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Back to article list Search Articles Add Comment Printer friendly Direct link Par2: A crash couse in TCP/IP 2001-12-04 -- Johan van Zyl 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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