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Classless Inter-Domain Routing
(CIDR)
IP Address Classes:
There are 5 different address classes which can be determined by its IP address
by examining the first 4 bits of the IP address; listed below:
Class A addresses begin with 0xxx, or 1 to 126 decimal.
Class B addresses begin with 10xx, or 128 to 191 decimal.
Class C addresses begin with 110x, or 192 to 223 decimal.
Class D addresses begin with 1110, or 224 to 239 decimal (reserved for
multicasting).
Class E addresses begin with 1111, or 240 to 254 decimal (reserved for future
use which should not be used for host addresses).
Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and internal testing on a local machine; example "ping 127.0.0.1".
Private Subnets:
The private addresses 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are reserved
for private networks . They can be used by anyone setting up internal IP
networks, since no routers on the Internet will ever forward packets coming from
these addresses; as defined in RFC 1918. Also, IP addresses in the range of
169.254.0.0 -169.254.255.255 are reserved for Automatic Private IP Addressing.
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
|
CIDR |
Dotted Decimal |
Equivalent Class C |
No. of Hosts |
| /1 |
|
||
| /2 |
192.0.0.0 |
||
| /3 |
224.0.0.0 |
||
| /4 |
240.0.0.0 |
||
| /5 |
248.0.0.0 |
||
| /6 |
252.0.0.0 |
||
| /7 |
254.0.0.0 |
||
| /8 |
255.0.0.0 |
||
| /9 |
255.128.0.0 |
||
| /10 |
255.192.0.0 |
||
| /11 |
255.224.0.0 |
||
| /12 |
255.240.0.0 |
||
| /13 |
255.248.0.0 |
2,048 Class C | 524288 hosts |
| /14 |
255.252.0.0 |
1,024 Class C | 262144 hosts |
| /15 |
255.254.0.0 |
512 Class C | 131072 hosts |
| /16 |
255.255.0.0 |
256 Class C (1 Class B) | 65536 hosts |
| /17 |
255.255.128.0 |
128 Class C | 32768 hosts |
| /18 |
255.255.192.0 |
64 Class C | 16384 hosts |
| /19 |
255.255.224.0 |
32 Class C | 8192 hosts |
| /20 |
255.255.240.0 |
16 Class C | 4096 hosts |
| /21 |
255.255.248.0 |
8 Class C | 2048 hosts |
| /22 |
255.255.252.0 |
4 Class C | 1024 hosts |
| /23 |
255.255.254.0 |
2 Class C | 512 hosts |
| /24 |
255.255.255.0 |
1 Class C | 256 hosts |
| /25 |
255.255.255.128 |
1/2 of a Class C | 128 hosts |
| /26 |
255.255.255.192 |
1/4th of a Class C | 64 hosts |
| /27 |
255.255.255.224 |
1/8th of a Class C | 32 hosts |
| /28 |
255.255.255.240 |
1/16th of a Class C | 16 hosts |
| /29 |
255.255.255.248 |
1/32th of a Class C | 8 hosts |
| /30 |
255.255.255.252 |
4 hosts | |
| /31 |
255.255.255.254 |
2 hosts | |
| /32 |
255.255.255.255 |
1 host |
