Connectivity Guide

● For PFC to be applied, the configured priority traffic must be supported by a PFC peer (as detected by DCBx).
● If you apply a DCB map with PFC disabled (pfc off), you can enable link-level flow control on the interface using
the flowcontrol rx on tx on command. To delete the DCB map, first disable link-level flow control. PFC is then
automatically enabled on the interface because an interface is PFC-enabled by default.
● To ensure no-drop handling of lossless traffic, PFC allows you to configure lossless queues on a port (see Configuring
Lossless Queues).
● When you configure a DCB map, an error message is displayed if the PFC dot1p priorities result in more than two lossless
queues.
● When you apply a DCB map, an error message is displayed if link-level flow control is already enabled on an interface. You
cannot enable PFC and link-level flow control at the same time on an interface.
● In a switch stack, configure all stacked ports with the same PFC configuration.
● Dell EMC Networking OS allows you to change the default dot1p priority-queue assignments only if the change satisfies the
following requirements in DCB maps already applied to the interfaces:
● All 802.1p priorities mapped to the same queue must be in the same priority group.
● A maximum of two PFC-enabled, lossless queues are supported on an interface.
Otherwise, the reconfiguration of a default dot1p-queue assignment is rejected.
● To ensure complete no-drop service, apply the same PFC parameters on all PFC-enabled peers.
PFC Prerequisites and Restrictions
On a switch, PFC is globally enabled by default, but not applied on specific 802.1p priorities. To enable PFC on 802.1p priorities,
create a DCB map.
The following prerequisites and restrictions apply when you configure PFC in a DCB map:
● You can enable PFC on a maximum of four priority queues on an interface. The default is two. Enabling PFC for dot1p
priorities configures the corresponding port queue as lossless.
● You cannot enable PFC and link-level flow control at the same time on an interface.
Applying a DCB Map on a Port
When you apply a DCB map with PFC enabled on a switch interface, a memory buffer for PFC-enabled priority traffic is
automatically allocated. The buffer size is allocated according to the number of PFC-enabled priorities in the assigned map.
To apply a DCB map to an Ethernet port, follow these steps:
Table 17. DCB Map to an Ethernet Port
Step Task Command Command Mode
1
Enter interface configuration mode on an Ethernet port.
interface interface-
type }
CONFIGURATION
2
Apply the DCB map on the Ethernet port to configure it
with the PFC and ETS settings in the map; for example:
DellEMC# interface tengigabitEthernet
1/1
DellEMC(config-if-te-1/1)# dcb-map
SAN_A_dcb_map1 Repeat Steps 1 and 2 to apply a DCB
map to more than one port.
You cannot apply a DCB map on an interface that
has been already configured for PFC using the pfc
dcb-map name
INTERFACE
254 Data Center Bridging (DCB)