IPv4

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CIDR Quick Reference

Notation Hosts Mask
/8 16,777,216 255.0.0.0
/9 8,388,608 255.128.0.0
/10 4,194,304 255.192.0.0
/11 2,097,152 255.224.0.0
/12 1,048,576 255.240.0.0
/13 524,288 255.248.0.0
/14 262,144 255.252.0.0
/15 131,072 255.254.0.0
/16 65,536 255.255.0.0
/17 32,768 255.255.128.0
/18 16,384 255.255.192.0
/19 8,192 255.255.224.0
/20 4,096 255.255.240.0
/21 2,048 255.255.248.0
/22 1,024 255.255.252.0
/23 512 255.255.254.0
/24 256 255.255.255.0
/25 128 255.255.255.128
/26 64 255.255.255.192
/27 32 255.255.255.224
/28 16 255.255.255.240
/29 8 255.255.255.248
/30 4 255.255.255.252

Classful Addresses

Class A Network

Binary address start with 0, therefore the decimal number can be anywhere from 1 to 126. The first 8 bits (the first octet) identify the network and the remaining 24 bits indicate the host within the network. An example of a Class A IP address is 102.168.212.226, where "102" identifies the network and "168.212.226" identifies the host on that network.

Class B Network

Binary addresses start with 10, therefore the decimal number can be anywhere from 128 to 191. (The number 127 is reserved for loopback and is used for internal testing on the local machine.) The first 16 bits (the first two octets) identify the network and the remaining 16 bits indicate the host within the network. An example of a Class B IP address is 168.212.226.204 where "168.212" identifies the network and "226.204" identifies the host on that network.

Class C Network

Binary addresses start with 110, therefore the decimal number can be anywhere from 192 to 223. The first 24 bits (the first three octets) identify the network and the remaining 8 bits indicate the host within the network. An example of a Class C IP address is 200.168.212.226 where "200.168.212" identifies the network and "226" identifies the host on that network.

Class D Network

Binary addresses start with 1110, therefore the decimal number can be anywhere from 224 to 239. Class D networks are used to support multicasting.

Class E Network

Binary addresses start with 1111, therefore the decimal number can be anywhere from 240 to 255. Class E networks are used for experimentation. They have never been documented or utilized in a standard way.

Map of the internet.jpg