NetXMS Support Forum

we have a strange phenomena:
We have a node in NetXMS which losts his SNMP conficuration. I set the SNMP settings in 'Communications' to SNMPv3 with authentication and encryption in the java console. Then I finish with 'ok'. When I just reopen the node properties the settings are still there. A few minutes later I open the properties again and the SNMP settings are reseted to SNMP version 2c community string 'public'.
Very strange, I never saw that on other nodes before. How is this possible? and how can I fix this. Please help.

thanks
Dani

(NetXMS 2.0M1 installed from sources on linux 64bit, but also saw this on V1.2.17)

Do you have 'public' as one of your SNMP discovery communities?

Is it possible the node actually responds to SNMP v2 using the public community?

Can you do nxsnmpwalk on the node using v2 public?

Thanks for your fast reply.

The DefaultCommunityString in server configuration is something different.
Network Discovery is disabled but there is still one of the community strings 'public'.

I tested the affected node with nxsnmpwalk and SNMPv2 community string 'public'. And yes I was surprised this node replyed to SNMPv2 and public too!
I have two other switches (the same modell, same software, same SNMP-configuration but different port number), these other switches do not reply to SNMPv2 and 'public'. That part of the problem must be a bug in the switch software.

Than I deleted 'public' from Network Discovery and waited a few minutes. Till now no change to 'public' in the affected node. Is this a bug or a feature? And if it is a feaure, is it in documentation?

Then I restarted the SNMP feature in the switch. The next test with nxsnmpwalk and 'public' doesn't worked anymore.

A little bit strange. It must be a combination between a bug in the switch and the part in NetXMS where I don't know is it a bug or feature :-)

thanks
Dani

Its a NetXMS feature to use all SNMP communities configured in network discovery.

Here is how it works:
During a configuration poll (which happens when a node is added), ALL v2 communities and all v3 user/pass combinations are tested against a node.
If a working one is found, its used for that node.
This is so you can have different sets of SNMP settings for different nodes - NetXMS will automatically discover what SNMP setting to use for a particular node.

I'm pretty sure its documented in the wiki or the admin manual.

I know that but only in descovery.
But this affected node is an existing node. SNMP was switched off on this node but later I set SNMP to SNMPv3 with credentials (explicit on this node) and activated snmp polling for this node.
Then after a while (I think after the first configuration poll) the settings where resetted to SNMPv2 and 'public'. So NetXMS changed my explicit settings on this node. That is the surprise for me.
I think it also based on a bug in the physical node (switch), as the switch answered suddeny only on SNMPv2 and 'public' and not on SNMPv3 as before (no configuration change).

During every configuration poll, if a node doesnt answer on the pre-defined SNMP settings in the node's "Communication" settings tab; all known SNMP communities and user/pass combinations are tested against a node.
If new functional SNMP settings are found, they are applied to the node.

So yes, switch had a bug, but NetXMS behaved as expected.

This is expected from NetXMS and good, since imagine if you needed to change your SNMP community on 100 devices. You would just add your new community in discovery, and NetXMS would automatically find out it needs to use it on all nodes, and you dont have to change the settings of a 100 nodes in NetXMS.
Of course, you would have to reconfigure the SNMP agent on all of the nodes, but NetXMS would pick up the change automatically.

ok, thank you tomaskir!