Administrator Guide

All the PFC-related settings such as the DCB input and output policies or DCB maps are saved in the DCB application and the
Dierentiated Services Manager (DSM) application. All of these congurations can be modied only for interfaces that are enabled
for DCB. The DCB buer congurations are also saved in the DCB and DSM databases.
Buer Sizes for Lossless or PFC Packets
You can congure up to a maximum of 4 lossless (PFC) queues. By conguring 4 lossless queues, you can congure 4 dierent
priorities and assign a particular priority to each application that your network is used to process. For example, you can assign a
higher priority for time-sensitive applications and a lower priority for other services, such as le transfers. You can congure the
amount of buer space to be allocated for each priority and the pause or resume thresholds for the buer. This method of
conguration enables you to eectively manage and administer the behavior of lossless queues.
Although the system contains 9 MB of space for shared buers, a minimum guaranteed buer is provided to all the internal and
external ports in the system for both unicast and multicast trac. This minimum guaranteed buer reduces the total available shared
buer to 7,787 KB. This shared buer can be used for lossy and lossless trac.
The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related trac. The remaining approximate space of 1
MB can be used by lossy trac. You can allocate all the remaining 1 MB to lossless PFC queues. If you allocate in such a way, the
performance of lossy trac is reduced and degraded. Although you can allocate a maximum buer size, it is used only if a PFC
priority is congured and applied on the interface.
The number of lossless queues supported on the system is dependent on the availability of total buers for PFC. The default
conguration in the system guarantees a minimum of 52 KB per queue if all the 128 queues are congested. However, modifying the
buer allocation per queue impacts this default behavior.
By default the total available buer for PFC is 6.6 MB and when you congure dynamic ingress buering, 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 MXL
platform.
This default behavior is impacted if you modify the total buer available for PFC or assign static buer congurations to the
individual PFC queues.
Interworking of DCB Map With DCB Buer Threshold Settings
The dcb-input and dcb-output conguration commands are deprecated. You must use the dcp-map command to create a
DCB map to congure priority ow control (PFC) and enhanced transmission selection (ETS) on Ethernet ports that support
converged Ethernet trac.
Congure the dcb-buffer-threshold command and its related parameters only on ports with either auto conguration or dcb-
map conguration. This command is not supported on existing front-panel interfaces or stack ports that are congured with the
dcb-input or dcb-output commands. Similarly, if the dcb-buer-threshold conguration 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-buer-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 congured on interfaces or stack ports with the dcb-buer 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 buer-threshold-policy is congured on the system.
Dell(conf)#service-class dot1p-mapping dot1p0 3
Data Center Bridging (DCB)
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