Users Guide

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.

When DCB is Disabled (Default) By default, Aggregator interfaces operate with DCB disabled and link-level flow control enabled. When

an interface comes up, it is automatically configured with:

• Flow control enabled on input interfaces.

• A DCB-MAP policy is applied with PFC disabled.

The following example shows a default interface configuration with DCB disabled and link-level flow control enabled.

show interfaces Command Example: DCB disabled and Flow Control enabled

Dell#show running-config interface te 0/4

interface TenGigabitEthernet 0/4

mtu 12000

portmode hybrid

switchport

auto vlan

flowcontrol rx on tx off

dcb-map DCB_MAP_PFC_OFF

protocol lldp

advertise management-tlv management-address system-name

dcbx port-role auto-downstream

no shutdown

Dell#

When DCB is Enabled When an interface receives a DCBx protocol packet, it automatically enables DCB and disables link-level flow

control. The dcb-map and flow control configurations are removed as shown in the following example.

show interfaces Command Example: DCB enabled and Flow Control disabled

Dell#show running-config interface te 0/3

interface TenGigabitEthernet 0/3