Chapter 2: Networks and the Internet – Study Notes

Network Basics

  • A network is two or more computers connected via a Network Interface Card (NIC).
  • Networks use radio signals to transmit to a nearby wireless router or hub.
  • A wireless router, hub, or NIC must have an antenna to transmit and receive signals.

The Physical Connection: Local Networks

  • Traditional wired NICs use an RJ-45 connection.
  • Most networks use Cat 5 cable or Cat 6 cable.

The Physical Connection: Local Networks (cont.)

  • The hub is the simplest connection device:
    • Creates a simple network.
    • Sends traffic out all ports (no routing or switching).
  • The repeater boosts signal:
    • Used when cables exceed the maximum length.
  • The switch is an intelligent hub:
    • Sends packets only to the intended host.
  • The router is more sophisticated:
    • Limits traffic to the intended network.

Faster Connection Speeds

  • Internet Connection Types and Speeds: (general overview of faster connection types; no specific figures provided in the transcript).

Wireless and Bluetooth

  • IEEE standard 802.11 governs wireless networking; various letter designations denote different wireless speeds (e.g., 802.11n).
  • Bluetooth is short-distance radio using the 2.4 GHz to 2.485 GHz frequency band.
  • Bluetooth enables devices to discover other Bluetooth devices within range.

Data Transmission

  • Networks transmit binary information in packets using certain protocols and ports.
  • Protocols are rules that govern network and Internet communication:
    • Transmission Control Protocol (TCP) is connection-oriented (stateful).
    • Internet Protocol (IP) is connectionless (stateless).
  • Ports are handles or connection points; each uses a numeric designation for a communication pathway.
  • The combination of your computer’s IP address and port number is referred to as a socket:
    • ext{socket} = ( ext{IP}, ext{port} ).

How the Internet Works

  • To connect to the Internet, you log on to your Internet Service Provider (ISP).
  • The ISP connects to another ISP or a backbone provider.
  • One backbone provider connects to another at a network access point (NAP).

IP Addresses

  • IP (Internet Protocol) Addresses are necessary to navigate the Internet.
  • An IP address is a unique identifier, like a Social Security number.
  • IP addresses are usually in binary form.
  • An IP address consists of four octets separated by decimals:
    • IP = a1.a2.a3.a4, \ a_i in {0,\dots, 255}}.
  • The first octet defines the class to which the IP belongs (classful addressing).
  • Availability of IP addresses:
    • IP addresses are not infinite.
    • An IP address can be IPv4 or IPv6.

IP Addresses (cont.)

  • A subnet is a portion of a network that shares the same subnet address.
  • Subnet masks describe what subnet the address belongs to.
  • Classless Inter-Domain Routing (CIDR) is a way to describe the subnet with the IP address.
  • CIDR notation example: 192.168.0.0/24. which corresponds to a subnet mask of 255.255.255.0 (as described by CIDR/prefix length).

Uniform Resource Locators (URLs)

  • URLs are the easy way to remember a website.
  • DNS translates URLs to IP addresses.
  • Error messages can be sent by the web server when a request cannot be fulfilled.

Uniform Resource Locators (URLs) cont. Error Messages

  • HTTP error message classes:
    • 100-series: informational.
    • 200-series: success (usually not seen because they indicate success).
    • 300-series: redirection.
    • 400-series: client errors.
    • 500-series: server errors.

History of the Internet

  • Cold War roots:
    • 1957: U.S. government formed ARPA (Advanced Research Projects Agency) within the Defense Department.
    • 1968: ARPA commissioned ARPANET, a simple Internet web of four points/nodes.
    • 1979: Usenet newsgroups became available.
    • 1990: Tim Berners-Lee developed Hypertext Transfer Protocol (HTTP).
    • 1993: The first graphical web browser, Mosaic, was invented.

Basic Network Utilities

  • Common utilities you can run from a command prompt (Windows) or shell (UNIX/Linux):
    • IPConfig
    • Ping
    • Tracert
    • Netstat
    • NSLookup
    • ARP
    • Route
    • PathPing

IPConfig

  • IPConfig displays information about your system.
  • Steps:
    • Type cmd in the search bar and press Enter.
    • At the command prompt, type ipconfig and press Enter.
  • IPConfig shows your system’s IP address, subnet mask, and default gateway.
  • Type ipconfig -? to see other options, such as ipconfig /all.

Ping and Tracert

  • Ping tests whether a system is connected to the network.
  • It measures how long it takes for an “echo request” packet to arrive at the destination host.
  • Type ping -? at the command prompt to find various ways to refine your ping request.
  • Tracert is a deluxe version of ping:
    • Shows every “hop” between the host and destination address.
    • Useful tool for technicians and hackers (note the ethical considerations about using such tools).

Netstat and NSLookup

  • Netstat:
    • Network status.
    • Shows active network connections.
  • NSLookup:
    • Name server lookup.
    • Verifies whether the DNS server is running.
    • Executes DNS related commands.

ARP, Route, and PathPing

  • ARP (Address Resolution Protocol):
    • Maps IP addresses to MAC addresses.
  • Route:
    • Displays the IP routing table.
  • PathPing:
    • Similar to tracert/traceroute and ping.
    • Provides detailed information regarding network latency at hops between source and destination.

Other Network Devices

  • Firewalls:
    • Hardware or software.
    • Filter packets as they enter the network.
    • Deny unacceptable packets.
  • Proxy servers:
    • Disguise the network.
    • Substitute their IP address for that of hosts accessing the Internet.

The OSI Model

  • Open Systems Interconnect (OSI) Model:
    • Seven-layer model created to describe how networks communicate.
    • Diagnostic and troubleshooting tool.
    • Each layer supports the layer above and performs a specific function.
  • Layer names (top to bottom): Application, Presentation, Session, Transport, Network, Data Link, and Physical.

The TCP/IP Model

  • Transmission Control Protocol/Internet Protocol (TCP/IP) Model:
  • Four-layer model that performs the same activities as the OSI model, compressed into fewer layers.
  • Layer names: Application, Transport, Internet, and Network Access.

MAC Addresses

  • MAC (Media Access Control) Addresses:
    • A unique address for a NIC.
    • A sublayer of the data link layer of the OSI model.
    • Physical address, as opposed to the IP address.
    • Represented by a 6-byte hexadecimal number.
    • ARP converts IP addresses to MAC addresses.
    • Format example: XX:XX:XX:XX:XX:XX, where each XX is a hexadecimal value.
    • Size: 6\text{ bytes} \rightarrow 48 \text{ bits}.

Cloud Computing

  • Cloud computing enables network access to a shared pool of resources.
  • Three primary classifications:
    • Public clouds: infrastructure or services offered to the general public or a large industry group.
    • Private clouds: used by a single organization, not offered to outside parties.
    • Community clouds: services for several organizations with shared community needs.

Summary

  • This chapter provides a basic understanding of how networks and the Internet work.
  • You should now understand:
    • The structure of networks and the Internet.
    • Basic hardware such as switches, NICs, routers, and hubs.
    • How to use some network utilities.
    • The basics of the OSI model.