Page 176 - DCAP106_OPERATING_SYSTEM_TOOLS

Unit 10: Servers

If you want to use a dynamic DNS provider for your own domain, then you have to point your Notes
registration record to the DNS servers of your dynamic DNS provider.

Task Illustrate how to use Dynamic DNS in your own domain.

Basic DNS Testing of DNS Resolution

As you know, DNS resolution maps a Fully Qualified Domain Name (FQDN), such as www.
Ignou.ac.in, to an IP address. This is also known as a forward lookup. The reverse is also true: By
performing a reverse lookup, DNS can determining the fully qualified domain name associated
with an IP address.
Many dissimilar Web sites can map to a single IP address, but the reverse isn’t true; an IP address
can map to only one FQDN. This means that forward and reverse entries frequently don’t match.
The reverse DNS entries are usually the responsibility of the ISP hosting your site, so it is quite
common for the reverse lookup to resolve to the ISP’s domain. This isn’t an important factor for
most small sites, but some e-commerce applications require matching entries to operate correctly.
You may have to ask your ISP to make a custom DNS change to correct this.
There are a number of commands you can use do these lookups. Linux uses the host command,
for example, but Windows uses nslookup.

z z The Host Command: The host command accepts arguments that are either the fully
qualified domain name or the IP address of the server when providing results. To carry out
a forward lookup, use the syntax:

[root@bigboy tmp]# host www.Ignou.ac.in
www.Ignou.ac.in has address 220.227.168.115
[root@bigboy tmp]#
To perform a reverse lookup:
[root@bigboy tmp]# host 220.227.168.115
34.71.115.65. in-addr.arpa domain name pointer 65-115-71-34.myisp.net.
[root@bigboy tmp]#
As you can see, the forward and reverse entries don’t match. The reverse entry matches
the entry of the ISP.

z z The nslookup Command: The nslookup command provides the same results on Windows
PCs. To perform forward lookup, use.
C:\> nslookup www.Ignou.ac.in
Server: 192-168-1-200.my-site.com
Address: 192.168.1.200
Non-authoritative answer:
Name: www.Ignou.ac.in
Address: 220.227.168.115
C :\>
To Perform a reverse lookup:
C:\> nslookup 220.227.168.115

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