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 linuxacademy.com:

[cloud_user@host]$ curl -I linuxacademy.com

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:

[cloud_user@host]$ 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:

[cloud_user@host]$ telnet 10.0.1.1 53
Check Resolution Using the 10.0.0.2 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 10.0.0.2:

[cloud_user@host]$ dig @10.0.0.2 linuxacademy.com
Change the Configuration to Use the 10.0.0.2 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 10.0.1.1 entry.

Additional Resources

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

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