Technical Literacy

The Guide

Computer Networking: Overview

Definition:

A computer network is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information.

  • Facilitates communications
  • Permits sharing of files, data, and other types of information
  • Shares network and computing resources
  • May be insecure
  • May interfere with other technologies
  • May be difficult to set up
  • Borrows from electrical engineering, telecommunications, computer science, information technology and computer engineering
  • Classified based on: data transport medium, communications protocol used, topology, organizational scope, and scale.

How it enables me to do what I need:

A computer network allows me to use the Internet at home, at school and on the go. It allows me to print wirelessly from my PC. It allowed me access to my old company's Intranet where I would enter my time. In college, it allowed me to listen to the music of other students. And so on.

Scale (purpose):

> Personal area network (PAN)

Used for communication between computer and different information technological devices close to one person (PCs, printers, telephones, PDAs, etc.). Reach typically extends to 10 meters. Wired: constructed with USB and Firewire connections. Wireless: constructed with Bluetooth and infrared.

> Local area network (LAN)

Connects computers and devices in a limited geographical area (home, school, computer lab, office, etc.). Each computer or device on the network is a node. Usually based on Ethernet technology, although new standards (ITU-T G.hn) also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).

The defining characteristics of LANs, in contrast to WANs (Wide Area Networks) are: higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. LANs can be connected to Wide area network by using routers.

> Home network (Residential LAN)

For communication between home digital devices (PCs and accessories like printers and mobile computing devices) through the sharing of Internet access like broadband service through a cable TV or Digital Subscriber Line (DSL) provider.

> Storage area network (SAN)

Used to make storage devices (disk arrays, tape libraries, and optical jukeboxes) accessible to servers so that the devices appear like locally attached devices to the operating system. Has its own network of storage devices not accessible through the local area network by other devices.

> Campus network

Interconnection of LANs within a limited geographical area.

> Backbone network

Interconnects various pieces of network, providing a path for the exchange of information between different LANs. Ties together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Capacity is greater than that of the networks connected to it.

Example: the Internet backbone—the set of wide-area network connections and core routers that interconnect all networks connected to the Internet. The Internet is also an aggregation of many connected Internetworks.

> Virtual private network (VPN)

Some links between nodes are carried by open connections or virtual circuits in some larger network instead of by physical wires. Example: secure communications through the public Internet.

Additional networks: Metropolitan area, Wide area, and Enterprise private.

Organizational Scope:

Networks are typically managed by organizations that own them. According to the owner's point of view, networks are seen as intranets or extranets.

> Intranet

Set of networks using web browsers and file transfer application that is under the control of a single administrative entity, which closes it to all but specific, authorized users. Example: the internal network of an organization.

> Extranet

Extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers). May also be categorized as a CAN, MAN, WAN, or other type of network but cannot consist of a single LAN; it must have at least one connection with an external network.

Topology (Node Layouts):

Bus, star, ring, mesh, fully connected, and overlay.

Basic Hardware:

> Router

Internetworking device that forwards packets between networks by processing information found in the datagram or packet and often the routing table, used to determine what interface to forward packets (this can include the “null” also known as the “black hole” interface because data can go into it, however, no further processing is done for said data).

> Firewall

Important security aspect of a network. It typically rejects access requests from unsafe sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in 'cyber' attacks for the purpose of stealing/corrupting data, planting viruses, etc.

Additional hardware: network card (or network adapter or NIC), repeater, hub, bridge and switch.

Internet Protocol (IP) address:

Binary number assigned to each device (computer, printer) in a network that uses the Internet Protocol for communication. Two functions: host/network interface identification and location addressing.

IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).

The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.

Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, have private IP addresses that are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Private networks typically connect to the Internet through network address translation (NAT).

Computer Networking: Domains

What is a “domain name”:

Domain names (or just domains) are humanly-memorable names for Internet participants (computers, networks, and services).

  • Formed by the rules and procedures of the Domain Name System (DNS).
  • Represent an Internet Protocol (IP) resource, such as a pc used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet.
  • Used as simple identification labels to indicate ownership or control of a resource.
  • Provide easily recognizable and memorizable names to numerically addressed Internet resources.
  • Organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. Top-level domains (TLDs) are first, including the generic top-level domains (gTLDs), such as com, net and org, and the country code top-level domains (ccTLDs). Below these are the second-level and third-level domain names that are typically open for reservation by end-users that wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
  • Registration is usually administered by domain name registrars who sell their services to the public.

What is a “subdomain”

The Domain Name System (DNS) has a tree structure hierarchy, with each node on the tree being a domain name.

  • A subdomain is domain that is part of a larger domain.
  • Expresses relative dependence, not absolute dependence.
  • The only domain that is not also a subdomain is the root domain.
  • For example, mail.example.com and calendar.example.com are subdomains of the example.com domain, which in turn is a subdomain of the com top-level domain (TLD).

What is a “DNS”

The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol (IP) address spaces. The Domain Name System (DNS) maintains the domain name hierarchy and provides translation services between it and the IP addresses.

  • A hierarchical distributed naming system for computers, services, or any resource
  • Translates domain names meaningful to humans into the numerical identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.
  • Stores other types of information, such as the list of mail servers that accept email for a given Internet domain.
  • By providing a worldwide, distributed keyword-based redirection service, it is an essential component of the functionality of the Internet.
  • A good analogy: the DNS serves as the phone book for the Internet by translating human-friendly computer hostnames into IP addresses. For example, the domain name www.example.com translates to the addresses 192.0.43.10 (IPv4) and 2620:0:2d0:200::10 (IPv6).

Why do we buy domain names and from what kind of entity?

You don't actually buy the domain name, you rent it from a domain name registrar, which is an organization or commercial entity accredited by both the Internet Corporation for Assigned Names and Numbers (ICANN) and generic top-level domain registry (gTLD) to sell gTLDs and/or by a country code top-level domain (ccTLD) registry to sell ccTLDs; to manage the reservation of domain names in accordance with the guidelines of the designated domain name registries and to offer such services to the public.

The price you pay a registrar is for the service of routing the domain name to an actual server. If the domain name isn't on a name server then no one will be able to reach your website. Registrars have to point visitors to the right server. They need servers to do that, which is what you pay for.

What is a TLD?

A top-level domain (TLD) is at the highest level in the DNS. TLD names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name. For example, in the domain name www.example.com, the TLD is .com.

Management of most top-level domains is delegated to responsible organizations by ICANN, which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.