Cisco MDS “fabric merge” and “switch add” prerequisites

Prerequisites when adding a new SAN switch to an existing SAN fabric

When using enhanced device aliases, make sure you enable this on the new switch as well:

device-alias mode enhanced
device-alias commit

You can verify if this is enabled on an existing switch by this command:

sh run | grep “device-alias mode”

Create necessary VSANs on the new switch (in this example only vsan 10 needs to be created):

vsan database
vsan 10

When using enhanced zoning in the existing fabric (VSAN), make sure you enable this on the new switch as well:

zone mode enhanced vsan 10

When using smart zoning, make sure you enable this on the new switch as well:

zone smart-zoning enable vsan 10

To see the current domain ids in the existing fabric, use this command on one of the switches in the existing fabric:

sh fcdomain domain-list

The output looks like:

Number of domains: 3
Domain ID WWN
——— ———————–
0x6e(110) 20:01:00:2a:6a:b4:81:11 [Principal]
0x33(51) 20:01:00:0d:ec:bc:3f:81
0x65(101) 20:01:8c:60:4f:b1:94:91 [Local]

Number of domains: 3
Domain ID WWN
——— ———————–
0x6e(110) 20:96:00:2a:6a:b4:81:11 [Principal]
0x34(52) 20:96:00:0d:ec:bc:3f:81
0x65(101) 20:96:8c:60:4f:b1:94:91 [Local]

Number of domains: 3
Domain ID WWN
——— ———————–
0x6e(110) 21:2c:00:2a:6a:b4:81:11 [Principal]
0x65(101) 21:2c:8c:60:4f:b1:94:91 [Local]
0x64(100) 21:2c:00:2e:6a:b4:7e:01

If this new switch needs to be the new principal, make sure the fcdomain priority is LOWER than of the existing principal switch. In the output of the above command, you can easily identify which switch is the principal switch for each vsan. Use the domain id to identify on which switch you need to verify the domain priority.

To display a switch’s priority on vsan 10:

sh fcdomain vsan 10

The output looks like:

The local switch is a Subordinated Switch.

Local switch run time information:
State: Stable
Local switch WWN: 25:dc:8c:61:4f:bd:9f:11
Running fabric name: 25:dc:01:2a:6a:b4:84:b1
Running priority: 32
Current domain ID: 0x66(102)

Local switch configuration information:
State: Enabled
FCID persistence: Enabled
Auto-reconfiguration: Disabled
Contiguous-allocation: Disabled
Configured fabric name: 20:01:10:05:31:00:28:df
Optimize Mode: Enabled (Scale Restart)
Configured priority: 32
Configured domain ID: 0x66(102) (static)

Principal switch run time information:
Running priority: 2

It’s a best practice to set the domain id for any switch to static. In this example we set the priority to 31 for vsan 10 and the domain id for this switch in vsan 10 to 101. Since the priority is lower than the current principal switch (=32), the new switch will become the new principal.

fcdomain priority 31 vsan 10
fcdomain domain 101 static vsan 10

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