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

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

 

Introduction

 

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.

 

 

Requirements

 

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)

 

 

Screen Shot 2018-10-13 at 00.15.45.pngStack 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.

 

Verify

 

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

 

 

Troubleshoot

 

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

 

Comments
Community Member

Can you help me if i can stack ( WS-C3850-48P-S ) with ( WS-C3850-48F-S ) .. Thanks in advance

Cisco Employee

Hello moh_ahm1985

It should be possible to stack both switches without problems WS-C3850-48P-S ) with ( WS-C3850-48F-S ).

Just make sure that stacking cables are properly connected and you should be good to go.

Kind Regards!

Beginner

I have a 4 stack of 3850's without the cable running from Switch 1 Port 2 to Switch 4 Port 1.

I now have the cable. 

Is the stack hot swappable? Or should I say; Can I attach this cable to a production stack of 3850's?

Thanks,

Bill

Cisco Employee

Hi Bill,

Since the stack is already formed and working properly the missing cable (from switch 1 port 2 to switch 4 port 1) can be connected and should cause no issues.

Regards.

Luis

Beginner

Hi There, 

You said we should use more than two switches for stacking so its means we will not able to stack only two 3850 switches, can you please elaborate.

Thanks in advance

Sam

Cisco Employee

Hi Sam,

What I mean is that in order for a stack to be formed two or more switches need to be properly connected. 

Therefore, yes you should be able to connect only two switches on a stack.

Fernando.

Beginner

Hi Luis

Thanks for reply, is there any kind of configuration that we have to complete to form the stack in 3850 switches or will switches automatically sense the cables and make stack

Thanks once again

Sam

Cisco Employee

Hello Sam,

As long as the stacking cables are properly connected between the switches the stack should form automatically. 

And no special configuration is needed for them to work as stack.

Kind Regards.

Luis

Beginner

Thanks Luis for your quick reply

Kind Regards

Sam

Beginner

Hi,

Let say for example, based on the diagram above. I would like to simulate a scenario wherein if I unplugged the data stack cable from Switch 1 Port 1 to Switch 2 Port 2. So even if the stack cable was removed, the show switch output should still be as follows (Switch 1: Active, Switch 2: Standby and the rest are members) assuming the priority is hard coded for each switch Priority 15 for Switch 1, Priority 14 for Switch 2, so on and so forth. And no traffic drop will occur. and the standby and member switches will not reboot?

Cisco Employee

Hello John,

If you remove the cable going from switch 1 port 1 to switch 2 port 2 the stack will remain in the same state as before removing the cable (This will only be true as long as there is another cable on switch 1 port 2 connected to another switch to ensure redundancy). As you mention, The active and standby switches will remain the same and none of the switches will reboot nor traffic drop should occur. 

Kind Regards

Beginner

Hi Luis,

Thank you for your answer. Last question, let say in a 4 switch stack ring. Switch 1(active), Switch 2(standby), Switch 3 and Switch 4 (member). Their switch priority are 15,14,13, and 12 respectively. If switch 1 failed, switch 2 will become active, switch 3 will be the standby and switch 4 will stay as member. And if switch 1 went back online, the switch 1 will not preempt, and should become as member. Is there any command to force the switch 1 to become active after it went online?

Cisco Employee

Hi John,

Sorry for my late response. As of now, there is no way to make the previous master switch preempt. That switch will be elected as master again once there is a stack or the current active and standby fail.

Kind Regards.

Community Member

Hello,

Would you be able to stack the different 3850 models together, say a WS-C3850-24XS and WS-C3850-48U model?

Thanks in advance!

Cisco Employee

Hi jppascua1,

Yes, stacking different models of 3850 switches is possible. However, when using the WS-C3850X models they need to be running at least version 3.7 in order to properly form the stack. Apart from that they stack should form properly.

Regards.

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