Reference Guide

Enabling Data Center Bridging
DCB is automatically configured when you configure FCoE or iSCSI optimization.
Data center bridging supports converged enhanced Ethernet (CEE) in a data center network. DCB is disabled by default. It must
be enabled to support CEE.
● Priority-based flow control
● Enhanced transmission selection
● Data center bridging exchange protocol
● FCoE initialization protocol (FIP) snooping
DCB processes virtual local area network (VLAN)-tagged packets and dot1p priority values. Untagged packets are treated with a
dot1p priority of 0.
For DCB to operate effectively, you can classify ingress traffic according to its dot1p priority so that it maps to different data
queues. The dot1p-queue assignments used are shown in the following table.
To enable DCB, enable either the iSCSI optimization configuration or the FCoE configuration.
NOTE: Dell Networking OS Behavior: DCB is not supported if you enable link-level flow control on one or more
interfaces. For more information, refer to Ethernet Pause Frames.
QoS dot1p Traffic Classification and Queue
Assignment
The following section describes QoS dot1P traffic classification and assignments.
DCB supports PFC, ETS, and DCBx to handle converged Ethernet traffic that is assigned to an egress queue according to the
following QoS methods:
Honor dot1p
You can honor dot1p priorities in ingress traffic at the port or global switch level (refer to Default dot1p to
Queue Mapping) using the service-class dynamic dot1p command in INTERFACE configuration
mode.
Layer 2 class
maps
You can use dot1p priorities to classify traffic in a class map and apply a service policy to an ingress port
to map traffic to egress queues.
NOTE: Dell Networking does not recommend mapping all ingress traffic to a single queue when using PFC and ETS.
However, Dell Networking does recommend using Ingress traffic classification using the service-class dynamic
dot1p command (honor dot1p) on all DCB-enabled interfaces. If you use L2 class maps to map dot1p priority traffic to
egress queues, take into account the default dot1p-queue assignments in the following table and the maximum number of
two lossless queues supported on a port (refer to Configuring Lossless Queues).
Although Dell Networking OS allows you to change the default dot1p priority-queue assignments (refer to Setting dot1p
Priorities for Incoming Traffic), DCB policies applied to an interface may become invalid if you reconfigure dot1p-queue
mapping. If the configured DCB policy remains valid, the change in the dot1p-queue assignment is allowed.
dot1p Value in
the Incoming
Frame
Egress Queue Assignment
0 2
1 0
2 1
3 3
4 4
5 5
6 6
Data Center Bridging (DCB) 205