About IP Addresses

On the Internet, web sites are uniquely identified by IP address, which is a set of set of four numbers, of maximum three digits each.

An IP address contains coded information about your web site, the host provider, where you are from, and more, acting like a descriptive identifier.

A typical IP looks something like this: 127.90.87.213, which although is very hard to remember, it is created to be read and interpreted by humans. Computers communicate in binary code (sequences of 1 and 0), so the same IP address translates into 1111111 for 127, 1011010 for 90, 1010111 for 87 and 11010101 for 213, so the final binary address would be 1111111.1011010.1010111.11010101, which machines understand perfectly, but which makes no sense to humans.

The numbers in the IP address are called octets, so an IP always contains four octets (octet comes from the number eight, because there are eight binary characters in each of the four numbers). Having four numbers of eight characters each adds up to 32, which is why, taken as a whole, an IP is considered a 32-bit number.

In binary form, any bit may have one of two values, either 1 or 0, which means that the maximum number of combinations per octet ranges between 28 and 256, meaning that each octet can contain any value between 0 and 256. This all adds up to around 4,2 billion possible combinations.

Special IP addresses (or reserved IPs) are 0.0.0.0, which is the default network address, and 255.255.255.255 which is used for broadcasts across the network, and 127.0.0.1, which is a loop-back address, meaning that when accessed, the network communicates with itself, sort of like a mirror imaging. For example, when setting up a web server, 127.0.0.1 is the internal address of the web server, when you access it, you access your server from the inside (an alternative in this situation is to type localhost instead of 127.0.0.1, which is a more user friendly alias).

The huge number of possible IP addresses demanded some sort of classification, so IPs are divided into five classes.

Class A addresses are used by very large networks, and count for about half of the total available IP addresses, with a total of around 2,2 billion possible combinations.

Class B addresses are used by medium sized networks, and make up about a quarter of the total available addresses, with about 1,1 billion possible combinations.

Class C addresses are used for medium and small sized networks and count about 500 thousand possible combinations.

Class D and E are different from the first three classes, and count for about 270 thousand possible combinations each. Class D is used for multicasts, and Class E is used for experimental purposes only.

IP addresses are constructed in such a way that they store information about the hosts they point to, so by following a set of guidelines, you can decode IPs and find out useful information, without actually accessing any web page.