Question

what is the motivation behind using a custom subnet mask versus a default subnet mask

Answer 1

The motivation behind using a custom subnet mask is that you can create more subnets out of the range of addresses. A Default subnet mask gives you classful addressing an octet boundaries whereas, a non-default subnet or custom subnet mask implies that you are subnetting a larger network into smaller ones.

Subnet mask id used to seperate the network address from the host address in IP address.An IP address is the combination of network address, host address.Subnet mask helps us to find the network portion & the host portion by identifying it.

Just like IP addresses ,subnet mask is also 32 bits in length and uses same notations which IP address uses to present itself.An IP address is always used with subnet mask,without subnet mask ,an IP address is an ambigious address in IP network.

IP address - 10.10.10.0

Subnet mask - 255.0.0.0 ( class A)

IP address - 172.168.10.1

Subnet mask - 255.255.0.0(Class B)

IP address - 192.168.1.1

Subnet mask - 255.255.255.0(Class C)

And in Custom subnetting we can split these three Classes network into different smaller networks based on the number of networks we need or the number of devices we want to connect in a particular network.

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