Because a socket is the equivalent of a phone extension, the program that picks up the call is the equivalent of the person within the house or company that you want to talk to (see Figure 1.4). The program can do things for you once you “talk”—either give you information or kick off a process that you need accomplished. Some requests can be a combination of both: When you search the Internet, you ask the program on the other end to do a search, and you ask for the answer to your search.

Figure 1.4  A socket is the equivalent of a phone extension.

Just like people, some programs (also called services because they’re server programs) on the other side of the line speak only one language. For example, standard Web servers speak only TCP/IP. However, as previously mentioned, Microsoft file and print sharing services can run on just about anything: TCP/IP, IPX/SPX, and NetBEUI. As with teaching a person a new language, it takes a bunch of effort to program multiple-protocol support into a service, and unless there’s payback involved, most programs just pick one protocol and stick with it. The most popular protocol for modern programs? You guessed it: TCP/IP.

What’s in a Name?

You’ve probably asked yourself in one of the preceding paragraphs, “How does www.co.chatham.ga.us get translated into 167.195.160.9?” Furthermore, why use names at all? People can deal with phone numbers, why not just use the IP number? These are good questions. The answer to the latter is that just because people can deal with a number doesn’t mean that they prefer to use a number. Which would you rather remember, 1-800-NETWORK or 1-800-638-9675? Obviously, most people prefer to remember a name. Actually, names are the better thing to use when networking, because numerical addresses can change during a reconfiguration or a move, whereas symbolic names typically stay the same.

Name-to-address translation (also known as name lookup or name resolution) occurs via name services. Very similar to the speed dial button on your phone, name services are the networking equivalent of an electronic phone book. They’re actually a lot cooler than your speed dial: For example, suppose you could say “Mom” to make your phone dial your mother.

DNS

Name services run as a service on any given name server; that is, a specific program runs on a name server that hands out an address when you give it a name. Like your speed dial buttons, you must program in a name entry; entering the correct number for a given name is important.

In particular, TCP/IP name services, although powerful and able to handle millions and millions of names, isn’t exactly plug-and-play. The DNS (Domain Name Service) that you use when surfing the Web works pretty automatically for you once it’s configured correctly, and it will translate www.co.chatham.ga.us to 167.195.160.9. However, you’ll need to know the exact number of your DNS server. Unlike telephone information, DNS servers all have different addresses; verifying that a workstation’s DNS server is correct can be an important troubleshooting step (see Figure 1.5).

Figure 1.5  Name resolution on DNS.

Note that most smaller sites that use TCP/IP usually don’t have DNS set up. Instead, each workstation has a local (hard drive) “hosts” file that lists the addresses and host names the workstation needs to get to. (Think of this as your personal phone book rather than the corporate directory.) As you can imagine, this gets hard to manage when you have more than a handful of workstations, unless the addresses of the servers never change. As sites grow, or as they get connected to the Internet, DNS servers are added. Can you imagine how big a single file with all the servers on the Internet would be? Fortunately, each DNS server for a given DNS zone is only responsible for its own information.

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A DNS zone (its scope of responsibility for naming) can be huge—for example, .com has millions of subzones (yahoo.com, jotto.com, and so on); on the other hand, it can be small—for example, feldman.org lists only one host (www.feldman.org) and no subzones.

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With DNS servers getting easier to manage and being a mandatory component of Internet access, you can expect to see more of them in smaller shops as time goes on. It’s worth mentioning that each DNS server is responsible for only its own zone, so if you can’t get to one particular address (say, yahoo.com) but can get to another (say, jotto.com), it may be that the name server responsible for that zone is down. On the Internet at large, this rarely happens, because the DNS organizers require back-up DNS servers for a zone. DNS problems are more likely to happen within a smaller organization’s intranet, particularly when all the eggs for that organization are in one basket.

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Remember that you can still dial a number yourself when your speed dial buttons are broken. Similarly, if you cannot get to something on your network, try getting to it by number. For example, rather than going to http://www.co.chatham.ga.us, you could try http://167.195.160.6. If this works, you know there’s something up with name services.

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