Definition of a Public IP Address

IP addresses are the mailing address of the Internet.

Public Internet Protocol Addresses, also called Public IP addresses, are addresses assigned to computers so that they can find each other on the Internet. They are the Internet's equivalent of a physical mailing address. A not-for-profit organization called ICANN, Internet Corporation for Assigned Names and Numbers, coordinates all public IP address assignments. IP addresses allow computers to send packets of information to each othe, which allows people to surf the Internet, send and receive email, instant message, and use many other Internet-based applications.

Public vs Private

Companies with internal networks can have private IP address assignments for their computers. These private IP addresses are not available for communication with computers outside the private network. On the other hand, public IP addresses are available for communication with any computer with another public IP address. Computers with private IP addresses can access the Internet by using a Network Address Translation service.

IP Address Assignment

ICANN was formed in 1998 to help keep the Internet secure and stable. It serves as a central repository for IP addresses that are distributed to regional registries, which then assign them to network providers. This helps to prevent any potential duplications of IP addresses, which would cause confusion when computers attempt to communicate with each other.

Types

IP addresses are written as four numbers between 0 and 255 separated by periods. Each number represents eight bits of storage. An example of an IP address is 190.1.3.50. There are more than 4 billion possible IP addresses with this setup. There are currently five possible classes of IP addresses: A, B, C, D and E. Class A IP addresses are 0.0.0.0 to 127.255.255.255. Class B addresses range from 128.0.0.0 to 191.255.255.255. Class C ranges from 192.0.0.0 to 223.255.255.255. Class D addresses support multicasting and range from 224.0.0.0 to 239.255.255.255. Class E addresses are reserved for experimental use, and are numbered from 240.0.0.0 to 247.255.255.255.

Dynamic vs Static

Routers, firewalls and servers are usually assigned fixed or static IP addresses. Personal computers that use a cable or DSL modem are usually leased IP addresses that are assigned by a protocol called Dynamic Host Configuration Protocol, or DHCP, each time the modem is booted. A network administrator can choose to assign a static IP address to a computer but this is usually not done.

DNS

When you access a website, you are actually sending and receiving information from a particular IP address. However, people do not actually type in IP addresses into browsers because the numbers would be too difficult to remember. The Internet relies on Domain Name Servers to map these numerical IP addresses to names such as www.ehow.com that are easier for users to work with. Each time you type in a url, such as www.ehow.com, your computer queries the DNS for a numerical IP address. The DNS looks up the name and returns a numerical IP address to your computer. Once this address is received, a computer can then send and receive information from the url www.ehow.com.

Finding an IP Address

Sometimes it is necessary to find a computer's IP address. On a Windows based computer, you can open the MSDOS or command window. Type "winipcfg" or "ipconfig" and your IP address will be listed to the right of "IPv4 address" in the window. On a Mac-based computer, you can find your IP address by checking your network control panel. There are also many web-based IP address sites available on the Internet.

References

• Private IP Addresses
• IP Address Classes
• ICANN
• PC Magazine: Definition of IP Address
• How the Internet Works