Now
that you have a basic idea of how computer communicate with each other over a
network, it is time to discuss how the Internet works. The Internet is
essentially just a large number of networks connected to each other. So, the
Internet works just like your local network. This is sent as data packets using
the protocol. These different networks are not connected to the main
transmission lines called backbones. The points where backbones connect to each
other are called Network Access Points (NAP). You may use an Internet Service
Provider (ISP) when you are logged in to the Internet. That ISP has connection
either to the Internet backbone or to yet another provider that has a backbone.
Thus, logging on to the Internet is a process of connecting your computer to
your ISP’s network, which is, in turn, connected to one of the backbone on the
Internet.
With
tens of thousands of millions of individual computers networking and sending
data and data, a probability problem arises. The problem then is to ensure that
the data packets go to the right computer. This task is accomplished in much
that same way as traditional letter mail is delivered to the right person: via
an address. With network communication, this address is a special one, referred
to as an IP address. An IP address is an address used to uniquely identify a
device a device on an IP network. The address consists of four 3 digit numbers
separated by period (an example would be 107, 22, 99, 198.) Each of the
three-digit numbers must be betw4en 0 & 255. This rule stems from the fact
that IP addresses are actually four binary numbers: you just see them in
decimal format. Recall that a byte is eight bits (1s & 0s), & and an
eight-bit binary number converted to decimal format will be.
|
IN PRACTICE: Converting
Binary Numbers |
|
For
those readers not familiar with converting binary numbers to decimal, there
are several methods. We will discuss one methods here. You should be aware
that the computer will do this for you in case of IP addresses, but some
readers may wish to know how this is done. While there are many methods,
perhaps the simplest is: Divide
repeatedly by 2, Using
“remainders” than decimal places, until you get down to 1. For
example, convert decimal 31 to binary: 31/2 = 15 Remainder
1 15/2 = 7 Remainder
1 7/2 = 3 Remainder
1 3/2 = 1 Remainder
1 1/2 = 0 Remainder
1 Now
read the remainders from bottom to top: the binary equivalent is 00011111.
(Note that you complete the octet by filling in the leading spaces with “0”s
to make an 8 bit numeral). While you can
step through the math to convert a decimal number to a binary number, you may
find it easier to use a converter. There are many converters available on the
Internet that can be found by searching for the keywords “binary converter”. |
IP
addresses come in two groups: public & private. Public IP addresses are for
those computers, which connected with Internet. Two public IP addresses can be
the same. However, a private IP address, such as one on a private company
network, only has to be unique within that network. Within an isolated network,
you can assign random IP addresses as long as each one is unique. It does not
matter whether other computers throughout the world have the same IP address
because this computer is never connected to those other worldwide computers. However,
making a copy requires using a registered IP address (called Internet address)
to avoid connecting to a private network for the Internet. Often, network
administrators use private IP addresses that begin with a 10 such as 10, 102,
230, and 17.
It
should also be pointed out that an ISP will often buy a pool of public IP
addresses and assign them to you when you log on. Therefore, an ISP might own
100 public IP addresses and have 10,000 customers. Not all 10,000 customers
will be online at the same time, because the ISP only gives one customer and IP
address when he and the ISP are logged on When the customer logs IP address
unassigns.
The
address of a computer tells you a great deal about that computer. The first
byte (or first decimal number) in an address tells you to what class of network
that machine belongs. Summarizes the five network classes.
Four
numbers of an IP address that are used in different ways to identify a
particular network and host on the network. There are four regional Internet
registries (ARIN, RIPE, NCC, LACNIC, APNIC) that assign Internet addresses from
the A, B & C classes.
These
five classes of networking will become more important later in this book (or
you should decide to study networking at a deeper level). You will probably
discover that limit IP 127.
|
Class |
IP Range for the |
Use |
|
A |
0 - 126 |
Extremely large networks. All Classes. A network IP addresses have been used and none are left |
|
B |
128 – 191 |
Large corporate and government networks. All Class B network IP
addresses have been used |
|
C |
192 – 223 |
The most common group of IP addresses. It is Class C IP address of
ISP. |
|
D |
224 – 247 |
These are reserved for multicasting. Note: Multicasting is transmitting the same data to multiple
(but not all) destinations. |
|
E |
248 – 255 |
Reserved for experimental use. |
was not listed. It
is forgotten because the limit is specific to the test. The IP address of
127.0.0.1 destinates the machine, on which you are working, regardless of the
machine’s assigned IP address. This address is called a loopback address. That
address will be used often in testing your machine & NIC.
