Getting started with networking tutorials for your certification exam?
- Bookmark this page (Press CTRL+B)
- Read the basic tutorial information on this page.
- Click the links below for more advanced networking tutorials
Bookmark this page as you will return here often. This tutorial is organized to get you started with computer networking and point you in the right direction. The links in this page lead to more detailed tutorials to help those studying for network certification exams. There's a lot to learn, but don't worry; we've broken it all down into easy-to learn pieces, and you can always ask questions.
- Definitions
- Network Models
- Physical Network Topologies
- Logical Network Topologies
- Peer-to-Peer
- Client-Server
- Distributed services
- Communication Methods
- Point-to-point
- Point-to-multipoint
- Broadcast multiaccess
- Nonbroadcast, multiple access
- Network Devices
- LAN Networking Protocols
- Network-Based Applications
- Network Time - Network Time Protocol (NTP)
- Domain Name Resolution - Domain Name Service (DNS)
- E-mail - Simple Mail Transfer Protocol (SMTP)
- File Transfer Protocol (FTP)
- rlogin, Telnet & Secure Shell (SSH)
- Web Browsing and Web services - Hypertext Transfer Protocol (HTTP)
- Networking
- Bridging & Switching - Spanning Tree
- Routing - RIP, RIP II, OSPF, IS-IS, EIGRP, BGP
Definition of a Network: What is a Network?
A network is set of computers linked together for the purpose of communicating and sharing information. The Internet is a global super-network, so is the local area network ( a LAN) at your workplace or your school, as is the wireless hotspot at your local coffee shop, hotel or library, the telehone and cellular systems, and the satellite communications in space.
What defines a network is often defined by who owns and operates the equipment and the computers that are part of the network. Thus, your school's network is separate from the Internet.
You know you have a network when you have two or more computers connected together and they are able to communicate. Plugged into the back of each computer is some sort of communications port. Nearly all computers today have one or more serial ports, parallel ports, Ethernet ports, modem ports, firewire ports, USB ports and more. All of these ports can be used in one way or another to connect computers to a network. The most common type of network port is an Ethernet port (the square port with the row of connectors on the bottom). The next most common is a wireless network connection, but that has no physical connector port.
Xerox was the first company to research and develop a network. Once upon a time, Xerox printers were extremely expensive, so companies wanted to share them. Xerox knew their printers were expensive and users were only able to print from one big computer (a mainframe) attached to the printer directly. You would print your document, and then walk down to the building next door where the mainframe was housed, with the printer, and pick up your printout. Xerox decided that they could sell more printers if they could make it possible for anyone to use the printer from any computer. To allow multiple computers to communicate with the printer, some means of sharing a connection to the printer was needed. Xerox put Bob Metcalf and others to work on researching and designing what eventually came to be called ethernet. Ethernet is now the most common networking protocol on the planet.
Hosts, End Stations and Workstations
When people talk about networks, they often refer to computers that are at the edge of the network as hosts, end stations, workstations, or servers. Its all just the same thing, a computer attached to the network; though the word HOST has the most general meaning and can include anything attached to the network including hubs, bridges, switches, routers, access points, firewalls, workstations, servers, mainframes, printers, scanners, copiers, fax machines and more!
Just about everything electronic that has a processor and which you would use in an office is 'network capable' today and lots of things that aren't currently networked probably will be networked in the future. In many offices the phone system already IS the network (Voice over IP).
LAN, MAN, WAN and er.. IPAN??
There are some terms, acronyms actually, that are used to describe the size and scope of a network: LAN, WAN, MAN. We've added our own term 'IPAN'
LAN
A Local Area Network (LAN) is usually a single set of connected computers that are in a single small location such as a room, a floor of a building, or the whole building.
MAN
A Metropolitan Area Network (MAN) is a network that encompasses a city or town. It is usually multiple point-to-point fiber-optic connections put together by a communications company and leased to their customers, but a small number of big corporations have built a few of these of their own and opened them to the local companies with which they do business. The automotive, travel and insurance industries are just a few examples of who has built a WAN.
WAN
A Wide Area Network (WAN) is usually composed of all the links that connect the buildings of a campus together, such as at a University or at a corporate headquarters. WAN connections can often span miles, so you frequently hear peole referring to the 'WAN' connection to an office half way around the world. Usually, what distinguishes a WAN from a LAN is that there are one or more links that span a large distance over serial, T-carrier or ISDN, Frame Relay or ATM links.
IPAN
So what the heck is an IPAN? An IPAN is an Inter-Planetary Area Network. NASA has built a Deep Space Internet that uses a store-and-forward communications protocol called Disruption Tolerant Networking (DTN). The mechanical rovers Spirit and Opportunity on the planet Mars, were given addresses on a NASA network and NASA uses Internet and IPAN protocols to communicate with the Mars rovers. While the communication with the rovers never crosses over the Internet, the NASA network does have hosts spanning space between the planets Earth and Mars. They also have probes they have sent into the outer solar system with which they use IPAN to communicate.
