Troubleshooting DNS

1 hour
  • 5 Learning Objectives

About this Hands-on Lab

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

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

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
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
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
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 @
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.

Additional Resources

A business unit is complaining that their job server is unable to connect to This is breaking integrations for multiple reporting applications.

What are Hands-on Labs

Hands-on Labs are real environments created by industry experts to help you learn. These environments help you gain knowledge and experience, practice without compromising your system, test without risk, destroy without fear, and let you learn from your mistakes. Hands-on Labs: practice your skills before delivering in the real world.

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