844 Configuring Data Center Bridging FeaturesPFC Configuration ExampleThe network in this example handles both data and voice traffic. Because thevoice traffic is time sensitive, it requires a higher priority than standard datatraffic. The voice traffic uses VLAN 100 and has an 802.1p priority of 5, whichis mapped to hardware queue 4. IP phones are connected to ports 3, 5, and 10,so PFC is enabled on these ports with 802.1p priority 5 traffic as no-drop. Theconfiguration also enables VLAN tagging so that the 802.1p priority isidentified. This example assumes the voice VLAN (VLAN 100) has alreadybeen configured. The administrator may need to perform other configurationsteps to ensure suitable network operation, including configuring thebandwidth allocation for the drop and no-drop priorities or to enable ordisable the DCBX protocol.1 Map 802.1p priority 5 to traffic class 4. The following command changesthe priority to traffic class mapping to be one-to-one, based upon thedefault switch settings. For lossless service, a priority must be mapped one-to-one to a traffic class. For more information about traffic classes, see"Configuring Class-of-Service" on page 1153.console#configureconsole(config)#classofservice dot1p-mapping 5 42 Enter Interface Configuration mode for ports 3, 5, and 10, and then enterData Center Bridging mode for these ports.console(config)#interface range te1/0/3, te1/0/5,te1/0/10console(config-if)#datacenter-bridging3 Enable PFC and configure traffic marked with 802.1p priority 5 to bepaused rather than dropped when congestion occurs.console(config-dcb)#priority-flow-control mode onconsole(config-dcb)#priority-flow-controlpriority 5 no-dropconsole(config-dcb)#exitCAUTION: All ports may be briefly shutdown when modifying either flowcontrol (FC) or PFC settings. PFC uses a control packet defined in802.1Qbb and is not compatible with IEEE 802.3 Annex 31B flowcontrol.
