(even if there are a large quantity of valid hosts that go unused)
I’ve been trying to understand IP addresses and subnet masks and I watched (and understood) the majority of this video https://youtu.be/s_Ntt6eTn94. This was a question I had at the end though. Is there some sort of disadvantage of having a class A subnet?
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Class A subnet masks are only used for really large networks because they allow for a very large number of host IP addresses.
There is just no point if you don’t need them. And given that VLANs exist there is rarely any point in having thousands and thousands of devices on the same subnet.
One of the biggest issues with using a large subnet is broadcast traffic.
On top of that, you are generally going to want to segregate hosts for either logical or security issues.
If I ever use a 10. address it will normally be a /24 or /23.
Having said that, I don’t work in big enterprise shops.
There are classes of address space that were originally defined/scoped using subnet masks. Nearly all routing is classless (it doesn’t care about strict class boundaries.)
To answer: because the classful host bits can be used to define subnets. For example 10.0.0.0/8 can be broken into 10.0.0.0/24 – 10.255.255.0/24. (65,536 subnets, 256 addresses per subnet.)
Originally it was about ease of allocation of various sizes of fixed netblocks to different organizations.
If it’s for a private local network, you absolutely can.
There’s one class A network – 10.0.0.0/8 – that’s reserved as non-routable.
This means it doesn’t exist on the internet – you try to send a packet to it over your internet link, your router will say lol no.
As such, that entire network is always available for *local* LAN addresses; they’ll never conflict with a real internet address. You can put every machine in your organization (assuming you have less than 16 million of them) in that address space and they’ll always be free to use – you just can’t reach them from outside, or reach the outside world from them without using NAT or such.
But any other class A? There’s only 256 of the things, and there’s not many people or organizations that have the money and clout to own 1/256th of *the entire internet* for their own personal sandbox.
That’s why.
Your question is like asking why do we sometimes use buses instead of cars to get people ftom A to B?
If you’ve only got 5 people to transport, then a car (/29) is perfect.
If you’ve got 200 people to transport, a bus (/24) may be more appropriate.
Finally, if you need to move 16,000,000 people…
In reality, you would never assign anything greater than a /23 to an enterprise host (too much broadcast spam) but you may find yourself using /16 or /8 for ‘summarising’ just like you might put all your bags of shopping in one trolley instead of trying to carry 11 bags.
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