Traditionally, while Ethernet networks were serving low end and non-performance driven applications, the network topology was based on an access layer with a very high port count and a very low rate of traffic generation. This drove a very high and acceptable blocking ratio and a situation where a single (or two in case of need for high availability) uplink would serve for all purposes and connect to an all mighty aggregation chassis that catered for the whole network.
While applications were continuously evolving into becoming more bandwidth hungry, latency sensitive and capacity driven, the need for a wider pipe between the access and aggregation elements in the network became the enabler for the entire evolution of the network. This in turn, drove users towards usage of more interfaces on the aggregation chassis and the network into a gridlock of price to performance ratio.
The need for a high port count of high capacity interfaces on the aggregation switch translates to a very large and complicated chassis. Now although these are available, they are traditionally a step behind the physical evolution or Ethernet technologies; late to arrive with the proper amount of higher speeds interfaces and limiting in terms of their capability to carry the extra volume in terms of power, cooling, control tables and switching matrix. This situation can be resolved by eventually replacing the existing chassis with a newer model with the promise to be more future tolerant than its predecessor and of course accepting the additional cost spent on a huge device (or two in case of need for high availability).
An alternative to hanging your entire network from a single element is to use a fabric of smaller, simpler and more cost effective elements, in order to create a network entity with the required port count, capacity and other performance attributes. This essentially means replacing your modular switch with a Virtual Modular Switch– or how we like to call it–the VMS.
A VMS is a fat tree topology of Ethernet switches with OSPF routing used for topology discovery and ECMP used for load balancing traffic between leaf (access) elements of the VMS via spine (core) elements of it.
Stay tuned to further exploration of the pros and cons in deploying a VMS vs. deploying a modular chassis.