The Domain Name System or Domain Name Server (DNS) is a system that stores information associated with domain names in a Distributed Database on networks, such as the Internet. The domain name system (Domain Name Server) associates many types of information with domain names, but most importantly, it provides the IP address associated with the domain name. It also lists mail exchange servers accepting e-mail for each domain. In providing a worldwide keyword-based redirection service, DNS is an essential component of contemporary Internet use.
Forward lookup:- Host name to IP Address.
Reverse lookup:- IP Address to Host name.
An A record or address record maps a hostname to a 32-bit IPv4 address.
An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address.
A CNAME record or canonical name record makes one domain name an alias of another. The aliased domain gets all the sub domains and DNS records of the original.
An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa domain that corresponds to an IP address implements reverse DNS lookup for that address. For example (at the time of writing), www.icann.net has the IP address 18.104.22.168, but a PTR record maps 22.214.171.124.in-addr.arpa to its canonical name, referrals.icann.org.
An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
An SRV record is a generalized service location record.
A TXT record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework specification.
Recursive Query:- Query is intranet query.
Iterative Query:- Query is internet or public query.
DNS is an application layer.
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