Summary CCNA 1

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Summary - CCNA 1

  • 1 Explore the Network

  • What is a host or end device?
    All computers connected to a network that participate directly in network communication are classified as hosts. Hosts are also called end devices.
    An end device is either the source or destination of a message transmitted over the network.
  • What is a server?
    Servers are computers with software that enable them to provide information, like email or web pages, to other end devices on the network. Each service requires separate server software.
  • What is a client?
    Clients are computers with software installed that enable them to request and display the information obtained from the server. An example of client software is a web browser, like Chrome or FireFox.
  • What is a peer-to-peer network?
    Computers function as the servers and clients on the network. This type of network is called a peer-to-peer network.
  • What are the advantages of peer-to-peer networking?

    The advantages of peer-to-peer networking:
    - Easy to set up
    - Less complexity
    - Lower cost since network devices and dedicated servers may not be required
    - Can be used for simple tasks such as transferring files and sharing printers
  • What are the disadvantages of peer-to-peer networking?

    The disadvantages of peer-to-peer networking:
    - No centralized administration
    - Not as secure
    - Not scalable
    - All devices may act as both clients and servers which can slow their performance
  • What categories of network components does the network infrastructure contain?
    - Devices
    - Media
    - Services  

    Devices and media are the physical elements of the network. Media connect devices. Sevices include network applications people use every day.
  • What is an intermediary network device?
    Intermediary divices connect the individual end devices to the network and can connect multiple individual networks to form an internetwork. These intermediary devices provide connectivity and ensure that data flows acress the network.
  • Intermediary Device
    LAN Switch
  • Intermediary Device
    Wireless Router
  • Intermediary Device
    Router
  • Intermediary Device
    Multilayer Switch
  • Intermediary Device
    Firewall Appliance
  • What are the three types of Network Media (medium)?
    • Metallic wires within cables - data is encoded into electrical impulses
    • Glass or plastic fibers (fiber optic cable) - data is encoded as pulses of light
    • Wireless transmission - data is encoded using wavelengths from the electromagnetic spectrum
  • What are the criteria to consider when choosing network media?

