Re: PROBLEM IN SUBNETs CLASSFULL AND CLASSLESS!!!!!!!
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Perhaps you're a bit confused about classful vs. classless addressing.
For both, we need some method to distinguish between the network portion of the address and the host portion of the address.
With classless, whenever we "send" a network IP address, we included a network mask. This allows the "recipient" to know what portion of the address is to be used for the network number and which portion contains a host number. This also allows us to have no predefined network/host boundaries. So we can have 10.0.0.1/24 or 126.96.36.199/8; pretty much anything we want except for the IP addresses set aside for multicast and experimental.
With classfull addresses (when both bandwidth and router memory were very expensive, i.e. we don't want to send or store the mask), we determine what the network and host portions of the IP address are by some rules. If the first bit of the IP address is zero, it's a class A (/8). If the first bit of the address is a one, but the second bit is a zero, it's a class B (/16). If both the first bit and second bits are ones, it's a class C (/24). (BTW, there are also performance advantages to looking at just the first or first two bits on very early computers.)
Classfull is a neat "trick", but having just 3 predefined network masks is often rather inconvenient. So, often the "natural" class networks were subdivided (i.e. subnetted). Doing so, though, comes with a bunch of dos and don'ts, because network masks are not provided with the IP address.
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