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Labs

Troubleshooting DNS

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

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Labs

Path Info

Level
Clock icon Intermediate
Duration
Clock icon 1h 0m
Published
Clock icon Nov 14, 2018

Contact sales

By filling out this form and clicking submit, you acknowledge our privacy policy.

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 acloudguru.com:

    curl -I https://acloudguru.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
    
  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 10.0.1.1 53
    
  4. Challenge

    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:

    dig @10.0.0.2 acloudguru.com
    
  5. Challenge

    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.

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