Network Ninja

As I posted after I passed BCMSN I was going to be doing things a little differently. This is the different I was talking about; I am going to crawl before I am going to try and fling myself off a building (baby steps). In this post I am going to go over the Foundation topics for Network Design.

Defining Scalability

As the course is called Building Scalable Cisco Internetworks (BSCI) one of the underlying topics covered is  scalability. This can be defined as the capacity of a network to keep pace with changes and growth. An example of this would exponential (full-mesh topology) versus linear network growth (hub and spoke topology or Star Topology).

When one compares the two topologies a full-mesh topology grows exponential and thus just isn’t realistically scalable, this would be because of the cost element associated to build a large network using this topology.

To illustrate the exponential growth pattern of a network using this topology use the following equation:

Connections = Sites ( Sites – 1 ) ÷ 2

Using this equation a table can be drawn up (left) where one can see just how quickly a relatively small number of nodes (sites) quickly require many connections to keep the one node has a connection to all other nodes true.

This is the reason why this topology isn’t practically scalable in real life (IRL). Calculating the number of point-to-point connections and related hardware requirements needed there are very few companies that would be able to bankroll this sustainably (maybe if they own the underlying network architecture like a telecom or a company where the network itself is the business).

A hub and spoke topology grows incrementally as the network increases in size. Look at the above diagram and you see 5 nodes and a central switching station in the centre. This type of topology is realistically scalable because adding the 10th node would cost the same as adding the 100th node; the only cost incurred would be a point-to-point connection and network kit.

To illustrate the linear growth pattern of this network using this topology use the following equation:

Connections = Sites – 1

Resources:

Aragoen Celtdra on BSCI: Network Architecture and Design

Notes and Notices:

This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.