DNS Definitions: DNS Stands for domain name systems. It is used to translate IP addresses to the human-readable domain name and vice versa. When a person uses a web URL like “wintelpro.com” the web browser performs a DNS query against a DNS server for “wintelpro.com” based hostname.
The DNS server takes the hostname and resolves it into a numeric IP address. It contains multiple DNS records for various different services of DNS.
A Local DNS Resolver is responsible for checking if the hostname is available in the local DNS cache, and if not, contacts specified DNS Name Server to receives the IP of the service the user is trying to reach and returns it to the browser. This usually takes very little time.
Types Of DNS Queries:
Iterative Query:- Iterative DNS query is one in which the DNS server is quarried and returns the best answers without querying other DNS servers. Iterative Query is also called a non-recursive query. DNS query between DNS client and the DNS server is always Iterative.
Recursive Query:- Recursive DNS query occurs when a DNS client query information which is not available on their local DNS server and the DNS server is set to query subsequent DNS servers until a definitive answer is returned to the client.
DNS Record Types:
Host (A and AAAA) Records: The A record maps an FQDN to an IP address, Ex – A record is used to point a domain name such as “wintelpro.com” to the IP address of wintelpro.com hosting server “126.96.36.199”.
(AAAA) record stores a hostname and its corresponding IPv6 address.
PTR Record: Allows a DNS resolver to provide an IP address and receive a hostname (reverse DNS lookup).
CNAME Records: CNAME is often called alias records and referred to a canonical name. When a name server finds a CNAME record it replaces the name with the canonical name and looks up the new name. This allows pointing multiple systems to one IP address.
Mail exchanger record (MX Record): MX records are used to identify mail servers for the DNS name to deliver emails for a domain. Multiple MX records can be pointed for a domain with lower and higher priorities. The lower one will take precedence to send emails.
SRV Record: It stores the location of the services on the network. Ex- Active Directory. SRV Stores the following data. Service (ex – LDAP), Target (Host that offers the service), Port, Priority. SRV records are usually created automatically by applications.
SOA Record: This contains information related to primary name servers. Each zone created on DNS contains one SOA record associated wif the zone. SOA records contain the email address of the administrator of the domain, and available publically to contact wif the DNS zone administrator. It contains a serial number that increases on every change of the DNS zone.
TXT Record: TXT records carry machine-readable data such as SPF, DKIM, and DMARC values. Multiple TXT records can be held on a DNS server.
NS record: NS record is also called name server record. It holds the DNS zone information and is delegated to a specific Authoritative Name Server, and provides the address of the name server.