Now let us take a quick look at IPv4 Class full addressing:
|
Class
|
Address Range
|
N/w’s
|
Hosts per N/w
|
|
A
|
0.0.0.0 – 127.255.255.255
|
128
|
16777216-2 =
16777214
|
|
B
|
128.0.0.0 – 191.255.255.255
|
16384
|
65536-2 = 65534
|
|
C
|
192.0.0.0 - 223.255.25.255
|
2,097,152
|
256-2 = 254
|
|
D
|
224.0.0.0 –
239.255.255.255
|
Reserved for
Multicasting
|
-
|
|
E
|
240.0.0.0 – 255.255.255.255
|
R & D
|
|
How can you say
whether an IP addressing scheme is classful or not?
The
subnet mask helps us to identify the type of IP addressing. The subnet mask is used to separate the
network and host bits. It is also a 32 bit field, the network portion will be
indicated by a 1 and the host portion will be indicated by 0.
For example, we know that a Class
A address has a network component of 8 bits (first 8 bits) and the host
component has 24 bits , so the subnet mask for the Class A addresses is: 11111111.00000000.00000000.00000000,
in decimal it would be: 255.0.0.0
Similarly for Class B: 11111111.11111111.00000000.00000000 =
255.255.0.0
For Class C: 11111111.11111111.11111111.00000000 =
255.255.255.0
So if you
see a network number that has the default subnet mask, then we can say that the
IP address is a Classful IP addressing.
Disadvantages of
Classful IP addressing:
Assume
that you have four LAN segments with 50 users each in your organization and you
want to assign separate network for each of those segments.
Then probably you will have to
choose four class C networks but in this type of scenario, since a single class
C address has 254 usable addresses and your segment has only 50 users then for
each network you are approximately wasting 200 IP addresses, so a total of 800
IP addresses. Since this is your private network that is fine.
But
if we use class full addressing in Public network then there will be a lot of
unusable IP addresses and we will fall short of IP address very soon. (Of
course we presently short of them and started using IPv6)
This
problem has been addressed by developing new concepts such as Sub-netting,
Classless Routing and Variable Length Subnet Masks, the upcoming posts will
discuss about them.
