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Enabling Data Center Bridging
Data center bridging is enabled by default on an FN IOM to support converged enhanced Ethernet (CEE) in a data center
network.
A prerequisite for configuring DCB:
● 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.
On the FN IOM Switch, by default, DCB is enabled and MMU buffers are reserved to achieve no-drop traffic handling for PFC.
Disabling DCB does not release the buffers reserved by default. To utilize reserved buffers for non-DCB applications, you have
to explicitly release the buffers (Refer to Configuring the PFC Buffer in a Switch Stack).
To disable or re-enable DCB on a switch, enter the following commands.
1. Disable DCB.
CONFIGURATION mode
no dcb enable
2. Re-enable DCB.
CONFIGURATION mode
dcb enable
NOTE:
Dell Networking OS Behavior: DCB is not supported if you enable link-level flow control on one or more
interfaces.
After you disable DCB, if link-level flow control is not automatically enabled on an interface, to enable flow control, manually shut
down the interface (the shutdown command) and re-enable it (the no shutdown command).
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 (refer to Honoring dot1p Values on Ingress Packets).
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 (refer to Policy-Based QoS Configurations).
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 the system 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. For DCB ETS enabled interfaces,
traffic destined to queue that is not mapped to any dot1p priority are dropped.
932 FC Flex IO Modules