Demystifying a Small Business Network A Digital Post Office Joe Moran
A Digital Post Office
Now that we've covered the physical components of network, lets take a look at how a network enables computers to send and receive information. This is where several acronyms that we love to hate but need to know come into play.
IP Address
Just like you need a postal address in order to send mail from one location to another, computers also use addresses in order to locate each other and exchange information on a network. Computers identify and communicate with one another using IP (Internet Protocol) addresses, and every computer must have one to be part of a network.
IP addresses are numeric in nature and contain four numbers separated by periods (e.g. 129.202.176.101). Each individual number in an IP address can range from one to 254, and while computers on the same network will have similar addresses, each address must be unique. Part of a computer's IP address refers to itself (like a house number) while the rest refers to the network a computer is on (like a street name).
DHCP
Although you can assign specific IP addresses to individual computers (known as static, or unchanging, addresses), most networks use a technology called DHCP (Dynamic Configuration Host Protocol) to assign addresses automatically, greatly simplifying network management. With DHCP, a special server (a server is simply a computer or a piece of software running on a computer that performs a particular service or function) sets aside a group of IP addresses and doles them out as needed. When a computer wants to join the network, it requests an address, and the DHCP server (which is usually built into the router) issues an address to the computer.
NAT
When you want to connect a network to the Internet, you don't just get to randomly pick the IP addresses you want to use, but must instead use ones issued by your ISP. The problem is that most ISPs only provide customers with a single IP address with which to access their network. Normally that would mean you couldn't connect more than one computer to the Internet, but you can get around this limitation with a technology called NAT, or Network Address Translation, which allows multiple computers to access the Internet using a single IP address.
NAT, which like DHCP is built into a router, essentially creates two networks, one public and one private. The public network is the one with access to the ISP's network and the Internet beyond, while the private network contains the company's computers and other devices.
When Internet engineers first created NAT, they reserved a range of special IP addressed that people could access and use in the private network. Because the private network is set up using these IP addresses, computers on this network can't communicate directly with the Internet.
With NAT, a router not only acts as an intermediary, but also as a translator between the public network and the private one. It receives information requests from the computers on the private network and in turn forwards them to the Internet via the public network.
The router also tracks the activity of all the computers linked to it, so that when a computer connected to the router requests information (say, a Web page) it can deliver that Web page to the particular computer that requested it. It's kind of like using a shopping delivery service; you tell the company what you want and where you live, and the item arrives without you having to go and get it yourself.
We hope this has helped you understand the basics of how a network works. Stay tuned for more articles explaining additional networking concepts.
Joe Moran spent six years as an editor and analyst with Ziff-Davis Publishing and several more as a freelance product reviewer. He's also worked in technology public relations and as a corporate IT manager, and he's currently principal of Neighborhood Techs, a technology service firm based in Naples, Fla. He holds several industry certifications, including Microsoft Certified Systems Engineer (MCSE) and Cisco Certified Network Associate (CCNA).
