Module 1: Network Design
Reliable Networks
As networks evolve, we have learned that there are 4 basic characteristics that network architects must address to meet user expectations: fault tolerance, scalability, QoS, and Security.
A fault tolerant network limits the number of affected devices during a failure. It allows quick recovery when such a failure occurs. These networks depend on multiple paths between the source and destination of a message. If one path fails, the messages are instantly sent over a different link.
A scalable network expands quickly to support new users and applications. It does this without degrading the performance of services that are being accessed by existing users. Networks can be scalable because the designers follow accepted standards and protocols.
QoS is an increasing requirement of networks today. As data, voice, and video content continue to converge onto the same network, QoS becomes a primary mechanism for managing congestion and ensuring reliable delivery of content to all users. Network bandwidth is measured in bps. When simultaneous communications are attempted accross the network, the demand for network bandwidth can exceed its availability, creating network congestion. The focus of QoS is to prioritize time-sensitive traffic. The type of traffic, not the content of the traffic, is what is important.
Network administrators must address two types of network security concerns: network infrastructure security and information security. Network administrators must also protect the information contained within the packets being transmitted over the network, and the information stored on network attached devices. There are three primary requirement to achieve the goals of network security: Confidentiality, Integrity, and Availability.
Hierarchical Network Design
IP addresses contain 2 parts. One part identifies the network portion. The network portion of the IP address will be the same for all hosts connected to the same local network. The second part of the IP address identifies the individual host on that network. Both the physical MAC and logical IP addresses are required for a computer to communicate on a hierarchical network.
The Network and Sharing Center on a Windows PC shows your basic network information and set up connections, including your active networks and whether you are connected wired or wirelessly to the internet and within your LAN. You can view the properties of your connections here.
On an Ethernet network, the host MAC address is similar to the person's name. A MAC address indicates the individual identity of a specific host, but it does not indicate where on the network the host is located. If all host on the internet (millions and millions of them) were each identified by their unique MAC address only, imagine how difficult it would be to locate a single one. It is better to divide larger networks into smaller, more manageable pieces. One way to divide larger networks is to use a hierarchical model.
Hierarchical networks scale well. The access layer provides a connection point for end user devices to the network and allows multiple hosts to connect to other hosts through a network device, usually a switch or WAP. Typically, all devices within a single access layer will have the same network portion of the IP address. The distribution layer provides a connection point for separate networks and controls the flow of information between the networks. Distribution layer devices control the type and amount of traffic that flows from the access layer to the core layer. The core layer is a high-speed backbone layer with redundant connections. It is responsible for transporting large amounts of data between multiple end networks. The main goal of the core layer is to transport data quickly.