/25 subnet and its practical use
/25 subnet is obtained through subnetting the different types of available default class a, b, and c addresses.
/25 in binary is 11111111.11111111.11111111.10000000 so in numbers, we have a subnet mask of 255.255.255.128
/25 subnet size
This subnet mask gives us two subnet ranges for eg. If we have an IP range of 193.168.1.0 to 193.168.1.255 then the IP range will be as follow
193.168.1.0 – 193.168.1.127
193.168.1.128 – 193.168.1.255
In one subnet range, we have 128 IPs and out of these IPs, we can assign 126 IPs to the host. The first IP address will be used as the network ID and the last one is reserved as a broadcast address.
/25 subnet use
If the network administrator is given a /24 subnet range that must be assigned to 2 available networks then to create a different subnet, an administrator can divide that one network into two by using subnetting however the number of IP addresses will be reduced to half.
Now, available IPs are 126 instead of 254 which can be assigned to hosts in one network.
IP addressing with /25 subnet mask
Use the appropriate IP address for devices in the image below
In this image, the IP address assigned to host PC0 is from subnet 193.168.1.128/25 so we can assign any IP from the range 193.168.1.129 to 193.168.1.254 to PC1.
The IP address assigned to the router’s interface is from subnet 193.168.1.0 so we can assign any IP from the range 193.168.1.1 to 193.168.1.126 to PC2.
Although PC2 is connected on the same switch however it is in another VLAN, each VLAN has a different subnet so we can assign any IP from subnet 193.168.1.128 to PC in VLAN 10.
Correct the IP addresses in the below configuration to establish connectivity.
IP assigned to the PC3 looks good but the subnet mask assigned is different so we should be using the same subnet for this PC which is 255.255.255.128.
One router interface connected to the LAN has been assigned the IP address 193.168.1.129/25 which is the valid IP address of the 255.255.255.128 subnet so we should be using the IP address from the same subnet that is assigned to the devices in the LAN. We should use the IP address from subnet 192.168.1.0/25.
Another router interface has been assigned the IP address 193.168.1.128/25 which is the network ID so we cannot use this address as a host address. We should use valid host IPs from this subnet.
PC4 has been assigned the IP which is the broadcast IP address so we should be using any other IP from the range 193.168.1.129 to 193.168.1.254.
