Cisco Stackwise

Lessons Discussion
81

Dear Lagapides

   Your explain are helpful!! Thank you so much.

Nattiya T.

1 Like
82

Hello sir,
Could you please make a summary about this topic on cisco website #how to manage switch stacks#.
Below is the link :
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_52_se/configuration/guide/3750scg/swstack.html#wp1206500

Best regard,

83

Hello Senan

Managing switch stacks is not a simple thing and cannot be summarized in a single post. The lesson shown above gives a good overview of the process and what it actually does. The Cisco documentation that you shared shows that in order to manage switch stacks, you must first understand concepts such as stack membership and election. Additional concepts that must be understood involves MAC addresses, member numbers, and priority values. Hardware compatibility must also be examined to verify that a stack can be created between two switches.

For a more detailed look, the lesson is the best place to begin. Once you master that, you should be able to examine portions of the document you shared and understand it more fully.

I hope this has been helpful!

Laz

84

Hello Guys,

thank you very much for the hard work you do with creating this website. I really appreciate it, and I think that money I pay for the subscription is a really good investment for the future.

Also, I want to ask, if you can create an article about StackWise Virtual, which should be the new virtualization technology that came in with Cisco 9000 products.

When I read some articles about it, it looks the same as Virtual Switching System for me. What are the biggest differences between those two technologies?

Thank You for your answer and time!

Lukas

85

Hello Lukas

I suggest you go to the Member Ideas page below and make your suggestion there. You may find that others have suggested similar lessons for the future, and if so, you can support their ideas as well.

Stackwise virtual does indeed sound a lot like VSS. In its simplest description, stackwise virtual is simply an implementation of stackwise that uses the 10 or 40Gbps interfaces rather than using specialized stacking cables for the connection between the switches. This allows stacked devices to operate at large distances between them (on different floors, or in different buildings) as long as they are connected (typically via fiber connections) to each other. This can be considered an evolution of the stackwise technology.

Now VSS and virtual stackwise, functionally are almost identical. They provide the same features and advantages, but the primary difference is that each technology has been developed for a different platform and IOS. VSS is used for chassis-based Catalyst 4K and 6K series devices that run IOS, while stackwise virtual, as you correctly stated, is for 9K series devices running IOS-XE.

Now having said that, even though the two technologies are quite similar, VSS is an older technology, and in general, is not being further developed while stackwise virtual is quite new and has a lot of potential to grow. Indeed, according to one particular Cisco employee:

It enables several new network design potentials, and with a combination of Cisco UADP ASIC technology and the next-generation Cisco IOS-XE Software operating system, it enables several new advanced technologies such as programmability, application visibility, Multiprotocol Label Switching (MPLS), and much more.

Thanks for sharing that, it really makes everything we’re doing worthwhile. We’re striving to do our best and we’re glad it’s paying off!

I hope this has been helpful!

Laz

1 Like
86

Hi Rene
I don’t have these switches in my lab and wondered if these are available on virl or similar?

Thanks
Frank Faith

87

Hello Frank

Similar to my response concerning VSS, StackWise is another hardware-specific feature that is not supported by emulators such as GNS3 or VIRL.

However, Cisco’s newer version of StackWise, called StackWise Virtual, may be supported on some emulators. I say this with caution because I haven’t tried it myself, but because no special hardware is needed, (because the stack is created via regular Ethernet ports) it may be possible to emulate.

In any case, if you really want to play around with StackWise, you’ll need to obtain physical switches. Because you can find such used switches easily online, and they’re not that expensive, it may be worth the investment.

I hope this has been helpful!

Laz

88

Hi Larz/Rene,

I have two stack switches each connected to distribution/core switch with uplink ports. Now for some reason the switches are removed from stack and are acting standalone.

Since they are stack switch they have one IP address, after getting removed from stack and acting as standalone which switch will have the previous IP address and what happens to the other switch. Will there be any impact on the end points connected to these switches.

89

Hello Tanya

So in other words, the question is, if you have two stacked switches, and they are interconnected to the topology as you describe, what happens if you disconnect the stack cable, or the stack cable fails, correct?

Well, each individual switch will maintain the same configuration that the stack had as a whole. This means that both switches will maintain the same IP addresses. So they would each act as a standalone switch with identical configurations including addressing.

What impact this will have on traffic depends upon whether the stack is using L3 or L2. If routing is being performed by the stack, any user devices connected to these switches will maintain their outgoing traffic, but incoming traffic would be a problem. Any traffic directed to an endpoint on one of these switches would have to be routed to an IP address on the former stack (assuming the stack uses L3). This results in duplicate IP addresses on both uplinks.

If the stack operated only on L2, then the network should continue to function, however, you will find that the management IP addresses which will be the same on both devices will cause an IP conflict, but that should not affect user traffic, because the two switches will simply act as an extension of the broadcast domains (VLANs) for which they have been configured.

More info about this can be found at the “Changes to Switch Stack Membership” section of this Cisco document:

I hope this has been helpful!

Laz

1 Like
90

Hello Rene,

2 questions.

Is there a cisco feature that makes 2 physicial switch into 1 logical switch much like Stackwise but without using a stackwise cable?

When 2 switches with SVI are in Stackwise mode. Do I still use FHRP?
Thank you.

