Owners Manual

bandwidth is allocated to priority group 0 and the bandwidth is equally assigned to each dot1p
priority.
If an error occurs when a port receives a peer’s ETS configuration, the port’s configuration resets to the
ETS configuration in the previously configured DCB map. If no DCB map was previously applied, the port
resets to the default ETS parameters.
ETS Prerequisites and Restrictions
On an S6000 switch, ETS is enabled by default on Ethernet ports with equal bandwidth assigned to each
802.1p priority. You can change the default ETS configuration only by using a DCB map.
The following prerequisites and restrictions apply when you configure ETS bandwidth allocation or strict-
priority queuing in a DCB map:
• When allocating bandwidth or configuring strict-priority queuing for dot1p priorities in a priority group
on a DCBx CIN interface, take into account the CIN bandwidth allocation (see Configuring Bandwidth
Allocation for DCBx CIN) and dot1p-queue mapping.
• Although ETS bandwidth allocation or strict-priority queuing does not support weighted random early
detection (WRED), explicit congestion notification (ECN), rate shaping, and rate limiting because these
parameters are not negotiated by DCBx with peer devices, you can apply a QoS output policy with
WRED and/or rate shaping on a DCBx CIN-enabled interface. In this case, the WRED or rate shaping
configuration in the QoS output policy must take into account the bandwidth allocation or queue
scheduler configured in the DCB map.
Priority-Group Configuration Notes
When you configure priority groups in a DCB map:
• A priority group consists of 802.1p priority values that are grouped together for similar bandwidth
allocation and scheduling, and that share the same latency and loss requirements. All 802.1p priorities
mapped to the same queue must be in the same priority group.
• In a DCB map, each 802.1p priority must map to a priority group.
• The maximum number of priority groups supported in a DCB map on an interface is equal to the
number of data queues (4) on the port. Each priority group can support more than one data queue.
• You can enable PFC on a maximum of two priority queues on an interface.
• If you configure more than one priority group as strict priority, the higher numbered priority queue is
given preference when scheduling data traffic.
Configuring Priority-Based Flow Control
Priority-Based Flow Control (PFC) provides a flow control mechanism based on the 802.1p priorities in
converged Ethernet traffic received on an interface and is enabled by default when you enable DCB.
As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for
specified priorities (Class of Service (CoS) values) without impacting other priority classes. Different traffic
types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of
the traffic that is to be stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level
exchange of PFC parameters between peer devices. PFC allows network administrators to create zero-
Data Center Bridging (DCB)
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