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

16.4 Testing the configuration

In this part you will use show commands to interrogate the configuration of the routers. Also you will use ping and traceroute commands to test connectivity between devices.

Watch the video below, which is about 2 minutes long. It demonstrates using the commands above to test connectivity, and then saving the configuration.

Testing the configuration

Download this video clip.Video player: 88_saving_the_configuration.mp4
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To test this we can use ping. From PC-A1 we will ping The A record for points to the IP address of the DNS server. If the ping is successful, we know everything is configured and working correctly. The first time you do this ping you may drop one to three pings. This depends on the ARP caches of each device on the network and whether an ARP request needs to be sent. So from PC-A1 if we ping we should get a successful ping – like that.

If we move to PC-B1 and try to ping the pings fail. This is because PC-B1 is only configured to use IPv6 and the DNS server does not have an IPv6 A record or quad A record configured. To test connectivity we can just ping the IPv6 address of the DNS server. So if we do ping 2001:DB8:FADE:1000::10 we should get a response – like that.

Another useful command to help troubleshoot when you have issues would be traceroute. Traceroute shows the hops taken to get to a destination. So if we type tracert into PC-A1, we can see that we get a response from and then and then This is what is expected. As you can see, it’s responding with Branch-A’s gigabit 0/0 interface and then the Central router’s gigabit 0/0 interface and then the DNS server’s IP address.

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Activity 9 Test yourself

2 minutes

  • Match the description to the correct command:

  • Using the following two lists, match each numbered item with the correct letter.

    1. ping

    2. tracert

    • a.A command that can be used to test whether there is end-to-end connectivity

    • b.A command that tracks the path of the traffic between routers and which can show you where in the device sequence a fault is.

    The correct answers are:
    • 1 = a
    • 2 = b

Activity 10 Try it out

Open PT Anywhere [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] in a new tab or window so you can read these instructions. This is the fully configured network.

1. In the last video you saw traceroute being used with an IPv4 address, but not with an IPv6 address. From PC-B2, use traceroute to check the route to the DNS server, which has an IPv6 address of 2001:DB8:FADE:1000::10. Is the result what you would expect?

2. The DNS server also has an IPv4 address, which is Try pinging this from PC-B2. Explain your result.


1. When I did this I got:

1 1 ms 0 ms 0 ms 2001:DB8:FADE:100::1

2 0 ms 0 ms 0 ms 2001:DB8:FFFF:FFFF::1

3 0 ms 1 ms 0 ms 2001:DB8:FADE:1000::10

The first line is the response from Branch-B router’s G0/1 interface. The second line is from Central router’s G0/1 interface. The third line is from the DNS server. This is what we would expect if the network is working properly.

2. The ping fails because the Branch-B router is configured for only IPv6 addresses (and also the Central router’s G0/1 interface is configured only for IPv6 addresses). Even if these were dual stack, and able to handle both IPv4 and IPv6, the ping would fail because PC-B2 has no IPv4 address, so there is no address to send the response to the ping to.


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