5.1.c Implement and troubleshoot control plane policing

Control Plane Policing (CoPP) is a Cisco IOS-wide feature designed to allow users to manage the flow of traffic handled by the route processor of their network devices. CoPP is designed to prevent unnecessary traffic from overwhelming the route processor that, if left unabated, could affect system performance. Route processor resource exhaustion, in this case, refers to all resources associated with the punt path and route processor( s) such as Cisco IOS process memory and buffers, and ingress packet queues.

More than just control plane packets can punt and affect the route processor and system resources. Management plane traffic, as well as certain data plane exceptions IP packets and some services plane packets , may also require the use of route processor resources. Even so, it is common practice to identify the resources associated with the punt path and route processor (s) as the Control Plane. The feature in Cisco IOS is CoPP.

CoPP protects the route processor on network devices by treating route processor resources as a separate entity with its own ingress interface (and in some implementations, egress also). Because of this behavior, a CoPP policy can be developed and applied only to those packets within the control plane. Unlike interface ACLs, for example, no effort is wasted investigating data plane ( transit) packets that will never reach the control plane. This action has a significant simplifying implication on the construction of policies for CoPP.

CoPP is implemented using the Cisco IOS Modular QoS CLI (MQC), a highly flexible framework that allows users to create and attach traffic polices to interfaces The Cisco Modular QoS CLI (MQC) mechanisms are used by CoPP to define the classification and policing descriptions for its policies. In this way, in addition to the limited permit and deny actions associated with simple ACLs, specific packets may be permitted but rate-limited when using the MQC structure. For example, you may wish to permit certain ICMP packet types, but rate limit them so that the route processor is not adversely impacted. This action adds tremendously to the capabilities and flexibility of developing and deploying a useable CoPP policy.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5086-5087).  . Kindle Edition.

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/copp.html