The DNS is the system that translates domain names to IP addresses on the internet. It was created in 1983 and allows users to reference internet resources by name. The document then describes the step-by-step resolution process where a client's request is recursively resolved through root servers, TLD servers, and authoritative name servers to return the requested IP address. It also discusses caching for improved performance and common issues like hostname-IP mismatches that can be resolved by editing host files and DNS records.

1. Domain Name System
(DNS)
Presented By:
Konkona Basu

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. The Resolution Process
Let’s look at the resolution process step-by-step:
Annie

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Files it goes through
/etc/nsswitch.conf
/etc/hosts
/etc/resolv.conf
/etc/named.conf
Zone file

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. 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. 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. 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. 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.