Reverse DNS
I want to know about Reverse DNS
Reverse DNS is the opposite of forward DNS, which is used to translate hostnames to IP addresses, Reverse DNS uses DNS to translate IP addresses to hostnames instead.
Hostnames are the names which we use to refer to websites on the Internet, such as www.freebsd.org.
IP addresses are the numbers which Internet routers use to move traffic across the Internet, such as 216.17.138.115 and 216.136.204.117
Reverse DNS “nslookup”
To understand all this better you can use the DNS testing tool, `nslookup` and do a reverse DNS lookup.
For example, lets use DNS lookup on the IP address 216.136.204.117:
bash-2.05a$ nslookup 216.136.204.117
Server: localhost.net
Address: 127.0.0.1
Name: www.freebsd.org
Address: 216.136.204.117
Reverse DNS PTR Records
Reverse DNS is setup by configuring PTR records (Pointer Records) while Forward DNS, uses A records (Address Records) in the DNS server.
Delegation of Reverse DNS
A domain is “delegated” to you when you register a domain name with a domain registrar, and you become responsible for that Forward DNS domain.
But you are not responsible for the reverse records. Those Reverse DNS records will remain the responsibility of your hosting service and/or ISP.
Any changes to your Reverse DNS PTR records, must be done by the company where you get your IP addresses from, usually an Internet Service Provider.
In some cases your ISP may delegate a range of IP addresses to you, in that case it is YOU who must configure Reverse DNS and PTR records in the DNS server.
Is all this necessary?
Some newbie DNS administrators configure forward DNS and ignore the configuration of reverse DNS.
When this happens some things like web browsing work fine but not everything works since Reverse DNS is required by some Internet protocols and without it there may be trouble with r-commands, IRC, some SMTP servers, enterprise management systems, and network backup systems.
It is much easier to configure Reverse DNS correctly from the beginning, so problems caused by faulty or non-existent reverse DNS can take considerable time and effort later.
