Okay, so let's complete the subnetting lab.
We were told that previously, network 192 168 1 0 slash 24 was broken up into four subnets to
support the various subnets in this lab.
So we have 192 168 1.0 slash 26, 64 slash 26 192 26 and 128 26.
So going back to my calculations we had 192 168 1.0 slash 24
we created 4 subnets.
We used this formula to get the subnet to remind you, 2 to the power of N minus 2 is used when asked
to work out the number of bits required for a certain number of hosts with subnets.
We don't have to subtract 2, so 2 to the power of N was used
which gave us four subnets.
So the formula 2 to the N or 2 to the power of 2 was used we only had to steal 2 bits from the
host portion for subnets and that gave us our 3 subnets.
We've now been told to subnet the subnet further, so in the lab we've been told to break up 192 168
1 64 slash 26 to support as many subnets as possible with 8 hosts per subnet
so this network 192 168 1 64 slash 26 needs to be broken up to support as many subnets as possible
with 8 hosts required per subnet, so the formula that we're gonna use is 2 to the power of N minus
2.
That gives us the number of hosts that we require.
So if we work through that, 2 to the power of 1 gives us 2 that will only give us 0 hosts, so
that's not enough, 2 to the power of 2 minus 2 gives us 2 hosts also not enough, 2 to the power
of 3 minus 2 would give us 6, 2 to the power of 3 is 8 minus 2 gives us 6 not enough, 2
to the power of 4 is 16 minus 2 gives us 14 hosts, so that is enough, 2 to the power of five
is 32 minus 2 would give us 30 hosts and we could continue with that but we already know
that this is the number of hosts that we require.
So we need 4 bits in the host portion which would give us 16 combinations minus 2, one for
broadcast, one for network gives us 14 hosts so this is what our original subnet looks like
at the moment this is the network subnet portion and this is the host portion we only require 4 bits
for the host portion so we can now move
2 bits to the new subnet portion so these 2 bits which, which I'll put in green are gonna be our
new subnet portion there are no spaces once again in an octet, this is a full octet so 0 1 0 0 followed
by 4 zeros but I've just split it to make it easier to see host portion is 4 bits subnet portion
is this so if we work out the subnets we have to go through the various binary combinations which would
look like that, which you can also do if you want to save time is this is 128, this is 64, this is 32 this
is 16 so you can just add 16 to 64 to get to the next subnet so that would be 80 and
just to verify that I've done it right 80 in decimal looks like this in binary notice 0101 followed
by 4 zeros that's what we've got there and then you can simply add 16 to that and that would
be 96
96
It looks like this in binary which is the same as what I've got here.
0110 followed by 4 zeros and then you can simply add 16 to that again which should give us 112.
If my math is right.
112 looks like that.
So zero followed by 3 one's followed by 4 zeros.
So those are our new subnets.
We've got 4 subnets, each supporting 14 hosts.
We only require 8 hosts but we had to use an additional bit because 3 bits wouldn't give us
enough hosts we'd only have 6 hosts.
So we've had to use 4 bits in binary to give us 16 less 2 which is 14 hosts.
We have 4 subnets because we have 2 bits, 2 to the power of 2 gives us 4 subnets.
So we've created 4 new subnets from that single subnet so we could allocate this subnet to our new
network so this new network would now be 192 168 1
64 and it's no longer a slash 26.
So I need to update that.
It's 8 plus 8
16 plus a binary bits 24 plus 4
it's 28
or if you prefer we originally had 26.
We've added an additional 2 bits to the subnet portion so slash 28
so this is now slash 28.
Now, before I configure the network I just wanna make sure that I've done things right.
This network needs to change now.
That's what we used originally.
What we've been told to do is use the last new subnet you got from 192 168 164 slash 26 and use
that with slash 30 mask.
So we need to take this subnet and then we need to subnet it again.
So this is the new subnet that we want to break up as a slash 30.
The reason why we use slash 30 is 2 to the power of 2 minus 2 gives us 2 hosts a WAN link
such as a serial link only requires two IP addresses, IP addresses on each side of the link so we can
steal 2 bits here for the subnet portion so that would be network.
This would be our new subnet and our host portion would only consist of 2 bits.
So that would be the first network
it's slash 30 mask now
next network would look like that.
Just go through the binary combinations.
So in decimal that's a 4 so it'd be 16, 20, 24 and we could once again verify that by using a calculator.
So 1 1 2 looks like that in binary 1 1 6.
It looks like that which is correct, 120 looks like that
notice 0 followed by 4 ones, 0 followed by 4 ones followed by 3 zeros
again there's no gap here.
In an octet, I'm only doing that to make it easier to read, 124
looks like that and that's also correct.
So what I'll do is I'll firstly configure the WAN links because they've changed now.
This WAN link needs to be 112 slash 30, 112 slash 30.
So this router needs to be configured with the first IP address in that subnet so show run and the serial
interface needs to be changed.
Interface serial 010 IP address is 192 168 1 113.
First IP address in that subnet it's a slash 30 mask OSPF neighbor relationship has come down, routers
require that they have the same subnet on both sides for them to form an OSPF neighbor relationship show
run on this side.
This IP address needs to change
so interface serial 01 slash 0 IP address 192 168 1 114 slash 30 mask, ping 192 168 1
113 ping works you can see that to the neighbor relationship has come up so that looks good.
So on router 1 neighbor relationship has come up again show IP route shows us default route via 11
4.
In other words this router is seeing this router as its default gateway or, or gateway of last resort so
ping cisco.com can we still get to Cisco.
Can this router IP domain lookup IP name server should be called quadruple 8 so ping cisco.com
maybe not a problem Packet Tracer let's see if this router can ping the DNS server, yes it can.
Can it ping Cisco.com name has resolved.
So Internet router can ping Cisco.com
What about router 1
I was just impatient there, notice it can ping Cisco.com and can it ping Facebook,com, again
it can so I can save the configuration I've now successfully updated the Internet router and router 1
with the new subnet.
Next thing I need to do is configure a subnet on this link so this will be 192 168 1 and I'll
choose the next one which is 116 slash 30
so notice how I've taken one original subnet this one and I've broken it up into these three.
This one is being used now so I can't use that anymore because I've subnetted that into these four subnets
but there's nothing stopping you taking one subnet and subdividing it and then subdividing it again
like I've done here.