Dell PowerEdge FX2/FX2s - Manual (Page 34)

Data Center Bridging in a Traffic Flow
The following figure shows how DCB handles a traffic flow on an interface.
Figure 3. DCB PFC and ETS Traffic Handling
Data Center Bridging: Auto-DCB-Enable Mode
On an Aggregator in standalone or VLT modes, the default mode of operation for data center bridging on
Ethernet ports is auto-DCB-enable mode. In this mode, Aggregator ports detect whether peer devices
support CEE or not, and enable ETS and PFC or link-level flow control accordingly:
• Interfaces come up with DCB disabled and link-level flow control enabled to control data
transmission between the Aggregator and other network devices (see Flow Control Using Ethernet
Pause Frames). When DCB is disabled on an interface, PFC, and ETS are also disabled.
• When DCBx protocol packets are received, interfaces automatically enable DCB and disable link-level
flow control.
DCB is required for PFC, ETS, DCBx, and FCoE initialization protocol (FIP) snooping to operate.
NOTE: Normally, interfaces do not flap when DCB is automatically enabled.
DCB processes VLAN-tagged packets and dot1p priority values. Untagged packets are treated with a
dot1p priority of 0.
For DCB to operate effectively, ingress traffic is classified according to its dot1p priority so that it maps to
different data queues. The dot1p-queue assignments used on an Aggregator are shown in Table 6-1 in
dcb enable auto-detect on-next-reload Command Example QoS dot1p Traffic Classification and Queue
Assignment.
34 Data Center Bridging (DCB)