Auto-discovery adds disabled interface

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:

• NICS not as intended after autodiscovery
• Enable Connection State Handling by default during autodiscovery
• Cisco Switching auto discovery ports
• Network adapter template (New! - This is somewhat a hack (and not officially supported) but may provide some "flexibility" on controlling the auto-discovery's behavior.)

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

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

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,

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

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