This default behavior is impacted if you modify the total buffer available for PFC or assign static bufferconfigurations to the individual PFC queues.Behavior of Tagged PacketsThe below is example for enabling PFC for priority 2 for tagged packets. Priority (Packet Dot1p) 2 will bemapped to PG6 on PRIO2PG setting. All other Priorities for which PFC is not enabled are mapped todefault PG – PG7.Classification rules on ingress (Ingress FP CAM region) matches incoming packet-dot1p and assigns aninternal priority (to select queue as per Table 1 and Table 2).The internal Priority assigned for the packet by Ingress FP is used by the memory management unit(MMU) to assign the packet to right queue by indexing the internal-priority to queue map table (TABLE 1)in hardware.PRIO2COS setting for honoring the PFC protocol packets from the Peer switches is as per above Packet-Dot1p->queue table (Table 2).The packets come in with packet-dot1p 2 alone are assign to PG6 on ingress.The packets come in with packet-dot1p 2 alone use Q1 (as per dot1p to Queue classification – Table 2)on the egress port.• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 1 ishalted.• Queue 1 starts buffering the packets with Dot1p 2. This causes PG6 buffer counter to increase on theingress, since P-dot1p 2 is mapped to PG6.• As the PG6 watermark threshold is reached, PFC generats for dot1p 2.Configuration Example for DSCP and PFC PrioritiesConsider a scenario in which the following DSCP and PFC priorities are necessary:DSCP 0 – 5, 10 - 15 20 – 25, 30 – 35Expected PFCPriority1 2To configure the aforementioned DSCP and PFC priority values, perform the following tasks:1. Create class-maps to group the DSCP subsetsclass-map match-any dscp-pfc-1match ip dscp 0-5,10-15!class-map match-any dscp-pfc-2match ip dscp 20-25,30-352. Associate above class-maps to Queues Queue assignment to be based on the below table (Thisinternal table has been modified for S6000 platform) .252 Data Center Bridging (DCB)
