This article provides information on how to configure Priority based Flow Control (PFC), on QFX3500 switches, for FCoE devices.

How to configure Priority based Flow Control (PFC), on QFX3500 switches, for FCoE devices.

Priority-based flow control (PFC, described in IEEE 802.1Qbb) is a link-level flow control mechanism, similar to Ethernet PAUSE (described in IEEE 802.3x). You can apply PFC at ingress interfaces. However, Ethernet PAUSE stops all the traffic on a link for a period of time.

PFC decouples the pause function from the physical link and enables you to divide traffic on one physical link into eight priorities. You can think of the eight priorities as eight 'lanes' of traffic, which correspond to queues (forwarding classes). Each priority is mapped to a 3-bit IEEE 802.1p CoS flag in the VLAN header.

A congestion notification profile enables priority-based flow control (PFC) for ingress traffic with a specified IEEE 802.1p code point (priority). Mapping a congestion notification profile to an interface enables PFC on all incoming traffic with the specified code point. You can configure PFC for a priority end-to-end, along the entire data path, to create a lossless lane of traffic on the network.

Congestion notification profiles will be under the Class of Service (CoS) configuration of the switch.

user@switch# set class-of-service congestion-notification-profile cnp-name input ieee-802.1 code-point bits pfc

user@switch# set class-of-service congestion-notification-profile fcoe-cnp input ieee-802.1 011 pfc

user@switch# set class-of-service interfaces interface congestion-notification-profile cnp-name

user@switch# set class-of-service interfaces xe-0/0/10 congestion-notification-profile fcoe-cnp