Now previously before cider was used we had class full address masks so we had class a addresses Class
B addresses and Class C addresses a class a subnet supports about 16 million addresses and uses the
mosque to far 5.0 dot 0 0 0.
Class B networks support about 65000 host addresses with a mask of 2 5 5 or 2 4 5 0 0 0 plus C networks
support 254 host addresses and use a mask of 255 or 2.5 by 5.2 per 5.0.
The problem with this method is what happens if a company wants to support 3000 hosts for example.
So if the network had 3000 hosts which of these three address classes.
Would the company get well they could get a Class B address but that's an awful waste of a lot of addresses.
About sixty five thousand addresses are available in a class B subnet.
But in this example the company only needs 3000 host addresses.
They could get multiple class C networks but that means that they going to be allocated many Class C
addresses which has a negative effect on Internet routing tables.
Now rather than doing that we can move the subnet mask insider.
Notice in Class A B and C addresses the subnet mask is set on the Octet boundary.
Notice in Class A B and C addresses the subnet mask is set on the Octet boundary plus a first 8 bits.
Class B first 16 bits.
Class C first 24 bits.
But rather than doing that with CIDA the subnet mosque can be somewhere in the middle.
It doesn't have to be on the test boundary.
Here's another example.
In this example we've got a subnet mask of 255 dot 2 2 4 0 0 2 4 5 in binary is 8 binary ones 2 to 4
is 3 binary ones followed by 5 binary zeros.
So if we count the number of binary ones that gives us 11 so 255 2 2 4 2 0 0 0 is the same as Slash
eleven the network portion is on the left hand side the host portion is on the right hand side.
But notice once again that the divider between network and host is not on the Octet boundary it's somewhere
within this octet.
So in this example the most significant three bits of that octet are network and the remaining portion
of the octet is host.
Now in the subheading videos I'm going to show you this in a lot more detail.
We're going to work out various types of sub netting.
What I need you to understand with regards to cider at this point is that cider allows us to implement
a variable length subnet masks no longer do we have plus a b and c networks where class A is always
slash 8.
Class B is always slash 16 and Class C is always slash 24 when cider is used.
The mosques can vary and that's what we use today.
So from 1993 cider is more preferable than classical network mosques.
Now once again in the subheading videos I'm going to discuss subletting in a lot more detail so please
refer to those videos if you want to learn more about how to subnet a network or how to work out the
maximum hosts that can be supported on a subnet or which addresses the first address or lost address
or what is the broadcast address and so forth for a specific subnet.