Stacking vs Chassis Access Switch Solutions

August 17, 2015 Jim Schrader

You’ve grown to the point where you need more than 48 ports in a wiring closet, but you’re not sure what your best option is. Should you go with non-stacking or stacking switches? Or does a modular chassis solution make more sense? In this video, we break down your options and give you some recommendations that should point you in the right direction. Simplicity is the basis of success, so we’re going to try to keep this one simple.

Let’s discuss the best way to scale a campus access switch deployment. If you’ve crossed the point where you need more than 48 ports in a closet, you’ve exceeded the capacity of the small fixed configuration switches. The decisions you make now are going to dictate what options you have in the future. So hopefully I’m catching you before you make a purchase. Whether we’re talking about Brocade, Cisco, HP or Juniper, there are basically only three options:

  • Non-Stacking Switches
  • Stacking Switches
  • Chassis Solutions
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Non-Stacking Switches

Let’s start with non-stacking switches. These are standalone devices without a stacking port in the back which means they can’t be combined together to form a single virtual switch. So in order to scale, we have to connect each switch directly to the distribution layer.

Positives of Non-Stacking Switches

  • Pay-as-you-grow
  • High Performance (2:1 Oversubscription)

If your requirements are only 12, 24 or 48 ports, these switches offer a pay-as-you-grow model that also offers strong performance and availability features. For instance, a 48 port switch with two 10 Gigabit uplinks, would essentially have a 2:1 oversubscription ratio. While this is overkill for nearly all campus access switch deployments, this design works well in a small server farm or data center deployment where a 2:1 or 1:1 oversubscription ratio would be a design best practice. It was also the perfect solution for one of our performing arts customers that used the network in a very a different way. They stream video feeds of their live shows to monitors in the lobbies and even the bathrooms.

Negatives of Non-Stacking Switches

  • Additional Cable Runs
  • Additional Distribution Ports
  • Expensive

Before you get all excited about having TV’s in the bathrooms, we need to talk about one of the major drawbacks of non-stacking switches. Each switch must have a separate cable run, plus ports on the distribution layer to terminate each of these switches. For larger deployments, this can get pricey.

Where does this make sense?

  • Small Deployments
  • Small Server Farm or Data Center
  • Top-of-Rack Datacenter

So do we recommend this? Yeah… in certain circumstances. This really only makes sense for small campus deployments or in a niche situation. For example, when distributed servers create a mixed-role scenario in the access layer. These are also very popular as top-of-rack switches in the data center and have largely replaced the end-of-row chassis based deployments.

Stacking Switches

Our next option is stacking fixed configuration switches, which allow us to connect additional devices together to form a single virtual switch. This is accomplished via a stacking cable port on the back of the box.

Positives of Stacking Switches

  • Pay-as-you-grow
  • Small Physical Footprint
  • Convenient 100v Power Standard

So why do people like stacking switches? Once again, you’re looking at a pay-as-you-grow model. We can add ports as we need them by simply purchasing another switch and adding it to the stack. We can stack up to nine 3750-X switches and have 432 x 10/100/1000 ports and 18 x 10 Gbps ports. We can do this using only 9RU’s of rack space. A chassis would require over double the rack space to achieve this access port density. This makes these switches very popular as top-of-rack switches in the data center. Not to mention, we can use 110v rather than 220v, which can be more convenient but is much less efficient.

Negatives of Stacking Switches

  • Stacking Cables
  • StackPower Cables
  • Software Complexity
  • Instability

Switch stacks have become extremely popular for good reason, and it sounds all good, but they’re not without their drawbacks. We need to realize that a switch stack is attempting to mimic the backplane and power redundancy features found in a chassis solution. These cable connections I mentioned a moment ago represent another point of failure. Experience shows that over time, these cables will require reseating or replacement when a switch fails. In that situation, we will be forced to bring down the entire stack.

There are a lot of rules to get a stack working correctly. Mixing switch generations, firmware and software all lower the reliability of the stack, and getting all of these variables to match can be quite the task. Like getting a root kit out of your computer. Seriously have you ever done that? It’s a nightmare. So you won’t get a working stack by just plugging these devices in. Configuration is crucial, and most people don’t realize this until something is already breaking.

Where does this make sense?

  • Flexibility Trumps Availability
  • Desire to Limit Upfront Capital Investment
  • Leverage Existing 110v Power
  • Limited Space Deployments

For most customers, achieving super high availability may not be the goal. And the pay-as-you-grow model is very attractive for customers that need flexibility, not only in their physical network, but also in the amount of traffic that is going through it. Combine a small form factor that will fit just about anywhere and the convenience of 110v, and you can really start to see where these make sense.

Chassis Solutions

Chassis have, and continue, to set the standard for the highest availability in the industry. They are the flagship models of every vendor’s switching line. In contrast to the fixed configuration switches, it is engineered to operate as single integrated system.

Positives of Stacking Switches

  • Solid High Availability Features
  • Modular Design
  • Supports Wide Range of Line Cards
  • Simple to Deploy

When a line card fails in a chassis, it’s isolated to the line card and will NOT impact or degrade the operations of the switch. Failover from the primary to the secondary supervisor is seamless with only a few seconds of disruption, in the worst case scenario. Because the line cards are firmly secured in the backplane of the chassis, we will not encounter the problems seen with the stackable switches. There aren’t any cables to be pulled out, and you won’t have to reseat anything. Performance stays at its peak.

Negatives of Stacking Switches

  • Physical Space (twice the space of stacks)
  • Expensive Power Supplies
  • 220v Power for PoE Solutions

Size, power and space are clear negatives for a chassis solution. For 4507R campus access switch running PoE on all 240 ports, we would need two 6000W power supplies with dual 220v inputs. This solution would also take 11u’s of rack space.

Where does this make sense?

  • High Availability Is a Priority
  • Simplistic Configurations
  • Uniform Deployments

When it comes to availability in the campus access, there is no question that the Catalyst 4507R chassis solution is the king. Configuring high availability is simple and it works every single time. A failed line card will not bring down the entire chassis. Additionally, a chassis will drive consistency in deployment. Deploying the same supervisor across our deployment ensure we can use the same exact software and configuration - a key secret to achieving high availability.

In Conclusion

As always, the most important part is to determine what your requirements are. Once we have this, finding the right hardware is very straightforward. It’s important to balance the cost of acquisition versus the cost of operations and impact to the business due to outages. This is where we begin to get a better picture of what we “should” do.

We have gone through each possible solution, and have given you enough information to make an educated decision on what works best for your network. We are trying to provide some simple conclusions from complicated material. It’s not easy... We get that. There are too many variables to give a one-size-fits-all recommendation, but in general we’re huge fans of Chassis solutions. Keep in mind, pricing shouldn’t be the focus here. We can get both designs for a pretty reasonable price, regardless of requirements. If your network can benefit from both stackables and chassis, go with the Chassis solution. Your life will get so much easier.

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