Thursday, 14 February 2013

Cisco Hierarchical Model

Posted by Puneet Sharma on 23:47 Networking No comments

Cisco Hierarchical model is a Three-Layered Hierarchical Model :

The Core layer: backbone:

Top layer of hierarchy.
The core layer is responsible for transporting large amount of traffic both reliably and quickly.
The only purpose of the network's core layer is to switch traffic as fast as possible.
The traffic transported across the core is common to a majority of users.
If there is failure in the core, every single user can be affected. Therefore, fault tolerance at this layer is an issue.
Speed and Latency are driving concern in this layer due to large amount of traffic.

Things we don't want to do:

Don't do anything to slow down traffic. This includes using access lists, routing between virtual local area network(VLANs)
Don't support work-group access here.
Avoid expanding the core (i.e., adding routers) when the internetwork grows.

Things we want to do:

Design the core for high reliability.Consider data-link technologies that facilitate both speed and redundancy, such as Gigabit Ethernet.
The core should have very little latency.
Select routing protocols with lower convergence times.

The distribution Layer:routing:

The distribution layer is sometimes referred to as the work-group layer and is the communication point between the access layer and the core.
This layer ensures that packets are properly routed between Subnets and VLANs in your enterprise.
The primary functions of the distribution layer are to provide routing, filtering, and WAN access.
The other function is to determine how packets can access the core, if needed.

Several action that should be done at the distribution layer:

Routing
Implementing tools(such as access lists), packet filtering, and queuing.
Implementation of security and network policies, including address translation firewalls.
Redistribution between routing protocols, including static routing.
Routing between VLANS and other work-group support functions
Defining broadcast and multicast domains.

The Access layer:switching:

The access layer control user and work-group access to inter-network resources.
It is also referred as Desktop layer.
The distribution layer handles any traffic for remote services.
The resources most users need will be available locally.
Gigabit or Fast Ethernet switching , DDR (Double Data Rate) and Static Routing technologies are frequently used in the access layer.

Functions to be included at the access layer:

Why Use a Hierarchical Model?

Reduces workload on network devices i.e avoid devices having to communicate with too many other devices (reduces CPU performance).
Constrains broadcast domains
Enhances simplicity and understanding

Cisco Hierarchical Design model:

A core layer of high-end routers and switches that are optimized for availability and speed and also include high speed cables such as fiber cables.
A distribution layer of routers and switches that implement policies and segment traffic. It include LAN-based routers and layer 3 switches.
An access layer that connects users via hubs, switches, and other devices.

Made By: P & V