IP Networking

Dear friends am confused with the logic behind subnetting. i am learning from video tutorial and quite didn't get it
so my question is as below

After subnetting class c address by borrowing one bit from host to network , it leaves host with 7 bit and network increases bit to 25 bits .

According to my video tutorial it stated that theoretically class C address has
one network and 255 hosts. And after subnetting 2 networks with 127 hosts. but i dont think so ....

i believe class c has around 2097150 network and 255 hosts. i didn't get that logic . please help me get that right in my head.

Say you have a class C network of 192.168.1.0/24 which has 254 usable host addresses, because 192.168.1.0 and 192.168.1.255 are not usable (2^8-2).

By changing the CIDR suffix to 25 , you create two networks:

Code:

192.168.1.0/25

and

Code:

192.168.1.128/25

The first has 126 usable host addresses (192.168.1.{1..126}, 2^7-2)
The second has 126 usable host addresses (192.168.1.{129..254}), 2^7-2)


--
The subnet mask of the /24 network is 255.255.255.0
The subnet mask of the two /25 networks is 255.255.255.128

thanks a lot for wonderful explanation. Does that means

Code:

192.168.1.0/24

has 254 usable host address and that 254 host has to share only one network address. ie i can have only one network and within that network i cannot have more than 254 computers.

And using that subnetting i get two network with each network having 126 usable host address.

can you please check what i quoted below make sense or its wrong

Hi,

To put it as simply as possible, in any given network range the very first address and the very last address are not usable for hosts. The first address is the network address, and the last address is the broadcast address.

So for 192.168.1.0/24 you'd have:

192.168.1.0 - Network address (NOT usable for hosts)
192.168.1.1 through 192.168.1.254 - Free IPs (Usable for hosts)
192.168.1.255 - Broadcast address (NOT usable for hosts)

And for /25 sub-nets (and all others besides) it'd be the same: the first address in the range and the last address in the range are not usable for hosts.

Thank you Drysdalk . i believe i didn't understood properly what a single ip address means. From your above explanation . for e.g.

Code:

192.168.1.1 through 192.168.1.254 - Free IPs (Usable for hosts)

Does all those ip are list of single ip address. i believe list of hosts in ip class means list of single ip address. Does my public ip address as mentioned

Code:

46.126.40.51

means one of hosts from class A public ip address .

Hi,

Firstly, from just looking at a single IP, you can't tell how large the network it's a part of is. You need to know the netmask. So for example, if I had an IP of 192.168.1.10, that doesn't tell you anything at all about how large or small the network I'm a part of is.

But if I tell you the netmask - e.g. 192.168.1.10/24 or 192.168.1.10/255.255.255.0 - then you know it's part of a network of 256 addresses, running from 192.168.1.0 to 192.168.1.255.

If on the other hand I'd told you the netmask was 192.168.1.10/25 or 192.168.1.10/255.255.255.128 - then you'd know it was part of a network of 128 addresses going from 192.168.1.0 to 192.168.1.127.

And again, in every network, the very first address and the very last address are not usable for hosts, as they are reserved for other purposes.

You can also get plenty of other netmasks than the old simple Class A, B, C notation tells you. For instance I could just have easily told you my netmask was 192.168.1.10/28, in which case you'd then be able to calculate that the network I was a part of runs from 192.168.1.0 to 192.168.1.15, and conists of 16 IP addresses.

So just from looking at an IP you can't tell anything about the size of the network. And these days, there are far more netmasks and subnet sizes that are far more common than the old Class A/B/C notation.

i just came to learn that my public ip address through whatsmyip

Code:

46.126.40.51

since its class A IP address so default subnet mask is

Code:

46.126.40.51/8  ie 255.0.0.0

does that means apart from from 46.0.0.0 and 46.255.255.255. i can use all the rest for host. And i believe its possible within one network

And when some one bought a class A static IP address for personal use. does that means i can have around 16777214 host within a single network.