Discovering computer networks: hands on in the Open Networking Lab
Discovering computer networks: hands on in the Open Networking Lab

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Discovering computer networks: hands on in the Open Networking Lab

16.1 Device connections

A local company has tasked you with configuring their routers to provide two branch offices with connectivity to their DNS server, which is connected to their central router located in the head office. Branch office A is using IPv4 and Branch office B is using IPv6. The routers will need to be configured so that both offices can access the server.

You will see how the network below is configured, tested and saved.

Watch the video below, which is about 2.5 minutes long. It shows this network being built in Packet Tracer.

Device connections

Download this video clip.Video player: 83_device_connections.mp4
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Transcript

This network will consist of PCs, switches, routers and a server.

Here is the topology we will be working towards. You can see we have four PCs, four switches, three routers and a DNS server to configure. The topology uses IPv4 in the top half and IPv6 in the bottom half. The Central router will need to be configured as a dual-stack router, allowing it to route for both versions. Along the way we will be using show commands to check our configuration. Once the configuration is complete we can use ping and traceroute to check connectivity.

Let’s start by adding the devices to the workspace in Packet Tracer and then connecting them up. I will have the reference topology in the top-right corner to make it easier. Here we are in the latest version of Packet Tracer. Let’s start making this topology.

I will add four PCs, four 2960 switches and three 2911 routers. I will also add a generic server. I have specifically chosen 2911 routers because they have three gigabit interfaces that will be needed to make this topology.

The generic server will be configured to act as an IPv4 DNS server, allowing the resolution of domain names to IP addresses. Unfortunately, at this time Packet Tracer does not support IPv6 DNS.

I am connecting the devices together by selecting a straight-through cable, then clicking the device and selecting the port that the cable needs to attach to. This is repeated at the other end. I am using straight-through cables on all devices. This is because, for gigabit interfaces, crossover cables become irrelevant as the device can auto-sense the connection type.

I will skip the video ahead to where all the devices are connected.

Now I am going to label the devices to avoid confusion later. I will edit the device name labels and then add labels for the IP addresses. Labels can be added by selecting the text tool at the top of the screen and clicking anywhere in the workspace. You may wish to add coloured shapes to your workspace to make a visual representation of the network boundaries.

I will fast forward and neaten the topology to save time.

End transcript
 
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Activity 1 Test yourself

5 minutes

In this scenario, PC-A1 is shown as being in network 172.20.16.0/23 and PC-A2 is shown as being in network 172.20.18.0/24. For both of these networks, write out the subnet mask in dotted decimal.

Answer

In CIDR notation a /23 subnet mask indicates that there are 23 bits in the network part of the address and 9 bits in the host part. In binary this would be shown as 11111111.11111111.11111110.00000000 which converts to 255.255.254.0 in dotted decimal.

A /24 mask indicates that there are 24 bits in the network part and 8 bits in the host part. In binary this would be shown as 11111111.11111111.11111111.00000000 or 255.255.255.0 in dotted decimal.

OPNL_1

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