How does a network work?
This networking tutorial section will teach you about running an Internet Protocol (IP)-based network on top of Ethernet. A typical plysically wired network is built with several layers of technologies layered one top of one another. The TCP-Model and the OSI Model tutorials will help you understand the layering concepts and you should probably start there first and come back to this page.
This list starts with the lower layer functions or protocols and works its way up.
- Ethernet is a Physical and Data
Link technology which
provides:
- Physical communication using
- Electricity over copper wiring (usually unshielded twisted pair or "UTP")
- Light over glass or plastic fibers
- Physical addresses (Media Access Control or MAC addresses)
- Ethernet frames containing data from the layers above it are sent and received across switched networks and VLANs.
- Because ethernet is a broadcast technology, it has either collision detection or collision avoidance mechanisms
- Physical communication using
-
Dynamic Host Control Protocol - DHCP
- Computers use DHCP to dynamically obtain a logical network address (an IP address)
- Address Resolution Protocol
(ARP) / Reverse Address Resolution Protocol
(RARP)
- Allows computers to announce a logical address (IP address) they are looking for and to discover which physical address (MAC address) is using that address.
- Internet Protocol
- Logical Addressing
- Routing
- Transmission Control Protocol or
User Datagram Protocol
- Ports and Sockets
- Domain Name Service (DNS)
- Other services or session-based protocols (such as HTTP which makes the World Wide Web possible)
All networks have several layers of functions stacked on top of each other. Ethernet is used to provide the means to transmit information encoded in electrical signals across copper wiring between two computers. Internet Protocol networking software running on the computers use the Ethernet network to send data back and forth inside IP packets. The Internet Protocol layer provides the means for the computer to connect to the network, obtain a logical address, to learn the logical addresses of other computers and to communicate with the other computers on the network. Internet Protocol provides the basic network functions.
Physical Network Topologies
(^ Top)
The hardware used to build a network will usually require that the structure of the network conform to a certain design. The word topology is used to describe what the network looks like when drawn on paper and to a large extent, how it operates.
Point to Point Topology (Daisy Chaining)
- The oldest network topology is point-to-point. A point-to-point topology is most often a dedicated communications connection between two stations over a single hardware connection. Both ends of the connection have to be smart enough to manage the connection themselves. Serial ports are most commonly used for this topology. Dedicated serial telecommunications services such as T1 and E1 can be used in point-to-point fashion. There will be exactly two and only two stations on the connection. Networks can be built using point-to-point topologies by daisy-chaining one station after another to form an end-to-end communications path.
Bus Topology
- A bus topology connects all computers together using a single wire, usually a piece of coaxial cable, that passes electricity over a copper core that all stations transmit and receive from. All stations hear all communication over the bus.
Ring Topology
- A ring topology usually involves connecting one or more computers together using paired physical interfaces. One interface is the clockwise side of the ring, the other connection is the counter-clockwise side of the ring. Stations connected to the ring can transmit and receive, but there is usually some other sort of method for controlling access to the common network hardware. Token Ring uses a ring topology as does CDDI and FDDI. All three of these network technologies use a token-passing scheme in which the computer holding the the token is allowed to transmit.
Star Topology
- A star topology is the most common network topology in use today. All stations in the network are connected to a single hub or repeater. The connected stations radiate outward from the hub like an asterisk '*' or star.
Hub and Spoke Topology
- Hub and spoke is another term often used to describe a star topology.
Point to Multipoint
- A single connection point on the network has network segments that run to several other points. Frame Relay and ATM have the ability to be wired to deliver point-to-multipoint connections. Point-to-multipoint is useful when your network relies on protocols that use broadcast or multicast communications.
Logical Network Topologies
Logical network topologies run on top of physical networks. Logical topologies organize sets of hardware and stations into discrete networks. Ethernet networks are physical networks using a bus topology. Internet Protocol, which runs on top of Ethernet, can be used to create several logical networks on top of the physical ethernet topology.
When you browse the web, share files, watch videos, or participate in online conferences, those services run on top of logical topologies, also called logical networks.
Peer-to-Peer
A peer-to-peer logical network is composed of two or more self-sufficient computers. Each computer handles all functions, logging in, storage, providing a user interface and more. The computers on a peer-to-peer network can communicate, but do not need the resources or services available from the other computers on the network. Peer-to-peer is the opposite of the client-server logical network model.
A Microsoft Windows Workgroup is one example of a peer-to-peer network. UNIX servers running as stand-alone systems are also a peer-to-peer network. Logins, services and files are local to the computer. You can only access resources on other peer computers if you have logins on the peer computers.
Client - Server
The simplest client-server network is the most common logical network arrangement. Client-server is composed of a server and one or more clients. The server provides a service that the client computer needs. Clients connect to the server across the network in order to access the service. A server can be a piece of software running on a computer, or it can be the computer itself.
