All language subtitles for 5. Class A and B addresses

The first class is once again class.

When looking at the first octet of an IP version 4 address.

In other words if we've got x x x x we're looking at the first octet of first 8 bits the first octet

always starts with a binary zero.

So in the first octet of the first eight bits the first bet is set to zero.

Now if we go through all the combinations in binary in the first octet that means we'll end up with

combinations from 0 in decimal up to 127 in decimal.

So the range for cross addresses is from 0 0 to 2.0 up to 127 or 2.5 to 2.5 2.5.

So for completeness Let's briefly look at that plus a in the first octet has binary values way the first

but is set to zero.

So the first entry would be 8 binary zeros which equates to 0 in decimal.

The next binary entry is seven zeros and a binary one which equates to decimal 1 going through all the

combinations to 3 4 and so forth and so on will end up at 127.

So in the first octet a class A address always starts with 0 for the first but and the combinations

are from 0 to 127 in decimal.

Now as always in life there are some exceptions.

So in Clauss say there are exceptions we 1:27 is reserved for the loopback.

I'll explain the loopback address in more detail in a moment.

You cannot as an example configure an IP address of 1:27 0.0 to one on a PC that is not an address that's

available for you to configure manually as a static address on a PC.

For example zero is reserved for the whole network so that can't be used either to configure an IP address

on a PC so you couldn't give your PC an IP address of 0.1 1.1.

So the actual range for Clauss races is the range one dot 0.00 going through all the combinations up

to 126 dot 255 255 255.

So in the first octet the values are from 1 to 1 26 for CLOS addresses.

Notice that on my PC as an example if I go to the local area connection properties and select IP version

4 and then I try and configure an IP address of 1:27.

The PC tells me that that's not possible.

IP addresses starting with 1:27 are not valid because they are reserved for loopback addresses.

We need to specify an IP address in the range 1 to 2 to 3 in the same way.

If we try and configure an IP address of zero windows and this example tells us that that IP address

is not valid and we need to specify a value between 1 and 2:58 so Clauss addresses are in the range

1 to 1 26 in the first octet.

So in summary in a class you address the first 8 bits.

Note network and the last 24 bits to note.

HOST.

This is determined by the owner.

So an address like 10.0 1.1 that one implies that this is a class A address the first 8 bits is network

and the remaining 24 bits is host.

The next class of address is class B Class B addresses talked with binary 1 0.

Please note that's not 10 in decimal.

It's binary 1 0.

Cl. addresses had the first but in the first octet set to 0 1 class B addresses the second position

in the first octet is set to 0.

So if you go through all the combinations you'll end up with numbers in the range of 128 to 191.

So clause B addresses are available in the range 128 to 191 in the first octet.

So in clause B addresses the first 16 bits denote network the second 16 bits denote the host portion.

So first two octets are network.

The last two octets are the host portion of the address.

So for example 1 7 to 16 of 1 1 to 1 7 2 in the first octet tells us that this is a Class B address

because it's in the range 128 to 191 So 1 7 2. 16 is the network portion 1.1 is the host portion of

this address and we know that because this is a class B.

Address.