Reference Guide

dot1p Value in the
Incoming Frame
Egress Queue Assignment
4 2
5 3
6 3
7 3
Configuring 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
(Class of Service (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. Data Center Bridging Exchange protocol (DCBx) provides the link-level exchange of PFC parameters
between peer devices. PFC allows network administrators to create zero-loss links for Storage Area Network (SAN)
traffic that requires no-drop service, while retaining packet-drop congestion management for Local Area Network (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.
1. Create a DCB input policy to apply pause or flow control for specified priorities using a configured delay time.
CONFIGURATION mode
dcb-input policy-name
The maximum is 32 alphanumeric characters.
2. Configure the link delay used to pause specified priority traffic.
DCB INPUT POLICY mode
pfc link-delay value
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.
3. Configure the CoS traffic to be stopped for the specified delay.
DCB INPUT POLICY mode
pfc priority priority-range
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.
4. Enable the PFC configuration on the port so that the priorities are included in DCBx negotiation with peer PFC
devices.
DCB INPUT POLICY mode
241