308 | Data Center Bridging (DCB)
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Table 13-1. dot1p Priority-Queue Assignment
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 DCB is enabled. 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:
dot1p Value in Incoming Frame Egress Queue Assignment
00
10
20
31
42
53
63
73
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.
Range (in quanta): 712-65535.
Default: 45556 quantum in link delay.
pfc link-delay value
DCB INPUT POLICY
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