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Okay, so let's complete the subnetting lab.

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We were told that previously, network 192 168 1 0 slash 24 was broken up into four subnets to

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support the various subnets in this lab.

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So we have 192 168 1.0 slash 26, 64 slash 26 192 26 and 128 26.

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So going back to my calculations we had 192 168 1.0 slash 24

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we created 4 subnets.

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We used this formula to get the subnet to remind you, 2 to the power of N minus 2 is used when asked

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to work out the number of bits required for a certain number of hosts with subnets.

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We don't have to subtract 2, so 2 to the power of N was used

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which gave us four subnets.

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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

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host portion for subnets and that gave us our 3 subnets.

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We've now been told to subnet the subnet further, so in the lab we've been told to break up 192 168

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1 64 slash 26 to support as many subnets as possible with 8 hosts per subnet

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so this network 192 168 1 64 slash 26 needs to be broken up to support as many subnets as possible

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with 8 hosts required per subnet, so the formula that we're gonna use is 2 to the power of N minus

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2.

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That gives us the number of hosts that we require.

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So if we work through that, 2 to the power of 1 gives us 2 that will only give us 0 hosts, so

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that's not enough, 2 to the power of 2 minus 2 gives us 2 hosts also not enough, 2 to the power

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of 3 minus 2 would give us 6, 2 to the power of 3 is 8 minus 2 gives us 6 not enough, 2 

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to the power of 4 is 16 minus 2 gives us 14 hosts, so that is enough, 2 to the power of five

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is 32 minus 2 would give us 30 hosts and we could continue with that but we already know

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that this is the number of hosts that we require.

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So we need 4 bits in the host portion which would give us 16 combinations minus 2, one for

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broadcast, one for network gives us 14 hosts so this is what our original subnet looks like

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at the moment this is the network subnet portion and this is the host portion we only require 4 bits

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for the host portion so we can now move

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2 bits to the new subnet portion so these 2 bits which, which I'll put in green are gonna be our

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new subnet portion there are no spaces once again in an octet, this is a full octet so 0 1 0 0 followed

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by 4 zeros but I've just split it to make it easier to see host portion is 4 bits subnet portion

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is this so if we work out the subnets we have to go through the various binary combinations which would

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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

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is 16 so you can just add 16 to 64 to get to the next subnet so that would be 80 and

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just to verify that I've done it right 80 in decimal looks like this in binary notice 0101 followed

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by 4 zeros that's what we've got there and then you can simply add 16 to that and that would

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be 96

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96

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It looks like this in binary which is the same as what I've got here.

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0110 followed by 4 zeros and then you can simply add 16 to that again which should give us 112.

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If my math is right.

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112 looks like that.

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So zero followed by 3 one's followed by 4 zeros.

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So those are our new subnets.

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We've got 4 subnets, each supporting 14 hosts.

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We only require 8 hosts but we had to use an additional bit because 3 bits wouldn't give us

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enough hosts we'd only have 6 hosts.

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So we've had to use 4 bits in binary to give us 16 less 2 which is 14 hosts.

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We have 4 subnets because we have 2 bits, 2 to the power of 2 gives us 4 subnets.

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So we've created 4 new subnets from that single subnet so we could allocate this subnet to our new

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network so this new network would now be 192 168 1

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64 and it's no longer a slash 26.

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So I need to update that.

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It's 8 plus 8

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16 plus a binary bits 24 plus 4

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it's 28

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or if you prefer we originally had 26.

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We've added an additional 2 bits to the subnet portion so slash 28

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so this is now slash 28.

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Now, before I configure the network I just wanna make sure that I've done things right.

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This network needs to change now.

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That's what we used originally.

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What we've been told to do is use the last new subnet you got from 192 168 164 slash 26 and use

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that with slash 30 mask.

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So we need to take this subnet and then we need to subnet it again.

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So this is the new subnet that we want to break up as a slash 30.

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The reason why we use slash 30 is 2 to the power of 2 minus 2 gives us 2 hosts a WAN link

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such as a serial link only requires two IP addresses, IP addresses on each side of the link so we can

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steal 2 bits here for the subnet portion so that would be network.

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This would be our new subnet and our host portion would only consist of 2 bits.

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So that would be the first network

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it's slash 30 mask now

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next network would look like that.

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Just go through the binary combinations.

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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.

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So 1 1 2 looks like that in binary 1 1 6.

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It looks like that which is correct, 120 looks like that

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notice 0 followed by 4 ones, 0 followed by 4 ones followed by 3 zeros

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again there's no gap here.

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In an octet, I'm only doing that to make it easier to read, 124

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looks like that and that's also correct.

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So what I'll do is I'll firstly configure the WAN links because they've changed now.

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This WAN link needs to be 112 slash 30, 112 slash 30.

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So this router needs to be configured with the first IP address in that subnet so show run and the serial

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interface needs to be changed.

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Interface serial 010 IP address is 192 168 1 113.

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First IP address in that subnet it's a slash 30 mask OSPF neighbor relationship has come down, routers 

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require that they have the same subnet on both sides for them to form an OSPF neighbor relationship show

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run on this side.

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This IP address needs to change

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so interface serial 01 slash 0 IP address 192 168 1 114 slash 30 mask, ping 192 168 1

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113 ping works you can see that to the neighbor relationship has come up so that looks good.

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So on router 1 neighbor relationship has come up again show IP route shows us default route via 11

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4.

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In other words this router is seeing this router as its default gateway or, or gateway of last resort so

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ping cisco.com can we still get to Cisco.

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Can this router IP domain lookup IP name server should be called quadruple 8 so ping cisco.com

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maybe not a problem Packet Tracer let's see if this router can ping the DNS server, yes it can.

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Can it ping Cisco.com name has resolved.

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So Internet router can ping Cisco.com

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What about router 1

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I was just impatient there, notice it can ping Cisco.com and can it ping Facebook,com, again

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it can so I can save the configuration I've now successfully updated the Internet router and router 1

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with the new subnet.

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Next thing I need to do is configure a subnet on this link so this will be 192 168 1 and I'll

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choose the next one which is 116 slash 30

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so notice how I've taken one original subnet this one and I've broken it up into these three.

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This one is being used now so I can't use that anymore because I've subnetted that into these four subnets

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but there's nothing stopping you taking one subnet and subdividing it and then subdividing it again

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like I've done here.