This is one of multiple IP addressing and submitting scenarios rather than just working out the subnets
for a scenario.
We're going to work them out and then configure the devices so that we can practically design and configure
a Cisco IP network in the previous video we can forget those genius three network.
And we proved that devices can ping one another as an example.
Xubuntu one PC one can ping both Ubuntu three and a boon to four.
In other words this host can ping these hosts on the right hand side.
Now one of the things that we did was we configure it to the serial link with Sublette 1 and 2 1 6 8
1 128 slice 26.
Now that subnet can support 62 hosts that's a waste of IP addresses when in actual fact a serial link
only requires two IP addresses.
So we allocated to this full subnet to the serial link the host portion currently contains six butts
to the power of six minus two gives you the option to configure 62 host addresses but we only require
two.
So actually all we need are two bets in the host portion which will give us the option of having to
host addresses in a subnet.
Again they are two formulas for network she use the formula 2 to the power of x where x is the number
of bits for host you use two to the power of x minus two.
Two is the number of bytes in the host portion.
We have to subtract two because we need a network address and a broadcast address in IP version 4.
So two to the power of two minus two gives us for minus two which equals two.
So taking this subnet which weve currently got configured on the Saral link lets submit it further.
So as an example one brought a one currently show IP interface serial to slash zero.
Shows us that 1 and 2 1 6 8 1 1:29 slice 26 is configured on the serial interface and that's because
we configure the address on the serial interface.
Now let's change that and optimize the subnet.
So we only need two bits for the host portion so we can extend the subnet portion as follows.
Now we are taking a already configured subnet and we submitting it again.
So I'm going to denote this portion as the network portion because that's what we were given.
This is the new subnet portion and this is the new host portion.
So that's what we had originally.
We've not changed it to slash 30.
So this would be then new first subnet
the second subnet would not be 128 we'd have to cycle through the binary options so we'd make this a
one which in decimal is four.
So 128 plus four.
And let me update the subnet mask portion while we're here.
So that's the new subnet mask.
So this would be 128 plus 4 which is 132.
So that would be the second Sublette.
Now you might notice a trend here the difference between 128 and 132 is full.
So the third subnet would be 132 plus 4 which would be 136 if you wanted to work out the binary you
would cycle through the various options so current on this wire no current on this wire.
That's an 8 in decimal 128 Plus 8 in decimal is 136.
So if I were you to only work out say the first two or three subnets and then just see the pattern.
These are incrementing in fours.
So the next one would be 140.
So just look at the pattern and it'll be a lot easier to work out to the next subnet.
Now some other tricks that you can use if this is the next subnet.
Then the first subnet broadcast address is one less than the next subnet.
The next subnet is 132.
So this subnets broad cross address is 131
again to work out the broadcast address you fool the host portions with the ones so this is 128 plus
two plus one or it's one less than the next subnet.
So that's the new first subnet broadcast address.
So the first host address is one more than the subnet address so it'll be a hundred and twenty nine
in binary it looks like that the new first subnet last host is one less than the broadcast address so
the broadcast address is 131.
So this will be 130 in binary file.
The host portion with Bhandari ones except for the last but here we've only got two bits.
This is on and this is off.
So that gives you the last host in the subnet.
So that's an example of taking a subnet that we've created from a previous subnet and submitting it
again to get new subnets in the network.
So currently on our network we are using a 26 year what we'll do is change that to a slash 30 with the
first host being 1 on 2 1 6 8 1 29 slash 30.
And the second host being 1 9 2 1 6 8 1 130 slash 30.
So that's the IP address on the first host of first Rodda.
This is the IP address on the second Rodda we are going to stay with 1:29 and 130 but we are going to
change the subnet mask its interface serial to slushes 0 IP address 1 9 2 1 6 8 1 1:29
and the scenario needs to be mosque is a slush 30 because it's 8 plus 8 plus 8 plus six of slush 30
mosque
so this needs to change to 1 2 1 6 8 1 128 slash city that's the mosque you'll often find on several
links because it supports two host addresses.
So again this is a slash 30 mosque because we've got 30 binary ones in the subnet mosque.
So this is 2:55 dot 2:55 dot 2:55 dot to 5 to.
So this is going to be 2:05 to as the IP address.
Notice the relationship goes down has come up again but we will probably have problems running it that
way.
So the site or say needs to be 2:05 to.
In other words a slash 30 relationship has come up show IP interface serial to slash zero.
Notice the mosque now used is a slash 30 and on side show IP interface serial to slushes zero.
Notice the mosque used to use a slash 30 second right of one ping brought it to.
Yes it can
Ken PC one still paying PC three yes it can and can ping
PC for yes it can.
So let's trace to 1 on 2 1 6 8 1 65.
You can see it goes to route 1 rather 2.
And then the remote PC so we've successfully updated the subnets in this typology to only use two IP
addresses on the serial link.
The reason for doing that is we can increase the number of subnets that we have.
So rather than only having a one subnet we've now increased the number of subnets to two to the power
of four.
So we've actually got 16 separate subnets that we can use each of which support to host addresses are
being joined to this video.
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