Workshop

Protocols
Previous Table of Contents Next
Your computer “talks” through its network card, but, unfortunately, technology has not advanced to the
point where it can speak English quite yet. Instead, your computer uses a more primitive language—a
protocol with a much more limited vocabulary. This protocol is most likely either TCP/IP, NetBEUI, or
IPX/SPX. You can think of these protocols as languages on a telephone; just as your telephone doesn’t
care whether you speak German or French, your network card doesn’t care whether your computer and
the programs that live in it speak TCP/IP or IPX/SPX.
Parlez Vous TCP/IP?
The good news is that you don’t have to know much about protocols to troubleshoot—most of the time,
your problems won’t be protocol related, because protocols are rather simple and well defined. For
example, TCP/IP has been around for more than 20 years (a huge life span in computer years), and its
feature additions have been rather modest. This means that unlike a typical desktop application, TCP/IP
has had an opportunity to stabilize.
This, among other factors, makes TCP/IP (short for Transmission Control Protocol/Internet Protocol)
pretty much the universal language of network protocols. The Internet has made TCP/IP a household
appliance, which means you probably already know something about it. For instance, you probably know
that a TCP/IP host name is something like myhost.mycompany.com, and a TCP/IP address looks
something like 167.195.160.6.
What’s with the three-dotted address? After all, didn’t I just say that an address is a six-byte hexadecimal
number? Well, it is for network cards, but it isn’t for protocols. Just as your telephone number sounds a
bit different when you say it in French, your network address is different when you “say” it in TCP/IP.
Although they look different, there is a distinct relationship between a TCP/IP address and a MAC
address. They are both, for their own purposes, the “telephone number” of your network card; it just
depends what language you’re speaking at the moment.
TCP/IP addresses are always four numbers between 0 and 254 that are represented in the decimal system
you know and love. These addresses are typically assigned by an administrator. An administrator’s task
is to assign unique addresses to each computer on his or her network.
Why should there be two different addresses? Since the OUI is guaranteed to be unique, why not just
represent the TCP/IP address in decimal? Long ago, network cards did not all have unique IEEEdistributed
MAC addresses; some were limited to 254 addresses! Because of this, using the MAC address