350-401 ENCOR - Cisco - Network design basics

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 Hierarchial Network Design


What is a FLAT NETWORK?

Flat Networks are networks in which all computers, servers, printers are connected together using just layer 2 switches, there is no use of subnets in flat networks, in addition,  all devices are located in the same broadcast domain and broadcast trafic is transmitted to all devices on the network and because of that BANDWIDTH is not used effectively.


FLAT networks CAN NOT meet the needs of most enterprise networks or small to medium size business.


What is a Hierarchical NETWORK?


Hierarchical Models allow to design the network by using different layers,

Layers of the Hierarchical Network are devided into specific functions that are categorized as CORE, DISTRIBUTION and ACCESS Layers.

This categorization privides FLEXIBLE design options and ease scaling of  network devices.

Here is an overview that explains the difference between a flat Network VS Hierarchical Network:



As you can see that in the FLAT network model, all devices are just connected to a Layer 2 switch,

The first FLAT architecture represents a ONE LARGE BROADCAST DOMAIN which is NOT recommended.


In the second Model which is the HIERARCHICAL Network we have three Layers:

 - ACCESS Layers

 - DISTRIBUTION Layer

 - Core Layer


And we can see that we have three seperate broadcast DOMAINS


Let's talk about HIERARCHICAL network layers in more details:


-  In a local area network LAN environnement, the ACCESS LAYER provides the end devices access to the network, the ACCESS LAYER serves a number of functions including Layer 2 SWITCHING, HIGH AVAILABILITY, Port Security, QoS or Quality of Service Classification marking, ARP INSPECTION, Virtual ACCESS Control lists, Spanning Tree or STP, PoE or Power Over Internet etc...


- The DISTRIBUTION LAYER aggregates the data received from ACCESS LAYER Switches before it's transmitted to the CORE LAYER for routing to its final destination.

- DISTRIBUTION Layer can provide AGGREGATION of LAN (Local Area Network) or Wide Area Network Links (WAN).


The CORE Layer is also referred to as the network BACKBONE, it consists of high speed network devices such as CISCO CATALYST 6500 or 6800 models.


These Cisco equipments are designed to switch packets as faster as possible and interconnect multiple campus components such as  DISTRIBUTION MODULES, Service Modules, the DATACENTER and the WAN

At the CORE LAYER, High Speed Switching is also considered as a main facor, which provides reliability and fault tolerance, scaling by using not so many equipements which they offer scalability due to their integrated circuits and better CPU, RAM etc...




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