Subnetting
Subnetting Sheet
Hosts double each increment of a CIDR
Always subtract 2 from host total
Network ID: First Address
Broadcast: Last Address
CIDR
/1
/2
/3
/4
/5
/6
/7
/8
Hosts
2,147,483,648
1,073,741,824
536,870,912
268,435,456
134,217,728
67,108,864
33,554,432
16,777,216
Class A
SUBNET
255.x.0.0
CIDR
/9
/10
/11
/12
/13
/14
/15
/16
Hosts
8,388,608
4,194,304
4,194,304
1,048,576
524,288
262,144
131,072
65,536
Class B
SUBNET
255.255.x.0
CIDR
/17
/18
/19
/20
/21
/22
/23
/24
Hosts
32,768
16,384
8,192
4,096
2,048
1,024
512
256
Class C
SUBNET
255.255.255.x
CIDR
/25
/26
/27
/28
/29
/30
/31
/32
Hosts
128
64
32
16
8
4
2
1
Subnet Mask (Replace X)
128
192
224
240
248
252
254
255
Cheat Sheet Examples
192.168.1.0/24
255.255.255.0
254
192.168.1.0
192.168.1.255
192.168.1.16/28
255.255.255.240
14
192.168.1.16
192.168.1.31
192.168.0.0/22
255.255.252.0
1022
192.168.0.0
192.168.3.255
Bits and Octets
First Octet
Total: 255
Second Octet
Total: 255
Third Octet
Total: 255
Fourth Octet
Total: 0
Result
/24
2^8
256
(bits on)
2^(bits off)
Resulting hosts
Meaning, a subnet of 255.255.255.0 has 24 bits switched on (3 sets of octets), 8 bits switched off (1 set of octets), which gives it 256 hosts available.
Example: A Class C Private IP Address network of 192.168.86.0/24 has a subnet of 255.255.255.0, and has 256 available hosts. Subtract 2 hosts for the Network ID and Broadcast address, leaves us with 254, So any IP in the range of 192.168.86.1-254 is available to be assigned on that network.
Last updated