Users Guide

each group. However, when three priority groups with different bandwidth allocations are used on an
interface:
• If priority group 3 has free bandwidth, it is distributed as follows: 20% of the free bandwidth to priority
group 1 and 30% of the free bandwidth to priority group 2.
• If priority group 1 or 2 has free bandwidth, (20 + 30)% of the free bandwidth is distributed to priority
group 3. Priority groups 1 and 2 retain whatever free bandwidth remains up to the (20+ 30)%.
Strict-priority
groups:
If two priority groups have strict-priority scheduling, traffic assigned from the priority group with the
higher priority-queue number is scheduled first. However, when three priority groups are used and two
groups have strict-priority scheduling (such as groups 1 and 3 in the example), the strict priority group
whose traffic is mapped to one queue takes precedence over the strict priority group whose traffic is
mapped to two queues.
Therefore, in this example, scheduling traffic to priority group 1 (mapped to one strict-priority queue) takes precedence over
scheduling traffic to priority group 3 (mapped to two strict-priority queues).
Using ETS to Manage Converged Ethernet Traffic
To use ETS for managing converged Ethernet traffic, use the following command:
dcb-map stack-unit all dcb-map-name
Applying DCB Policies in a Switch Stack
You can apply DCB policies with PFC and ETS configurations to all stacked ports in a switch stack or on a stacked switch.
To apply DCB policies in a switch stack, follow this step.
NOTE
: Use only 40G ports as stacking ports when you enable DCB. S4820T does not support DCB when you use
10GBaseT ports as stacking ports.
• Apply the specified DCB policy on all ports of the switch stack or a single stacked switch.
CONFIGURATION mode
dcb-map {stack-unit all | stack-ports all} dcb-map-name
Configure a DCBx Operation
DCB devices use data center bridging exchange protocol (DCBx) to exchange configuration information with directly
connected peers using the link layer discovery protocol (LLDP) protocol.
DCBx can detect the misconfiguration of a peer DCB device, and optionally, configure peer DCB devices with DCB feature
settings to ensure consistent operation in a data center network.
DCBx is a prerequisite for using DCB features, such as priority-based flow control (PFC) and enhanced traffic selection (ETS), to
exchange link-level configurations in a converged Ethernet environment. DCBx is also deployed in topologies that support
lossless operation for FCoE or iSCSI traffic. In these scenarios, all network devices are DCBx-enabled (DCBx is enabled end-to-
end). For more information about how these features are implemented and used, refer to:
• Configure Enhanced Transmission Selection
DCBx supports the following versions: CIN, CEE, and IEEE2.5.
Prerequisite: For DCBx, enable LLDP on all DCB devices.
Data Center Bridging (DCB) 254