Addendum

• When you apply a DCB map, an error message displays if:

• Link-level flow control is already enabled on an interface. You cannot enable PFC and link-level flow

control at the same time on an interface.

• In a switch stack, configure all stacked ports with the same PFC configuration.

• FTOS allows you to change the default dot1p priority-queue assignments only if the change satisfies

the following requirements in DCB maps already applied to S6000 interfaces:

• All 802.1p priorities mapped to the same queue must be in the same priority group.

• A maximum of two PFC-enabled, lossless queues are supported on an interface.

Otherwise the reconfiguration of a default dot1p-queue assignment is rejected.

• To ensure complete no-drop service, apply the same PFC parameters on all PFC-enabled peers.

PFC Prerequisites and Restrictions

On an S6000 switch, PFC is globally enabled by default, but not applied on specific 802.1p priorities. To

enable PFC on 802.1p priorities, create a DCB map. For more information, see Configuring DCB Maps

and its Attributes.

The following prerequisites and restrictions apply when you configure PFC in a DCB map:

• You can enable PFC on a maximum of two priority queues on an interface. Enabling PFC for dot1p

priorities configures the corresponding port queue as lossless.

• You cannot enable PFC and link-level flow control at the same time on an interface.

ETS Configuration Notes

ETS provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet

traffic. Different traffic types have different service needs. Using ETS, you can create groups within an

802.1p priority class to configure different treatment for traffic with different bandwidth, latency, and

best-effort needs.

When you configure ETS in a DCB map:

• The DCB map associates a priority group with a PFC operational mode (on or off) and an ETS

scheduling and bandwidth allocation. You can apply a DCB map on multiple egress ports.

• Use the ETS configuration associated with 802.1p priority traffic in a DCB map in DCBx negotiation

with ETS peers.

• Traffic in priority groups is assigned to strict-queue or weighted round-robin (WRR) scheduling in an

ETS configuration and is managed using the ETS bandwidth-assignment algorithm. FTOS de-queues

all frames of strict-priority traffic before servicing any other queues. A queue with strict-priority traffic

can starve other queues in the same port.

• ETS-assigned bandwidth allocation and strict-priority scheduling apply only to data queues, not to

control queues.

• FTOS supports hierarchical scheduling on an interface. FTOS control traffic is redirected to control

queues as higher priority traffic with strict priority scheduling. After the control queues drain out, the

remaining data traffic is scheduled to queues according to the bandwidth and scheduler configuration

in the DCB map. The available bandwidth calculated by the ETS algorithm is equal to the link

bandwidth after scheduling non-ETS higher-priority traffic.

Data Center Bridging (DCB)