Users Guide

Table 17. DCB Map to an Ethernet Port (continued)
Step Task Command Command Mode
You cannot apply a DCB map on an interface that has
been already configured for PFC using the pfc
priority command or which is already configured for
lossless queues (pfc no-drop queues command).
Configuring PFC without a DCB Map
In a network topology that uses the default ETS bandwidth allocation (assigns equal bandwidth to each priority), you can also
enable PFC for specific dot1p-priorities on individual interfaces without using a DCB map. This type of DCB configuration is
useful on interfaces that require PFC for lossless traffic, but do not transmit converged Ethernet traffic.
Table 18. Configuring PFC without a DCB Map
Step Task Command Command Mode
1 Enter interface configuration mode on an Ethernet
port.
interface interface-
type}
CONFIGURATION
2 Enable PFC on specified priorities. Range: 0-7. Default:
None.
Maximum number of lossless queues supported on an
Ethernet port: 2.
Separate priority values with a comma. Specify a
priority range with a dash, for example: pfc priority
3,5-7
1. You cannot configure PFC using the pfc
priority command on an interface on which a
DCB map has been applied or which is already
configured for lossless queues (pfc no-drop
queues command).
pfc priority priority-
range
INTERFACE
Configuring Lossless Queues
DCB also supports the manual configuration of lossless queues on an interface when PFC mode is disabled in a DCB map, apply
the map on the interface. The configuration of no-drop queues provides flexibility for ports on which PFC is not needed, but
lossless traffic should egress from the interface.
Configuring no-drop queues is applicable only on the interfaces which do not need PFC.
Example:
Port A —> Port B
Port C —> Port B
PFC no-drop queues are configured for queues 1, 2 on Port B. PFC capability is enabled on priorities 3, 4 on PORT A and C.
Port B acting as Egress
During the congestion, [traffic pump on priorities 3 and 4 from PORT A and PORT C is at full line rate], PORT A and C send out
the PFCs to rate the traffic limit. Egress drops are not observed on Port B since traffic flow on priorities is mapped to loss less
queues.
Port B acting as Ingress
If the traffic congestion is on PORT B , Egress DROP is on PORT A or C, as the PFC is not enabled on PORT B.
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Data Center Bridging (DCB)