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rewrite-value (Fibre Channel Interfaces)

 

Syntax

Hierarchy Level

Description

Configure the IEEE 802.1p code point value (priority) for all traffic received from the Fibre Channel (FC) network on the specified FC interface. Instead of using the default priority 3 (011) for FCoE traffic, the priority is rewritten to the specified priority before being forwarded. This works in conjunction with configuring a fixed classifier on the FC interface. The fixed classifier maps all traffic from the FC network into one lossless forwarding class (the lossless forwarding class must be mapped to the code point specified in the rewrite value). Traffic mapped to the lossless forwarding class uses the IEEE 802.1p priority specified by the code point bits in the rewrite value.

FCoE traffic typically uses priority 3 (IEEE code point 011). The QFX Series default configuration uses IEEE 802.1p priority 3 for FCoE traffic. Rewriting the code point value enables you to change the IEEE 802.1p priority of the FCoE traffic if the Ethernet network uses a different priority than priority 3 (code point 011) for FCoE traffic.

The system supports only one IEEE 802.1p code point value per FC interface, so you cannot configure more than one IEEE 802.1p rewrite value per FC interface. In addition, you can specify only one rewrite value per local FCoE-FC gateway fabric; all interfaces in the local fabric must use the same rewrite value. Attempting to configure FC interfaces in the same local fabric with different rewrite values generates a commit error. You can specify different rewrite values for interfaces that belong to different local FCoE-FC gateway fabrics.

Note

In order to avoid fate sharing (separate flows that affect each others’ throughput), the code point used for the rewrite value should be the only code point used for the lossless FCoE forwarding class (the forwarding class used for the fixed classifier on the Fibre Channel interface). When you configure classifiers for ingress Ethernet interfaces, map only the rewrite value code point to the forwarding class.

For example, if the rewrite value uses code point 101 for lossless FCoE forwarding class fcoe_fc1, then in the classifier configuration attached to ingress Ethernet interfaces, code point 101 is the only code point that should be classified to the fcoe_fc1 forwarding class. Now if you also attach a classifier to an interface that maps code point 110 to forwarding class fcoe_fc1, then congestion on priority 110 unfairly (and unintentionally) affects the FCoE traffic that uses priority 101. Both priorities 101 and 110 are classified into forwarding class fcoe_fc1, so the traffic from both priorities shares the same fate.

The remaining statements are described separately.

Required Privilege Level

interfaces—To view this statement in the configuration.

interface-control—To add this statement to the configuration.