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ERS/VSP Stackable: How To Add/Replace a Unit To Existing Stack

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TitleERS/VSP Stackable: How To Add/Replace a Unit To Existing Stack
ERS/VSP Stackable: How To Add/Replace a Unit To Existing Stack


Below is procedure to be followed to replace a unit in the existing Stack:


Before adding or replacing a unit in stack, ensure to backup the configuration in ASCII and Binary format. Below are the commands to take backup.
Ascii-->   copy running-config tftp address [A.B.C.D | WORD] filename [WORD]

Binary--> copy config tftp address [A.B.C.D | WORD] filename [WORD]


Check if the software of the replacement unit is same as the base unit, perform loop back test on new unit before adding unit to stack. For more information refer "" to perform loop back test



 verify if the stack auto-unit-replaced is enable. use #show stack auto-unit-replacement command for AUR configuration.

  1. Enter the #stack auto-unit-replacement config save enable command to enable AUR.
  2. Enter the stack auto unit replacement auto-restore enable command to configure AUR to automatically restore the configuration to the new unit.
  3. verify if autosave is enabled, use #show autosave command
  4. Enter autosave to enable autosave feature
  5. In case of Hybrid stack make sure stacking mode is set as hybrid, verify by using # show stack oper-mode command
  6. Enter stack oper-mode hybrid

Note: In case of hybrid stack it is recommended to user higher hardware model as base unit


Ensure the new unit being added doesn't have  "BASE-UNIT" set at rear panel of the unit. Once unit is added in stack, as per the requirement base unit can be set by moving base knob. Make sure only one unit in the stack has the base knob set. In case of two or more units have base knob set  then the stack will get unstable.

Connect Cascade DOWN connector on one switch to Cascade UP connector of the other unit in the stack and follow the same until all the units are connected to each other via Cascade UP and DOWN connector.

Below picture gives the clarity on stack physical connections :



To check the status and to find out whether all units are present in stack use the following command:

#show stack health


5530-24TFD#show stack health

UNIT#            Switch Model       Cascade Up    Cascade Down
1 (Base)          5530-24TFD          OK                     OK
2                       5520-48T-PWR     OK                    OK
3                       5520-48T-PWR     OK                    OK
4                        5530-24TFD        OK                     OK
Switch Units Found = 4
Stack Health Check = OK - RESILIENT
Stack Diagnosis = Stack in full resilient mode.

  • User can add maximum 8 units in stack or up to 400 ports in a stack.
  • The Firmware versions and Software versions should match on all the units of the stack.
  • AUR (Auto Unit Replacement) and DAUR (Diagnostic Auto Unit Replacement) feature should be  will upgrade the Agent and Diagnostic image on the Non base unit when stack is formed to that of the base unit. In case, If the Agent image size exceeds 6 Mb, the switch cannot perform the DAUR. The switch sends an error message to the base unit and must perform a manual image upgrade or downgrade.

How AUR and DAUR Works : 

Auto Unit Replacement (AUR) is enabled by default. AUR is the ability to retain the configuration (CFG) image of a unit in a stack during a unit replacement. The retained CFG image from the old unit is restored to the new unit. Diagnostic Auto Unit Replacement (DAUR) is responsible for replacing  the Diagnostic Image (Firmware) on the newly added unit to the stack to that old unit The replaced device will automatically reset after DAUR has copied the Diagnostic Image (Firmware).

Below are few commands which could be used while troubleshooting:

  • #show tech
  • #show auto save
  • #show stack auto-unit-replacement
  • #show stack auto-unit-replacement-image
  • #show stack forced-mode
  • #show stack reboot-on-failure
  • #show stack port-statistics
  • #show stack-info uptime
  • #show stack-monitor
  • #show stack health
  • #show stack oper-mode
  • #show stack-info
  • #show stack port-statistics unit <1-8>
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