Hierarchical Policer Overview
Hierarchial policers rate-limit premium traffic separately from the aggregate traffic on an interface as determined by different configured rates. Hierarchical policing uses two token buckets to maintain two rates: an aggregate and a high priority rate, such as 10Mbps and 2Mbps. The traffic is marked differently based on the class of service. Two classes of service are defined for this use: expedited forwarding (EF) and non-expedited forwarding (non-EF). The EF traffic has a user-selectable rate, such as 2Mbps, that is guaranteed before being subject to marking. If there is no EF traffic present, then the non-EF traffic can use up to the 10Mbps rate before being marked. If there is EF traffic present, then the EF traffic is assured up to the 2Mbps (from the 10Mbps) before it becomes subject to marking, but also consumes from the non-EF rate. In this example the EF traffic is guaranteed the 2Mbps and the non-EF traffic has the remaining 8Mbps before being marked.
Hierarchical Policing has the following characteristics:
- Ingress traffic is first classified into premium and non-premium traffic prior to applying a policer.
- The hierarchal policer contains two policers: premium and aggregate. The premium traffic is policed by both the premium policer and aggregate policer. Although premium policer rate-limits the premium traffic, the aggregate policer only decrements the credits but does not drop the packets. The non-premium traffic is rate-limited only by the aggregate policer. Therefore, the premium traffic is assured to have the bandwidth configured for premium and the non-premium traffic is policed to the remaining bandwidth.
