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Peter WilsonFlag for France

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Classlful vs Classless subneting

Hi Experts,

I need help in understanding the difference between Classlful vs Classless subneting. Is 10.11.0.0/24 a classless subnet because I am not utilizing all of the IPs?

Thanks!
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Dr. Klahn

"Classful" is now considered obsolete.  It sliced up the 32-bit address space into class A, B and C blocks.  Class A blocks fixed the bits in the top octet; class B the top two octets, class C blocks the top three octets.  There was no in-between; these were the choices.

So 8 was a class A block, 10.32 was a class B block, and 193.187.233 was a class C block.  These correspond approximately (depending on whose definition of a CIDR block and a subnet is used) to CIDR /8, /16 and /24 subnets.

As address space became more precious it was necessary to slice more finely and so CIDR came into use.  Any number of bits can be fixed in the address for a CIDR block.  So 180.237.240.0/23 refers to IP addresses ranging from 180.237.240.0 to 180.237.241.255.

To answer your specific question:  The abstract IP space specified by 10.11.0.0/24 is a classless subnet because you have specified it in CIDR format.
The range of IPs is also tied to classes, so the above example of 10.32 is wrong as 10. is always class A, so it is indeed more complicated ;-). I cannot remember the exact rules, but as stated correctly, it doesn't really matter anymore.
Class A is /8
Class B is /16
Class C is /24

Any other subnet mask is considered classless. A subnet mask is a subnet mask, no matter how many addresses within that subnet you make use of it.

10.11.0.0/24 is a class C. The only thing that would change that is if you were to change the subnet mask.
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THx!
the the others mentioned, classful is obsolete, but here is the breakdown, it has to do with the binary format.

Classful networks use the 'classful' subnet mask according to the leading bits in the first block of the IP address:
Class A begins with binary 0 (0-127.x.x.x)
So and IP address 0.0.0.0 to 127.255.255.255 use subnet mask = 255.0.0.0

Class B begins with binary 10 (128-191)
So IPaddresses 128.0.0.0 to 192.255.255.255 use subnet mask = 255.255.0.0

Class C begin with binary 110 (192-223)
So IP addresses 192.0.0.0 to 255.255.255.0 use a subnet mask = 255.255.255.0

The above posts are correct in the subnetting but address matters in classful as well.  The prive reserved ranges are just reserved space for internal addresses.
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@Qlemo - I feel my question closure was accurate - please all of you help me sort this out.

Dr. Klan's comment https:#a41936616 is inaccurate.
10.32 was a class B block.
10.32 has never been a class B!

Qlemo's comment https:#a41936674 simply points out the error discovered above.

Masnrock's comment https:#a41936840 is the most straightforward to me, which is why I awarded it best.

Predrag Jovek's comment https:#a41936893 is the most technacilly accurate (IMO) but less easy to grasp, which is why I voted it Assisted (mind you points were evenly split between Masnrock & Predrag.

Bryant Schaper's comment https:#a41938072 is actually from Predrag Jovek's comment https:#a41936893 (https://en.wikipedia.org/wiki/Classful_network#Classful_addressing_definition) but again is inaccurate.
Class B begins with binary 10 (128-191) So IPaddresses 128.0.0.0 to 192.255.255.255 use subnet mask = 255.255.0.0
Not true either, the accurate range is actually 1280.0.0 to 191.255.255.255. and
Class C begin with binary 110 (192-223) So IP addresses 192.0.0.0 to 255.255.255.0 use a subnet mask = 255.255.255.0
is incorrect too, the range is actually 192.0.0.0 to 223.255.255.0.

I don't award points for incorrect info even in a partial capacity...it makes no sense to do so for future users to see an answer that is partially correct. We are in the sciences...it is either correct or it is not.

Please explain why Masnrock's comment https:#a41936840 is incorrect!
@Predrag Jovic You are correct, i missed the link.  I just wanted to clarify that class A,B,C,D,E ect are more than just a subnet, the actually network address is important as well, without breaking out all the private addresses and ranges, which are not really part of the classful addressing, and fall into the ranges.
@Peter Wilson

Sorry I did have a typo, however, and I actually little about points, but it seems you didnt care as much about classful vs classless and just wanted a simple YES it is classless answer
Can someone please explain to me why Masnrock's comment https:#a41936840 is incorrect. I'd really like to understand this concept. Thx!
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@Bryant Schaper - I don't see how you arrived at that conclusion...that I only want a "yes" to my answer, quite the contrary, I want a "technically correct answer." I understand the concept that you were making...the network address plays into this concept. Thank you for that.
@Bryant Schaper I provided link not to type everything I think is decent explanation. If Author need more details after reading to understand it he should ask for more.
:)
And I typically tend to explain too much and "overreact" with explanation...
Thank you Predrag, you have helped me understand this concept. So to my original question, 10.11.0.0/24 is a classless address because it breaks the classful convention of 10.0.0.0/8, correct? in order for 10.11.0.0 network to be classful it would have to be 10.11.0.0/8.
Yes, that's right.

And, yes, we all make error, typos and poor explainations.
:)

You are welcome.
Thx Qlemo for pointing out this error in my question closing...I'm grateful you caught it!!!