Ip addressing
What is an ip address?

An ip address is a unique number that identifies a host(computer) on a network. It is similar to the your telephone number but not everyone can ring you if they have it. There are two main types.

Internal and External.

An internal address can be of any of these ranges. -    -  -
These are the addresses that are used on a local area network or your network at home. If you try and use these addresses to go out to the internet your packets will get stopped by Your ISP which uses superior routing technology to route on the internet(BGP).

The Internet uses most of the other addresses. As long as you are connected to the internet you will have an Global IP address that can be used to create connections with any other global IP address on the internet. Yours may looks something like this.

Static and dynamic
Your isp only usually assigns you one. They may assign your address in 2 ways.

Static (fixed).
Dynamic (changes).

If yours is static it may be very convinient for using programs such as netmeeting and epsecially for dns servers. but if its Dynamic you must check your ip address every so often but each isp has a different period of time before it changes. Dial up accounts change ip on every dial while some dsl change every month. Static Ip's never change but they cost more.

Any computer that has two ip addresses(which usually requires to network ports) and is a bridge between them(One port is internal the other is external it is called a router(yes, even your home network). This can be done through the internet connection sharing wizard or through dedicated router. Before an ip address is sent onto an external network such as the Internet it is translated using a thing called

NAT - Network Address translation.

This is often transparent to the end user but it maps internal address to port adresses of your internet address. This is useful to know since you cannot create a connection to something like a webserver with its Internal address. You must connect to its global ip address via its port number read on ports.

Loopback address
The special adress of which has the DNS entry of localhost is mapped to your own ip address.

To find your ip you can either go to http://whatismyip.com or if on a windows machine go to run > command> ipconfig.

A ping uses a small special type of packet which is called an ICMP echo reply. It is used to test connectivity and to measure latency(network delay).

Finally if you want to test Your knowledge. go start > run > command >
C:\ping - ping yourself
C:\ping localhost - ping yourself again(in ASCII :P)
C:\ipconfig - find your ip address.

Ask your friend to tell him his ip address and C:\ping (friends ip address).

If you get a reply that means his ip is active and hes online. Because IP is a special type of packet you dont need a port number so it is the first and best test of connectivity.

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