FC Addressing

This answer comes from Debasish Chakrabarty on our Content Development Team:

Fabric services:

Fibre Channel or FC is a high-speed network technology. FC networks support FC technology. An FC network consisting of one or more FC switches is known as fabric. All FC switches in a fabric provide a common set of services as defined in the FC standards. These services are available at certain predefined addresses. Some of these services are Fabric Login Server, Fabric Controller, Name Server, and Management Server.

• Fabric Server/Fabric Login Server: It is located at the predefined address of FFFFFE and is used during the initial part of the node’s fabric login process.

• Name Server (formally known as Distributed Name Server): It is located at the predefined address FFFFFC and is responsible for name registration and management of node ports. Each switch exchanges its Name Server information with other switches in the fabric to maintain a synchronized, distributed name service.

• Fabric Controller: Each switch has a Fabric Controller located at the predefined address FFFFFD. The Fabric Controller is responsible for managing and distributing Registered State Change Notifications (RSCNs) to the node ports registered with the Fabric Controller. If there is a change in the fabric, RSCNs are sent out by a switch to the attached node ports. The Fabric Controller also generates Switch Registered State Change Notifications (SW-RSCNs) to every other domain (switch) in the fabric. These SW-RSCNs keep the name server up-to-date on all switches in the fabric.

• Management Server: FFFFFA is the FC address for the Management Server. The Management Server enables the FC SAN management software to retrieve information and administer the fabric.

Fabric login types:

Fabric services define three login types:

• Fabric login (FLOGI): FLOGI is used in Fibre Channel by an N_Port to detect the presence of a fabric and, if there is a fabric present, to establish a connection by exchanging certain parameters. The Fabric Login process also ensures the attached N_Port is assigned an FC address by the fabric. Fabric login is initiated by an N_Port by sending a FLOGI frame with the WWNN and WWPN parameters to the fabric login service at the predefined FC address FFFFFE (Fabric Login Server). In turn, the switch returns an Accept (ACC) frame with the assigned FC address for the node. Immediately after the FLOGI, the N_Port registers itself with the Name Server on the attached switch, indicating its WWNN, WWPN, port type, class of service,  assigned FC address, and so on. After the N_Port registration, it can query the name server database for information about all other logged in ports.

• Port login (PLOGI): PLOGI is used by an N_Port to send its service parameters to another port and to get back the service parameters of the receiving port. The initiator N_Port sends a PLOGI request frame to the target port, which accepts it. The target port returns an ACC to the initiator N_Port containing service parameters.

• Process login (PRLI): PRLI is required to establish communication between two FC-4 layer protocols (in our case SCSI) existing at two different N_Ports. It provides a way of allowing these two ports exchange SCSI information.