Lab
A Cloud Guru

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

Level

Intermediate

Duration

1h 0m

Published

Nov 14, 2018

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
```
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
```
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
```
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
```
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.

Author

A Cloud Guru

The Cloud Content team comprises subject matter experts hyper focused on services offered by the leading cloud vendors (AWS, GCP, and Azure), as well as cloud-related technologies such as Linux and DevOps. The team is thrilled to share their knowledge to help you build modern tech solutions from the ground up, secure and optimize your environments, and so much more!

What's a lab?

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