Setup Guide

• The configuration of bandwidth allocation and strict-queue scheduling is not supported at the same time for a priority group.
• Bandwidth assignment: By default, equal bandwidth is assigned to each dot1p priority in a priority group. To configure the bandwidth
assigned to the port queues associated with dot1p priorities in a priority group, use the bandwidth percentage parameter. The sum of
the bandwidth allocated to all priority groups in a DCB map must be 100% of the bandwidth on the link. You must allocate at least 1%
of the total bandwidth to each priority group.
• Scheduling of priority traffic: dot1p priority traffic on the switch is scheduled to the current queue mapping. dot1p priorities within
the same queue must have the same traffic properties and scheduling method.
• ETS configuration error: If an error occurs in an ETS configuration, the configuration is ignored and the scheduler and bandwidth
allocation settings are reset to the ETS default value: 100% of available 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 a 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:
• Because all the priorities mapped to a priority group is scheduled using a single queue, the priorities are treated with first come first
served basis.
• 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. 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.
Hierarchical Scheduling in ETS Output Policies
ETS supports up to three levels of hierarchical scheduling.
For example, you can apply ETS output policies with the following configurations:
Priority group 1
Assigns traffic to one priority queue with 20% of the link bandwidth and strict-priority scheduling.
Priority group 2 Assigns traffic to one priority queue with 30% of the link bandwidth.
Priority group 3 Assigns traffic to two priority queues with 50% of the link bandwidth and strict-priority scheduling.
In this example, the configured ETS bandwidth allocation and scheduler behavior is as follows:
Unused bandwidth
usage:
Normally, if there is no traffic or unused bandwidth for a priority group, the bandwidth allocated to the group is
distributed to the other priority groups according to the bandwidth percentage allocated to 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.
Data Center Bridging (DCB) 253