Administrator Guide

Table 20. 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.
Dynamic ingress buffering enables the sending of pause frames at different thresholds based on the number of ports that experience
congestion at a time. This behavior impacts the total buffer size used by a particular lossless priority on an interface. The pause and
resume thresholds can also be configured dynamically. You can configure a buffer size, pause threshold, ingress shared threshold weight,
and resume threshold to control and manage the total amount of buffers that are to be used in your network environment.
Buffer Sizes for Lossless or PFC Packets
You can configure up to a maximum of 4 lossless (PFC) queues. By configuring 4 lossless queues, you can configure 4 different priorities
and assign a particular priority to each application that your network is used to process. For example, you can assign a higher priority for
time-sensitive applications and a lower priority for other services, such as file transfers. You can configure the amount of buffer space to
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Data Center Bridging (DCB)