Basics of Campus network Design part 1

A complex network in this context, can either be an Enterprise network or a Campus network. When we talk about designing a complex network, we should be able to apply the same engineering principles in other not to make a mess of our network. 

So in my brief article today, i am going to highlight some two obvious reasons we should endeavor to structure our network designs. 

In Engineering, especially software Engineering, we were taught that to write or design a complex program, that will meet all requirements and run smoothly, we have to follow some laid down design principles. 

As in Engineering design, it also applies to Network design, in that, to design a network that is highly available (in our world today, some organizations require close to 100% availability), airtight security, High flexibility, manageability and very crucially, scalability. 

If after designing a beautiful network and there arise need in the future for more devices to be connected to the network and it warrants tearing down all or most part of the already functional network to do this, then i must tell you, it was never a good design and unscalable. 

So we are looking at design principles of Hierarchy and Modularity, there are others like Resiliency and Flexibility, but my focus on this particular article is on Hierarchy and modularity. These are principles that are inter-connected, meaning they are all equally important in your network designs. 

Now whenever one is designing any large network entity, it is very beneficial to build it using a set of modularised components that can be put together in a hierarchical manner. 

When these systems are divided into components or modules, each of them can be designed with some independence from the entire system and all these modules can be operated as semi independent elements, meaning you have higher availability, simpler management and operation, which is very crucial. 

Now when you don't isolate these modules, to make changes to your network without affecting the whole network, then it would be absolutely challenging to maintain and run the network smoothly, which is not supposed to be so. 

It is the best design practice that you can routinely make repairs or changes to some parts of your network without compromising the whole network availability, also, if one part of your network experiences problem and it affects the entire network, then the design is not proper at all. 

This is a serous design flaw, which many a time some network engineers fall victim of, maybe in a rush or in a bid to beat deadline, one decide to take the less challenging route which at the end of the day will come back and hunt him. 

Looking at the hierarchical design, a Cisco publication on this pointed out that we should ask two questions before diving in to this particular structured principle of design. 

"First, what is the overall hierarchical structure of the campus and what features and functions should be implemented at each layer of the hierarchy. Second, what are the key modules or building blocks and how do they relate to each other and work in the overall hierarchy." 

Campus networks ordinarily have a three tier-hierarchical model, which are , the core, the distribution layer and the Access layer. 

Hierarchical Design of a Campus Network

The Core:
The core layer from the diagram above comprises of four high speed router-switch processor, which as can be seen above is the building block of the network. 

At the core, it serves a specific functions and services, just like the other parts, which is the beauty of hierarchical design, in that every of the three layer has a specific role to play in each of the design. 

This core is designed to be highly available, (its non-negotiable) and operate non stop. To design this core the best way is to provide a good level of redundancy, in the case of disaster or link failure or any form of interruption, there will be immediate data-flow recovery. 

It should also be designed bearing in mind that occasional hardware and software upgrade/change cannot interfer with network apps. As we know, this is the backbone of the network, it holds all the parts of the network architecture together, so it provides connectivities to both the end devices, data storage services and other computing in the network, making its availability extremely important. 

Now it's not like in every campus design, we look to establish these three hierarchy, in some campus designs, core can be collapsed into the distribution layer depending on how closely the buildings are or if it's in one building. But regardless of the campus setting, the major aim of establishing the core is for fault isolation and backbone connectivity. 

Distribution:
From my diagram, distribution and access layers are together, well, distribution layer acts as the linkage and control boundary between the core and access layers. 

So it serves multiple purposes here, one of which is it being an aggregation point for all of the access layer switches and also participate in the core routing design. 

Another role being the provision of  policy control, aggregation and isolation demarcation point between the campus distribution building block and the other parts of the network. 

So by the need to act as an interface to both the access and core, distribution layer functions depend on the requirements of both the core and access layers.

Access:
This is the edge of your network, the first point of design. This is where your end devices reside, (printers, PCs, scanners, cameras etc) and attach to the wired potion of the network.

If you are looking at where your wireless APs reside or the IP phones, it is here at access layer. This is where the demarcation between the network infrastructure and the computing devices take place, meaning it is the first layer of defense in the network security architecture.

When we look at the hierarchical design image above, we see a design that is scalable, a design that has potential to be extended as much as you want it without disrupting the entire structure, unlike the type in the image below,

Network Topology without a core

Designing a campus network without a core, as we can see above has several limitations, chief among which is scalability. 

It does not have room at all for future expansion without compromising the entire or most part of the network, which greatly undermines the 100% availability cravings of some Establishments. More to follow in the subsequent articles concerning network designs fundamental.