Reference Guide

50 | Data Center Bridging (DCB)
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• PFC uses the DCB MIB IEEE802.1azd2.5 and the PFC MIB IEEE802.1bb-d2.2.
If DCBx negotiation is not successful (for example, due to a version or TLV mismatch), DCBx is disabled
and you cannot enable PFC or ETS.
Configuring Priority-Based Flow Control
Priority-based flow control (PFC) provides a flow control mechanism based on the 802.1p priorities in
converged Ethernet traffic received on an interface and is enabled by default when you enable DCB.
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 is 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 retaining packet-drop congestion management for LAN traffic.
To ensure complete no-drop service, 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
Syntax Command Mode
1 Create a DCB input policy to apply pause or flow
control for specified priorities using a configured delay
time.
The maximum is 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.
The range (in quanta) is from 712 to 65535.
The default is 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.
The range is from 0 to 7.
The default is 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