Hi,
This post will be on Networks - IP Classification
This post will be on Networks - IP Classification
•
When Internet addresses were
standardized (early 1980s), the Internet address space was divided up into
classes:
Class A:
Network prefix is 8 bits long
Class B:
Network prefix is 16 bits long
Class C:
Network prefix is 24 bits long
•
Each IP address contained a key which
identifies the class:
Class A:
IP address starts with “0”
Class B:
IP address starts with “10”
Class C:
IP address starts with “110”
Class
|
Leading
bits |
Size
of network
number bit field |
Size
of rest
bit field |
Number
of networks |
Addresses
per network |
Start
address
|
End
address
|
Class
A
|
0
|
8
|
24
|
128
(27)
|
16,777,216
(224)
|
0.0.0.0
|
127.255.255.255
|
Class
B
|
10
|
16
|
16
|
16,384
(214)
|
65,536
(216)
|
128.0.0.0
|
191.255.255.255
|
Class
C
|
110
|
24
|
8
|
2,097,152
(221)
|
256
(28)
|
192.0.0.0
|
223.255.255.255
|
Class
D (multicast)
|
1110
|
not
defined
|
not
defined
|
not
defined
|
not
defined
|
224.0.0.0
|
239.255.255.255
|
Class
E (reserved)
|
1111
|
not
defined
|
not
defined
|
not
defined
|
not
defined
|
240.0.0.0
|
255.255.255.255
|
CIDR - Classless
Interdomain Routing
•
Blocks are used when allocating IP
addresses for a company and for routing tables (route aggregation)
•
New interpretation of the IP address
space
•
Restructure IP address assignments to
increase efficiency
•
Permits route aggregation to minimize
route table entries
CIDR Block Prefix # of Host Addresses
/27 32
/26 64
/25 128
/24 256
/23 512
/22 1,024
/21 2,048
/20 4,096
/19 8,192
/18 16,384
/17 32,768
/16 65,536
/15 131,072
/14 262,144
/13 524,288
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