Are same IP address with different submask unique?

Question

Possible Duplicate:
How does Subnetting Work?

In a same block of IPv4 addresses, can there be same IPs with different submasks? For example, can I have this:

180.70.65.140/26
180.70.65.140/25
180.70.65.140/24

All the 3 addresses above have the same numbers but different subnet mask. Are all the 3 addresses distinct of their own? In other words, 180.70.65.140/25 belongs to User A, 180.70.65.140/25 belongs to User B and 180.70.65.140/24 belongs to User C?

After applying the submask, their network addresses look like this:

180.70.65.140/26 --> 180.70.65.128/26
180.70.65.140/25 --> 180.70.65.128/25
180.70.65.140/24 --> 180.70.65.0/24

If the addresses are recognised uniquely, how is it so? How would each of the these addresses being recognised to be unique?

I am thinking like once I have 180.70.65.140/26, I can't reuse the same numbers of 180.70.65.140 again but since classless is meant to increase the number of IP addresses, it would do much if I can't reuse.

Solution 1

There are numerous reasons, but the simplest is that this will break any routing, because a host will have no way of knowing that they're going to an address on a different network.

So, basically, no. An IP address needs to be unique, regardless of subnet.

In other words, if I'm on

192.168.1.1 255.255.0.0

And I try to access 192.168.1.2, then it's going to assume it's on the same subnet.

On a fundamental level, subnets are there to separate broadcast domains and improve efficiency. They're not for sharing IP addresses.

Solution 2

As an answer to your question above, the answer is: No you can't... It is the address itself that must be unique.

The IP(v4) address in each of the three examples would be: 180.70.65.140 (regardless of subnet mask)

The subnet mask can be thought of as: "what defines the limits of my LOCAL network" In order to reach any IP outside of this range, the computer would need to contact the "gateway" to pass the IP-packet to an external route.

So, for example

180.70.65.140/26 just means that IPs 180.70.65.129 -> 180.170.65.191 are accessible
180.70.65.140/25 just means that IPs 180.70.65.129 -> 180.170.65.255 are accessible
180.70.65.140/24 just means that IPs 180.70.65.1 -> 180.170.65.255 are accessible

Wikipedia has a reasonable link here