Reference Guide

allocated for each priority and the pause or resume thresholds for the buffer. This method of
configuration enables you to effectively manage and administer the behavior of lossless queues.
Although the system contains 4 MB of space for shared buffers, a minimum guaranteed buffer is provided
to all the internal and external ports in the system for both unicast and multicast traffic. This minimum
guaranteed buffer reduces the total available shared buffer to 3456 KB. This shared buffer can be used for
lossy and lossless traffic.
The default behavior causes up to a maximum of 3664 KB to be used for PFC-related traffic. The
remaining approximate space of 208 KB can be used by lossy traffic. You can allocate all the remaining
208 KB to lossless PFC queues. If you allocate in such a way, the performance of lossy traffic is reduced
and degraded. Although you can allocate a maximum buffer size, it is used only if a PFC priority is
configured and applied on the interface.
The number of lossless queues supported on the system is dependent on the availability of total buffers
for PFC. The default configuration in the system guarantees a minimum of 54 KB (for 10G) per queue if all
the 64 queues are congested. However, modifying the buffer allocation per queue impacts this default
behavior.
The following table lists the PFC buffer space required for one lossless queue corresponding to the port
speeds supported by the Z9100–ON platform:
Table 16. Buffer Space Required
Interface Speed PFC Buffer Space required for one Lossless Queue
10G 54 KB
25G 94 KB
40G 94 KB
50G 161 KB
100G 161 KB
This default behavior is impacted if you modify the total buffer available for PFC or assign static buffer
configurations to the individual PFC queues.
Behavior of Tagged Packets
The below is example for enabling PFC for priority 2 for tagged packets. Priority (Packet Dot1p) 2 will be
mapped to PG6 on PRIO2PG setting. All other Priorities for which PFC is not enabled are mapped to
default PG – PG7.
Classification rules on ingress (Ingress FP CAM region) matches incoming packet-dot1p and assigns an
internal 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.
254
Data Center Bridging (DCB)