There are three Fibre Channel network topologies, the simplest and least expensive of which is point-to-point. The most expensive and complex Fibre Channel topology is the fabric topology, but it also has the greatest amount of functionality. The remaining topology is arbitrated loop, which fits right between point-to-point and fabric with regards to cost and functionality.
A point-to-point Fibre Channel network is the simplest and least expensive of the three topologies, and is simply two N_Ports communicating via a point-to-point connection. As seen in Figure 2-2, a Fibre Channel array connected to a host is an example of a point-to-point connection.
Figure 2-2. Point-to-point topology
An illustration of a basic fabric network can be found in Figure 2-3. In a true fabric-only environment, each N_Port plugs into one F_Port on the switch. Each node is then assigned its native address identifier by the switch when it "logs into" the fabric. (This is why this topology is sometimes referred to as "fabric login.") This 24-bit address allows for up to 16 million unique addresses within a single fabric, which should be enough for even the biggest SANs. (At this point, I can't possibly imagine a SAN with 16 million nodes on it, but then I keep thinking about what the popularity of the Internet did to the original IP specification.)
Figure 2-3. Fabric ...