Classless Ip Vs Classful Ip address

Hello Friends,

1. I have confusion in between classless and classfull ip addresses.Please tell me major differences b/w them?
2. how we w'll find which ip address lies in which?
3. how we can decide these?
4. how this effect to the subnetting?
5. Is this also related to CIDR somewhat?



Regards,
Sumit

Hello masteronearth,

To understand classful/classless terms one should understand the available class ranges A/B/C beforehand. Not assuming here that you don't know this but I'll brief you just in case. The usable IP range is divided into these main ranges:

Class A: 1.0.0.0 -> 126.255.255.255 MASK: 255.0.0.0
Class B: 128.0.0.0 -> 191.255.255.255 MASK: 255.255.0.0
Class C: 192.0.0.0 -> 223.255.255.255 MASK: 255.255.255.0

There is also class D and E which are not of interest here.

To say that a Network/LAN is CLASSFUL, it should have the same subnet mask of it's corresponding range. For example, Say a PC in this network has the IP 170.3.4.5. This IP lies within the Class B range, so if the PC has a 255.255.0.0 subnet mask, then this network is said to be classful. If it had any other subnet mask like 255.128.0.0 or 255.255.255.0 or..... then it is classless. In short, it's all about the subnet mask used.

In the early stages of the internet, we didn't need a MASK. All networks were classful. And the mask was concluded once you know the network is within which range (A, B or C). CIDR (Classless Inter-Domain Routing) is where we are now, networks can have classless addresses and routing will still work.

Other terms that you might encounter is classful/classless routing protocols. Or the ip classless command. These don't have the exact same meanings as the above but they are very closely related. And again they all depend on the subnet mask.

Experts, please correct me if I'm wrong.