Converged networks with Fibre Channel over Ethernet and Data Center Bridging

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Figure 3. Illustration of an FCoE frame
Layer 2 encapsulation provides several advantages to FCoE over previous converged network
implementations:
• Because devices use existing FC logic, FCoE devices use existing FC driver models for the new converged
network adapters.
• We can easily implement FCoE in switches because the logic necessary to convert between FCoE and FC
is simple.
• Existing FC security and management operations, procedures, and applications do not change when
using an FCoE/DCB infrastructure for a partial or completely converged network.
• FCoE takes advantage of a lossless 10 GbE fabric with significantly higher bandwidth than 8 Gb FC
fabrics (actually 6.4 Gb plus encoding overhead in the FC protocol).
• Future protocols can use enhanced DCB Ethernet features that support FCoE.
Fibre Channel Forwarder
Fibre Channel Forwarder (FCF) is a function within a switch that acts as a translation point that supports
converting FCoE traffic between DCB-enabled Ethernet ports and native FC ports. There is one FCF function
in a switch for each upstream FC fabric connected to the FC ports of that switch. In other words, there can
be more than one FCF function in a switch. An FCF also provides the portal where converged network
adapters access the traditional SAN fabric services, for example fabric login, name services, and zoning
services. When first initialized, converged network adapters discover the available FCFs in a DCB network.
Through management direction, they attach themselves to at least one FCF to begin communication with a
SAN fabric. During fabric login, FCFs provide the mechanism that negotiates the MAC address
provisioning to the FCoE portion of a converged network adapter. The most commonly used mechanism is
“Fabric Provisioned MAC Addresses,” or FPMA. It operates as FC addresses in an FC network where the
address used in the frames is allocated at fabric login time. This is different from normal Ethernet NIC
functions, which typically have a static address burned in to them in the factory.
ENode
ENode is a device that takes the place of the traditional LAN NIC and the FC HBA in a host or server. It is
commonly called a converged network adapter (CNA). It provides both data communications and block
storage communications through a converged network implemented with DCB-capable Ethernet. An ENode
merges the traffic from the NIC and from the SCSI/FC functions into a stream of Ethernet frames to the DCB-
enabled Ethernet network. Within the DCB network, a DCB/FCoE/FC switch disaggregates the converged
traffic streams and sends the different TCs to their appropriate destinations: legacy LANs, legacy FC nodes,
or DCB network nodes.
Header
Header
Start of
Frame
Payload
Frame
Check
End of
Frame