Administrator Guide

ETS Operation with DCBx
The following section describes DCBx negotiation with peer ETS devices.
In DCBx negotiation with peer ETS devices, ETS configuration is handled as follows:
• ETS TLVs are supported in DCBx versions CIN, CEE, and IEEE2.5.
• The DCBx port-role configurations determine the ETS operational parameters (refer to Configure a DCBx Operation).
• ETS configurations received from TLVs from a peer are validated.
• If there is a hardware limitation or TLV error:
• DCBx operation on an ETS port goes down.
• New ETS configurations are ignored and existing ETS configurations are reset to the default ETS settings.
• ETS operates with legacy DCBx versions as follows:
• In the CEE version, the priority group/traffic class group (TCG) ID 15 represents a non-ETS priority group. Any priority group
configured with a scheduler type is treated as a strict-priority group and is given the priority-group (TCG) ID 15.
Configuring ETS in a DCB Map
A switch supports the use of a DCB map in which you configure enhanced transmission selection (ETS) setting. To configure ETS
parameters, you must apply a DCB map 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 traffics
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. Dell EMC Networking OS 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.
• Dell EMC Networking OS supports hierarchical scheduling on an interface. The control traffic on Dell EMC Networking OS 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.
• 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.
Data Center Bridging (DCB)
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