FLOGI Process
After the N_Port and the F_Port are physically connected, the negotiations at the physical layer are successful, and the electrical parameters are in sync, the link negotiation and the registration to the fabric start. This is the FLOGI process, which can be described as the initial bootstrap process that occurs when an N_Port is connected to an F_Port. The FLOGI process is used by the N_Port to discover whether a fabric is present and what its capabilities are as well as to register to it. The fabric uses FLOGI to get the information for the node and assign it an FCID. Once the FLOGI process is successful, the N_Port can start the next process of attempting to communicate with other N_Ports (that is, the PLOGI process).
The steps of the FLOGI process are as follows:
The F_Port and the N_Port will reset the link between them, as shown in Figure 11-8. The goal is for the link initialization to start from fresh and for both parties to verify the exchanged parameters and information for this link establishment. This happens by exchanging the LR and LRR commands.
Figure 11-8 FLOGI Link Reset
After the link is initialized, as shown in Figure 11-9, it will be active and IDLE fill words will flow in both directions on the link. The N_Port will use a source FCID (SID) of 0x000000, as at this time it does not have an FCID assigned by the address manager.
Figure 11-9 FLOGI Link Initialize
The N_Port will send a FLOGI link services command to the switch login server using the well-known address 0xFFFFFE. The N_Port will include its Node name, N_Port name, or the WWNN and the WWPN it uses as well as its service parameters.
The login server sends an ACC response frame, as shown in Figure 11-10, that contains the N_Port address in the Destination FCID (DID) field.
Figure 11-10 FLOGI FCID Assignment
After an FCID, the N_Port logs in to the fabric name server at the address 0xFFFFFC. The N_Port transmits its service parameters, such as the number of buffer credits it supports, its maximum payload size, and the supported Classes of Services (CoSs).
The name server responds with an LS_ACC frame, shown in Figure 11-11, that acknowledges the information is registered. After that comes the next login process—the port login between two N_Ports, when the initiator prepares to communicate with a specific target.
Figure 11-11 FLOGI Fabric Registration
To verify a successful FLOGI on Cisco MDS switches, the command show flogi database can be used on the command-line interface (CLI), as demonstrated in Figure 11-12. This command provides in the output the information for the N_Ports that performed the successful FLOGI. Which WWNN and WWPNs are used, to which F_Port is connected, and to which VSAN belongs the communication of an N_Port. This is a simple and effective way to find out which node is connected to which switch port.
Figure 11-12 Verify the FLOGI Process
The same information can also be seen in the Cisco MDS switch graphical user interface (GUI), which is the Device Manager (see Figure 11-13). When you select the FC-enabled interfaces from the menu, you will be taken to a new window where the FLOGI database entries can be seen.
Figure 11-13 Verify the FLOGI Process in the Cisco MDS Device Manager
One of the results of the FLOGI process is that the N_Port will be assigned an FCID, and the FCID is also provided in the output of the command.
All the information for the N_Port is also registered in the FCNS. In the CLI, the command to verify this, and also to get information for the N_Ports (or end devices) connected or registered to the switch fabric (not limited to the local switch), is show fcns database. In the output of this command, we can see information for the vendor of the end node and its capabilities (is it an initiator or a target?).
Cisco-MDS-Switch#
show fcns database
VSAN 100:
———————————————————————-
FCID TYPE PWWN (VENDOR) FC4-TYPE:FEATURE
———————————————————————-
0x2b273b N 21:00:c4:19:b4:12:d8:24 scsi-fcp:init
0x4e0041 N 50:06:00:a0:98:cc:c3:0e (NetApp) scsi-fcp:target
0x4e0061 N 50:06:00:a0:98:cc:c3:ea (NetApp) scsi-fcp:target
Total number of entries = 3
From the Cisco MDs Device Manager, you can select the Name Server option under the FC options to check the FCNS database. In a new window will open the Name Server database, as shown in Figure 11-14.
Figure 11-14 Verifying the FCNS Database in the Cisco MDS Device Manager