Users Guide

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.
Therefore, in this example, scheduling traffic to priority group 1 (mapped to one strict-priority queue)
takes precedence over scheduling traffic to priority group 3 (mapped to two strict-priority queues).
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.
DCBx Operation
DCBx performs the following operations:
• Discovers DCB configuration (such as PFC and ETS) in a peer device.
• Detects DCB mis-configuration in a peer device; that is, when DCB features are not compatibly
configured on a peer device and the local switch. Mis-configuration detection is feature-specific
because some DCB features support asymmetric configuration.
• Reconfigures a peer device with the DCB configuration from its configuration source if the peer
device is willing to accept configuration.
• Accepts the DCB configuration from a peer if a DCBx port is in “willing” mode to accept a peer’s DCB
settings and then internally propagates the received DCB configuration to its peer ports.
DCBx Port Roles
The following DCBx port roles are auto-configured on an Aggregator to propagate DCB configurations
learned from peer DCBx devices internally to other switch ports:
Auto-upstream The port advertises its own configuration to DCBx peers and receives its
configuration from DCBx peers (ToR or FCF device). The port also propagates its
configuration to other ports on the switch.
The first auto-upstream that is capable of receiving a peer configuration is elected
as the configuration source. The elected configuration source then internally
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Data Center Bridging (DCB)