By default, the switch assigns the same FC ID to a device. However, if the switch is rebooted, this database of pwwn/FC ID mapping is not maintained. Enabling persistent FC IDs makes this database persistent across reboots.
In the following procedure, the existing VSAN (3000) has a switch address of xx.xx.xx.xx and a domain ID of 239. This procedure configures a static Domain_ID for a VSAN and enables persistent FC_ID for the same VSAN.
Step 1 
Display the current domain_ID for VSAN 3000 using the command show domain-list.
switch# show fcdomain domain-list vsan 3000
Number of domains: 2
Domain ID WWN
--------- -----------------------
0xef(239) 2b:b8:00:05:30:00:68:5f [Local] [Principal]
Step 2 Configure the static domain_ID with the domain static command.
switch# conf t
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)# fcdomain domain 239 static vsan 3000
Step 3 Enable persistent FC_ID with fcid persistent.
switch(config)# fcdomain fcid persistent vsan 3000
switch(config)# end
Step 4 Save the configuration.
switch# copy running-config startup-config
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