Brocade Communications Systems Network Advisor 12.3.0, User Manual

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602 Brocade Network Advisor SAN User Manual
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Enhanced Ethernet features
16
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.