CCNA Study Notes – Chapter 1

Networks

When designing and maintaining a network, remember these factors:

Cost, security, speed, topology, scalability, reliability, availability

VoIP and video traffic is sensitive to delay and latency. Therefore QoS is commonly implemented to ensure these applications have enough bandwidth and are prioritised throughout the network to limit the amount of delay they incur.

Security appliances are specialised network components that typically provide many security functions, such as Cisco ASA’s and PIX, Cisco 4200 intrusion prevention and detection systems(IPS & IDS), and Cisco 3000 VPN Concentrators.

The media types used in LAN’s include copper and fibre cabling. Ethernet, Fast Ethernet(FE), Gigabit Ethernet(GE), Token Ring, and fibre distributed data interface(FDDI) are frame types used to communicate between components on fibre and copper.

Four basic types of connections or circuits are used in WAN services:

Circuit-Switched, Cell-Switched, Packet-Switched, and dedicated connections.

LAN’s provide high-speed bandwidth connections to interconnect components is geographically close locations, such as building or campus. WAN’s provide lower speed bandwidth connections to interconnect multiple locations or sites. WAN’s involve paying recurring monthly costs to a service provider.

Examples of networking devices used in WAN connections include cable and DSL modems, carrier switches, CSU/DSUs, firewalls, modems, NT1s and routers.

Network Topologies

A topology defines how the components are connected. A point-to-point topology has a single connection between two components.

In a star topology, a central device has many point-to-point connections to other components. The main problem with a star topology is that if the center of the star fails, no components can communicate with each other.

In a bus topology, all components are connected to and share a single wire.

In a ring topology, device one connects to device two, device two connects to device three, and so on to the last device, which connects back to the first device. Ring topologies can be implemented with a single or dual ring. Dual rings are for redundancy.

Fibre Distribute Data Interface(FDDI) is an example of a media technology that uses dual rings to connect computer components.

A physical topology describes how components are physically cabled together. A logical topology describes how components communicate across the physical topology. The physical and logical topologies are independent of each other.

For example, any variety of Ethernet uses a logical bus topology when components communicate, regardless of the physical layout of the cabling.

Two types of meshed topologies are used: partial and full.

In a partially meshed environment, every device is not connected to every other device. In a fully meshed environment, every component is connected to every other component.

The formula used to determine the number of links needed to fully mesh a WAN is N x (N-1) ÷ 2, where N is the number of locations.

Network Security

Before you even consider designing a security solution for a network, you must have a sound security policy in place. The security policy will determine the security solution you will design, implement, and maintain. The Securing Cisco Network Devices course and book briefly talks about security policies. A better reference is RFC 2196 on www.ietf.org.

Four categories of common threats to networks and their components can occur: physical installations, reconnaissance attacks, access attacks, and denial of service(DoS) attacks.

Physical installations involve four types of threats: hardware, electrical, environmental, and maintenance.

Remember that most threats to a network are internal; therefore, developing a security plan to deal with physical threats is very important.

Electrical threats include irregular fluctuations in voltage, such as brownouts and voltage spikes, and complete loss of power.

Environmental threats include very low or high temperatures, moisture, electrostatic, and magnetic interference.

Maintenance threats include not having backup parts or components for critical network components; not labelling components and their cabling correctly, causing problems when performing maintenance in and around network components; and not following electrostatic discharge procedures before handling network components.

A reconnaissance attack occurs when an adversary tries to learn information about your network.

An access attack occurs when someone tries to gain unauthorised access to a component, tries to gain unauthorised access to information on a component, or increases their privileges on a network component.

DoS attacks involve an adversary reducing the level of operation or service, preventing access to, or completely crashing  a network component or service.

Designing and maintaining  networks includes factors such as cost, speed, topology, type, scalability, reliability, and availability. Certain kinds of traffic, such as VoIP and video, are sensitive to delay and latency and therefore your design should include QoS features to deal with these types of traffic. The kinds of network components you’ll see in a network include routers, switches, bridges,  hubs, and security appliances such as firewalls and IDS/IPS security appliances.