Subnetting Chart

Table 1

---Network ID and Host ID bits

Class Network ID Bits (used) Host ID Bits (used)
A w. 8 x.y.z 24
B w.x. 16 y.z 16
C w.x.y. 14 z 8

In a Class A network 8 bits are used for the network ID while 24 bits are used for the host ids. (32 bits)

In a Class B network 16 bits are used for the network ID while 16 bits are used for the host ids. (32 bits)

In a Class C network 24 bits are used for the network ID while 8 bits are used for the host ids. (32 bits)

Table 2

---Determining Number of Subnets and Noumber of Hosts

Network Class Number of Subnets Number of Hosts
Class A 2^n-2 2^(24-n)-2
Class B 2^n-2 2^(16-n)-2
Class C 2^n-2 2^(8-n)-2

 

Table 3

Class A Network

# Bits in Mask # of Subnets Binary/(Decimal) Subnet Mask # of Bits for host # of Hosts/Subnet
0 2^0- 2 = 0 00000000/(0) 255.0.0.0 24 - 0 = 24 16,777,214
1 2^1 - 2 = 1 Invalid(10000000) (128) 255.128.0.0 24 - 1 - 23 8,388,606
2 2^2 - 2 = 2 11000000 /(192) 255.192.0.0 24 - 2 = 22 4,194,302
3 2^3 - 2 = 6 11100000 /(224) 255.224.0.0 24 - 3 = 21 2,097,150
4 2^4 - 2 = 14 11110000 /(240) 255.240.0.0 24 - 4 = 20 1,048,574
5 2^5 - 2 = 30 11111000 /(248) 255.248.0.0 24 - 5 = 19 524,286
6 2^6- 2 = 62 11111100 /(252) 255.252.0.0 24 - 6 = 18 262,142
7 12^7 - 2 = 26 11111110 /(254) 255.254.0.0 24 - 7 = 17 131,070
8 2^8 - 2 = 254 11111111 /(255) 255.255.0.0 24 - 8 = 16 65,534

Class B Network

# Bits in Mask # of Subnets Binary/Decimal Subnet Mask # of Bits for host # of Hosts/Subnet
0 2^0- 2 = 0 00000000/(0) 255.255.0.0 16 - 0 = 16 65,534
1 2^1 - 2 Invalid(10000000) (128) 255.255.128.0 16 - 1 = 15 32,766
2 2^2 - 2 = 2 11000000 (192) 255.255.192.0 16 - 2 = 14 16,382
3 2^3 - 2 = 6 11100000 (224) 255.255.224.0 16- 3 = 13 8,190
4 2^4 - 2 = 14 11110000 (240) 255.255.240.0 16- 4 = 12 4,094
5 2^5 - 2 = 30 11111000 (248) 255.255.248.0 16 - 5 = 11 2,046
6 2^6- 2 = 62 11111100 (252) 255.255.252.0 16 - 6 = 10 1,022
7 12^7 - 2 = 126 11111110 (254) 255.255.254.0 16 - 7 = 9 510
8 2^8 - 2 = 254 11111111 (255) 255.255.255.0 16 - 8 = 8 254

 

Class C Network

# Bits in Mask # of Subnets Binary/Decimal Subnet Mask # of Bits for host # of Hosts/Subnet
0 2^0- 2 = 0 00000000/(0) 255.255.255.0 8 - 0 = 8 -
1 2^1 - 2 Invalid(10000000) (128) 255.255.255.128 8 - 1 = 7 -
2 2^2 - 2 = 2 11000000 (192) 255.255.255.192 8 - 2 = 6 62
3 2^3 - 2 = 6 11100000 (224) 255.255.255.224 8- 3 = 5 30
4 2^4 - 2 = 14 11110000 (240) 255.255.255.240 8- 4 = 4 14
5 2^5 - 2 = 30 11111000 (248) 255.255.255.248 8 - 5 = 3 6
6 2^6- 2 = 62 11111100 (252) 255.255.255.252 8 - 6 = 2 2
7 12^7 - 2 = 126 11111110 (254) 255.255.255.254 8 - 7 = 1 -
8 2^8 - 2 = 254 11111111 (255) 255.255.255.255 8 - 8 = 0 Invalid

Table 4 (Cheat Sheet)

2n 20 21 22 23 24 25 26 27 28
decimal 1 2 4 8 16 32 64 128 256
Network Bits 0 1 2 3 4 5 6 7 8
Subnet 0 128 192 224 240 248 252 254 255
# Subnets 0 1 2 6 14 30 62 126 254
Host Bits 8 7 6 5 4 3 2 1 0