So once again, the format of an IP address in this case, IP version four is a 32 bit binary number.
It's divided into four parts or four octets, which are eight bits or one byte in size.
So an IP address could be written as follows in binary in dotted decimal notation, or it could be written
as follows in dotted decimal notation.
So just to summarize, it's a four byte number or 32 bit number, typically written in dotted decimal
notation, but be aware that it's actually a binary address of 32 bits.
Please refer to the binary videos if you're not sure about the formatting or conversion of binary to
decimal and back again.
An octet is eight binary bits or one byte.
One byte equates to eight binary bits, so an IP version for address consists of four octets such as
x x x x, where x is an octet or eight bits or one byte.
Now using our street analogy, again, it's possible to have the same house number on different streets.
So a house one could be on Oxford Street as well as Cambridge Street.
House number one should just not appear twice on the same street, but number one is permitted on different
streets in the same way.
Here, it's possible to have number one on network 10.1, 1.0 slash 24, as well as number one on network
12 .1.1.0 slash 24.
The same number can appear on different networks.
I'll explain the slash 24 in a moment when we discuss network mosques.
But in this example, we have network 10.1, .1.0 and 12.1 and 1.0.
And it's possible to have multiple devices with the host portion of the IP address set to one.
The same host portion can appear twice as in in this example or many times in a network or the internet,
as long as the network portion is different.
Now, one thing you'll learn about networking is that things are constantly changing.
Address classes or class ful networks were used in the internet from 1981 until the introduction of
classless inter domain routing in 1993, which is commonly known as CIDR or C IDR.
Now, prior to 1993, address classes were used to divide the IP version for address space into five
address classes.
The three that we're going to concentrate on here are class A, B and C, which are used for unicast
traffic.
Class D is used for multicast and class E is reserved for future or experimental purposes.
Address classes have been superseded in IP version six.
IP Version six does not use address classes, and an IP version for address classes have been replaced
with CIDR.
So the different classes of addresses A, B and C were used to accommodate different sizes of networks,
which aided in the classification of those networks.
So as an example, a class full, a address supports about 16 million IP addresses.
So once again, we had Class A, B and C, these have been replaced or superseded by CIDR or C, IDR
and address classes such as A, B and C were determined and then allocated by the honor or Internet
assigned numbers authority.
This format is not used entirely in its original format today.
Here's an entry on Wikipedia showing the list of Class A addresses.
So each class A address has approximately 16 million IP addresses.
And if we scroll down the list, we can see various examples.
AT&T have 12, Xerox 13, HP 15 Dec 16, so 15 and 16 are now owned by HP.
Apple have 17, MIT 18 for 19 and so forth and so on.
So notice as an example, Apple Own 17 0.0.08 Apple have 16 odd million public IP addresses that are
part of the class a address.
So in the original IP address format, a class address consists of eight network bits and 24 host bits.
Hence it's written a/8 denoting eight network bits.
Now this was fine when the internet was small, but it quickly became a limiting factor and thus multiple
addresses were introduced with different size and network portions.
Hence we have Class A, class B and class C addresses.
Please note once again that class full addresses were replaced in 1993 with classless into domain routing
or c IDR, also called CIDR.
However, you may still come across commands that use the class full address format.
An example of that is the network command within routing protocols.
So as an example, if you use the network command on a rip routing process, the command is written
in a class full format.
It's also worth knowing a bit of the history and understanding why we have problems with a lack of IP
addressing today.
Hence it's worth your learning about Crossville addresses.
For completeness, the breaking up of addresses was originally used to try and save or conserve IP addresses
but did not work in its original format and thus was expanded and changed by CIDR.
I'll explain CIDR in a moment, but let's first look at the various address classes in more detail.