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Configuring Priority-Based Flow Control for an EX Series Switch (CLI Procedure)

You can configure priority-based flow control (PFC) on EX4500 switches to apply link-level flow control on a specific traffic class so that different types of traffic can efficiently use the same network interface card (NIC). You must configure PFC for all interfaces carrying Fibre Channel over Ethernet (FCoE) traffic. You can also configure PFC on interfaces carrying other traffic types, such as Internet small computer system interface (iSCSI) traffic. Using PFC is optional for traffic types other than FCoE.

Note: PFC is supported only on 10-Gigabit Ethernet interfaces. If you are using PFC for a non-FCoE DCBX application, use the same 802.1p code points for the PFC congestion notification profile and for the application map that is carrying that application traffic.

Data Center Bridging Capability Exchange protocol (DCBX) is enabled by default on all 10-Gigabit Ethernet interfaces on EX4500 switches. DCBX enables or disables PFC on the local interface depending on whether the PFC configuration on that interface is the same as the PFC configuration of the connected interface on the data center bridging (DCB) peer.

Note: When you configure PFC, we recommend that you: Configure at least 20 percent of the buffer for the queue that is using PFC. Configure an appropriate percent of the buffer for any other forwarding classes (default forwarding classes and the user-defined forwarding classes) that you are using. Do not specify the exact option when configuring the buffer for the queue that is using PFC. Configure the loss-priority statement to low for a traffic class that is using PFC. Verify that the PFC configurations of the local interfaces are the same as the PFC configurations of the connected interfaces on the DCB peer. See show dcbx neighbors.

EX Series switches support up to six congestion notification profiles for PFC.

1. Configure a congestion notification profile, specifying the name of the profile and specifying the three-bit pattern of the User Priority bits in an incoming frame that will trigger the priority-based flow control on that traffic class:
   [edit class-of-service]
user@switch# set congestion-notification-profile profile-name input ieee-802.1 code-point up-bits pfc
2. Disable standard Ethernet flow control on the interfaces that will be used for the traffic class that you have selected for PFC:
   [edit interfaces]
user@switch# set interface-name ether-options no-flow-control

   Note: You cannot apply PFC to interfaces that are using standard Ethernet flow control. You must first disable flow control on those interfaces.

3. Bind the congestion notification profile to the interfaces that will be used for the traffic class that you have selected for PFC:
   [edit class-of-service]
user@switch# set interfaces interface-name congestion-notification-profile profile-name
4. Create a CoS classifier for a traffic class that will use PFC:
   [edit class-of-service]
user@switch# set classifiers ieee-802.1 classifier-name import default
5. Configure this traffic class (classifier-name) to use a user-defined or default forwarding class with a low loss priority value and specify the 802.1p code points::
   [edit class-of-service]
user@switch# set classifiers ieee-802.1 classifier-name forwarding-class class-name loss-priority low code-points 3 bit-patterns
6. Bind the classifier-name classifier to all interfaces that require PFC:
   [edit class-of-service]
user@switch# set interfaces interface-name unit logical-unit-number classifiers ieee-802.1 classifier-name
7. Assign the specified forwarding-class to an egress queue:
   [edit class-of-service]
user@switch# set forwarding-classes class-name queue-number
8. Set a scheduler for this queue, allocating at least 20 percent of the buffer to be used for FCoE traffic:
   [edit class-of-service]
user@switch# set schedulers scheduler-name buffer-size percent
9. Set a scheduler to allocate buffer space for forwarding classes carrying other traffic:

   Note: You must explicitly allocate some buffer space for the other forwarding classes. The default allocation of buffer space for forwarding classes is overridden when you manually configure the requisite amount of buffer space for the FCoE traffic.

   [edit class-of-service]
user@switch# set scheduler-name buffer-size percent
10. Configure a scheduler map that associates the specified scheduler with the specified forwarding class:
    [edit class-of-service]
user@switch# set scheduler-maps map-name forwarding-class class-name scheduler scheduler-name

    For example:

    [edit class-of-service]
user@switch# set scheduler-maps pfc-map forwarding-class af2 scheduler pfc-sched user@switch# set scheduler-maps pfc-map forwarding-class best-effort scheduler default-sched user@switch# set scheduler-maps pfc-map forwarding-class network-control scheduler default-sched
user@switch# set scheduler-maps pfc-map forwarding-class expedited-forwarding scheduler default-sched
11. Assign the scheduler map to the egress interface:
    [edit class-of-service]
user@switch# set interfaces interface-name scheduler-map pfc-map