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Troubleshooting DNS

In this hands-on lab, we will walk though troubleshooting DNS resolution issues on the provided host.

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Path Info

Clock icon Intermediate
Clock icon 1h 0m
Clock icon Nov 14, 2018

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Table of Contents

  1. Challenge

    Verify the Issue and Check `/etc/nsswitch.conf`

    We'll first need to verify that the issue exists by attempting the curl the header of

    curl -I

    Then we need to verify that nothing is missing in this file, and we should pay attention to the ordering of the hosts value:

    hosts:      files dns myhostname
  2. Challenge

    Verify `/etc/hosts` Contents

    We'll want to make sure there aren't any entries in this file that would cause issues:

    cat /etc/hosts
  3. Challenge

    Determine If the DNS Host is Listening on TCP Port 53

    If the host is listening on TCP port 53, we'll know by running this:

    telnet 53
  4. Challenge

    Check Resolution Using the DNS Host

    Now that we've verified that the host listed in /etc/resolv.conf isn't available on TCP port 53, check if resolution is working on the DNS host

    dig @
  5. Challenge

    Change the Configuration to Use the Host

    We can do this with network manager, or by editing /etc/resolv.conf. If we restart networking, this is the IP that will be used via DHCP. Remove the entry.

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