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DNS and Troubleshooting DNS issues in Linux

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A presentation on DNS

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DNS and Troubleshooting DNS issues in Linux

  1. 1. Domain Name System (DNS) Presented By: Konkona Basu
  2. 2. The DNS is…  The “Domain Name System” Created in 1983 by Paul Mockapetris (RFCs 1034 and 1035), modified, updated, and enhanced by a myriad of subsequent RFCs  What Internet users use to reference anything by name on the Internet  The mechanism by which Internet software translates names to addresses and vice versa
  3. 3. The Resolution Process Let’s look at the resolution process step-by-step: Annie
  4. 4. The Resolution Process The workstation Annie asks its configured name server, NS, for www.skyfall.com’s address NS Annie What’s the IP address of www.skyfall.com?
  5. 5. The Resolution Process The name server NS asks a root name server, m, for www.skyfall.com’s address NS Annie m.root-servers.net What’s the IP address of www.skyfall.com?
  6. 6. The Resolution Process  The root server m refers NS to the com name servers  This type of response is called a “referral” NS Annie m.root-servers.net Here’s a list of the com name servers. Ask one of them.
  7. 7. The Resolution Process The name server NS asks a com name server, f, for www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net What’s the IP address of www.skyfall.com?
  8. 8. The Resolution Process The com name server f refers NS to the skyfall.com name servers NS Annie m.root-servers.net f.gtld-servers.net Here’s a list of the skyfall.com name servers. Ask one of them.
  9. 9. The Resolution Process The name server NS asks an skyfall.com name server, ns1, for www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.mydomain.net What’s the IP address of www.skyfall.com?
  10. 10. The Resolution Process The skyfall.com name server ns1 responds with www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.mydomain.net Here’s the IP address for www.skyfall.com
  11. 11. The Resolution Process The name server NS responds to Annie with www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.nominum.net Here’s the IP address for www.skyfall.com
  12. 12. Resolution Process (Caching)  After the previous query, the name server NS now knows:  The names and IP addresses of the com name servers  The names and IP addresses of the skyfall.com name servers  The IP address of www.skyfall.com  Let’s look at the resolution process again Annie
  13. 13. Resolution Process (Caching) The workstation Annie asks its configured name server, NS, for www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.mydomain.net What’s the IP address of www.skyfall.com?
  14. 14. Resolution Process (Caching) NS has cached a name server record indicating ns1 is an skyfall.com name server, so it asks it for www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.mydomain.net What’s the IP address of www.skyfall.com?
  15. 15. Resolution Process (Caching) The name server NS responds to Annie with www.skyfall.com’s address NS Annie m.root-servers.net f.gtld-servers.net ns1.mydomain.net Here’s the IP address for www.skyfall.com
  16. 16. Files it goes through /etc/nsswitch.conf /etc/hosts /etc/resolv.conf /etc/named.conf Zone file
  17. 17. Common Issues... Mail Delivery Failure: host lookup did not complete Error Message: ========= 2012-11-14 21:08:10 1TYhN3-0000n4-2S == bradg@granbygroup.com R=lookuphost defer (-1): host lookup did not complete =========
  18. 18. Solution Add below content in /etc/resolv.conf ========= root@server [/]# cat /etc/resolv.conf nameserver 8.8.8.8 nameserver 8.8.4.4 root@server [/]# =========
  19. 19. Hostname – IP mismatch warning Mail: IMPORTANT: Do not ignore this email. The hostname (hostname.server.com) resolves to xx.xx.xx.xx. It should resolve to xx.xx.xx.xx. Please be sure to correct /etc/hosts as well as the ‘A’ entry in zone file for the domain. Some are all of these problems can be caused by /etc/resolv.conf being setup incorrectly. Please check this file if you believe everything else is correct. You may be able to automatically correct this problem by using the ‘Add an A entry for your hostname’ under ‘Dns Functions’ in your Web Host Manager
  20. 20. Solution  Check if the domain is using external nameserver. If so then the hostname should be missing an A record there.  If its using our name servers then check for the A record entry in our name servers.  If a record is correct then execute the following command in backend: root@myserver [~]# /scripts/ipcheck  If there are errors, we should go ahead and edit /etc/hosts file root@myserver [~]# cat /etc/hosts 127.0.0.1 localhost xx.xx.xx.xx myserver.mydomain.com myserver  Then execute the command /scripts/ipcheck again. If there are no errors then it will not return any message.
  21. 21. A VPS Customer wants to have an addon domain. He wants to register the domain with us.  Move to sales.  If the domain is registered check the name servers.  If its our central name server check if the DNS entries are there in our name servers.  If its his custom name server in VPS, check if the A record is set correctly in the zone file.  Check if the addon domain is resolving properly or not.

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