Administrator Guide

• 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.

Conguring Priority-Based Flow Control

PFC provides a ow control mechanism based on the 802.1p priorities in converged Ethernet trac received on an interface and is

enabled by default when you enable DCB.

As an enhancement to the existing Ethernet pause mechanism, PFC stops trac transmission for specied priorities (Class of

Service (CoS) values) without impacting other priority classes. Dierent trac types are assigned to dierent priority classes.

When trac congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the trac 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) trac that requires no-drop

service, while retaining packet-drop congestion management for Local Area Network (LAN) trac.

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 congure PFC and apply a PFC input policy to an interface, follow these steps.

1. Create a DCB input policy to apply pause or ow control for specied priorities using a congured delay time.

CONFIGURATION mode

dcb-input policy-name

The maximum is 32 alphanumeric characters.

2. Congure the link delay used to pause specied priority trac.

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. Congure the CoS trac to be stopped for the specied 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 conguration on the port so that the priorities are included in DCBx negotiation with peer PFC devices.

DCB INPUT POLICY mode

pfc mode on

The default is PFC mode is on.

Data Center Bridging (DCB)