Cisco Switch Virtualization

This topic is to discuss the following lesson:

awesome lesson! is there a disadvantage on making them 1 logical switch then bundling the links using etherchannel?

Hi John,

There are a couple of things to consider that come to mind:

  • When all switches are added to a stack, it might become a "single point of failure" if something crazy happens like a bug in IOS that takes down your switch. Instead of a single switch, your entire stack will be affected.
  • The stack ports could become a bottleneck if there is a lot of traffic, this might not happen easily but it's something to think about.
Rene

Really nice lesson, Thanks Rene!

Hi Rene,

awesome:)

What will be the client conectivity at access layer.There should be multiple physical connectivity to every SW in stack for a user , right ?

Switch Virtualization is all about redundancy also make the switchng path more simpler , right ??

br/zaman

Hi Zaman,

Switch virtualization is great for redundancy but it also simplifies your switching a bit. You’ll have less spanning-tree to deal with since all switches in the stack are one “logical” switch.

What you use on the access layer really depends on your design and your budget. Normally we do have redundant connections from the access layer to the distribution layer.

Rene

Can you give an example configuration of linking two separate vss together via port channel. So lets say 2 Layer three switches make up VSS 1 in the distribution layer and 2 layer three switches make up VSS 2 in the core layer – how would you connect VSS 1 (dist) to VSS 2(core) via etherchannel?

Hi Jason,

It’s difficult to give a quick answer to this since there are many different design options.

If you want to learn more about this, I can recommend to take a look at Cisco’s (campus) design guides:

http://www.cisco.com/c/en/us/solutions/enterprise/design-zone-campus/index.html#~validate

Rene

hi Rene,
I want to know vPC related to this topic.

Hi @the.prince.of.nyinyi,

That’s something I will cover once I start with my Nexus material. Here’s quick example though:

With VPC, you can configure a port channel on those Nexus 2000s with the physical links that connect to the 5000 switches. From the 2000’s perspective, it will appear as if it’s connected to a single switch.

Hi Rene,
this is very useful article, and it’s very important topic…thanks

regards,

1 Like

Rene’,

In part of your discussion, you note that “When one of the distribution layer switches fails, the other one can take over. We don’t have this luxury in the access layer…when either of the switches fails then the other one can’t take over. One way of solving this problem is to create a logical switch.”

From what I’ve seen, using stackwise still doesn’t provide redundancy at the access layer. Let’s say that the third switch in the stack dies. All users that are plugged into that third switch are now dead in the water, right?. I don’t see how stackwise is providing any redunancy at the access layer. It just makes switch management easier. Am I missing something?

Hello Andy

The redundancy that is lacking at the access layer has to do with the fact that each end device has a single link to an access switch. Although it is possible to connect a workstation PC to two different access switches for redundancy, this is generally not done and is to expensive for the benefits it provides.

Stackwise however does provide redundancy at quite a few levels. If a whole switch “dies” then of course, redundancy is not maintained for the devices connected directly to it. However, stackwise will provide the following advantages:

  1. In newer models, switches can be powered through the stackwise cables in the event that a power supply or a power source fails.
  2. A stackwise switch can have multiple uplinks, one on each switch, such that even if one switch fails, devices on all other switches will maintain access to the rest of the network.
  3. Stackwise cables are connected in a ring topology, so even if a single stackwise link fails, all switches will remain up

I hope this has been helpful!

Laz