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How to Form a Catalyst 3850 Data-Stack and Power-Stack


How to Form a Catalyst 3850 Data-Stack and Power-Stack




This document describes the process to properly form a stack-wise and power stack with Cisco Catalyst 3850 switches. It also shows the use of some commands that will help to troubleshoot why a stack is not forming properly.





In order to be able to form a switch stack more than 2 switches must be used.

The IOS version used must be the same for all switches. (Software auto upgrade can be configure on a existing stack in order to automatically upgrade newly added switches).


The same mode must be used on all the switches INSTALL or BUNDLE mode.


The right type of cables must be used to achive stack completion. Be aware that cables for the 3750 platform do not work on the 3850 platform.


Components Used


Cisco Catalyst 3850 switches.

Cisco 3850 Stack wise cables. 

Cisco 3850 stack power cables.


Network Diagram


The example below, shows how to properly connect a stack of six 3850 switches, together with a power-stack connection example.


Note: The process will be similar for stacks of 2,3,4,5,7,8 and 9 switches.


Each switch has two stack-wise ports(left), let's name the stack wise ports P1 and P2 as shown in the picture.


switch_1 P1 connects to switch_2 P2 (Green cable)

switch_2 P1 connects to switch_3 P2 ( Orange cable)

switch_3 P1 connects to switch_4 P2 (Purple cable)

switch_4 P1 connects to switch_5 P2 (Violet cable)

switch_5 P1 connects to switch_6 P2 (Yellow cable)

switch_6 P1 connects to switch_1 P2 (Brown cable)



Stack of six C3850 Switches.Stack of six C3850 Switches. 




Picture 1 Switches in a stack.



Below the steps that show how to cable the stack for power-stack configuration:


StackPower is a feature that allows the power supplies to share the load across multiple devices in a stack. By connecting the switches with power stack cables, the power supplies of up to four stack members can be managed as a one large power supply that provides power to all switches and to the powered devices connected to switch ports.






Each switch has two power-stack ports, lets call the ports A and B ( A top, B bottom)


From switch 1 port A we connect to switch 2 port B (pink cable).
From switch 1 port B we connect to switch 4 port A (pale green cable)
From switch 2 port A we connect to switch 3 port B (blue cable)
From switch 3 port A we connect to switch 4 port B (red cable)


From switch 5 port A we connect to switch 6 port B (Red cable).
From switch 6 port A we connect to switch 5 port B (pale blue cable) 


Note: Be aware that currently up to four switches can be used on a power-stack configuration and up to nine for a data stack.


Adding a switch to the stack


Note: The switch to be added to the stack must be off. Otherwise, the hole stack will reload.


1.- Add the new switch to the stack by connecting the stack cables to the switch (every cable has a cisco logo on the connector, it must be in the upright position) as shown in the picture below (1):



Screen Shot 2018-10-13 at 00.18.06.png

Picture 2. How to connect the stack-wise cable.  (Data cables)



2.- Once the stack-wise cables have been properly connected to the switch, power on the newly added switch either using the power supplies or the power-stack cables.




After the switch has come up, collect the following :

                * show switch

                * show switch stack-ports

                * sh version


On the show switch output verify that the current state of all switches is READY. 


Switch#show switch

Switch/Stack Mac Address : 6400.f125.1b80 - Local Mac Address
Mac persistency wait time: Indefinite


                                                                              H/W        Current
Switch#     Role          Mac Address            Priority  Version      State
*1              Active        6400.f125.1b80           15         0          Ready
 2              Standby     6400.f155.1dF0           14         0           Ready





On the show switch stack-ports verify that all the ports are shown as OK, that is an indication that the stack-wise cables are working properly:


Switch#show switch stack-ports

Switch #                               Port 1    Port 2
--------                                    ------       ------
1                                         OK          OK
2                                         OK          OK

3                                         OK          OK

4                                         OK          OK
5                                         OK          OK

6                                         OK          OK




With the show version command, verify that all the switches on the stack have the same IOS version installed and that all of them have the same mode install or bundle.


Switch Ports Model                    SW Version          SW Image                     Mode  

------ -   ------  ------------------------     -----------------------    --------------------------------     ----------          

  1        56    WS-C3850-48P       03.02.03.SE         cat3k_caa-universalk9     INSTALL

  2        56    WS-C3850-48P       03.02.03.SE         cat3k_caa-universalk9     INSTALL

  3        56    WS-C3850-48P       03.02.03.SE         cat3k_caa-universalk9     INSTALL





The stack might not form properly, this can be due to several reasons. Below there are some of the most common situations showing why a stack does not form propelry.


This can be due to a cable not properly connected or to a faulty stack port on the switch:


Make sure that the cable logo (Cisco logo) is in the upright position on both ends of the cable.

Make sure the cable is plugged in correctly and is not loose.



It can be due to a version mismatch, make sure that all the switches on the stack have the same IOS image.

The auto-upgrade feature can be configured so everytime a switch is added to the stack this will be automatically upgraded to the IOS version used on the stack.


#sh switch

Switch#  Role        Mac Address        Priority                   Version  State 


*1            Active      6400.f125.1480    15                              V01         Ready               

2             Standby   6400.f125.2680    14                              0              V-Mismatch          

3             Member   6400.f125.2500    13                              0              V-Mismatch          

4             Member   6400.f125.2480    12                              0              V-Mismatch



It might be due to a license version mismatch, verify that all the switches on the stack have the same license level.


The license level can be verified with the show licence-right-to.use command.


