Configure Network Services - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 87

Alias Record
Closely related to the host record is the alias record , or canonical name (CNAME) record .
The syntax of an alias record is as follows:
aliasoptional_TTL IN CNAME hostname
Aliases are used to point more than one DNS record toward a host for which an A
record already exists. For example, if the hostname of your web server was actually chaos ,
you would likely have an A record such as this:
chaos IN A 192.168.1.10
Then you could make an alias or CNAME for the record so that www.example.com
would point to chaos :
www IN CNAME chaos.example.com.
Note the trailing dot ( . ) on the end of the CNAME record. This means the root domain
is not appended to the entry.
Pointer Record
A or AAAA records are probably the most visible component of the DNS database
because Internet users depend on them to turn FQDNs like www.microsoft.com into the IP
addresses that browsers and other components require to find Internet resources. However,
the host record has a lesser-known but still important twin: the pointer (PTR) record. The
format of a PTR record appears as follows:
reversed_address.in-addr.arpa. optional_TTL IN PTR targeted_domain_name
The A or AAAA record maps a hostname to an IP address, and the PTR record does just the
opposite—mapping an IP address to a hostname through the use of the in-addr.arpa zone.
The PTR record is necessary because IP addresses begin with the least-specific portion first
(the network) and end with the most-specific portion (the host), whereas hostnames begin
with the most-specific portion at the beginning and the least-specific portion at the end.
Consider the example 192.168.1.10 with a subnet mask 255.255.255.0. The portion
192.168.1 defines the network and the final .10 defines the host, or the most-specific
portion of the address. DNS is just the opposite: The hostname www.example.com. defines
the most-specific portion, www , at the beginning and then traverses the DNS tree to the
least-specific part, the dot ( . ), at the root of the tree.
Reverse DNS records, therefore, need to be represented in this most-specific-to-least-
specific manner. The PTR record for mapping 192.168.1.10 to www.example.com would
look like this:
10.1.168.192.in-addr.arpa. IN PTR www.example.com.
Now a DNS query for that record can follow the logical DNS hierarchy from the root of
the DNS tree all the way to the most-specific portion.