DNS Records
The following are examples of DNS resource record types:
A record: Used to map host names to the IPv4 address of the host. In an A record, multiple IP addresses can correspond to a single hostname. There can also be multiple host names each of which maps to the same IP address. There must be a valid A record in the DNS for the host.domain.name in order for a command, such as telnet host.domain.name, to work.
AAAA record: AAAA is used to map hostnames to the IPv6 address of the host.
MX record: MX maps a domain name to a list of mail servers for that domain.
PTR record: A PTR points to a canonical name. The most common use is for implementing reverse DNS lookups, mapping an IP address to the hostname.
NS record: An NS record identifies the DNS servers that are responsible (authoritative) for a zone.
CNAME record: A CNAME record is used to specify that a domain name is an alias for another domain name, which is the "canonical" domain name.
TXT record: A TXT record is used to associate any arbitrary text with a hostname. This record type is only used in specific cases such as Domain Keys Identified Mail, used as a method to detect email spoofing.
SOA record: Each zone contains an SOA record. The SOA record identifies the name server that is the best source of information for the data within the zone. The SOA record also contains various other parameters that define the behavior of the DNS server.
A record: Using the nslookup utility, it shows that the dmz.secure-x.public host that is resolved to the IP address of 192.0.2.50 from the 209.165.200.233 DNS server, and the 209.165.200.233 DNS server is not the authoritative DNS server for the secure-x.public domain.
-----------------------------PTR record: In this example, using the nslookup utility, the set q=ptr option can be used to examine the PTR record. In this example, the PTR record from DNS shows 192.0.2.50 resolves to the various hostnames in the secure-x.public domain, such as dmz.secure-x.public.
MX record: In this example, using the nslookup utility, the set q=mx option can be used to examine the MX record. In this example, the MX record from DNS shows that 192.0.2.55 is the mail server for the secure-x.public domain.
The DNS resolver (DNS client) sends a query message to the DNS recursor (DNS recursive resolver) asking for the address of www.devsysops.com.com.
The DNS recursor sends a query message to the root name servers looking for the .com domain name space.
The root name servers send a DNS referral response message to the DNS recursor informing it to ask the generic Top-Level Domain (gTLD) name servers for the .com domain name space.
The DNS recursor sends a query message to the gTLD name servers looking for the .devsysops.com.com domain name space.
The gTLD name servers send a DNS referral response message to the DNS recursor informing it to ask the .devsysops.com.com name servers, ns1.devsysops.com.com or ns2.devsysops.com.com, about this domain name space.
The DNS recursor sends a query to ns1.devsysops.com.com or ns2.devsysops.com.com, asking for www.devsysops.com.com.
The .devsysops.com.com name servers, ns1.devsysops.com.com or ns2.devsysops.com.com, send an authoritative DNS query response message to the DNS recursor with the A (address) RR information for www.devsysops.com.com.
The DNS recursor sends a DNS query response message to the DNS resolver with the A (address) RR information for www.devsysops.com.com.