Switch Stacking

Stacking for switches might not sound very sexy or complicating when compared to routing protocols; however it makes a great deal when being used in a suitable environment. Many times when we have discussions with our clients its this small matter that is being left out & eventually creates the friction between us. There is some good in this & when implemented it truly can benefit them big time.

What is it?

It is a method to connect two or more switches together so it can look & operate as one single unit by means of using a cable. Firstly the switches must support stacking feature. There are many out in the market such as Aruba, Cisco, Arista, Netgear, FS and many more. The first switch is called the stack master switch and it contains the running and saved configuration for the whole stack.

These cables are connected to specific ports on the switch in two methods:

• Backplane stacking (BPS), where specific stacking modules (usually on the back of the switch) are used with specific cables (depending on the vendor).
• Front-plane stacking (FPS)-VSF, where usually are used standard Ethernet ports to build the stack, using standard Ethernet cables.

The stacking topology that can be deployed for resiliency would be:-

• Daisy chain or bus is not usually used because it does not provide resiliency
• Ring or redundant dual ring provide resiliency, but with more than two switches the packet paths can be not optimal
• Mesh or full mesh provide higher resiliency and also optimal packet paths

Why to use stacking?

One thing we find it is much easier to view the switches in a logical view with a single management interface & that makes management and operational tasks very easy. It also allows for link aggregation between ports of different switches within the same stack. This provides better bandwidth and resiliency for the downstream links and simplifying network design implementation where multiple cables are just one single logical link using LAG, LACP, EtherChannel or any link aggregation solutions. When compared to modular switches we find it less expansive & similar scalability & usually with better flexibility. When speaking regarding flexibility, we were able to mix a combination of different port speed and media types, but also mix different models of switches with also different capabilities. Stacking is more related to bandwidths and stacking topology instead of performance.

Issues that we faced!

At times in discussion with clients we have trouble getting the suitable switch for addressing their needs due to in-house or regulatory guidelines. Some of the secondary issues would be performance, manageability & resiliency. Even if its a great technology clients are forced to use a specific vendor in order to use the stacking feature which results in vendor lock-in. Each vendor have their own unique set of features and functionalities, different types of connectors, cables and software for their stackable switches. This creates a limitation. Latency and decreased overall performance can be noticed when the stack expands or when the client require higher speed. Here are some serious issues we faced during adding new stack member where all the switches will reboot & cause service disruption; however this happens only from certain vendors. Even upgrading firmware will require rebooting of the switches.

Last words!

Stacking is a super cool tool when used in the right environment. One method we use is to look at previous records of switch changes, upgrades to determine if stacking is a good option for the client.