Administrator Guide

On the MXL Switch, by default, DCB is enabled and MMU buers are reserved to achieve no-drop trac handling for PFC. Disabling
DCB does not release the buers reserved by default. To utilize reserved buers for non-DCB applications, you have to explicitly
release the buers (Refer to Conguring the PFC Buer 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 ow control on one or more interfaces.
After you disable DCB, if link-level ow control is not automatically enabled on an interface, to enable ow control, manually shut
down the interface (the shutdown command) and re-enable it (the no shutdown command).
QoS dot1p Trac Classication and Queue Assignment
The following section describes QoS dot1P trac classication and assignments.
DCB supports PFC, ETS, and DCBx to handle converged Ethernet trac that is assigned to an egress queue according to the
following QoS methods:
Honor dot1p
You can honor dot1p priorities in ingress trac at the port or global switch level (refer to Default dot1p to
Queue Mapping) using the service-class dynamic dot1p command in INTERFACE conguration
mode (refer to Honoring dot1p Values on Ingress Packets).
Layer 2 class maps You can use dot1p priorities to classify trac in a class map and apply a service policy to an ingress port to
map trac to egress queues (refer to Policy-Based QoS Congurations).
NOTE: Dell Networking does not recommend mapping all ingress trac to a single queue when using PFC and ETS.
However, Dell Networking does recommend using Ingress trac classication using the service-class dynamic
dot1p command (honor dot1p) on all DCB-enabled interfaces. If you use L2 class maps to map dot1p priority trac 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
Conguring Lossless Queues).
Although the system allows you to change the default dot1p priority-queue assignments (refer to Setting dot1p Priorities for
Incoming Trac), DCB policies applied to an interface may become invalid if you recongure dot1p-queue mapping. If the
congured DCB policy remains valid, the change in the dot1p-queue assignment is allowed. For DCB ETS enabled interfaces,
trac destined to queue that is not mapped to any dot1p priority are dropped.
dot1p Value in
the Incoming
Frame
Egress Queue Assignment
0 0
1 0
2 0
3 1
4 2
5 3
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Data Center Bridging (DCB)