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Chapter 11. SAN Connections and Configuration 
445
Draft Document for Review January 29, 2013 12:52 pm
8068ch11-SAN Config.fm
Figure 11-10   Compute node with CNA and FCF I/O module switch
Fibre Channel Forwarders
The IBM Flex System Fabric CN4093 10Gb Converged Scalable Switch has an optional Fibre 
Channel Forwarder. The FCF function is the FC switching element in an FCoE SAN. It 
provides functions that are analogous to the functions provided by the FC switch in a 
traditional FC SAN. The most basic function is the forwarding of FCoE frames received on 
one port to another port based on the destination address in the encapsulated FC frame. The 
FCF is also the entity that handles FC logins, routing, zoning, and other FC services. As 
shown in Figure 11-8 on page 443 the lower layers of FC have changed with FCoE, but the 
upper layers are intact. The forwarding of FCoE frames between a compute node and an IBM 
Flex System V7000 Storage Node are therefore contained within the IBM Flex System 
Enterprise Chassis where the CN4093 provides the FCF switching functionality. 
The CN4093 switch with its FCF function and FC ports can connect to external Fibre Channel 
SANs. In this case, the CN4093 10Gb Ethernet switch provides a gateway device function 
between FCoE and FC, transmitting frames between the two types of networks. As shown in 
Figure 11-10 the IBM Flex System V7000 Storage Node can manage external storage 
controllers using this capability to attach to FC SAN fabrics.
11.4.2  FCoE port types
In an FCoE network, virtual links are used across the lossless Ethernet network in place of 
the physical links in the FC network. The server negotiates a connection to the FCF device 
across the Ethernet network by using the FCoE Initialization Protocol (FIP). The server end of 
this connection is called a 
VN_Port
. The FCF end is called the 
VF_Port
. Two FCFs can also 
negotiate a connection across the Ethernet network, in which case the (virtual) ISL has 
VE_Ports at both ends. Figure 11-11 on page 446 shows the connection types between the 
compute node and the I/O module switches. As shown, if the IBM Flex System Enterprise 
Chassis I/O module switches were connected they would use VE_Ports at each end. In the 
IBM Flex System Enterprise Chassis the FCFs will not be connected, the VE_Port connection 
is used as an illustration example only in Figure 11-11 on page 446.