Virtual Chassis Technology : Stack/Combine Access Switches across a Campus

Stacking multiple Switches has its advantages but often it is only possible to combine/ stack switches that are physically located within a few meters. A proprietary technology called Virtual Chassis technology offered by a few vendors can combine / stack access switches that are located far away (even a few KM) into a single virtual chassis group with a common management domain and multiple 10GE interlink (backplane) capacity.

Multiple Network Switches can be Stacked together and this approach has some advantages.

Network Switch Stacking provides a common management domain for all the switches in the stack group, allows network administrators to start with a single 2U Switch and grow the density as required, keeping initial costs low and provides a good backplane capacity for all the switches.

But there is one limitation with Stacking Switches – Physical proximity is required between all the individual switch units.

In many organizations, there are multiple departments which are located over a distance of even few Kilometers, at times. So, it can be difficult to manage multiple switches in multiple departments.

The Virtual Chassis technology combines multiple switches (irrespective of their location, as long as they can be connected with optical fiber cables) into one VC Group that can have a single management domain and single IP address. So, all these switches can be managed as a single switch. Like in Stacking, there is a master which is the main switch and all the configuration changes/ firmware updates can be done to the master switch, which automatically gets propagated to other switches in the VC group.

The key enabler of this concept is the availability of high speed 10 GE links (Even multiple 10GE links using Link Aggregation if ports are available) that can give a decent interconnect bandwidth between the members of the VC group, even if the switches are located at different places. Of course, if they are located nearby, the interconnect bandwidth could be much higher using special cables/ interfaces. Of course, there is a limitation to the maximum number of switches that can be a part of the VC group (like a maximum 10 switches as in some cases).

For example, consider there is a campus with three buildings that are interconnected with sufficient fiber cores. Each building has the following requirement – 96 Ports, 48 ports & 48 ports. So, two 48 port switches could be deployed in the first location, and single 48 port switches could be deployed in the other two locations for network connectivity and all these switches can be a part of a virtual chassis group with a single management interface and high speed 10 GE interconnects.

The single 48 Port switch could be replaced with two 24 port switches if 50% port availability is desired at any time, even in case of individual switch failures in order to have some level of redundancy. Still, all these switches could be a part of the same VC group.

The Virtual Chassis technology can also be used in TOR – Top of the Rack configurations in Data Centers, where multiple servers in a single rack are connected in a dual homed fashion to two switches on the top of each rack to provide complete hardware redundancy even in the case of a switch failure. Multiple such switches in multiple racks within a data center could be a part of a Virtual Chassis that can be managed as a single unit.

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