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Understanding Using an FCoE Transit Switch

You can use an EX4500 switch as a Fibre Channel over Ethernet (FCoE) transit switch. An FCoE transit switch is a Layer 2 data center bridging (DCB) switch that can transport FCoE frames and implement FCoE Initialization Protocol (FIP) snooping. The switch can transport both FCoE and Ethernet LAN traffic over the same network infrastructure while preserving the class of service (CoS) that Fibre Channel (FC) traffic requires.

An FCoE transit switch does not encapsulate or decapsulate FC frames in Ethernet. It is an access switch that transports FC frames that have already been encapsulated in Ethernet between FCoE initiators such as servers and an FCoE forwarder (FCF), which is in an FC storage area network (SAN). The transit switch acts as a passthrough switch and is transparent to the FCF, which detects each connection to an FCoE server as a direct point-to-point link.

When the switch acts as a transit switch, the VLANs you configure for FCoE traffic can use any of the switch ingress and egress ports, because the traffic in both directions is Ethernet traffic. FCoE traffic must use a VLAN dedicated only to FCoE traffic that does not carry any other traffic.

When the switch acts as a transit switch, you must enable priority-based flow control (PFC, IEEE standard 802.1Qbb) as a link-level flow control mechanism. See Understanding Priority-Based Flow Control for additional information. FIP snooping adds security by filtering access so that only traffic from servers that have successfully logged in to the FC network passes through the transit switch and reaches the FC network.

The transit switch transparently connects FCoE-capable servers in an Ethernet LAN to an FCF, which has both FCoE and FC interfaces and processes both the FCoE and FC protocol stacks. The transit switch acts as a transparent access layer between FCoE servers and the FCF.

Encapsulated FCoE server traffic flows through the transit switch to the FCoE ports on the FCF. The FCF removes the Ethernet encapsulation from the FCoE frames to restore the native FC frames. Native FC traffic travels out FCF FC ports to storage devices in the FC SAN.

Native FC traffic from storage devices flows to the FCF FC ports, and the FCF encapsulates that traffic in Ethernet as FCoE traffic. The FCoE traffic flows through the transit switch to the appropriate server, and the server decapsulates the traffic.