    - What is the maximum distance that the media can successfully carry a signal?
    - Into what type of environment will the media be installed?
    - What is the amount of data and the speed at which it must be transmitted?
    - What is the cost of the media and installation?
  • What is a Topology diagram?
    A diagram that represent the different devices and connections that make up a network.
  • What is a Network Interface Card (NIC)?
    A NIC, or LAN adapter, provides the physical connection to the network at the PC or other end device. The media that are connecting the PC to the networking device, plug directly into the NIC. 
  • What is a Phycical Port?
    A connector or outlet on a networking device where the media is connected to an end device or another networking device.
  • What is an Interface/port?
    Specialized ports on a networking device that connect to individual networks. Because routers are used to interconnect networks, the ports on a router are referred to as network interfaces.
  • End Devices
    Desktop Computer
  • End Devices
    Laptop
  • End Devices
    Printer
  • End Devices
    IP Phone
  • End Devices
    Wireless Tablet
  • End Devices
    TelePresence Endpoint
  • Network Media
    Wireless Media
  • Network Media
    LAN Media
  • Network Media
    WAN Media
  • Name two types of topology diagrams
    - Physical topology diagrams - Identify the physical location of intermediary devices and cable installation. 
    - Logical topology diagrams - Identify devices, ports, and addressing scheme. 
  • Name the two most common types of network infrastructures
    • Local Area Network (LAN) - A network infrastructure that provides access to users and end devices in a small geographical area, which is typically an enterprise, home, or small business network owned and managed by an individual or IT department.
    • Wide Area Network (WAN) - A network infrastructure that provides access to other networks over a wide geographical area, which is typically owned and managed by a telecommunications service provider.
  • Name five types of network infrastructures?
    • Local Area Network (LAN) - A network infrastructure that provides access to users and end devices in a small geographical area, which is typically an enterprise, home, or small business network owned and managed by an individual or IT department.
    • Wide Area Network (WAN) - A network infrastructure that provides access to other networks over a wide geographical area, which is typically owned and managed by a telecommunications service provider.
    • Metropolitan Area Network (MAN) - A network infrastructure that spans a physical area larger than a LAN but smaller than a WAN (e.g., a city). MANs are typically operated by a single entity such as a large organization.
    • Wireless LAN (WLAN) - Similar to a LAN but wirelessly interconnects users and end points in a small geographical area.
    • Storage Area Network (SAN) - A network infrastructure designed to support file servers and provide data storage, retrieval, and replication.
  • Name specific features of a LAN network infrastructure
    LANs are a network infrastructure that spans a small geographical area. Specific features of LANs include:
    • LANs interconnect end devices in a limited area such as a home, school, office building, or campus.
    • A LAN is usually administered by a single organization or individual. The administrative control that governs the security and access control policies are enforced on the network level.
    • LANs provide high speed bandwidth to internal end devices and intermediary devices.
  • Name specific features of a WAN network infrastructure
    WANs are a network infrastructure that spans a wide geographical area. WANs are typically managed by service providers (SP) or Internet Service Providers (ISP).
    Specific features of WANs include:
    • WANs interconnect LANs over wide geographical areas such as between cities, states, provinces, countries, or continents.
    • WANs are usually administered by multiple service providers.
    • WANs typically provide slower speed links between LANs.
  • Describe 'The Internet'
    The Internet is a worldwide collection of interconnected networks (internetworks or internet for short).
    The Internet is not owned by any individual or group.  Ensuring effective communication across this diverse infrastructure requires the application of consistent and commonly recognized technologies and standards as well as the cooperation of many network administration agencies. 
  • Name the organizations that have been developed for the purpose of helping to maintain structure and standardization of Internet protocols and processes.
    - IETF: Internet Engineering Task Force
    - ICANN: Internet Corporation for Assigned Names and NUmbers
    - IAB: Internet Architecture Board
    - many others
  • What's the diffrence between internet and Internet?
    The term internet (with a lower case “i") is used to describe multiple networks interconnected. When referring to the global system of interconnected computer networks or the World Wide Web, the term Internet (with a capital “I”) is used.
  • What is an Intranet?
    Intranet is a term often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization's members, employees, or others with authorization.
  • What is an Extranet?
    An organization may use an extranet to provide secure and safe access to individuals who work for a different organization, but require access to the organization’s data. Examples of extranets include:
    • A company that is providing access to outside suppliers and contractors.
    • A hospital that is providing a booking system to doctors so they can make appointments for their patients.
    • A local office of education that is providing budget and personnel information to the schools in its district.
  • Name two diffrent ways to connect to the internet.
    - Internet Service Provider (ISP): Home users, teleworkers (remote workers), and small offices typically require a connection to an Internet Service Provider (ISP) to access the Internet. Connection options vary greatly between ISP and geographical location. However, popular choices include broadband cable, broadband digital subscriber line (DSL), wireless WANs, and mobile services.
    - Service Provider (SP): Business-class interconnections are usually provided by service providers (SP). Popular business-class services include business DSL, leased lines, and Metro Ethernet.
  • Name five common connection options for small office and home office users.
    • Cable - Typically offered by cable television service providers, the Internet data signal is carried on the same cable that delivers cable television. It provides a high bandwidth, always on, connection to the Internet.
    • DSL - Digital Subscriber Lines provide a high bandwidth, always on, connection to the Internet. DSL runs over a telephone line. In general, small office and home office users connect using Asymmetrical DSL (ADSL), which means that the download speed is faster than the upload speed.
    • Cellular - Cellular Internet access uses a cell phone network to connect. Wherever you can get a cellular signal, you can get cellular Internet access. Performance will be limited by the capabilities of the phone and the cell tower to which it is connected.
    • Satellite - The availability of satellite Internet access is a real benefit in those areas that would otherwise have no Internet connectivity at all. Satellite dishes require a clear line of sight to the satellite.
    • Dial-up Telephone - An inexpensive option that uses any phone line and a modem. The low bandwidth provided by a dial-up modem connection is usually not sufficient for large data transfer, although it is useful for mobile access while traveling.