91

Hello Joseph

There are a few options that are available:

  • Virtual Switching System (VSS) is a feature available on chassis models similar to the Catalyst 6500/6800 and 4500/4800. You can find out more about it at this lesson.
  • Virtual Port Channel (vPC) which is a feature of Nexus devices.
  • StackWise Virtual, which is a new feature available in the 9000 series devices that allows you to implement StackWise over normal Ethernet interfaces (typically in the form of EtherChannel) instead of using specialized stack cables. You can find out more about it here.

I hope this has been helpful!

Laz

92

Hi,
If I wantto stack 3 switches I can use switch 1 priority 15 to make it the master.
But I want for example allso be in control of what will be switch 2 and switch 3.

In my lab I create a stack of three switches.
Top switch is mastter but how can I be sure that the second switch is allways the second switch and have interfaces 2/x/x and switch 3 has interfaces 3/x/x
And how Can I switch this?

Hope you understand what I mean

93

Hello Ronald

The way a master switch is elected and the actual numbering of the switches are two different and independent procedures. You can even have a stack master with a switch number of 2 or 3 for example.

From what I understand, you would like to change the switch number of each switch, so that the port numbers appear in the order of the actual physical switches. In order to change these switch numbers, you can use the procedure described in this Cisco documentation.

Specifically, from the master switch CLI, you must issue the following command:

Switch(config)#switch X renumber Y

where X is the current stack number and Y is the new stack number. Once you do this you will have to reload the specific stack member using the following command:

Switch(config)#reload slot X

where X is the current stack number. This will reload that particular switch. When it comes back up, it will have the new number assigned to it. Valid numbers are 1 to 9. If you assign a number that already exists on another switch, the master will choose the next lowest available number.

This procedure does not affect the election of the master switch.

I hope this has been helpful!

Laz

94

Hello Lazaros,

Thanks for your reply.
I have a question about this.
You wrote the command:

Switch(confdig)# switch X renumber x
Switch(config)# reload slot X

But this commands can’t be given in the Configuration Mode.
I must do this in excecute mode I think (like this)

Switch# switch X renumber X
Switch# reload slot X

In my cast to shuffel switch 3 and 2

Switch# switch 2 renumber 3
Switch# switch 3 renumber 2
Switch# reload slot 2
Switch# reload slot 3

Is that right?
I try it on Cisco Catalyst 9200L-48P-4X switches

Kind regards,

Ronald Verheij

95

Hello Ronald

Yes you are correct. The syntax I gave you was for the 3750 switches, where this command is given in global configuration mode ( Switch(config)# ) . However for the 9200 series switches, it is done in the privileged executive mode: (Switch#).

For more details on how to apply the same changes to your 9200 series switches, take a look at this Cisco documentation:

Well, not quite. When you apply the switch X renumber Y command, you have to make sure that the value of Y is not in use at that time. So you may need to do it in three steps:

Switch# switch 2 renumber 4
Switch# switch 3 renumber 2
Switch# switch 4 renumber 3
Switch# reload slot 2
Switch# reload slot 3

I hope this has been helpful!

Laz

96

I have a pair of new switches to add to an exiting 3750 stack. The existing stack carries critical infrastructure and cannot be taken down.

The new infrastructure to be added, was built on the new switches which are already configured- they were numbered as 3 and 4 in the stack prior to build

What I would like to know, is if on adding to the stack, switches 1 and 2 will learn the config that is on switches 3 and 4- I just provision the two new switch models on the master. Or, will the config on switches 3 and 4 be erased, and replaced with the config that is on the master now (blank).

Thanks,
Charles.

97

Hello Charles

Managing stacks can be a challenging issue, especially when you’re working with production networks that hundreds or more people are depending upon. You want to minimize your downtime and avoid unnecessary hassle…

The following Cisco documentation describes the various scenarios in detail:

However, one particular section to note, for your specific situation is:

Scenario: the stack member numbers and the switch types match

  1. If the stack member number of the provisioned switch matches the stack member number in the provisioned configuration on the stack, and
  2. If the switch type of the provisioned switch matches the switch type in the provisioned configuration on the stack.

Then the switch stack applies the provisioned configuration to the provisioned switch and adds it to the stack.

You’ll find multiple scenarios that describe what happens in each case, so you can be sure that the process you follow will give you the right result.

I hope this has been helpful!

Laz

98

Thanks Laz, that’s a big help!

1 Like
99

Hello,

Why should you specify a master switch? If the configuration copies over to all the switches, why would you need to specify one? What are the benefits of specifying a master switch and are there any negatives to not specifying one?

Marlo

100

Hello Marlo

Cisco StackWise functions kind of like a server/client model. One of the switches must function as a master. This is the device that actually does most of the management of the stack, and coordinates with the other devices. In this sense, it is the server that administrates the stack. The members act like clients. They get the commands from the master and respond in the required manner. Even so, all devices share the same configuration. The fact that you need a master switch is simply because StackWise has been designed in this way.

Now if you don’t choose a master, a master will be chosen automatically based on the criteria listed in the lesson. In most cases this is fine, however, it’s always best to have control over these types of choices. For example, the master should be the device that has at least one uplink to the rest of the network. Secondly, you should be aware of which device physically, is the master (the one on top? the one on the bottom?) so that when the time comes for modifications, such as adding or removing a stack member, you have a clearer picture of which is which.

I hope this has been helpful!

Laz