Cisco Stackwise

Thank you. This is helpful. We have not always specified a master switch and I was just wondering what ramifications there could be, if any. It seems that there really aren’t many. Let me ask you this, if there were a power outage and no master switch was set in the beginning (we just let it select one on its own) and a different master switch was selected after the power came back up, would there be any cons? It seems we always have issues after a power outage and I was just wondering if this could be the problem. To me it seems it would not since the configuration is pushed down to all the switches in the stack (if it is written to memory). Everyone swears they write to memory, but I also know this could be the issue if the changes weren’t saved. I am just wondering if we should make setting a master switch part of our best practices going forward, if that would alleviate some of our issues.

Hello Marlo

Yes indeed you’re right, in most cases it shouldn’t make a difference.

If you don’t specify a master switch, then the selection process is always the same (user priority, default config, hardware/software priority, uptime, MAC address). So unless something drastic happens, the same switch will be chosen as the master every time.

There is one exception here, however. In the lesson, you’ll notice that criterion number 4 is uptime. If at the time when the power comes back on, for some reason one switch powers on a couple of seconds before the other, then you may have a change in master/member roles. This is not very likely, but it is possible.

Now even if another master switch is selected, the overall operation of the stack should not be affected, assuming, as you say, that all switches still have their configs saved. So under normal operation, there should be no cons in the unlikely event that another switch is chosen as master.

Because there are so many situations in which “normal” operation is never the case, and because sometimes in networking there are so many variables involved when problems arise, it’s always best to limit the number of variables. For this reason, it wouldn’t hurt to assign a user priority to one of the switches to become master, just to ensure that the election process is not contributing to the problem you perceive whenever power goes out…

I hope this has been helpful!

Laz

Thank you very much. This answered my question and I have a much better understanding.

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1:10 says the default priority is 15, but It’s 1. can you please correct it in the text below.
Thanks

Hello Abdulrahman

Yes, you are correct, the default priority value is indeed 1. I will let Rene know to make the necessary adjustments.

Thanks!

Laz

2 Likes

Hello Laz,

What is precise difference of stack & VSD in cisco switches?
And where is stack configuration used mostly

bR//
Nitin Arora

Hello Nitin

Cisco Stackwise and Virtual Service Domain (VSD) are two completely different features. Stackwise allows you to create a single logical switch from multiple individual switches, while VSD is used to classify and separate traffic for network services, such as firewalls and traffic monitoring. For more info on VSD, take a look at the following documentation:

Are you sure you meant VSD? Maybe you meant VSS? If you meant VSS, then take a look at the following NetworkLessons note on various Switch high availability options for more details.

I hope this has been helpful!

Laz

Hello,

I have a stack of 2 switches, and I need to add 2 more members.
What would be the steps?
The current stack of two switches will reboot when I add the other 2 ?
They are Cat 9200.

Thank you in advance.
Regards.

Hello Alexis

Take a look at this Cisco documentation:

In it, it states that a stack of 9200 switches can have a stack member added by doing the following:

  1. Power off the new switch.
  2. Through their StackWise ports, connect the new switch to a powered-on switch stack.
  3. Power on the new switch.

In this process, you don’t have to turn off the active switches, they will continue to operate normally.

I hope this has been helpful!

Laz

hello sir Rene; please what software do you use for virtualization?

Hello Berthol

I assume you mean which emulator is Rene using for the labs? In the past, it was Cisco VIRL that was used, but more recently he uses CML.

I hope this has been helpful!

Laz

2 Likes

Hi Rene,

Thanks for nice article. I have a question regarding stackwise.

I connect end device (which has 2 ethernet ports) to one of the master switch port and another port to member switch port. When master switch goes down, does the member switch port remain connected?

Basically, I want to know what will happen if end device is connected to master switch port and member switch port.

End device: port 1 → master switch port 1/1
port 2 → member switch port 2/1

Thanks,
Abhi

Hello Abhishek

What you are describing is considered best practice, especially for devices such as servers. Typically servers will have two (or more) NICs that will connect ideally to two different switches. Now those switches may be stacked, or may use some other redundancy mechanism (VSS, vPC, StackWise virtual etc). In any case, such a connection can take one of several forms:

  1. Two separate connections using different IP addresses for each NIC
  2. Link aggregation that allows the two NICs to operate as a single virtual NIC

When you use stackwise, it’s always best practice to connect one NIC to one switch in the stack, and the other NIC to a separate switch in the stack. This ensures redundancy in the event of a hardware failure of one of the switches.

Now it doesn’t matter whether it’s the master or the member switch. The behavior will be the same whether the connections are made on the same physical switch or not. What matters is what redundancy configuration is applied to the actual end device. For example, the following lesson shows an example of using EtherChannel on a device with two NICs:

I hope this has been helpful!

Laz

thanks for this. but do you guys have a link that will us to purchase CML

Hello Chris

If you’re interested in purchasing a license for CML, take a look at this link:

On this same page, you will find much more information about CML, as well as the opportunity to do a free test drive of the environment.

I hope this has been helpful!

Laz

Hi guys,

Let’s say we have 2 physically stacked switches at 2 different places. Is it possible to combine those 2 stacks to one stack by using sackwise virtual, for example?

Thanks in advance.

Hello CTE

If you use Stackwise Virtual on all switches involved, it doesn’t matter where each switch is. You can have two switches in one location, and two in another, and stack them all together. Or you can have each switch at different physical locations, you can still stack them.

I assume your question however was, if you have two “traditionally stacked switches” using normal StackWise in one location, and another two in another location, can you stack those two stacks with StackWise Virtual?

StackWise and StackWise virtual are not compatible. Although there are some platforms that support both (such as the 9200 and the 3850 for example) you can’t have a switch participate in traditional StackWise AND StackWise VIrtual.

I hope this has been helpful!

Laz

1 Like

Hello,
I have a question,
We have 3 cisco 9200 in stack with priority set 15,14 and 13. UPlink is connected on data port of switch having 14 priority (standby), whenever we reload active switch we loose ssh connection and then after unplug and plug of uplink ssh connection gets restored.

Hello Nihal

In a switch stack, the switch with the highest priority becomes the master switch. If the master switch fails, the switch with the next highest priority would take over. In your case, when you reload the active switch (priority 15), the standby switch (priority 14) should take over.

So if I understand correctly, after you reload the switch with a priority of 15, you no longer have SSH connectivity. Only when you disconnect and connect the link between the two do you regain connectivity, right?

Well, if that’s the case, it could be because the standby switch is not fully taking over the master role as expected, and is thus not accepting SSH connections. To identify the exact problem, you should check the switch logs and stack status after reloading the active switch to see if there are any issues with the failover process.

I hope this has been helpful!

Laz