Fibre Channel Protocol Port Types
The FC switched fabric includes three participants: the initiator, the target, and the FC switch. The initiator and the target are end devices, or nodes, that connect to the FC switches that build the switched fabric. All of the participants connect to each other through physical ports. In the FCP world, these ports are assigned different roles, depending on which participant they belong to, what they are connected to, and what communication is allowed through them. The assigned role defines the port type.
Here are the main FC port types (see Figure 11-2):
Figure 11-2 Main FC Port Types
- N_Port: This stands for “node port.” This is the port of the HBA that is installed on an initiator or a target node. The N_Port represents a node. A node can have more than one N_Port.
- F_Port: The “fabric port” is a port on the FC switch that connects to an N_Port. The F_Port is the point where the end node, initiator, or target connects to the fabric. In standard connectivity, one N_Port always connects to one F_Port. Later will be mentioned some virtualized FC port types, but they will be discussed in more detail when we discuss the topics NPV/NPIV and FCoE.
- E_Port: The “expansion port” describes a port on the fabric switch that connects to another fabric switch, thus expanding the switched fabric. The E_Port to E_Port links are called Inter-Switch Links (ISLs).
After that, we have the FC-AL topology, where the devices are connected in a loop directly to each other, or through an FC hub. Here are the FC port types for this connectivity (see Figure 11-3):
Figure 11-3 FC-AL Port Types
- L_Port: This is the “loop port,” which supports the arbitrated loop (AL) topology functions.
- NL_Port: This is a “node loop port,” which connects to an FC hub in an AL topology.
- FL_Port: This is the “fabric loop port,” which is an FC port on a switch and is used to connect an FC-AL to the FC switched fabric.
Additionally, you can encounter the Fx_Port and the Nx_Port, which are ports that can function as either F_Port/FL_Port or as N_Port/NL_Port, respectively.
When the FCP connectivity communicates over some other transport infrastructure, such as an IP network, the physical connectivity is not native FC. In this situation, virtual FC interfaces, or overlays, are created that are assigned the needed port types and connect to each other using the FCP mechanisms. As illustrated in Figure 11-4, these virtual FC port types are as follows:
Figure 11-4 Virtual FC Port Types
- VF_Port: The “virtual fabric port” is used as an overlay port on a switch when the communication goes through an Ethernet port. The VF_Port is mapped to the underlying physical port.
- VN_Port: This is the “virtual node port,” which is the overly FC port, mapped to a physical Ethernet interface in an end node. The VF_Port and the VN_Port are used in FCoE and FCIP communication.
Some additional port types will be discussed later in this chapter.