#sh switch

Switch#     Role           Mac Address      Priority                 Version State 


*1             Active          6400.f125.1480     15                        V01        Ready               

2              Standby       6400.f125.2680      14                        V01        Ready         

3              Member       6400.f125.2500      13                         V01        Ready         

4              Member       6400.f125.2480      12                           0          Lic-Mismatch




The 4 switch limit on the power stack is to limit the stack from receiving too much power to the entire stack.  While the data stack can accept 9 switches the power stack is limited to 4 to protect from power overload.

To eliminate the need for a longer cable I always run this config:

1/1 to 2/1

1/2 to 3/1

2/2 to 4/1

3/2 to 5/1

4/2 to 6/1

5/2 to 6/2.

This approach will allow for future expansion with ease as well as eliminate the need for the long cable.

To add a switch to the stack, simply pull the cable end from 6/2 and run it to 7/1 then run an additional cable from 6/2 to 7/2.

Best regards.

Chris Lhamon

I have a stack of 3750X switches that have been in production for a while, and I'm not able to get any of the "stack-power" commands to work.  Not even .show stack-power."  I have been looking for a solution.  I feel that it since it isn't in IOS help that it might be the IOS version, but I have not been able to confirm that.  I am running 12.2(58)SE2 on all switches.

Does anyone know what I'm doing wrong?  Thanks!

Ronald Hillberg
Community Member

I have a stack of two 3850-48U running version 3.3.5SE and the show switch stack-ring speed command shows 480Gbps/full ring configuration and show switch stack-ports summary command shows each ports ok, linked, active and synced.

I have to create a procedure to test a loss of a StackWise cable without loss of connectivity. If I remove a cable or disable a StackWise port the active switch losses visibility with the standby switch and the standby switch reboots. I've tried each of the two cables separately and disabling single ports on both switches. This does not happen with our four switch stacks.

This would also prevent us from adding a switch to the stack in the future without disruption.

Any thoughts?

Thank you for your time.

Luis Villanueva
Cisco Employee

Hi Ronald,

This is a curious case, as the objective of having a switch stack is to have some kind of redundancy in case one of the switches fails.

If only one cable is disconnected or only one port is shouted down the stack should remain up and running without issues.

You can test the cables with the command below 3 times:

sh platform port-asic 0 read register SifRacRwCrcErrorCnt switch 1
sh platform port-asic 1 read register SifRacRwCrcErrorCnt switch 1
sh platform port-asic 0 read register SifRacRwCrcErrorCnt switch 2
sh platform port-asic 1 read register SifRacRwCrcErrorCnt switch 2
The result should look like this:
R1-R2-3850#sh platform port-asic 0 read register SifRacRwCrcErrorCnt switch 2

For asic 0

SifRacRwCrcErrorCnt on Asic 0


count 0x00000004


count 0x00000002


count 0x0000005b <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


count 0x00000008


count 0x00000011


count 0x00000007

R1-R2-3850#sh platform port-asic 0 read register SifRacRwCrcErrorCnt switch 2

For asic 0

SifRacRwCrcErrorCnt on Asic 0


count 0x00000004


count 0x00000002


count 0x000000cd <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


count 0x00000008


count 0x00000011


count 0x00000007

From the output above, you can see that the value for register [2] is different on both switches. Indicating a physical problem with the cable. If that is the case a new cable should be used.

Also, I have noticed that the IOS version used has been deferred. It might by that something on the IOS is not properly working so the redundancy is lost once a cable or a port is down.

I would suggest to test this behaviour with a newer IOS such as 03.06.06.


Abhishek Dave
Cisco Employee

Hi Luis

how to form a stack with 8 switches in stack .

i do have stack-power diagram for 5 switches  but I am not sure how to do the same for 8 switches – can you help please ?


Luis Villanueva
Cisco Employee

Hello Abhishek,

Up to four switches can be part of a power stack in a ring topology, and up to nine switches can share power in a star topology by using an XPS.

Please find below a link that explains this process in more detail:




Regarding power stack, if using two non-PoE switches like 3850-12xs in a stack of only two switches :

Can we use only one 350w power supply in each switch + power stack and still have full redundancy?  Can one 350w power supply run two "data-only" switches like thoses?

I had some issues in the past with 3750-12s... I want to make sure!


Luis Villanueva
Cisco Employee

Hello JP,

The answer to your question is yes. A 350W power supply can be used in each switch along with stack power. Also, the 350W power supply will be able to support both switches if one of the PS fails, meaning they both will remain up with only one PS.

However, if for some reason one of the switches goes down or it is manually powered down then it will not be able to come up with only one PS in the stack.

Kind Regards.

Luís Gil


How many stack cables do I need for two switches stack?
I want to make a stack with just two WS-C3850-48P switches, I want to know how many stacking cables I need in order to get my stack?


Best Regards


John Supple



This is probably out of context for the discussion, but I'm in need of a command to display total power consumption of a WS-C3850-48P - Show env power gives me the power supply model number and the fact that it can provide 715 watts, but nothing on what it's actually consuming.  

A "show power inline" shows me total POE consumption, but not the overhead power on the switch.  There's not much on the web about this. 

Any ideas?  Thanks for the help.



Martin Hernandez


For the same scenario using 6 Cat 3850 switches but using only the standard small Data-stack cables. Can you provide best possible Data-stack cable configuration that I can use to achieve the same results?


Hi Luis,


Thank you for your great input in the stack wise data and power topic, I appreciate your work.

I find this really educational! I am following this guide to implement stack wise for our clients and it works great!


Thank you!


Martin L
VIP Advocate

Very Useful Doc; thanks for sharing


I am trying to add a third switch to 2 switches already stacked. I have both PSU plugged in on the first switch and one PSU plugged into the second switch. I do have power-stacking cables attached to both. I do not have enough outlets to power the third switch. My question is can all switches run off one PSU? Also what will be the best way to stack the switches. I have 2 additional data stacking cables and 1 power stacking cable. Please advise. thanks.