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linux_wiki:troubleshoot_dns_client_issues [2016/10/08 17:58] billdozor |
linux_wiki:troubleshoot_dns_client_issues [2019/05/25 23:50] |
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- | ====== Troubleshoot DNS Client Issues ====== | ||
- | |||
- | **General Information** | ||
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- | Client perspective checking DNS configuration. | ||
- | |||
- | ---- | ||
- | |||
- | ====== 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 | ||
- | |||
- | ---- | ||
- | |||
- | ====== Troubleshooting: | ||
- | |||
- | View (dump) the current contents of the unbound cache | ||
- | <code bash> | ||
- | unbound-control dump_cache | ||
- | </ | ||
- | * This can be also redirected to a file to make edits and load back into cache | ||
- | |||
- | \\ | ||
- | Purge the cache: Single record | ||
- | <code bash> | ||
- | unbound-control flush myhost1.example.com | ||
- | </ | ||
- | |||
- | \\ | ||
- | Purge the cache: Entire Zone | ||
- | <code bash> | ||
- | unbound-control flush example.com | ||
- | </ | ||
- | |||
- | \\ | ||
- | Load cache from a file (dumped there previously) | ||
- | <code bash> | ||
- | unbound-control load_cache < cache.txt | ||
- | </ | ||
- | |||
- | ---- | ||
- | |||
- | ====== Troubleshoot DNS From a Client ====== | ||
- | |||
- | Check to see what DNS servers are configured | ||
- | <code bash> | ||
- | cat / | ||
- | </ | ||
- | * Take note of whether the file is controlled via NetworkManager. If so, then the DNS servers are set via that service/ | ||
- | |||
- | \\ | ||
- | Ensure a route exists to the DNS server | ||
- | <code bash> | ||
- | ip route sh | ||
- | </ | ||
- | |||
- | \\ | ||
- | Ping the DNS server | ||
- | <code bash> | ||
- | ping -c4 < | ||
- | </ | ||
- | |||
- | \\ | ||
- | Check to see if you can connect to port 53 | ||
- | <code bash> | ||
- | telnet < | ||
- | |||
- | OR | ||
- | |||
- | nc -v -w 3 < | ||
- | </ | ||
- | |||
- | \\ | ||
- | Test a domain lookup against the DNS server directly | ||
- | <code bash> | ||
- | dig @< | ||
- | </ | ||
- | |||
- | \\ | ||
- | Dig returns a status indicator in the "Got Answer" | ||
- | * NOERROR - DNS resolve was successful | ||
- | * NXDOMAIN - DNS info requested could not be found | ||
- | * SERVFAIL - Error contacting a DNS server | ||
- | |||
- | ---- | ||