Deployment Guide

When configuring lossless queues on a port interface, consider the following points:
● By default, no lossless queues are configured on a port.
● A limit of two lossless queues is supported on a port. If the number of lossless queues configured exceeds the maximum
supported limit per port (two), an error message is displayed. Reconfigure the value to a smaller number of queues.
● If you configure lossless queues on an interface that already has a DCB map with PFC enabled (pfc on), an error message is
displayed.
Table 18. Configuring Lossless Queues on a Port Interface
Step Task Command Command Mode
1 Enter INTERFACE Configuration mode.
interface interface-type
CONFIGURATION
2
Open a DCB map and enter DCB map configuration
mode.
dcb-map name
INTERFACE
3
Disable PFC.
no pfc mode on
DCB MAP
4
Return to interface configuration mode.
exit
DCB MAP
5
Apply the DCB map, created to disable the PFC
operation, on the interface
dcb-map {name | default}
INTERFACE
6
Configure the port queues that still function as no-
drop queues for lossless traffic. For the dot1p-queue
assignments.
The maximum number of lossless queues globally
supported on a port is 2.
You cannot configure PFC no-drop queues on an
interface on which a DCB map with PFC enabled has
been applied, or which is already configured for PFC
using the pfc priority command.
Range: 0-3. Separate queue values with a comma;
specify a priority range with a dash; for example: pfc
no-drop queues 1,3 or pfc no-drop queues 2-3 Default:
No lossless queues are configured.
pfc no-drop
queuesqueue-range
INTERFACE
Priority-Based Flow Control Using Dynamic Buffer
Method
In a data center network, priority-based flow control (PFC) manages large bursts of one traffic type in multiprotocol links so
that it does not affect other traffic types and no frames are lost due to congestion. When PFC detects congestion on a queue
for a specified priority, it sends a pause frame for the 802.1p priority traffic to the transmitting device.
Pause and Resume of Traffic
The pause message is used by the sending device to inform the receiving device about a congested, heavily-loaded traffic state
that has been identified. When the interface of a sending device transmits a pause frame, the recipient acknowledges this frame
by temporarily halting the transmission of data packets. The sending device requests the recipient to restart the transmission of
data traffic when the congestion eases and reduces. The time period that is specified in the pause frame defines the duration
for which the flow of data packets is halted. When the time period elapses, the transmission restarts.
When a device sends a pause frame to another device, the time for which the sending of packets from the other device must be
stopped is contained in the pause frame. The device that sent the pause frame empties the buffer to be less than the threshold
value and restarts the acceptance of data packets.
244
Data Center Bridging (DCB)