Hi,

I'm monitoring network interface on one of our equipment and I keep getting "No such instance" errors on some.

I've read the KB on automatic name update but my problem is I don't want PRTG to update the name of the sensor, I want it to just update the port number when it changes (the ifalias is unique and never changes on those interfaces) and keep the sensor working for that interface.

The name of the sensor cannot change as is contains our customers names, locations and link type (we are an ISP) which is essential for us to bring support to them quickly.

Monitoring those links are the primary reason we are in the process of buying 1000+ licences.

Do you have any solutions for this ?

Regards,

Marc

Article Comments

When you get the "No such instance" error, it usually means that the OID the sensor is configured for doesn't exist anymore. Can you try to recreate the sensor to see if a new one works? You'll have to configure ifindex persistency in order to overcome this issue.


Sep, 2016 - Permalink

Hi,

I have a support ticket on this matter as I needed a fast answer (it is a bit critical).

When I get a resolution on this issue i'll post it here for everyone to see.

FYI yes I can see the sensors if I create a new one, the ifindex changed but is not capture by PRTG automatically (support tells me it should).

I'm waiting on your developper's answer on this.

Have a nice day.


Sep, 2016 - Permalink

Okay then :)


Sep, 2016 - Permalink

We've received Marc's contact/logs. While PRTG is able to handle index changes in most cases, this is one where due to the way that the monitored device implements it's SNMP Agent it does not.

What happens is that interfaces "disappear" for a while. Then shows up later under a different index.

Initial "data"
15/09/2016 15:52:31 (1152 ms) : 1.3.6.1.2.1.2.2.1.1.65994 = "65994"
15/09/2016 15:52:33 (2586 ms) : 1.3.6.1.2.1.2.2.1.2.65994 = "myuniqueifDescr"
Intermediate "data"
(no information about the interface)
Latest "data"
16/09/2016 12:58:26 (865 ms) : 1.3.6.1.2.1.2.2.1.1.66055 = "66055"
16/09/2016 12:58:27 (1753 ms) : 1.3.6.1.2.1.2.2.1.2.66055 = "myuniqueifDescr"



The issue is that PRTG's index change detection algorithm checks for the interface under a different number at the very moment that it "vanishes". If there is no interface with that ifDescr at this point PRTG "forgets" the unique ifDescr.
Should the interface later show up it SHOULD retain the same index, but it doesn't and shows up under a new index. For PRTG this is a new interface with a duplicate ifDescr and not the same interface. Thus the originally deployed sensor stays in an error status:

No such object (SNMP error # 222)



There is no configuration in PRTG that can be changed for this, the monitored device needs to be adjusted, the interface should either be persistent in the ifTable or should retain the same index when it is re-created.

Best Regards,
Luciano Lingnau [Paessler Support]


Sep, 2016 - Permalink