Refer to Cisco’s technote on this:
It is not recommended to employ their “Recommendation 1” of disabling access to the affected OIDs. This would prevent our product from being able to learn the route tables and ARP tables on the switch. PathSolutions recommends employing their “Recommedation 2” by enabling CEF on the switch to improve performance.
Recommendation 2: Turn on CEF
A change was made in the Cisco IOS code to allow SNMP to query the Cisco Express Forwarding (CEF) table for routing entries if CEF switching is used. This significantly improves the situation. With CEF enabled, the SNMP agent responds to a get-next/get-bulk operation for the routing or ARP tables with information from the Forwarding Information Base (FIB). The FIB is stored in lexicographical order and no sorting is needed. Without CEF enabled, the SNMP agent responds with information from the Routing Information Base (RIB), which must be sorted into lexicographical order causing high-CPU.
Details on enabling CEF can be found at Cisco’s Website: