--- tags: Network, Class --- # 109-1 CCNA [TOC] [Cisco](https://www.netacad.com/zh-hant) ![](https://i.imgur.com/Mqncpx0.jpg) ### Networks of Many Sizes #### Small Home Networks - connect a few computers to each other and the Internet #### Small Office/Home Office - enables computer within a home or remote office to connect to a corporate network #### Medium to Large Networks - many locations with hundreds or thousands of interconnected computers #### World Wide Networks - connects hundreds of millions of computers world-wide , such as the Internet ### Clients and Servers - Every computer connected to a network is called a **host** or **end device**. #### Servers - Computers that provide information to end devices on the network. For example, email servers, web servers, or file server. #### Clients - Computers that send requests to the servers to retrieve information such as a web page from a web server or email from an email server. ### Peer-to-Peer - In small businesses or homes, it is typical for a client to also function as the server. These networks are called peer-to-peer networks. - Advantages: - easy to set up - less complex - lower cost - Disadvantages: - no centralized administration - not as secure - not scalable - slower performance ### Network Components - Network infrastructure contains three broad categories of network components: - Devices - Media - Services #### End Device - where a message originates from or where it is received. > Data originates with an end device, flows through the network, and arrives at an end device. #### Intermediary Network Devices - An intermediary device interconnects end devices in a network. Examples include: switches, wireless access points, routers, and firewalls. - The management of data as it flows through a network is also the role of an intermediary device including: - Regenerate and retransmit data signals - Maintain information about what pathways exist through the network and internetwork - Notify other devices of errors and communication failures #### Network Media - Networks typically use three types of media: - Metallic wires within cables, such as copper - Glass, such as fiber optic cables - Wireless transmission #### Network diagrams - Often called topology diagrams, use symbols to represent devices within the network. - terms needed to understand - Network Interface Card (NIC) - Physical Port - Interface ### Local Area Network (LAN) - spans a small geographic area owned or operated by an individual or IT department. - Three characteristics of LANs: - Spans a small geographic area such as a home, school, office building, or campus. - Usually administered by a single organization or individual. - Provides high speed bandwidth to end and intermediary devices within the network. ### Wide Area Network (WAN) - spans a large geographic area typically involving a telecommunications service provider. - Three characteristics of WANs: - WANs interconnect LANs over wide geographical areas such as between cities, states, or countries. - Usually administered by multiple service providers. - WANs typically provide slower speed links between LANs. > Other types of networks: >>Metropolitan Area Network (MAN) Wireless LAN (WLAN) Storage Area Network (SAN) ### Internet - LANs are connected to each other using WANs. - WANs are then connected to each other using copper wires, fiber optic cables, and wireless transmissions. #### Intranet - Unlike the Internet, an intranet is a private collection of LANs and WANs internal to an organization that is meant to be accessible only to the organizations members or others with authorization. #### Extranet - An organization might use an extranet to provide secure access to their network for individuals who work for a different organization that need access to their data on their network. ### Home and Small Office Internet Connections - Cable – high bandwidth, always on, Internet connection offered by cable television service providers. - DSL – high bandwidth, always on, Internet connection that runs over a telephone line. - Cellular – uses a cell phone network to connect to the Internet; only available where you can get a cellular signal. - Satellite – major benefit to rural areas without Internet Service Providers. - Dial-up telephone – an inexpensive, low bandwidth option using a modem. ### Businesses Internet Connections > Require higher bandwidth, dedicated connections, or managed services. - Dedicated Leased Line – reserved circuits within the service provider’s network that connect distant offices with private voice and/or data networking. - Ethernet WAN – extends LAN access technology into the WAN. - DSL – Business DSL is available in various formats including Symmetric Digital Subscriber Lines (SDSL). - Satellite – can provide a connection when a wired solution is not available. #### Packet Tracer - Packet Tracer is a fun software program which will help you with your CCNA studies by allowing you to experiment with network behavior, build networks, and find the answers to your “what if” questions. >Traditional Separate Networks --> The Converging Network ### Network Architecture - There are four basic characteristics that the underlying architectures need to address to meet user expectations: - Fault Tolerance - A fault tolerant network limits the impact of a failure by limiting the number of affected devices. - Multiple paths are required for fault tolerance. - Reliable networks provide redundancy by implementing a packet switched network. Packet switching splits traffic into packets that are routed over a network. Each packet could theoretically take a different path to the destination. - This is not possible with circuit-switched networks which establish dedicated circuits. - Scalability - A scalable network can expand quickly and easily to support new users and applications without impacting the performance of services to existing users. - Network designers follow accepted standards and protocols in order to make the networks scalable. - Quality of Service (QoS) - Voice and live video transmissions require higher expectations for those services being delivered. - Have you ever watched a live video with constant breaks and pauses? This is caused when there is a higher demand for bandwidth than available – and QoS isn’t configured. - Quality of Service (QoS) is the primary mechanism used to ensure reliable delivery of content for all users. - With a QoS policy in place, the router can more easily manage the flow of data and voice traffic. - Security - There are two main types of network security that must be addressed: - Network infrastructure security - Information Security - Three goals of network security: - Confidentiality – only intended recipients can read the data - Integrity – assurance that the data has not be altered with during transmission - Availability – assurance of timely and reliable access to data for authorized users ### Cloud Computing - Public Clouds - Services and applications are made available to the general public through a pay-per-use model or for free. - Private Clouds - Applications and services are intended for a specific organization or entity such as the government. - Hybrid Clouds - Made up of two or more Cloud types – for example, part custom and part public. Each part remains a distinctive object but both are connected using the same architecture. - Custom Clouds ### Security - External threats: - Viruses, worms, and Trojan horses - Spyware and adware - Zero-day attacks, also called zero-hour attacks - Hacker attacks - Denial of Service attacks - Data interception and theft - Internal threats: - Whether intentional or not, many studies show that the internal users of the network cause the most security breaches. - With BYOD strategies, corporate data is more vulnerable. - Larger networks have additional security requirements: - Dedicated firewall system to provide more advanced firewall capabilities. - Access control lists (ACL) – used to further filter access and traffic forwarding. - Intrusion prevention systems (IPS) – used to identify fast-spreading threats such as zero-day attacks. - Virtual private networks (VPN) – used to provide secure access for remote workers. [Warriors of the Net](http://www.warriorsofthe.net/)