This is a very common question that I am asked and it is very fundamental to troubleshooting and diagnosing networking issues.

What an IP address is:

Think of an IP address like a address to your home. The city/state gives you an address based on your home location. The post office is the ISP(internet service provider) that directs traffic from a business or another residential location. If your home address is incorrect you don’t get the messages or packages you requested from the world.

When you sign up with a ISP or internet traffic director they assign an IP address to your modem/router that commonly connects to a phone line or cable line. This way the ISP knows where to send all your messages. Now where it gets more complicated is the modem/router then assigns a IP address to your computer,xbox360,wireless device or any other internet connected device that is only local to the modem/router. So in a way the modem/router is a gateway to the internet directing traffic and sending it to the ISP.

As usual the following info is quite technical but if you look at the info it will make sense how an IP address is designed.

    
An IP address is often displayed as a numeric number in dotted decimal format (#.#.#.#), and represents the address for any host on a TCP/IP network. The address is made up of four 8 bit octets, for a total of 32 bits. Every octet is comprised of a number between 0 and 255. The limit of 255 for each octet is because, in binary the number equals 11111111. Computers don’t see the IP address in dotted decimal format, it is only done to simplify things for ourselves. The computers actually see an IP address as a continuous binary string.

Classes-
There are two different parts to an IP address, the network and host portions. The network portion defines the network address, and the host portion defines the individual host address of a device. There are five different classes of IP addresses all of which define different network and host sections. They are as follows (n = network and h = host):

Class A:
Decimal – n.h.h.h
Binary- 0#######.########.########.########
Address range -1.0.0.0 to 126.0.0.0
Number of networks – 126
Number of hosts per network – 16,777,214

Class B:
Decimal – n.n.h.h
Binary- 10######.########.########.########
Address range – 128.0.0.0 to 191.255.0.0
Number of networks – 16,382
Number of hosts per network – 65,534

Class C:
Decimal – n.n.n.h
Binary- 110#####.########.########.########
Address Range – 192.0.1.0 to 233.255.255.255
Number of networks – 2,097,150
Number of hosts per network – 254

Class D addresses are used for multicast, and class E addresses are only used for experimental purposes only.

Private Addresses-
It may look like there are many more IP addresses then we could ever use but that is not the case. The number of publicly available IP addresses we currently have available will run out eventually. Some say in 5-10 years the available number of IPv4 addresses will all be used up. To help slow the processes there was the introduction of private IP’s for use on privately owned networks that don’t need a publicly assigned address. Numbers from classes A though C were set aside for private use. The numbers are:

Class A Private: 10.0.0.0
Class B Private: 172.16.0.0 to 172.31.255.255
Class C Private: 192.168.0.0 to 192.168.255.255

The version of IP used today is IPv4. Because of the address shortage, there is an IPv6 on the way to help solve the problem. IPv6 addresses will be 128 bits long and will use hexadecimal notation rather than the current dotted decimal. With 128 bits to work with, there should be plenty of addresses for every living person on this planet and then some.

Questions? Please let me know.

-Mike Dopp