In the Ethernet world, an ARP table maintains a database for resolution between the MAC address (Layer 2) and IP address (Layer 3). Similarly, in the Fibre Channel world, every switch maintains an FLOGI and an FCNS database that maintains the resolution between WWNs (Layer 2) and FCIDs (Layer 3).
The FLOGI database logs every end device (server or storage) that has successfully performed a fabric login and obtained an FCID from the switch.
Fibre Channel switches share the FLOGI database information with each other using the Fibre Channel Name Service (FCNS). The name server functionality running on each switch maintains the FCNS database, which contains the attributes for all hosts and storage devices in each VSAN. Hence, each switch in the fabric learns where each WWN is and how to route traffic to specific WWNs. The name server permits an N port to register attributes during a PLOGI (to the name server) to obtain attributes of other hosts. These attributes are deregistered when the N port logs out either explicitly or implicitly.
In short, the FCNS database lists devices that are currently logged in to each VSAN, and the FLOGI database displays devices logged in to per switch. Example 8-2 shows sample output of the FLOGI and FCNS databases.
Example 8-2 Sample Output of show flogi database and show fcns database Commands
switch# show flogi database
————————————————————————-
———
INTERFACE VSAN FCID PORT NAME NODE NAME
————————————————————————–
——–
sup-fc0 2 0xb30100 10:00:00:05:30:00:49:63
20:00:00:05:30:00:49:5e
fc9/13 1 0xb200e2 21:00:00:04:cf:27:25:2c
20:00:00:04:cf:27:25:2c
fc9/13 1 0xb200e1 21:00:00:04:cf:4c:18:61
20:00:00:04:cf:4c:18:61
fc9/13 1 0xb200d1 21:00:00:04:cf:4c:18:64
20:00:00:04:cf:4c:18:64
fc9/13 1 0xb200ce 21:00:00:04:cf:4c:16:fb
20:00:00:04:cf:4c:16:fb
fc9/13 1 0xb200cd 21:00:00:04:cf:4c:18:f7
20:00:00:04:cf:4c:18:f7
Total number of flogi = 6.
switch# show fcns database
————————————————————————
——-
FCID TYPE PWWN (VENDOR)
FC4-TYPE:FEATURE
————————————————————————-
——-
0x010000 N 50:06:0b:00:00:10:a7:80 scsi-fcp fc-gs
0x010001 N 10:00:00:05:30:00:24:63 (Cisco) ipfc
0x010002 N 50:06:04:82:c3:a0:98:52 (Company 1) scsi-fcp 250
0x010100 N 21:00:00:e0:8b:02:99:36 (Company A) scsi-fcp
0x020000 N 21:00:00:e0:8b:08:4b:20 (Company A)
0x020100 N 10:00:00:05:30:00:24:23 (Cisco) ipfc
0x020200 N 21:01:00:e0:8b:22:99:36 (Company A) scsi-fcp
CFS
Cisco Fabric Services (CFS) provides a common infrastructure for automatic configuration synchronization in the fabric. It provides the transport function as well as a rich set of common services to the applications. CFS has the ability to discover CFS-capable switches in the fabric and discover application capabilities in all CFS-capable switches.
The Cisco MDS NX-OS software uses the CFS infrastructure to enable efficient database distribution and to foster device flexibility. It simplifies SAN provisioning by automatically distributing configuration information to all switches in a fabric. Several Cisco MDS NX-OS applications use the CFS infrastructure to maintain and distribute the contents of a particular application’s database.
Many features in the Cisco MDS switches require configuration synchronization in all switches in the fabric. Maintaining configuration synchronization across a fabric is important to maintain fabric consistency. In the absence of a common infrastructure, such synchronization is achieved through manual configuration at each switch in the fabric. This process is tedious and error prone.