Administrator Guide

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
mtu 12000
portmode hybrid
switchport
auto vlan
!
protocol lldp
advertise management-tlv management-address system-name
dcbx port-role auto-downstream
no shutdown
Dell#
When no DCBx TLVs are received on a DCB-enabled interface for 180 seconds, DCB is automatically disabled
and flow control is re-enabled.
Lossless Traffic Handling In auto-DCB-enable mode, Aggregator ports operate with the auto-detection of
DCBx traffic. At any moment, some ports may operate with link-level flow control while others operate with
DCB-based PFC enabled.
Data Center Bridging (DCB) 283