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Changing a Switch Member Number in a 3850 Stack

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Introduction

 

This document describes how to change the logical switch assigned number in a stack manually so it matches a desired order. Commonly used to match the physical order of the stacked switches in a rack.

 

Components used

 

The information in this document is based on the Cisco Catalyst 3850 Series Switch that runs Cisco IOS-XE Versions 03.03.00 and later.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

 

Switch number

 

New switches have number 1 as stack member number by default, however when a switch joins a stack it changes to the lowest available number. For example, if SW 1 has 1 and SW2 has 3 as their stack member number, when the new switch SW3 joins the stack it will change its member number from 1 to number 2 since it is the lowest available number in the stack.

 

Verifying the actual stack members number

 

 

In order to verify the roles and numbers of member switches in the stack, enter the show switch command:

 

SW3#show switch
 
Switch/Stack Mac Address : f84f.576f.f500 - Local Mac Address
Mac persistency wait time: Indefinite
                                        

Switch#   Role    Mac Address     Priority Version  State 
--------------------------------------------------​----------
 2       Member   0008.2f12.8000     0      V01     Ready         
 1       Standby  0008.2f06.7200     1      V02     Ready               
*3       Active   f84f.576f.f500     15     V01     Ready  

 


There is a direct relation between the stack member number of the switch and the interface number at configuration level:

 

Switch#   Role    Mac Address     Priority Version  State 
--------------------------------------------------​----------
 2       Member   0008.2f12.8000     0      V01     Ready         
 1       Standby  0008.2f06.7200     1      V02     Ready               
*3       Active   f84f.576f.f500     15     V01     Ready  


Gigabitethernet [switch-number/interface-number]   Interfaces related to switch number 1 GigabitEthernet1/0/1 unassigned YES unset up up GigabitEthernet1/0/2 unassigned YES unset up up
GigabitEthernet1/0/3 unassigned YES unset up up

Gigabitethernet [switch-number/interface-number]   Interfaces related to switch number 3 GigabitEthernet3/0/1 unassigned YES unset up up GigabitEthernet3/0/2 unassigned YES unset up up
GigabitEthernet3/0/3 unassigned YES unset up up

 

 

 

Changing the stack members number manually


In order to change the stack members number manually, use the switch [current number] renumber [desired number] command:

 

SW3#switch 3 renumber 1 
WARNING: Changing the switch number may result in a configuration change for that switch.
The interface configuration associated with the old switch number will remain as a
provisioned configuration. Do you want to continue?[y/n] y

 

 

In this case, we are changing the member number of the switch 3 to number 1. A WARNING message is logged after the command is used stating that a configuration change will occur.

 

As an example regarding this Warning message, lets say configuration in Gigabitethernet 3/0/1 is an access port in vlan 10, and Gigabitethernet 1/0/1 was a trunk interface connecting to another switch.
When the renumbering change from switch 3 to switch 1 occurs, the trunk interface that should be connecting another switch is now connected to a PC and the interface which is configured as access is now connected to a switch!

 

Renumbering2.png

 

 

 

Renumbering members of the stack manually should be done in a mantenaince window since issues like the one described above could cause a network outage.

Comments
Beginner

Carlos,

Thank you for taking an (to me) ambiguous message and providing a clear and concise explanation!

Now, if only there was a method to renumber the switch, and have that renumber apply to the interface numbering as well, retaining the port configuration.

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