Section 4.5. Fibre Channel Port Types

   

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4.5 Fibre Channel Port Types

Fibre Channel defines several port types based on the topology of the SAN and the device on which the port exists. The various different types of ports are summarized in Table 4.2.

To simplify life for SAN administrators, device vendors typically build logic to let the port configure itself. The order in which such configuration is attempted is as follows :

Table 4.2. Fibre Channel Port Types

Port Type	Device on Which It Can Exist	Description	Port Types That Can Connect to This Type
F	Fabric switch	Fabric-capable only. Never a source or destination for data; acts as middleman to allow two devices to communicate.	N
FL	Fabric switch	Can connect to loop only. Provides connectivity between a Fibre Channel loop and a fabric-switched network. Never a source or destination for data.	NL
E	Fabric switch	Expansion port used to connect fabric switches to other fabric switches. Never a data source or destination; simply acts as a middleman.	E
N	HBA or storage device	Not loop-capable. Always a data source or destination. Exists in either point-to-point or switched-fabric networks.	F or N
NL	HBA or storage device	Similar to N, but loop-capable. Always a data source or destination.	NL or FL
U		Universal port that is simply a port that is not yet used. Once it is used, it can become an E, F, or FL port.	none
L		Generic term used to refer to NL or FL port.
G		Can be either an E or an F port.	E or N

1. The port first attempts to initialize as a loop (FL) port. If the initialization succeeds, the port is configured as an FL port.

2. If the loop initialization fails, the port attempts to initialize as an E port; that is, it checks for connectivity to a fabric switch.

3. If the initialization as an E port fails, the port attempts Fabric Login. If the login succeeds, the port initializes as an F port.

One should not assume that all device vendors are equal in their capability to dynamically configure any port as any kind of port. Some devices have this capability built in and can reconfigure a port on the fly without a reboot or power cycle, but some devices need firmware upgrades or swapping of option cards for the particular port that may require a power cycle.

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