I was reading Data Communication book by Forouzan in which there is a one restriction put on CIDR subnetting by Internet authorities:
First IP address in the block should be evenly divisible by the number of addresses. For example, below, the first address, when converted to a decimal number, is 3440387360, which when divided by 16 (block size) results in 215024210.
Since this did not clear the practical significance behind this restriction I went on exploring and came across the video where it is explained as follows:
Whenever we divide any number by kth power of 2 (another restriction being that the block size should be 2^k), the reminder is least significant k bits. So evenly divisible by 2^k means that least significant k bits should all be 0. This way the first address of the allocated address block can be used as a block ID since it has all 0s in the host ID part.
Now that seems more logical despite the fact that I dont understand how
evenly divisible by the number of addresses 2^k
least significant k bits should all be 0
Can't it be just that the decimal equivalent of least significant k bits should be divisible by 2. I mean if least significant 4 bits (for a block of 2^4 addresses) is binary 1010, then it translates to decinal 10 which is divisible by 2.
So in short why is evenly divisible translates to all 0 LSBs?