Reference Guide

Data Center Bridging (DCB) | 61
• New ETS configurations are ignored and existing ETS configurations are reset to the previously
configured ETS output policy on the port or to the default ETS settings if no ETS output policy
was previously applied.
• 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.
• The CIN version supports two types of strict-priority scheduling:
— Group strict priority: Allows a single priority flow in a priority group to increase its
bandwidth usage to the bandwidth total of the priority group. A single flow in a group can
use all the bandwidth allocated to the group.
— Link strict priority: Allows a flow in any priority group to increase to the maximum link
bandwidth.
CIN supports only the default dot1p priority-queue assignment in a priority group.
Bandwidth Allocation for DCBx CIN
After an ETS output policy is applied to an interface, if the DCBX version used in your data center
network is CIN, a QoS output policy is automatically configured to overwrite the default CIN bandwidth
allocation. This default setting divides the bandwidth allocated to each port queue equally between the
dot1p priority traffic assigned to the queue.
DCB Policies in a Switch Stack
A DCB input policy with PFC and ETS configuration is applied to all stacked ports in a switch stack or on
a stacked switch.
DCBX Operation
The data center bridging exchange protocol (DCBx) is used by DCB devices 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).
The following versions of DCBx are supported on an Aggregator: CIN, CEE, and IEEE2.5.
DCBx requires the LLDP to be enabled on all DCB devices.