Configuring CoS Fixed Classifier Rewrite Values for Native FC Interfaces (NP_Ports)
Fibre Channel over Ethernet (FCoE) traffic typically uses IEEE 802.1p priority 3 (code point 011). When Fibre Channel (FC) traffic arrives on a native FC interface (NP_Port) on an FCoE-FC gateway, the interface encapsulates the FC traffic in Ethernet to create FCoE frames. By default, the native FC interface assigns priority 3 to the FCoE traffic. The traffic is then forwarded internally to the gateway Ethernet interfaces, and then forwarded to the FCoE network.
If your FCoE network uses priority 3 for FCoE traffic, you do not need to use a rewrite value to remap the FCoE priority on native FC interfaces, because the default configuration maps priority 3 to the FCoE forwarding class.
However, if the FCoE network uses a different priority than priority 3 for FCoE traffic, then you can configure a rewrite value to remap incoming traffic from the FC SAN to that priority after the interface encapsulates the FC packets in Ethernet. Setting a rewrite value for the IEEE 802.1p code point (priority) configures the gateway native FC interface to assign the rewrite value to the encapsulated FCoE frames before forwarding the FCoE frames to the gateway Ethernet interface. Instead of a priority of 3, the FCoE frames use the priority specified in the rewrite value.
Traffic coming from the FC SAN is classified into a lossless forwarding class, and that lossless forwarding class is mapped to the rewrite value (the priority used for FCoE traffic on the converged Ethernet network). You specify the lossless forwarding class used for FCoE traffic on a native FC interface by configuring a fixed classifier and applying it to the native FC interface. (The same forwarding class must also be mapped to the rewrite value priority in the ingress classifier applied to the FCoE Ethernet interfaces.) All traffic received from the FC SAN on that FC interface is encapsulated in Ethernet, classified into the forwarding class specified in the fixed classifier, and assigned the rewrite value priority.
Configuring a rewrite value consists of:
Configuring a fixed classifier on the native FC interface. The fixed classifier assigns all the traffic that arrives at the interface from the connected peer in the FC SAN to one fixed forwarding class. The forwarding class must be a lossless forwarding class and must be classified to the rewrite value priority in the ingress classifier configuration on the FCoE Ethernet interfaces.
Specifying an IEEE 802.1p rewrite value for the native FC interface. The traffic mapped to the forwarding class in the fixed classifier is marked with the priority you specify in the rewrite value when the traffic is encapsulated in Ethernet. The rewrite value must be the IEEE 802.1p priority used for FCoE traffic in your converged Ethernet network.
You can configure one rewrite value for each local FCoE-FC gateway fabric. All of the native FC interfaces in a particular fabric must use the same rewrite value. Native FC interfaces that belong to different FCoE-FC gateway fabrics can use different rewrite values.
In the example, all traffic from the FC SAN that arrives at FCoE-FC gateway interface fc-0/0/2 is encapsulated in Ethernet, classified into the lossless fcoe1 forwarding class, and tagged with the IEEE 802.1p priority 5 (code point 101). In this example, we assume that the converged Ethernet network uses priority 5 for FCoE traffic, and that the fcoe1 forwarding class is mapped to priority 5 in the ingress classifier configuration on the Ethernet interfaces. To achieve lossless transport, you must also enable PFC on priority 5 on the Ethernet interfaces that connect the FCoE traffic to the Ethernet network.