The Cisco Three-Layer Hierarchical Model

The Cisco hierarchical model can help you to design implement and maintain salable, reliable, cost-effective hierarchical Internet-work.

Cisco defines three layer of Hierarchy

The following are the three layers and their typical functions

. The core layer: Backbone

. The distribution layer: Routing

. The access layer: Switching

The core layer

The core layer is literally the core of the network. Record layer is responsible for transporting large amount of traffic both reliably and quickly.

Only the Purpose of the network code layer is to switch traffic as fast as possible.

Traffic transported across the code is common to a measurity of users however remember that user data is proceeds at the distribution layer which forward the requests to the core layer if needed.

 The Distribution Layer

Distribution layer is sometimes referred to as the workgroup layer and is the communication. Between the access layer and the core layer.

Primary functions of the distribution layer are to provide routing, filtering, and WAN access and to determine how packets can access the core, if needed.

The distribution layer must determine the fastest way the network service requests are handled.

Example- #.  how a file request is forwarded to a server. After the distribution layer determines the best path it forwards the request to the core layer if needed the core layer then quickly transports the request to the correct service.

There are several actions that generally should be done at the distribution layer they include the following

1. Routing

2. Implementation of tools such as access list, of packet filtering, and of queuing.

3. Implementation of security and network policies including address translation and firewalls

4. Redistribution between routing protocols including static routing.

5. Routing between VLANs and other workgroup support functions.

6. Definitions of Broadcast and multicast domains.

The access layer

The access layer controls user and work-group access to Internet-work resources. The access layer is sometimes referred to as a desktop layer.  The network resources must users need will be available locally the distribution layer handles any traffic for remote services.

The followings are some of the functions to be included at the access layer.

1. Continued (from distribution layer ) access control and policies.

2. Creation of separate collision domains (segmentation)

3. Workgroup connectivity into the distribution layer.

Technologies such as DDR and Ethernet switching are frequently seen in the access layer static routing (instead of dynamic routing protocols) is Seen here as well.