Availability
of Addresses
If
you do the math, you will find that our current addressing method means there
are a total of over 4.2 million possible IP addresses. That seems like a very
large number but, in reality; the number of unassigned Internet addresses is
running out. You should not be concerned, however, as methods are already in
place to extend the use of addresses. The new addressing system will be a
classless scheme called CIDR (Classless Inter – Domain Routing), & it is
tied to the replacement of IP V4 with IP V6.
The
entire discussion of IP addresses up to this point is based on IP V4 (version
4.0), the current standard. IP V6 (version 6.0), however, is likely t be
implemented in future. Rather than 32 – bit addresses (four 8 – bit number),
the IP V6 uses 128 – bit addresses. IP V6 is configured for backward
compatibility, which means that to use the new IP V6, there will fortunately
not be a need to change ever IP address in the world. Keep in mind that, when
we discuss the packet structure of an IP packet, we are talking about both the
IP V4 & IP V6 packets. In comparison IP V4 packet, IP V6 packets have
longer header segments and the header is structured a little differently.
With
CIDR, a single IP address can be used to designate many different and unique IP
addresses. In contrast to an IP address, a CIDR IP address ends with a slash
followed by a number, called the IP network prefix. An example of a CIDR IP
address is 156.201.10.10/12. The IP network prefix specifies how many addresses
are covered by the CIDR address. Lower numbers specify more addresses. In other
hands to providing more addresses within organization, CIDR addresses also
reduce the size of routing table.
A
subnet is a portion of a network that shares a particular subnet address (a
common address component). Subnets of all devices on a TCP / IP network that
IIP addresses are the same as the previous one. For example, all devices with
an IP address that starts with 200.200.200. Would be part of the same subnet. It
is useful for network security as well as its performance that we divide the
network into sub networks. Sub-netting enables the network administrator to
further divide the host part of the address into two or more subnets. In this
case, the host address is reserved to identification the particular subnet. IP
networks are divided using a subnet mask.
As we discussed earlier, an IP address is made up of 32 binary bits. These bits can be divided into two components: the network address and the host address. A subnet mask is a 32 – bit combination used to describe which portion of an address refer to the subnet (network) and which part refers to the host. This mask is used to determine what subnet an IP address belongs to. For example, in the IP address 185.201.20.2 (assuming this is part of a Class B network), the first two numbers (185.201) represent the Class B network address, and the second two numbers (20.2) identify a particular host on this network.
Uniform Resource Locators
After
you connect to your ISP you will, of course, want to visit some Websites. You probably
type name into your browser’s address bar rather than IP addresses. i.e., you
might type in www.chuckeasttom.com to
go my Website. Your computer or your ISP must translate the name you typed (caked
a Uniform Resource Locator (URL) into an IP address. The DNS protocol handles
this translation process. You type a name, which has meant by human, but your
computer is using a finding specific IP address to connect. Packet 80 is sent
by your browser. If that target computer has software that listens and responds
to such request (like Web server software such as Apache or Microsoft Internet
Information Server), then the request of your browser is excepted and
communication will continue. This method is how Web pages are viewed.
If
you have ever received an Error 404: File Not Found message, what you are
seeing is that your browser received back a packet (from the Web server) with
error code 404, denoting that Web page you requested could not be found. The error
message by web server you will receive on your web browser to point out your
mistakes. Many of these problems can be
handled by the browser itself and you never see the error message. All error
messages in the 400 series are client error. This term means that something is wrong
on your side, not the Web server. Messages in the 500 series are server errors,
which mean that there is a problem on the Web server. Massages of 100-series
are only informative; 200-series messages indicate success; 300-series messages
are re-directional, meaning the Web page you are moved and your browser is directed
to the new location.
E-mail
works the same way as visiting Web sites. Your e-mail client (the software you
use to manage your e-mail account) will seek out the address of your e-mail
server. Your e-mail client will then use either POP3 to retrieve your incoming
e-mail or SMTP to send your outgoing e-mail. Your e-mail server (probably at
your ISP or company) will then try to resolve the address you are sending to. If
you send something to chuckeasttom@yohoo.com
, your e-mail server at yahoo.com;
your server will then send your e-mail there. Not that there are newer e-mail
protocol available, but POP3 is still the most commonly used.