====== Troubleshoot DNS Client Issues ======

**General Information**

Client perspective checking DNS configuration.

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====== Lab Setup ======

The following virtual machines will be used:
  * server1.example.com (192.168.1.150) -> Perform all connectivity tests from here
  * server2.example.com (192.168.1.151) -> Install DNS caching here

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====== Troubleshooting: Unbound ======

View (dump) the current contents of the unbound cache
<code bash>
unbound-control dump_cache
</code>
  * This can be also redirected to a file to make edits and load back into cache

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Purge the cache: Single record
<code bash>
unbound-control flush myhost1.example.com
</code>

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Purge the cache: Entire Zone
<code bash>
unbound-control flush example.com
</code>

\\
Load cache from a file (dumped there previously)
<code bash>
unbound-control load_cache < cache.txt
</code>

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====== Troubleshoot DNS From a Client ======

Check to see what DNS servers are configured
<code bash>
cat /etc/resolv.conf
</code>
  * Take note of whether the file is controlled via NetworkManager. If so, then the DNS servers are set via that service/from /etc/sysconfig/network-scripts/

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Ensure a route exists to the DNS server
<code bash>
ip route sh
</code>

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Ping the DNS server
<code bash>
ping -c4 <ip-of-dns>
</code>

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Check to see if you can connect to port 53
<code bash>
telnet <ip-of-dns> 53

OR

nc -v -w 3 <ip-of-dns> 53
</code>

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Test a domain lookup against the DNS server directly
<code bash>
dig @<ip-of-dns> google.com
</code>

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Dig returns a status indicator in the "Got Answer" section. Values can be:
  * NOERROR - DNS resolve was successful
  * NXDOMAIN - DNS info requested could not be found
  * SERVFAIL - Error contacting a DNS server

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