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# System prepended metadata

title: 109-1 CCNA
tags: [' Class', Network]

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tags: Network, Class
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# 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.

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