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Benefits of Configuring IEEE 802.1p Priority Remapping on an FCoE-FC Gateway

 

A priority is a 3-bit IEEE 802.1p value (code point) in the priority code point (PCP) field of the Ethernet header. The IEEE 802.1p priority identifies traffic so that you can classify (map) the traffic into forwarding classes and apply class of service (CoS) to the forwarding classes, based on the priority value.

When a QFX Series switch acts as a Fibre Channel over Ethernet (FCoE) to Fibre Channel (FC) gateway (an FCoE-FC gateway), it connects an Ethernet network that carries FCoE traffic to an FC storage area network (SAN). The FCoE-FC gateway connects directly to the FC switch in the SAN. The industry-standard default priority assigned to FCoE traffic is priority 3 (IEEE 802.1p code point 011).

The default configuration of Juniper Networks® QFX Series switches classifies priority 3 to FCoE traffic. To support the default FCoE traffic configuration, by default the native FC interfaces on the QFX Series switch encapsulate FC traffic coming from the SAN in Ethernet with the IEEE 802.1p priority value 3 (011). So if your network uses priority 3 for FCoE traffic, you only need to configure priority-based flow control (PFC) to achieve lossless handling of FCoE traffic.

However, if your FCoE network uses a different priority than priority 3 to identify FCoE traffic, priority remapping enables you to classify FCoE traffic based on the IEEE 802.1p priority your network uses.

Priority remapping gives you the flexibility to use any IEEE 802.1p priority to identify FCoE traffic on your converged SAN and Ethernet network, so you can configure your converged network the way you want. In addition, if your network uses a priority other than priority 3 for FCoE traffic, you do not have to reconfigure your existing FCoE network to use the standard default priority for FCoE traffic, saving you time and money.

Priority remapping also means that you can use different priorities to identify FCoE traffic between the Ethernet (FCoE) network and different SAN networks. For example, you could map traffic between the Ethernet network and SAN A to a lossless forwarding class classified to priority 5 (101), and map traffic between the same Ethernet network and SAN B to a lossless forwarding class classified to priority 6 (110).

Each local FC fabric on an FCoE-FC gateway can connect to a different SAN, and the traffic destined for each SAN can be identified by its own priority. Using different priorities for FCoE flows to different SANs can help with accounting, and can reduce congestion if there are multiple FCoE flows destined for multiple SANs that come in to the same ingress interfaces.