Configure Switch Priority for Principal Switch Selection on a Cisco MDS Switch - Connectrix Any new switch can become the principal switch when it joins a stable fabric. During the principal switch selection phase, the switch with the highest priority becomes the principal switch. If two switches have the same configured priority, the switch with the lowest WWN becomes the principal switch. By default, the configured priority is 128. The valid range of the priority is between 1 and 254. Priority 1 has the highest priority. A value of 255 is accepted from other switches but cannot be locally configured. You can configure the priority value on the switch, for example for VSAN, using these steps : switch # configure terminal switch (config) # fcdomain priority x vsan vsan-id {x is the priority value} The priority configuration is applied to runtime when the fcdomain is restarted. This configuration is applicable to both disruptive and non-disruptive restarts. To restart the fabric non-disruptively in VSAN, use the following configuration steps : switch # configure terminal switch (config) # fcdomain restart vsan vsan-id To restart the fabric disruptively, use the fcdomain restart disruptive vsan vsan-id command. This command will cause all devices of all switches in that VSAN to log out, causing data traffic disruption.
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How to configure Switch Priority for Principal switch selection on a Cisco MDS switch. Reference Dell Knowledge Base Article # 203079.
This video was created to: Demonstrate how the principal switch is elected in a fabric. Any new switch can become the principal switch when it joins a stable fabric.
In a Fibre Channel network, the principal switch assigns the domain ID when a new switch is added to an existing fabric. The principal switch assigns the FC IDs for a disk or host that exited and re-entered the fabric.
When two fabrics merge, the principal switch selection process determines which one of the pre-existing switches becomes the principal switch for the merged fabric.
The election of the new principal switch is characterized by the following rules: A switch with a populated domain ID list takes priority over a switch that has an empty domain ID list.
The principal switch becomes the one in the fabric with the populated domain ID list. If both fabrics have a domain ID list, the priority between the two principal switches is determined by the configured switch priority. This is a user-settable parameter.
The switch with the highest priority becomes the principal switch. If two switches have the same configured priority, the switch with the lowest WWN becomes the principal switch.
By default, the configured priority is 128 The valid range to set the priority is between 1 and 254 Priority 1 has the highest priority.
Value 255 is accepted from other switches, but cannot be locally configured. When to do this: When you want to change priority on any switch and make that the principal switch based on user requirements. Before you begin: You can configure the priority value on the switch for VSAN using these steps.
Enter into "configuration" mode and run the command fcdomain priority x vsan vsan-id ID where "x" is the priority value. The priority configuration is applied to runtime when the fcdomain is restarted.
This configuration is applicable to both disruptive and nondisruptive restarts. To restart the fabric nondisruptively in VSAN, use the following configuration steps: Enter into "configuration" mode and run the command fcdomain restart vsan vsan-id.
To restart the fabric disruptively, use the "fcdomain restart disruptive vsan vsan-id" command. This command will cause all devices of all switches in that VSAN to log out, causing data traffic disruption.
Here is the demonstration. Check the "Fibre Channel Domain" information for vsan 1 on both the switches. You can notice that Switch 1 is a subordinate switch as it has a runtime priority of 128, and Switch 2 is the principal switch as it has a runtime of priority 2, which is a greater priority than 128 Now, let us make Switch 1 the principal switch by setting a greater priority than Switch 2 To configure a priority value on Switch 1, enter into "configuration" mode. Run the command "fcdomain priority 1 vsan 1".
Verify the domain information on vsan 1 128 is still the runtime priority, but the configured priority is changed to 1 The configured priority is applied to runtime when the fcdomain is restarted. Run the command "fcdomain restart vsan 1".
Check the fcdomain information again on both the switches. You can notice that Switch 1 is now the principal switch as the runtime priority is changed to 1, and Switch 2 is a subordinate switch.
When you merge two fabric switches that have the same configured priority, the switch with the lowest WWN becomes the principal switch.
In this example, both the switches have the same runtime and configured priority, 1, but Switch 2 has the lowest WWN. Hence, when these two switches merge, Switch 2 becomes the principal switch, and Switch 1 becomes a subordinate switch.
Important notes: Fibre Channel domains can be restarted disruptively or nondesruptively. If you perform a disruptive restart, reconfigure fabric frames are sent to other switches in the fabric, and data traffic is disrupted on all the switches in the VSAN including remotely segmented ISLs.
If you perform a nondisruptive restart, build fabric frames are sent to other switches in the fabric, and data traffic is disrupted only on that switch.
Refer to the following for more information: Dell Knowledge Base Article # 203079 Cisco MDS 9000 Family CLI Configuration Guide Chapter: Configuring Domain Parameters - About Switch Priority.
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