Chapter 3

Chapter 3. Structuring and Modularizing The Network.

Introduction. To optimize bandwidth the network must be organized Three-layer hierarchical design model helps to organize the network. This model divides the network functionality into three distinct layers: Access Layer Distribution Layer and Core Layer Each layer is designed to meet specific functions..

Hierarchical Network Design Layers. ■ The access layer Provides connectivity for the users. ■ The distribution layer Used to forward traffic from one local network to another. ■ The core (or backbone) layer Provides high-speed connectivity and transport needs of the distribution layer devices.

[image] Core Layer Distibutbn Layer Access Layer Email Ser,/er DNS sen,er Web Server.

Access Layer. It connects end devices, such as PCs, printers, and IP phones, to provide access to the rest of the network. It can include routers, switches, bridges, hubs, and wireless access points (AP). Its main purpose are:- To provide a means of connecting devices to the network and Controlling which devices are allowed to communicate on the network..

Distribution Layer. Aggregates the data received from the access layer switches before it is transmitted to the core layer. Perform routing functions between virtual LANs (VLANs) defined at the access layer. VLANs allow you to segment the traffic on a switch into separate subnetworks. E.g. In a university you might separate traffic according to faculty, students, and guests. Distribution layer switches are high-performance devices that have redundancy to ensure reliability..

Core Layer. Is the high-speed backbone of the internetwork. The core layer is critical for interconnectivity between distribution layer devices. It should be highly available and redundant. The core area can also connect to Internet resources. The core aggregates the traffic from all the distribution layer, so it must be capable of forwarding large amounts of data quickly..

[image] A Hierarchical Network in a Medium-Sized Business Access Layer Switch istribution Switch User Cornputers Logical Layout E-mail Servers and Database Servers Physical Layout.

Benefits of a Hierarchical Network. Scalability Redundancy Performance Security Manageability.

Scalability. The modularity of the design allows you to replicate design elements as the network grows. Because each instance of the module is consistent, expansion is easy to plan and implement. As you add more distribution layer switches to accommodate the load from the access layer switches, you can add additional core layer switches to handle the additional load on the core..

Redundancy. As a network grows, availability becomes more important. You can increase availability through redundant implementations with hierarchical networks. The primary purpose of redundancy is to meet availability requirements; A secondary goal is to improve performance by supporting load sharing across parallel links. Load sharing, sometimes called load balancing, allows two or more interfaces or paths to share traffic load. Access layer switches are connected to two different distribution layer switches to ensure path redundancy..

Cont.…. [image]. If one of the distribution layer switches fails, the access layer switch can switch to the other distribution layer switch. Additionally, distribution layer switches are connected to two or more core layer switches to ensure path availability if a core switch fails. The only layer where redundancy is limited is at the access layer. End node devices, such as PCs, printers, and IP phones, do not have the ability to connect to multiple access layer switches for redundancy..

Performance. Communication performance is enhanced by increasing the performance of the networking devices. Data is sent through aggregated switch port links from the access layer to the distribution layer. The distribution layer then uses its high performance switching capabilities to forward the traffic up to the core. Because the core and distribution layers perform their operations at very high speeds, there is less controversy for network bandwidth..

Security. Security is improved and easier to manage, in heretical design. Access layer switches can be configured with various port security options that provide control over which devices are allowed to connect to the network. You also have the flexibility to use more advanced security policies at the distribution layer. You may apply access control policies that define which protocols are deployed on your network and where they are permitted to go. For example, if you want to limit the use of HTTP to a specific user connected at the access layer, you could apply a policy that blocks HTTP traffic at the distribution layer.

Manageability. Manageability is relatively simple on a hierarchical network. Each layer of the hierarchical design performs specific functions that are consistent throughout that layer. If you need to change the functionality of an access layer switch, you could repeat that change across all access layer switches in the network because they perform the same functions at their layer. Deployment of new switches is also simplified because switch configurations can be copied between devices with very few modifications. All configurations should be documented..

Flat Network. The flat network is not segmented or separated into different broadcast areas by using routers The network is not divided into layers or modules in a flat network topology. It is easy to design and implement However, it is not suitable for expansion because a change in the network affects the whole network. A flat network will become very slow when the network becomes large. Troubleshooting the network becomes very difficult because you may need to inspect the entire network rather than concentrate on just one area of the network..