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A presentation on DNS
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Domain Name System(DNS)
Presented By: Konkona Basu
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 RFCsWhat Internet users use to reference anything by name on the InternetThe mechanism by which Internet software translates names to addresses and vice versa
The Resolution Process
Let’s look at the resolution process step-by-step:
Annie
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?
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?
The Resolution Process
The root server m refers NS to the com name serversThis 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.
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?
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.
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?
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
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
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.comLet’s look at the resolution process again
Annie
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?
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?
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
Files it goes through
/etc/nsswitch.conf
/etc/hosts
/etc/resolv.conf
/etc/named.conf
Zone file
Common Issues...
Mail Delivery Failure: host lookup did not complete
Error Message:
=========2012-11-14 21:08:10 1TYhN3-0000n4-2S ==
[email protected] R=lookuphostdefer (-1): host lookup did not complete
=========
Solution
Add below content in /etc/resolv.conf
=========root@server [/]# cat /etc/resolv.confnameserver 8.8.8.8nameserver 8.8.4.4root@server [/]#=========
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
SolutionCheck 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 fileroot@myserver [~]# cat /etc/hosts127.0.0.1 localhostxx.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.
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.
