To make CIDR easier to understand, let us consider an example in which a block of 8192 IP addresses is available starting at 194.24.0.0. Suppose that Cam- bridge University needs 2048 addresses and is assigned the addresses 194.24.0.0 through 194.24.7.255, along with mask 255.255.248.0. This is a /21 prefix. Next, Oxford University asks for 4096 addresses. Since a block of 4096 addresses must lie on a 4096-byte boundary, Oxford cannot be given addresses starting at 194.24.8.0. Instead, it gets 194.24.16.0 through 194.24.31.255, along with subnet mask 255.255.240.0.
Above is an example from Tanenbaum's book, Computer Networks. I do understand in general why random subnet splitting is error-prone and how important it is to avoid overlapping, but I don't get the "4096-byte boundary". What does it mean? The first subnet address should be divisible by the number of blocks, 4096 in this case, but what does it have to do with byte boundaries?
Maybe, I'm missing something.
