In recent network designs, the big, hot and heavy chassis switch has become the last option for a number of reasons.
Switch Performance and Capacity.
Port Density In the past, the most common decision for buying a chassis has been port density. A chassis backplane provides a high speed connection for the line cards to transfer data to the switching fabric. In the early 2000’s when 1 GbE was emerging, chassis backplanes offered from 20 to 40Gbps of performance per slot so that more than 48 ports could be connected at low levels of over-subscription or even non-blocking.
Performance the cost of silicon manufacture has been historically expensive. Large initial investments combined with expensive
Features once you have a costly chassis switch, then it helps the sale process if you can justify the price with extra features. In the end, those features might be important on paper but are rarely used in the real world. Today, physical features like redundant power supplies and fast performance can be found in 1RU switches as well.
Spanning Tree Roots
Loops were not considered during the design of the Ethernet protocol on a single wire. When Ethernet Bridges arrived to scale up the network diameter it was decided that bridges should be self configuring by using a flood and prune mechanism. So the Root Bridges of the Spanning Tree became critical to network stability and limit to scalability because there could only be one root to the tree.
ECMP networking architectures use the same principles that modern chassis switches with mid-plane architectures. Simpler and older chassis switches like the Cisco Catalyst 6500 using VSS have just two spine units feeding the line cards while more modern chassis like Arista 7500E and Nexus 7×00 have fabric cards acting as Spine switches.
You can build a Leaf/Spine network which delivers the port density and scalability of a chassis solution at fraction of the price. There are features specific to a chassis that might make it the right choice but if you can build an L2 or L3 ECMP design, the lower price can forgive a few missing features.
I forgot to highlight a similar post from Lindsay Hill – The Chassis Switch is Dead (whose blog should definitely be in your RSS feed).