Question

A network engineer configures CoPP on an ISR to protect the router. A policy-map named CONTROL-PLANE-POLICY classifies and polices SNMP, SSH, and OSPF traffic and is applied with 'service-policy input CONTROL-PLANE-POLICY' under control-plane. Users report that the router is no longer sending SNMP traps to the NMS, although SNMP GET polling from the NMS still works and traps were confirmed working before CoPP was applied. What is the MOST likely cause?

Accepted Answer

SNMP traps are router-generated (egress) traffic and are not evaluated by an input CoPP policy; another feature or ACL is dropping them.

Answer

The SNMP class in the input CoPP policy is policing the outbound traps below the required rate, causing them to be dropped.

Answer

Traps require the policy to be applied with 'service-policy output' on the control plane, which was omitted.

Answer

The class map matching UDP 161 does not include UDP 162, so the input policy silently drops all trap packets.