Brocade Communications Systems IP250 user manual Enhanced Ethernet features, Dcbx protocol

16 Enhanced Ethernet features

DCBX protocol

Data Center Bridging Exchange (DCBX) protocol allows enhanced Ethernet devices to convey and configure their DCB capabilities and ensures a consistent configuration across the network. DCBX protocol is used between DCB devices, such as a converged network adapter (CNA) and an FCoE switch, to exchange configuration with directly connected peers.

NOTE

When DCBX protocol is used, any other Link Layer Discovery Protocol (LLDP) implementation must be disabled on the host systems.

Enhanced Ethernet features

Data Center Bridging (DCB) is a set of IEEE 802 standard Ethernet enhancements that enable Fibre Channel convergence with Ethernet. The two basic requirements in a lossless Ethernet environment are Enhanced Transmission Selection (ETS) and priority-based flow control. These capabilities allow the Fibre Channel frames to run directly over 10 Gbps Ethernet segments without adversely affecting performance.

Enhanced Transmission Selection

Enhanced Transmission Selection (ETS) allows lower priority traffic classes to use available bandwidth that is not being used by higher priority traffic classes and maximizes the use of available bandwidth.

ETS allows configuration of bandwidth per priority group. Priority group ID (PG ID) usage is defined as follows:

•PG ID 0, 7 are used when the priority group is limited for its bandwidth use.

•PG ID 8, 14 are reserved.

•PG ID 15.0 through 15.7 are used for priorities that are not limited for their bandwidth use.

The configured priority group percentage refers to the maximum percentage of available link bandwidth after PG ID 15.0 to 15.7 is serviced, assuming all priority groups are fully subscribed. If one of the priority groups does not consume its allocated bandwidth, then any unused portion is available for use by other priority groups.

Priority-based flow control

Priority-based flow control (PFC) allows the network to selectively pause different classes of traffic and create lossless lanes for Fibre Channel, while retaining packet drop congestion management for IP traffic. A high-level pause example follows:

•During periods of heavy congestion, the receive buffers reach high threshold and generate a pause.

•The pause tells transmission (Tx) queues to stop transmitting.

•After the receive (Rx) buffers reach low threshold, a zero pause is generated.

•The zero pause signals the Tx queues to resume transmitting.

482	Brocade Network Advisor IP User Manual
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