The policer instances are a limited hardware resource on a specific forwarding plane. DCP policers (static, dynamic, local-monitor) are consumed from the overall forwarding plane policer resources (from the ingress resources if ingress and egress are partitioned). Each per-protocol policer instantiated reduces the number of FP child policers available for other purposes.
When DCP is configured with dynamic enforcement, then the operator must set aside a pool of policers that can be instantiated as dynamic enforcement policers. The number of policers reserved for this function are configurable per card or FP. The policers in this pool are not available for other purposes (normal SLA enforcement).
Static enforcement policers and local monitoring policers use policers from the normal or global policer pool on the card or FP. After a static policer is configured in a DCP policy and it is referenced by a protocol in the policy, this policer will be instantiated for each object (SAP or network interface) that is created and references the policy. If there is no policer free on the associated card or FP, then the object will not be created. Similarly, for local monitors, after a local monitoring policer is configured and referenced by a protocol, then this policer will be instantiated for each object that is created and references the policy. If there is no policer free, then the object will not be created.
Dynamic enforcement policers are allocated as needed (when the local monitor detects nonconformance) from the reserved dynamic enforcement policer pool.
When a DCP policy is applied to an object on a LAG, then a set of policers is allocated on each FP (on each line card that contains a member of the LAG). The LAG mode is ignored and the policers are always shared by all ports in the LAG on that forwarding plane on the SAP or interface. In other words, with link-mode lag a set of DCP policers are not allocated per-port in the LAG on the SAP.
To support large scale operation of DCP, and also to avoid overload conditions, a polling process is used to monitor state changes in the policers. This means there can be a delay between when an event occurs in the data plane and when the relevant state change or event notification occurs toward an operator, but in the meantime the policers are still operating and protecting the control plane.