DNS

DNS Records

Record	Description
Resource Record	A domain name, usually a fully qualified domain name, is the first part of a Resource Record. If you don't use a fully qualified domain name, the zone's name where the record is located will be appended to the end of the name.
TTL	In seconds, the Time-To-Live (TTL) defaults to the minimum value specified in the SOA record.
Record Class	Internet, Hesiod, or Chaos
Start Of Authority (SOA)	It should be first in a zone file because it indicates the start of a zone. Each zone can only have one SOA record, and additionally, it contains the zone's values, such as a serial number and multiple expiration timeouts.
Name Servers (NS)	The distributed database is bound together by NS Records. They are in charge of a zone's authoritative name server and the authority for a child zone to a name server.
IPv4 Addresses (A)	The A record is only a mapping between a hostname and an IP address. 'Forward' zones are those with A records.
Pointer (PTR)	The PTR record is a mapping between an IP address and a hostname. 'Reverse' zones are those that have PTR records.
Canonical Name (CNAME)	An alias hostname is mapped to an A record hostname using the CNAME record.
Mail Exchange (MX)	The MX record identifies a host that will accept emails for a specific host. A priority value has been assigned to the specified host. Multiple MX records can exist on the same host, and a prioritized list is made consisting of the records for a specific host.

nslookup/dig

Command	Description
nslookup $TARGET	Identify the A record for the target domain.
nslookup -query=A $TARGET	Identify the A record for the target domain.
dig $TARGET @<nameserver/IP>	Identify the A record for the target domain.
dig a $TARGET @<nameserver/IP>	Identify the A record for the target domain.
nslookup -query=PTR <IP>	Identify the PTR record for the target IP address.
dig -x <IP> @<nameserver/IP>	Identify the PTR record for the target IP address.
nslookup -query=ANY $TARGET	Identify ANY records for the target domain.
dig any $TARGET @<nameserver/IP>	Identify ANY records for the target domain.
nslookup -query=TXT $TARGET	Identify the TXT records for the target domain.
dig txt $TARGET @<nameserver/IP>	Identify the TXT records for the target domain.
nslookup -query=MX $TARGET	Identify the MX records for the target domain.
dig mx $TARGET @<nameserver/IP>	Identify the MX records for the target domain.