...but my question really was is there any reason anyone can think of that this would happen? Could NPM be causing it?
We have changed some OIDs we poll for Cisco since Orion 9.1. We now manage the polling for Cisco devices better and as far as I know we still poll Old and New OID's.
Example of this is Polling Cisco CPU: Pre Orion 9, we used... OID name: cpmCPUTOTAL5min/cpmCPUTotal1min OID number: 18.104.22.168.22.214.171.124.126.96.36.199.1.5/4
Since 9.1 (9.5 included therefore) they started using the following OIDs
And the reason is because of this from Cisco:https://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a94.shtml
The IOS version you are running has a bug that prevents the IP SNMP process to release memory when these OIDs were polled. Upgrading NPM just revealed you it was time upgrading the IOS :).
Thanks to kevin2me who forwarded me this info,
Great, thanks for the reply
I had found the IOS upgrade fixed it, was just curious what caused it so thank-you for the explaination.