Nagios causes 3750 stack to fail

[achesney]

Hello,

I am working with a Nagios system that was setup by another tech who is no longer with the company. after we changed our core switch from a stack of 3750G's to a stack of 3750X's every time we connect the Nagios to the network the core switch starts to perform irregular. one of the routers connected to the core losses communication (cisco 1800, unable to ping in or out), and our cisco wireless controller has the same issue. all other devices seem to act normally but performance seems to be slightly compromised. after disconnecting the Nagios box the router comes back but the issues with performance and the wireless controller remain.

we did realize that nagios was configured to monitor the old stack which has the same IP as the new stack so nagios was reaching out to the stack. we have found that restarting the stack resolves the issues until nagios is reconnected. several debugs on the stack show no errors.

so my question is this:
What could Nagios be doing to the stack to cause this behavior?

thanks for any help you can give.

[sreinhardt]

What is causing this, really depends on what kind of check you are doing on that system. Is it just snmp checks, or do you have other checks as well? I would probably suggest disabling the checks for the stack on nagios, then reconnecting to see if it continues to have an issue. If so, it is an issue with the stack passing the traffic that nagios needs more than likely. If it does not, then look into what checks you are performing against that device(s) and slowly re-enable them.