Stacking 2960-S and 2960-X


At the time of writing, Cisco released the Catalyst 2960X not too long ago. It is the new version of the Cisco Catalyst 2960S, which allows stacking of up to eight switches. It provides up to 80 Gbps bandwidth using the optional FlexStack+ module. For more information about the specifications of the switch, head over to Cisco’s site.

I was not really a fan of the 2960S because of the four switches in a stack limitation. With the introduction of 2960X, network professionals can now pick it over 3750 or 3850 in certain scenarios and also save money. Speaking of money, since Cisco designed 2960X to be backward compatible, companies can take advantage of deploying the switch to join existing 2960S stacks. Therefore, provides their customer’s investment protection.

Mixed Stack

The 2960X allows stacking of up to eight switches and can provide up to 80 Gbps bandwidth with FlexStack+. Since 2960S can only stack up to four and provides up to 40 Gbps bandwidth, both switches are architecturally different and one would think that it shouldn’t stack – but, it does. Since both switches are architecturally different, there have to be some restrictions with mixed stack configuration. If you agreed, then you are correct that there are restrictions with mixed stack and are listed below:

  • Stacking is not supported on switches running the LAN Lite image. All switches in the stack must be running the LAN Base image.
  • In a mixed stack of Catalyst 2960-X and Catalyst 2960-S switches, the number of supported stack members is reduced from eight to four.
  • In a mixed stack of Catalyst 2960-X and Catalyst 2960-S switches, full stack bandwidth is reduced from 80 Gbps to 40 Gbps.
  • In a mixed stack of Catalyst 2960-X and Catalyst 2960-S switches, stack convergence time is increased from milliseconds to 1 to 2 seconds.

Preparation

As with the stacking of 2960S or 3750, network professionals do not need to configure the switches. The stacking is done automatically by the switch by connecting the FlexStack or StackWise cables. However, there will be some work for the network professional to get the mixed stack configuration working properly.

In this scenario, the existing stack is 2960S with 12.2 IOS image and 2960X with 15.0 IOS image. As with the stacking of 2960S and 3750, the IOS needs to match first before the switch can join the stack properly. That said, the 2960S needs to be upgraded to the same software train as the 2960X.

The output shown here is a familiar log message and show switch output that informs the user that there is a software version mismatch.

The 2960X are designed to work with the 15.0 code. That said, we need to make sure the 2960S is upgraded to the same software train as the 2960X in order for it to form the stack. While the 2960S is being upgraded, we need to prepare the 2960X to ensure it forms the stack. Preparing 2960X to join the stack is as simple as issuing only one command. However, my recommendation is to issue another command for the preparation, which will be covered in a bit.

The switch stack port-speed 10 is the command we need to ensure the switch forms the stack. As the command implies, it sets the port speed of the stack port to 10 Gbps since the default of 2960X is 20 Gbps. Without this command, the 2960S will not recognize anything connected to the stack ports. As a result, the stack will not form. The sample output of the command is shown below. As always, make sure to save the configuration before reload.

Optional

The second command that I recommend ensures that both switches are running on the same SDM preference. By default, at least in my testing, the 2960S is set to default as the SDM preference. Make sure to check the SDM preference of the 2960S before changing the 2960X.

In addition, the second command helps with the booting process. Without it, the booting will take a little bit of time since the 2960X will attempt to match the existing stack’s SDM preference. By matching the SDM preference ahead of time, we are bypassing another process that the stack goes through for boot up sequence. A snippet of the boot up output is shown below.

SDM Preference

In the previous section, the output displays that the SDM preference of the switches do not match. The output below shows the default SDM preference of the switches.

To change the SDM preference on the 2960X, please issue the command below. Don’t forget to save the configuration before reloading. Once the configurations are done, the 2960X is ready to join the 2960S stack.

Verification

Just as any other Cisco stack, to verify if the switch(es) join the stack properly is to issue the command show switch, as shown below.

Thoughts

It is a good thing that Cisco is providing investment protection for their customers. It is also good that Cisco released a new version of 2960 platform that supports more than four switches in a stack. The limitation of the 2960S platform that allows only up to four switches in a stack has always been my complaint with it. That said, I don’t normally deploy them in a stack. As a standalone switch, it is a good platform and cheaper than 3750. Having said that, I’ve always liked the 3750 platform for scenarios where I need to have stacking capability since it can go up to nine switches. But with this new 2960 platform, it has earned a place with me.

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.


About Andrew Roderos

As an IT professional, I have a strong passion for technology and a desire to learn more about it. Technologies that I am mostly interested in are computer networking, network security, virtualization, and programming. Outside of the information technology world, I enjoy traveling, reading science fiction books and manga, watching movies, and photography.