Tutorials

## Free Class B Subnetting Tutorial, How to subnet Class B Network, Subnetting Study Guides

External Resources

This lesson is only a part of a series of IPv4 subnetting lessons. Please visit the below links to learn IPv4 subnetting completely.

• Class C Subnetting Tutorial - Part 1
• Class C Subnetting Tutorial - Part 2
• Class B Subnetting Tutorial - Part 1
• Class B Subnetting Tutorial - Part 2
• Class A Subnetting Tutorial - Part 1
• Class A Subnetting Tutorial - Part 2
• Variable Length Subnet Masking (VLSM)
• Supernetting

In this Class B Subnetting Tutorial - Part 1, you will learn how to subnet a Class B network.

### Class B Subnetting

Remember, the first two octets of a Class B network is used to represent the network and the last two octets are used to represent the host. The default format for a Class B IPv4 address is Network.Network.Host.Host.

Let us consider an example of Class B network 172.16.0.0 - 255.255.0.0. The binary representation of the above network and subnet mask is

Component Binary Decimal

Once again,

If all the bits in the host part are "0", that represents the network id.

If all the bits in the host part are "0" except the last bit, it is the first usable IPv4 address.

If all the bits in the host part are "1" except the last bit, it is the last usable IPv4 address.

If all the bits in the host part are "1", that represents the directed broadcast address.

All the IPv4 addresses between the first and last IPv4 addresses (including the first and last) can be used to configure the devices.

#### Class B - One Bit Subnetting

If we include one bit from the host part to the network part, the subnet mask is changed into 255.255.128.0 The single bit can have two values in third octet, either 0 or 1.

10101100.00010000.0 | 0000000.00000000
11111111.11111111.1 | 0000000.00000000

That means, we can get two subnets if we do a single bit subnetting.

SN No Description Binaries Decimal

The network 172.16.0.0 is divided into two networks, each network has 32768 total IPv4 addresses and 32766 usable IPv4 addresses (two IPv4 addresses are used in each subnet to represent the network address and the directed broadcast address). The subnet mask for one bit subnetting is 255.255.128.0.

#### Class B - Two Bit Subnetting

If we include two bits from the host part to the network part, the subnet mask is changed into 255.255.192.0. The two bits added to network part can have four possible values in third octet, 00, 01, 10, and 11.

10101100.00010000.00 | 000000.00000000
11111111.11111111.11 | 000000.00000000

That means, we can get four networks if we do a two bit subnetting.

SN No Description Binaries Decimal

The network 172.16.0.0 is divided into four networks, each network has 16384 total IPv4 addresses and 16382 usable IPv4 addresses (two IPv4 addresses are used in each subnet to represent the network address and the directed broadcast address). The subnet mask for one bit subnetting is 255.255.192.0.

#### Class B - 3 Bit Subnetting

If we include three bits from the host part to the network part, the subnet mask is changed into 255.255.224.0 The three bits added to network part can have eight possible values in the third octet and that are 000, 001, 010, and 011, 100, 101, 110 and 111.

10101100.00010000.000 | 00000.00000000
11111111.11111111.111 | 00000.00000000

That means, we can get eight networks if we do a three bit subnetting.

SN No Description Binaries Decimal