Deployment Guide

Data Center Bridging in a Trac Flow
The following gure shows how DCB handles a trac ow on an interface.
Figure 29. DCB PFC and ETS Trac 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 ow
control accordingly:
• Interfaces come up with DCB disabled and link-level ow 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 ow control.
DCB is required for PFC, ETS, DCBx, and FCoE initialization protocol (FIP) snooping to operate.
NOTE
: Normally, interfaces do not ap 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 eectively, ingress trac is classied according to its dot1p priority so that it maps to dierent 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
Trac Classication and Queue Assignment.
When DCB is Disabled (Default) By default, Aggregator interfaces operate with DCB disabled and link-level ow control enabled. When an
interface comes up, it is automatically congured with:
• Flow control enabled on input interfaces.
• A DCB-MAP policy is applied with PFC disabled.
The following example shows a default interface conguration with DCB disabled and link-level ow control enabled.
Data Center Bridging (DCB)
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