Reference Guide

120 | Data Center Bridging (DCB)
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Configuring Priority-Based Flow Control
Priority-based flow control provides a flow control mechanism based on the 802.1p priorities in converged
Ethernet traffic received on an interface and is enabled by default. As an enhancement to the existing
Ethernet pause mechanism, PFC stops traffic transmission for specified priorities (CoS values) without
impacting other priority classes. Different traffic types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of
the traffic that needs to be stopped. DCBX provides the link-level exchange of PFC parameters between
peer devices. PFC allows network administrators to create zero-loss links for SAN traffic that requires
no-drop service, while at the same time retaining packet-drop congestion management for LAN traffic.
To ensure complete no-drop service, you must apply the same DCB input policy with the same pause time
and dot1p priorities on all PFC-enabled peer interfaces.
To configure PFC and apply a PFC input policy to an interface, follow these steps:
Step Task Command Command Mode
1 Create a DCB input policy to apply pause or flow
control for specified priorities using a configured delay
time.
Maximum: 32 alphanumeric characters.
dcb-input policy-name
CONFIGURATION
2 Configure the link delay used to pause specified priority
traffic.One quantum is equal to a 512-bit transmission.
Valid values (in quanta): 712-65535.
Default: 45556 quantum in link delay.
pfc link-delay value
DCB INPUT POLICY
3 Configure the CoS traffic to be stopped for the specified
delay. Enter the 802.1p values of the frames to be
paused.
Valid values: 0-7.
Default: None.
Maximum number of loss less queues supported on the
switch: 2.
Separate priority values with a comma; specify a
priority range with a dash; for example: pfc priority
1,3,5-7.
pfc priority priority-range
DCB INPUT POLICY
4 Enable the PFC configuration on the port so that the
priorities are included in DCBX negotiation with peer
PFC devices. Default: PFC mode is on.
pfc mode on
DCB INPUT POLICY
5 (Optional) Enter a text description of the input policy.
Maximum: 32 characters.
description text
DCB INPUT POLICY
6 Exit DCB input policy configuration mode.
exit
DCB INPUT POLICY
7 Enter interface configuration mode.
interface type slot/port
CONFIGURATION
8 Apply the input policy with the PFC configuration to an
ingress interface.
dcb-policy input
policy-name
INTERFACE
9 Repeat Steps 1 to 8 on all PFC-enabled peer interfaces to ensure lossless traffic service.