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Introduction to Computer Networks

What is a Computer Network?

Computers that are connected together to share information and resources make up a network

Server

PC

PC PC

What is a LAN (Local Area Network)?

Computers that are connected to other computers near each other make up a network called a LAN

Server

PC

PC PC

Server

PC

PC PC

Server

PC

PC PC

INTERNET

What is a WAN (Wide Area Network)?

A WAN spans a large geographic area, such as a state, province or country. WANs often connect multiple smaller networks, such as local

area networks (LANs). The most common WAN is the Internet.

What is an IP (Internet Protocol) Address?

192.168.1.200

An IP address is a series of numbers that allows one computer to talk with another over a network. IP addresses allow the location of literally billions of computers that are connected to the Internet to be pinpointed.

In the same way that someone needs your mailing address to send you a letter, a remote computer needs your IP address to communicate with your computer. An IP address gives your computer an identity.

What is an IP (Internet Protocol) Address?

IP addresses are made up of four numbers, each of which contains one to three digits, with a single dot (.) separating each number. This is called IPv4 (Internet Protocol version 4).

Here is an example of an IP address:

192.168.1.200

Each of the four numbers can range from 0 to 255. Considering all the number combinations, with IPv4 there are about 4.3 billion IP addresses to choose from.

192.168.1.125

192.168.1.200 192.168.1.84

192.168.1.2

What is an IP (Internet Protocol) Address?

Each computer in a network has a unique IP address that no other computer in that network has.

192.168.1.2

192.168.1.125

192.168.1.200 192.168.1.84

192.168.1.2

192.168.1.125

192.168.1.200 192.168.1.84

INTERNET

ROUTER ROUTER

What is an IP (Internet Protocol) Address?

Computers in different networks can use the same IP address as long as those networks are separated from each other by routers.

Any computer or device connected directly to the Internet must have a unique IP address that no other device in the world has.

INTERNET

ROUTER ROUTER

192.168.1.1 192.168.1.167.93.125.212 87.18.3.198

LAN

WAN Side

LAN

LAN SideWAN SideLAN Side

What is a Router?

A router is a specialized computer that separates two networks and transmits information between the two, such as a LAN and the Internet.

A router has two IP addresses, one on the LAN side and one on the WAN side. The one on the WAN side is unique because no other device in the world has it, whereas the one on the LAN side might be also used by other computers in another LAN.

Who Picks The IP Address?

IP address are determined in one of two ways:

Static – You manually select an IP address and enter it into the computer. It does not change unless you change it.

Dynamic – A router automatically selects an available IP address and sends it to the computer. When a router is configured to do this it is also referred to as a DHCP (Dynamic Host Configuration Protocol) server. It may “lease” this address for a period of time and then assign the same number or another number when the time is up. Computers that get an IP address automatically from a DCHP server are “clients” whereas the server is the “host”.

What is a Subnet Mask?

In simple terms, a subnet mask allows computers to know what “neighborhood” it is in and where in that neighborhood it is. It is similar to a person who lives in an apartment complex. Imagine the complex is located at 123 Main Street and that there are 100 apartments there. Your apartment might be Apt 25 and a friend of yours may live in Apt 72. Both of you live at 123 Main Street, but in different apartments.

An IP address has two components, the network address (the address of the apartment complex) and the host address (the apartment number). A subnet mask separates the IP address into the network and host addresses (<network><host>).

What is a Subnet Mask?

Similar to IP addresses, a subnet mask is made up of four numbers, each of which contains one to three digits, with a single dot (.) separating each number.

Here is an example of a subnet mask:

255.255.255.0

What is a Subnet Mask?

What is a Default Gateway?

A default gateway is the IP address of the computer or device that lets you get out of your “neighborhood”. It is just like a guardhouse in a gated community. In order to leave your neighborhood you need to drive by the guardhouse to get to the outside world. In a similar way a default gateway is the exit path a computer takes to get out of its LAN and out to another network, such as the Internet.

In most cases the job of guardhouse in a network falls to routers that monitor all traffic coming in and out of the neighborhood, effectively isolating one network from another.

What is a Port?

As we discussed, IP addresses allow individual computers to be pinpointed, like a house address. Ports, on the other hand, refer to ways to get into that computer.

Just like a house can have many ways to get in and out, IP addresses allow for 65,535 different openings (ports) to get in and out of a computer. This means that many, many devices can be communicating with a computer at the same time.

IP Address:

192.168.1.200

Number of Ports:

65,535

What is Port Forwarding?

INTERNET

ROUTER ROUTER

192.168.1.1 192.168.1.167.93.125.212 87.18.3.198

WAN Side LAN SideWAN SideLAN Side

192.168.1.50

PC running MCS-Connectwants to communicate witha Magnum at 67.93.125.212

port 5001192.168.1.75

MCS-MAGNUM

Port 5001

Port Forwarding allow us to communicate with a Magnum at a remote location based on the port number of the Magnum.

In the example above a PC running MCS-Connect wants to talk with a Magnum at 67.93.125.212 on port 5001. The router on the Magnum side sees this request and forwards all communication on that port to the Magnum at 192.168.1.75 Routers can be programmed with these instructions, or rules.

Magnum Ethernet Setup Screens

Magnum Ethernet Setup Screens

Magnum Ethernet Setup Screens