DNS (Domain Name System) is just like address book of internet. Each domain has unique + static IPaddress in internet. It eliminates humans to memorize IP address of server (it's easy to memorize omniguru.in rather than IP address like 192.168.1.234).
DNS consists many domain name servers and provides name-to-IPAddress mapping for registered servers.
URL structure: https://telugu.OmniGuru.in
DNS Server types
DNS Server performs forward NS lookup & reverse NS lookup. Forward DNS Lookup is resolving a host name to IP address. Reverse DNS lookup is resolving IP address to host name.
Type
Description
[1] DNS Resolver
Acts as middleware between client & DNS nameserver.aka recursive resolver.
Get DNS query from client, if it has cache for that query, will send cache data.
Otherwise [1] <=> [2], [1] <=> [3], [1]<=> [4].
Then save data in cache and send it to client.
*librarian
[2] Root Nameservers
It responds by pointing the DNS resolver to a TLD NS.
*racks of books
[3] TLD Nameservers
It responds by pointing to the authoritative NS.
E.g. .com, .in
omniguru.in will be in .in TLD NS.
*specific rack
[4] Authoritative NS
Provides IP address of domain from DNS records.
*dictionary of rack
DNS Records
DNS records also known as Zone files
Common DNS record types
Record Type
Description
A
contains IP address of a domain
CNAME
Canonical name forwards one domain or subdomain to another domain, No IP address.
DNAME
Delegate name record creates a domain alias, like CNAME, but it will redirect all subdomains also.
MX
Mail exchanger directs mail to an email server
NS
Name server record stores the name server for a DNS entry.
TXT
Admin can store text notes in the record.
SOA
Start of authority record stores admin information about a domain.
SRV
Service record specifies a port for specific services.
PTR
Pinter record provides a domain name in reverse-lookups.
MISC:
DNS database contains name server records, host-name-to-address records, host-name-aliases records.
The 3 strategies for updating DNS servers are dynamic, read-write, and read-only
The entire hostname has a maximum of 255 characters
Basic function of NS lookup program is to probe the DNS database for various types of information.
/etc/resolv.conf is the name of DNS client configuration file and does the nslookup program to locate a name server.
/etc/hosts file resolves hostname to IP addresses locally.
A record is most common used record type out of all DNS records.
OmniGuru