One of the simplest examples of client-server is a File Transfer Protocol (FTP) session. File Transfer Protocol (FTP) is a protocol and service that allows your computer to get or put files to a second computer using a network connection. A computer running FTP software opens a session to an FTP server to download or upload a file. The FTP server is providing file storage services over the network. Because it is providing file storage services, it is said to be a 'file server'. A client software application is required to access the FTP service running on the file server.
Most computer networks today control logins on all machines from a centralized logon server. When you sit down in front of a computer and type in your username and password, your username and password are sent by the computer to the logon server. UNIX servers use NIS, NIS+ or LDAP to provide these login services. Microsoft Windows comptuers use Active Directory (which supports LDAP queries) and Windows Logon.
Users on a client-server based network will usually only need one login to access resources on the network.
Distributed Services
Computer networks using distributed services provide those services to client computers, but not from a centralized server. The services are running on more than one computer and some or all of the functions provided by the service are provided by more than one server.
The simplest example of a distributed service is Domain Name Service (DNS) which performs the function of turning human-understandable domain names into numerical (dotted quad) computer addresses called IP addresses. Whenever you browse a web page, your computer uses DNS. Your computer sends a DNS request to your local DNS server. Your local DNS server will then contact a remote server on the Internet called a "DNS Root Server" to begin the lookup process. This DNS Root Server will then direct your local DNS server to the owner of the domain name the website belongs to. Thus, for any name that has not previously been looked-up, there are at least three DNS servers involved in the process of finding and providing the IP address of the website you intended to browse. Your local DNS server provides the query functions and asks other servers for information. The Root DNS server tells your local DNS server where to find an answer. The DNS server that 'owns' the domain of the website you are trying to browse tells your local DNS server the correct IP address. Your computer stores that IP address in its own local DNS cache for a limited time, so that it does not have to go out to get the address any time soon. Your computer also caches the IP address of the website for a limited time as well. This caching occurs at nearly all levels, and reduces load on the Domain Name resolution system overall. Because all the lookups occur in a distributed fashion, DNS is a distributed service that runs everywhere. No single one computer can do the job by itself.
Communication Methods
As technology advances, the line where the network stops and where there is services start continues to blur. It is common to explain network communication using the same terms as the
Point-to-point communication is direct between two endpoints and both end points have to be smart enough to manage the connection and all aspects of the communication including signalling, flow control, error checking and control.
Point-to-multipoint communication occurs in environments where a single station transmits to all end stations. This type of communication is most common in wireless and cellular environments where radio waves are heard by all stations tuned to the specific radio frequencies used by the network. Early mainframes also used point-to-multipoint communications to allow the mainframe to send a commands to multiple peripheral stations at the same time with one transmission. The "cable" connected to the mainframe was "split" to carry the signal to all the attached stations.
Broadcast, multiaccess communication allows any station to talk and be heard by all the other stations at the same time. This is convenient because printers and other devices can be shared. However, it also means that only one station can be talking at a time, or they will talk over each other; they "collide". The signals they are transmitting will get smashed together and the data in the transmission is lost. The portion of the network where multiple stations can broadcast to each other and where their broadcasts could collide is called a "collision domain". Ethernet (especially wireless ethernet) is the best example of broadcast multiaccess communication.
Nonbroadcast, multiaccess (NBMA) is the communications model for a fully meshed networks of physcial point-to-point connections as is frequently seen in Frame Relay, X.25 and ATM. All stations connected to the network can communicate with each other, but they cannot send out a broadcast to all other stations.
Network Devices
Today's network environment is predominently Ethernet technologies. Ethernet is a broadcast protocol that provides the physical layer and data-link layer functions within a network. To connect devices that use ethernet, you need a hub, bridge, switch or router, and which device you use depends on how you will use the network and the computers.
Hubs
A hub is a device used to create a broadcast domain so that several computers can communicate. Hubs are very inexpensive. Hubs receive frames and broadcast the frame on all ports. Hubs are dying out of existence and the only place you see them today is in extremely small networks, especially in homes. Once there are too many computers connected to a hub, communication begins to break down and a more intelligent solution is required.
Bridges
A bridge is a smarter version of a hub, and performs the same function. A learning bridge can figure out where a given computer is located and transmit frames only on the port connected to that device.
Switches
A switch is a specialized type of learning bridge that segments collision domains, learns physical addresses and asociates them with the ports they are attached to, and will forward frames only to those ports that are supposed to hear the transmission. Bridges maintain a forwarding table. Switches are the most common way in which ethernet networks are wired together.
Routers
Routers are network layer devices which can break up broadcast domains and segment networks, route packets, allow network administrators to control broadcasts and control access to various network resources. Routers provide a means to interconnect different kinds of networks. Routers are used to connect several ethernet networks together to make a larger network. Routers can further extend the network by connecting local networks to the global network called the "Internet".
Networking
Bridging and Switching
Routing