Reference Guide

The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related traffic. The remaining
approximate space of 1 MB can be used by lossy traffic. You can allocate all the remaining 1 MB 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 52 KB per queue if all the 128
queues are congested. However, modifying the buffer allocation per queue impacts this default behavior.
By default the total available buffer for PFC is 6.6 MB and when you configure dynamic ingress buffering,
a minimum of least 52 KB per queue is used when all ports are congested. By default, the system enables
a maximum of two lossless queues on the S4820T platform.
This default behavior is impacted if you modify the total buffer available for PFC or assign static buffer
configurations to the individual PFC queues.
Interworking of DCB Map With DCB Buffer Threshold
Settings
DCB map functionality is supported on the S4820T platform.
The dcb-input and dcb-output configuration commands are deprecated. You must use the dcp-map
command to create a DCB map to configure priority flow control (PFC) and enhanced transmission
selection (ETS) on Ethernet ports that support converged Ethernet traffic.
Configure the dcb-buffer-threshold command and its related parameters only on ports with either
auto configuration or dcb-map configuration. This command is not supported on existing front-panel
interfaces or stack ports that are configured with the dcb-input or dcb-output commands. Similarly, if
the dcb-buffer-threshold configuration is present on a stack port or any interface, the dcb-input or dcb-
ouput policies cannot be applied on those interfaces.
Example: When the dcb-buffer-threshold policy is applied on interfaces or stack ports with the dcb-input
or dcb-output policies, the following error message is displayed:
%Error: dcb-buffer-threshold not supported on interfaces with deprecated
commands
Example: When the dcb-input or dcb-output policy is configured on interfaces or stack ports with the
dcb-buffer threshold policy, the following error message is displayed:
%Error: Deprecated command is not supported on interfaces with dcb-buffer-
threshold configured
You must not modify the service-class dot1p mappings when any buffer-threshold-policy is configured
on the system.
S4810-1(conf)#service-class dot1p-mapping dot1p0 3
% Error: PFC buffer-threshold policies conflict with dot1p mappings. Please
remove all dcb-buffer-threshold policies to change mappings.
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Data Center Bridging (DCB)