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With classful addressing there are basically three classes of networks, a public or
private organization can request,for its hosts,a network of class A,B or C
with A being the largest followed by B and C.

I'm having an hard time understanding whether kor not this logic also applies to networks of routers.

Suppose routers X,Y and Z have an interface on the same LAN, in my understanding this LAN is also an IP network of class A,B or C, am I right?

What class should be required for such a network and in general for routers netoworks where there are only an handful of routers?
In this case even a class C network would be way too large and a many IP addresses would be wasted.

I'm only starting studying IP protocol,maybe I'm getting something wrong here.

I first want to learn how classful addressing works, and then go to CIDR.

EDIT:
The main reason I've asked this question is beacause I always read on textbooks
that the major drawbacks of classful addressing were:
- The fact that class A was too large for many organizations.
- Class B was just right but there were not many nets of this class.
- Class C nets were too small for many organizations.

Another important drawback was,in my opinion, the fact that many class C networks were in fact routers networks,so the number of class C networks available to organizations was further limited by this fact, am I right ?

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closed as off-topic by CharlieRB, Canadian Luke, MariusMatutiae, harrymc, Kevin Panko Jun 4 at 2:16

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2  
It's all pretty much laid out right here: en.wikipedia.org/wiki/IPv4 –  Digital Chris Apr 7 at 17:57
2  
Does it really make sense to learn classful addressing first, given that you will need to unlearn it anyway? –  grawity Apr 7 at 17:59
    
What if you mention network range ? I am not a network expert but something like 192.168.1.1/24 may give you limited number of IP's and no waste. what do you say ? –  shekhar Apr 7 at 18:01
    
class C has 8 bits to identify its hosts, so if we have a router network of an handful of routers, let's say 10, we would waste more than 246 IP addresses. –  user986437 Apr 7 at 18:06
    
But because of how local each device is, it's not going to affect network performance enough to only use 4 bits for the address... –  Canadian Luke Apr 7 at 18:14

1 Answer 1

Note that classful addressing is not used any more. Division of the address between network and host is not done on the three 8-bit boundaries anymore, but at any arbitrary bit between 32 (all the way to the left) and 0 (all the way to the right).

So now, you specify that boundary explicitly, i.e. 192.168.99.1/25. You can also specify the subnet mask, 255.255.255.128. I purposely picked an example you won't commonly see for illustration.

Suppose routers X,Y and Z have an interface on the same LAN, in my understanding this LAN is also an IP network of class A,B or C, am I right?

A class, in the classful routing sense, is equivalent to one of three netmasks

A - /8 - 255.0.0.0

B - /16 - 255.255.0.0

C - /24 - 255.255.255.0

All nodes on a LAN have to have the same subnet mask to communicate. This is true whether we express the subnet masks by class or CIDR. In the classful days, the subnet mask would be one of these, and the one interface of a router that's in that LAN would also be the same.

In CIDR times, the subnet mask can be anything, but it will still be the same for all nodes on a LAN, including the one interface of a router that's in that LAN.

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thanks for your answer I'm also starting learning CIDR, please read my edit, an answer would be very appreciated.:D –  user986437 Apr 7 at 19:05

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