/28 subnet mask

/28 subnet mask with practice lab

/28 subnet mask is the subnetted mask that can be created from the default IP ranges.

In binary, we can write the /28 subnet as below.

11111111.11111111.11111111.11110000

In numeric, this will be written as 255.255.255.240

In 4 octets, we have 28 network bits and only 4 host bits which gives us 16 IPs in one subnet and 14 usable IPs in one subnet.

In smaller networks where fewer hosts are required, this subnet mask can be used to efficiently use the IP addressing and save the other IPs for other networks within the organization.

Let us take an example of the default class c network where we can create smaller networks by using the /28 subnet mask.

We have a default network 192.168.1.0 network and we will divide this into several smaller networks.

We will take 16 as an increment to create the subnet ranges.

Network ID              Broadcast ID

192.168.1.0               192.168.1.15

192.168.1.16             192.168.1.31

192.168.1.32            192.168.1.47

192.168.1.48            192.168.1.63

192.168.1.64            192.168.1.79

We can continue with creating the ranges until we have the available IPs remaining in the subnet, we will be able to create 16 small networks from only 1 available class c network using the /28 subnet mask.

Below is the network created using 28 subnet mask, guess the missing IP addresses, and correct the wrongly assigned IP addresses in the network.

Answers

1. 192.168.1.0 is the subnet ID so this cannot be assigned to the router, we can assign any other IP address 192.168.1.1 to 192.168.1.14
2. The IP address assigned to the router is the broadcast address which cannot be assigned to the device, we can use any other address mentioned in the above range.
3. 192.168.1.64 again is the network ID so this is a wrong configuration, we can correct the configuration by assigning the valid IP address from 192.168.1.65 to 192.168.1.78
4. Configuration on the PC is correct so we can keep the configuration as it is.
5. The IP address assigned to the router that is connecting to the PC has been assigned the IP 192.168.1.40 so we can assign any IP to PC from the 192.168.1.32 – 192.168.1.47 range.
6. PC attached to the router has been assigned the IP address from the 192.168.1.16 – 192.168.1.31 range so we can assign any IP from 192.168.1.17 to 192.168.1.29
7. IP assigned to PC is valid.
8. IP assigned to the IP phone is a broadcast address so we have to assign any other IP from the above-mentioned range.
9. IP assigned to the router is valid.