1
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Now, we've been told to configure router 1 with the last IP address in that subnet.

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Now, this is the subnet that we concentrating on initially, so let's start with that subnet.

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The way you work out first

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last and broadcast addresses as follows.

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The network has the host portion populated with binary zeros.

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So notice host portion is all zeros.

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The first host has the host portion populated with binary zeros except for the last bit which is set

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to a 1 in binary.

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So that's the first host in the subnet. The last host in the subnet has the host portion populated with

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binary ones except for the last bit which is set to binary 0 and I'll show you in a moment what that

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is but it's easier to work out the broadcast address first.

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So the broadcast address equals that subnet

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and the host portion is populated with binary ones.

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So it's 1 1 followed by 4 ones.

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Now you can work this out by saying 32 plus 16 plus 8 plus 4 plus 2 plus 1.

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But I find it easier to do the following if this is set to 1 and everything else is set to zeros so

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it looks like this, that equals 64 one less than that equals 63.

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So if you asked for something like this, what is the broadcast address?

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Have a look at the next subnet and subtract 1 to get to the broadcast address of the previous subnet.

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The next subnet is 1 9 2 1 6 8 1 64.

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The broadcast address of the previous subnet is that subnet minus 1.

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So in other words it's 63 and then this is 62.

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So for this subnet that's the network and first host, this is the last and broadcast address.

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Second last which we need for this switch is essentially 1 less than that can work out the binary

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but it may be easier just to subtract 1 from the decimal.

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So that's 61.

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And the third last is 1 less than that which is 60

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so we now know the network, the first host, the broadcast the last host.

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Second last host and third last host.

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Easiest way to work this out is, to work out to the network and then work out the next network, one less

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then the next network gives you the broadcast address for the current subnet and then you can just subtract

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1 from that to get to the last host.

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Second last host and third last host, first host is equal to the network portion plus 1.

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So there are our values.

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That means we can now configure this router with the last IP address in the subnet.

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So currently on this router it only has a loopback interface configured it doesn't have an IP address

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configured on gigabit

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0 0 0.

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Remember the network 1 9 2 1 6 8 1.0 slash 26 has 2 bits that are part of the network portion 2

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binary bits.

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Looks like that which equals a 192.

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So we can configure the gigabit

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0 0 0 interface with an IP address of 1 8 2 1 6 8 1 62 because that's the last IP address in the subnet.

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So 62 and the mask is 2 5 5 2 5 5 2 5 5 1 92.

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And that's because these 2 bits are part of the network.

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So we've got 255 255 255, 2 bits there which equates to a 192.

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So show IP interface brief we can now ping our local IP address.

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The switch needs to be configured with the second last IP address in the subnet.

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Per these instructions so configure the switches with the second last IP address and then the DHCP servers

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with the third last IP address.

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So again here's our switch

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I'll give it a name.

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Switch 1 interface VLAN 1, no shut IP address 1 9 2 1 6 8 1 and the next IP address that we can

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use is 61 2 5 5 2 5 5 2 5 5 1 92.

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So show IP interface brief, that's the IP address of the switch can the switch now ping the router, yes

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it can switch has been successfully configured, router has been successfully configured, let's configure

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the DHCP server so on the Ethernet interface we're going to configure a static IP address of 1 9 2 1 6 8

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1 and the IP address will be 60 in this example third last IP address subnet mask will be 2 5 5 2

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5 5 2 5 5 1 92.

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Now the default gateway will be the router 1 9 2 1 6 8 1 and the router once again has IP address 62 so

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62, DNS server and this example will be 8.8.8.8 this is the internet DNS server it's

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configured with DNS names for cisco.com and facebook.com, so the server has been configured.

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Can we ping the switch?

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Yes we can.

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What about the router?

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Yes we can.

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So we've configured IP addresses and default gateways on the network devices.

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Now one thing I still need to do on the switch is specify a default gateway which will be the router,

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router has IP address 62

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so again the switch can ping the router, we've finished configuring the switch now on the DHCP server

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we need to configure a DHCP pool default gateway is going to be the router 62 DNS server is gonna

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be the Google DNS server and we can allocate IP addresses from 1 9 2 1 6 8 1. 1.

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So from the first IP address in the subnet to a number that we decide.

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So we could as an example allocate 100 IP addresses, so I'll save that.

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So we've specified the pool name default gateway DNS server starting IP address in the pool and the

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number of IP addresses that can be allocated, now can I specify a hundred hosted addresses the answer

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is, No, I should actually specify only something like 50 because the subnet only supports 62 IP addresses

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so remember the formula, 2 to the power of something which is the number of bits minus 2 gives you the

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number of hosts that are supported in a subnet.

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Here we've got 6 binary bits.

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So 2 to the power of 6

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that's the number of bits in the host portion, what's 2 to the power of 6, 2 to the power 4

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is 16, 2 to the power of 5 equals 32

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2 to the power of 6 equals 64, so 64 minus 2 gives us 62 hosts that are supported in a subnet

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00:08:32,570 --> 00:08:39,740
but we want to allocate some of those IP addresses to network devices so we don't want to allocate the

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full subnet to the DHCP server we'll only allocate a portion of the addresses to hosts via DHCP, so on

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PC 1, does the PC have an IP address? Yes it does, it's been allocated 1 9 2 1 6 8 1. 3

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Can it ping the default gateway? Yes it can.

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PC1 as an example IP config it's also been allocated an IP address 1 9 2 1 6 8 1. 2. Can it ping

90
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its default gateway? Yes, it can and on PC 2 do something similar.

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IP address has been allocated and it can ping its a default gateway, so we've successfully configured

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subnet 1.

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Now, we need to configure the serial link and then once I've done that I'll check whether these devices

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can access devices on the Internet and then I'll configure the other subnets.