Dce Bridging Capability Exchange Protocol; Dcbx Feature Negotiation - Cisco AJ732A - MDS 9134 Fabric Switch Configuration Manual
Cisco nexus 5000 series switch cli software configuration guide, nx-os 4.0(1a)n1 (ol-16597-01, january 2009)
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Chapter 29
Configuring FCoE
S e n d f e e d b a c k t o n x 5 0 0 0 - d o c f e e d b a c k @ c i s c o . c o m
Logical Link Up/Down
On a native Fibre Channel link, some configuration actions (such as changing the VSAN) require you to
reset the interface status. The switch achieves the reset by disabling the interface, and then immediately
reenabling the interface.
If an Ethernet link is providing FCoE service, the physical link should not be reset because this action
is disruptive to all traffic on the link.
The logical link up/down feature provides the ability to reset an individual virtual link. The switch sends
a DCBX message to request the adapter to reset only the virtual Fibre Channel interface.
If the adapter does not support the logical link level up/down feature, the adapter resets the physical link.
Note
In this case, all traffic on the Ethernet interface is disrupted.
DCE Bridging Capability Exchange Protocol
DCBX protocol is an extension of the Link Layer Discovery Protocol (LLDP). DCBX end points
exchange request and acknowledgment messages. For flexibility, parameters are coded in a
type-length-value (TLV) format.
DCBX runs on the physical Ethernet link between the Cisco Nexus 5000 Series switch and the converged
network adapter on the server. By default, DCBX is enabled on Ethernet interfaces. When an Ethernet
interface is brought up, the switch automatically starts to communicate with the adapter.
During normal operation of FCoE between the switch and the adapter, the DCBX protocol provides
link-error detection.
DCBX is also used to negotiate capabilities between the switch and the adapter and to send configuration
values to the adapter.
Adapters connected to a Cisco Nexus 5000 Series switch are programmed to accept the configuration
values sent by the switch, allowing the switch to distribute configuration values to all attached adapters.
The capability reduces the possibility of configuration error and simplifies administration of the
adapters.
The switch provides a manual configuration override for each parameter negotiated using DCBX. The
override takes effect if the adapter does not support DCBX, or if the adapter does not support the specific
capability requested by the switch.
DCBX Feature Negotiation
The switch and adapter exchange capability information and configuration values. The Cisco Nexus
5000 Series switches support the following capabilities:
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OL-16597-01
FCoE
If the adapter supports FCoE capability, the switch sends the IEEE 802.1p CoS value to be used with
FCoE packets.
Priority Flow Control (PFC)
If the adapter supports PFC, the switch sends the IEEE 802.1p CoS values to be enabled with PFC.
Ethernet logical link up and down signal
FCoE logical link up and down signal
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
Information About FCoE
29-3
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