  • Name four connection options for businesses.
    • Dedicated Leased Line - Leased lines are actually reserved circuits within the service provider’s network that connect geographically separated offices for private voice and/or data networking. The circuits are typically rented at a monthly or yearly rate. They can be expensive.
    • Ethernet WAN - Ethernet WANs extend LAN access technology into the WAN. Ethernet is a LAN technology you will learn about in a later chapter. The benefits of Ethernet are now being extended into the WAN.
    • DSL - Business DSL is available in various formats. A popular choice is Symmetric Digital Subscriber Lines (SDSL) which is similar to the consumer version of DSL, but provides uploads and downloads at the same speeds.
    • Satellite - Similar to small office and home office users, satellite service can provide a connection when a wired solution is not available.
  • What is a converging network?
    Back in the day, there was a seperate network for computer networks, telephone networks and broadcast networks. Today, the separate data, telephone, and video networks are converging. Unlike dedicated networks, converged networks are capable of delivering data, voice, and video between many different types of devices over the same network infrastructure. This network infrastructure uses the same set of rules, agreements, and implementation standards.
  • What is the physical infrastructure in a network?
    The many different types of cables and devices make up the physical infrastructure.
  • What is network architecture?
    The technologies that support the infrastructure and the programmed services and rules, or protocols, that move data across the network.
  • What are the four basic characteristics that the underlying architectures need to address in order to meet user expectations?
    • Fault Tolerance
    • Scalability
    • Quality of Service (QoS)
    • Security
  • Explain 'Fault Tolerance'
    A fault tolerant network is one that limits the impact of a failure, so that the fewest number of devices are affected. It is also built in a way that 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 can be instantly sent over a different link. Having multiple paths to a destination is known as redundancy.
  • What is a packet-switched network?
    One way reliable networks provide redundancy (Fault Tolerance) is by implementing a packet-switched network. Packet switching splits traffic into packets that are routed over a shared network. A single message, such as an email or a video stream, is broken into multiple message blocks, called packets. Each packet has the necessary addressing information of the source and destination of the message. The routers within the network switch the packets based on the condition of the network at that moment. This means that all the packets in a single message could take very different paths to the destination.
  • What is a 'Circuit-switched network'?
    A circuit-switched network is one that establishes a dedicated circuit between the source and destination before the users may communicate. If the call is unexpectedly terminated, the users must initiate a new connection.
  • Explain 'Scalability'
    A scalable network can expand quickly to support new users and applications without impacting the performance of the service being delivered to existing users.
  • Explain 'Quality of Service'
    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.
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What is ARP spoofing?
In some cases, the use of ARP can lead to a potential security risk known as ARP spoofing or ARP poisoning. This is a technique used by an attacker to reply to an ARP request for an IPv4 address belonging to another device, such as the default gateway, as shown in the figure. The attacker sends an ARP reply with its own MAC address. The receiver of the ARP reply will add the wrong MAC address to its ARP table and send these packets to the attacker.
What happens when an ARP reply is received?
Only the device that originally sent the ARP request will receive the unicast ARP reply. Once the ARP reply is received, the device will add the IPv4 address and the corresponding MAC address to its ARP table. Packets destined for that IPv4 address can now be encapsulated in frames using its corresponding MAC address.
The ARP reply is encapsulated in an Ethernet frame using the following header information:
  • Destination MAC address – This is the MAC address of the sender of the ARP request.
  • Source MAC address – This is the sender of the ARP reply’s MAC address.
  • Type - ARP messages have a type field of 0x806. This informs the receiving NIC that the data portion of the frame needs to be passed to the ARP process.
Only the device with an IPv4 address associated with the target IPv4 address in the ARP request will respond with an ARP reply. The ARP reply message includes:
  • Sender’s IPv4 address – This is the IPv4 address of the sender, the device whose MAC address was requested.
  • Sender’s MAC address – This is the MAC address of the sender, the MAC address needed by the sender of the ARP request.
The ARP request is encapsulated in an Ethernet frame using the following header information:
  • Destination MAC address – This is a broadcast address requiring all Ethernet NICs on the LAN to accept and process the ARP request.
  • Source MAC address – This is the sender of the ARP request’s MAC address.
  • Type - ARP messages have a type field of 0x806. This informs the receiving NIC that the data portion of the frame needs to be passed to the ARP process.
ARP messages are encapsulated directly within an Ethernet frame. There is no IPv4 header. The ARP request message includes:
  • Target IPv4 address – This is the IPv4 address that requires a corresponding MAC address.
  • Target MAC address - This is the unknown MAC address and will be empty in the ARP request message.
When is an ARP request sent?
An ARP request is sent when a device needs a MAC address associated with an IPv4 address, and it does not have an entry for the IPv4 address in its ARP table.
The sending device will search its ARP table for a destination IPv4 address and a corresponding MAC address. Explain what happens is the destinations IPv4 address is on the same network as well as on a different network.
  • If the packet’s destination IPv4 address is on the same network as the source IPv4 address, the device will search the ARP table for the destination IPv4 address.
  • If the destination IPv4 address is on a different network than the source IPv4 address, the device will search the ARP table for the IPv4 address of the default gateway.
In both cases, the search is for an IPv4 address and a corresponding MAC address for the device.
Each entry, or row, of the ARP table binds an IPv4 address with a MAC address. We call the relationship between the two values a map - it simply means that you can locate an IPv4 address in the table and discover the corresponding MAC address. The ARP table temporarily saves (caches) the mapping for the devices on the LAN.
If the device locates the IPv4 address, its corresponding MAC address is used as the destination MAC address in the frame. If there is no entry is found, then the device sends an ARP request.
What is the ARP table?
Resolving IPv4 Addresses to MAC Addresses
When a packet is sent to the data link layer to be encapsulated into an Ethernet frame, the device refers to a table in its memory to find the MAC address that is mapped to the IPv4 address. This table is called the ARP table or the ARP cache. The ARP table is stored in the RAM of the device.
To determine the destination MAC address, the device uses ARP. ARP provides two basic functions:
  • Resolving IPv4 addresses to MAC addresses
  • Maintaining a table of mappings