auto-discovery on switches as it will add those unwanted interfaces. We like auto-discovery so it will auto-add interfaces who have become active/enabled without the admin have to add them in PRTG.

Please reconsider your point of view.

Kind Regards, Bastiaan

Created on Jul 23, 2015 12:16:33 PM

Last change on Jul 24, 2015 7:06:31 AM by  Luciano Lingnau [Paessler]



Hello Bastiaan, your point is legit, I'm not saying that we reject your opinion or suggestion, we believe that you're making a fair and valid point, but as we want to be as honest and transparent as possible there are no plans to change this in the (near) future.

We try to focus on features that have high request rates and affect the higest number of customers as possible. There's an blog entry from our CEO explaining how we handle feature requests.

Kind Regards,
Luciano Lingnau

Created on Jul 24, 2015 8:07:30 AM by  Luciano Lingnau [Paessler]

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.