DNS Troubleshooting

IS THE PROBLEM DNS?

• Can you ping a device by IP address.
  • Yes. Can you ping the device by name?
    • Yes. This is not a DNS problem.
    • No. Time to check your DNS configuration.
  • No. This is not a DNS problem.

TROUBLESHOOTING DNS ON THE WORKSTATION

• Does your computer know where a DNS server is?
  • WINDOWS: use the ipconfig /all  command to verify that the IP address of a DNS server is listed.
  • Do you have bad cached information on your MS-Windows workstation?
    ipconfig /displaydns
    There should be an IP address for every name listed in your DNS cache
  • Delete bad information in your cache
    ipconfig /flushdns
  • UNIX/SOLARIS
    • Check the /etc/nsswitch.conf to see if resolution is set for hostfiles or DNS.
    • Check /etc/resolv.conf to make sure you have the correct nameservers listed.
  • MacOS 9 and older
    • Check the DNS server setting in the TCP/IP control panel (MacTCP panel prior to OS 8)

TROUBLESHOOTING DNS SERVERS

If possible, use dig, it utilizes non-recursive lookups, assuring you that the answers you are receiving come from that server and nowhere else. dig comes with BIND.