TCP/IP At
first glance, TCP/IP (Transmission Control
Protocol/Internet Protocol) may seem baffling. Many other protocols,
such as NetBEUI and IPX/SPX, require no configuration. TCP/IP is different. Due
to the seemingly endless number of options that you can configure within
TCP/IP, many people become intimidated at first. In reality, however, TCP/IP
isn’t very difficult, but you have to gain some understanding of what you’re
configuring. So, I’m going to give you a crash course in TCP/IP. Although I
won’t be able to explore every feature in detail, I’ll cover the important
points. The IP address The
most basic element of TCP/IP is the IP address. The IP address is a number
that’s unique to each computer. If you know a computer’s IP address, you can
communicate with that computer from anywhere in the world. Since TCP/IP is the
protocol that the Internet uses and since Internet servers are located all over
the world, TCP/IP must be routable. Thus, when you try to access an IP address,
your computer must be able to tell whether or not that IP address is located on
your local network. If the desired address is located on your local network,
you won’t have a problem reaching it. If it isn’t on your local network, TCP/IP
must know which network the IP address is located on in order to reach the
address. The
network number represents the network that contains a given IP address. If you
look through the various tabs of the TCP/IP properties sheet, you’ll see that
there’s no field that allows you to specify the network number. Instead, the
network number is part of the IP address. An
IP address is composed of a network number and a computer number. Your computer
can distinguish those two numbers because of something called the subnet mask.
The subnet mask is located in a field directly below the IP address on the
TCP/IP properties sheet. A simple subnet mask would be something like
255.255.0.0. The numbers that make up the subnet mask indicate which portion of
the IP address is the network number and which portion is the computer number.
The four numbers of the subnet mask correspond directly to the four numbers in
the IP address. For example, if you had a computer with an IP address of
147.100.100.25 and a subnet mask of 255.255.0.0, the first two numbers in the
subnet mask (both are 255) indicate that the first two numbers of the IP
address are the network number. The second two numbers (both are 0) indicate
that the second two numbers of the IP address are the computer number.
Therefore, in the IP address 147.100.100.25, the 147.100 portion denotes which
network the computer is located on, and the 100.25 portion represents a
particular computer on that network. Of course, subnet masks become much more
complex than this example. For instance, you can subdivide an individual
network. The default gateway Now
that you know how TCP/IP determines whether a destination address is located on
a local network or on a foreign network, you may wonder how it attaches to a
foreign network, especially if that network is halfway around the world. Well,
it completes this job by using routing tables. Routing tables, which are stored
in your routers, tell the router where to connect in certain situations. You
should note that one of the TCP/IP configuration options is for a default
gateway. The default gateway is the address where a TCP/IP packet is sent if
TCP/IP can’t locate the destination IP address on the local network. Usually,
the default gateway points to the router that controls your building’s link to
the outside world (often through an Internet connection). Since this router has
a table of other routers, it knows the address and location of these routers.
The destination IP address helps the router determine to which router to pass
the packet. Typically, a TCP/IP packet is passed through several routers before
it arrives on the destination network and, finally, on the destination PC. DHCP If
all of this information is making your head spin, there’s one TCP/IP feature
that will make your life easier: Dynamic Host Configuration Protocol (DHCP).
DHCP allows you to set one or more servers on your network to act as a DHCP
server. When a client computer that’s set to use the DHCP option comes online,
the DHCP server automatically configures TCP/IP on this computer. Of course,
you still have to configure the DHCP server, but using DHCP saves you from all
of the effort of configuring each client manually. It also keeps you from
accidentally using a particular IP address more than once. DHCP is also useful
if you have a limited number of IP addresses to work with; only the computers
that are turned on at a given moment will use IP addresses. WINS On
Windows-based networks, each computer has a name. The WINS option can be
configured to contain the IP address of a Windows NT Server that’s running a
WINS service. The WINS service resolves computer names (NetBIOS names) to IP
addresses. Thus, if you try to access a computer by its name, your computer
will go directly to the WINS database and search for the name and IP address.
It won’t have to query every computer on the network to determine the right IP
address. As you can imagine, using WINS really cuts down on network traffic. DNS DNS functions similarly to WINS, except that it manages domain names
rather than computer names. A domain name is the type of name that you use on
the Internet. For example, Microsoft.com is a domain name. When you point your
browser to www.microsoft.com,
your computer will query a DNS server for the IP address that corresponds to the
domain name. If the DNS server doesn’t know the address, it asks another DNS
server. This process continues until a DNS server somewhere along the line
knows the address. Then, that server informs your computer—and all of the other
DNS servers that are involved—of the domain name’s IP address. Conclusion TCP/IP
is more intimidating than other protocols because there are so many different
options to configure. I’ve provided you with a brief explanation of how TCP/IP
works. Now, you should have a better understanding of those options.
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