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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
priority command or which is already configured for
lossless queues (pfc no-drop queues command).
dcb-map name
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
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Data Center Bridging (DCB)