Domain Name System $(2*6=12$ points$).$

$($a$)$ Why do we need the domain name system $($DNS$)?$ What problem does it solve?

$($b$)$ Explain how hierarchy helps DNS meet the scaling needs of serving Internet users.

$($c$)$ Explain how replication helps DNS meet the scaling needs of serving Internet users.

$($d$)$ Explain how caching helps DNS meet the scaling needs of serving Internet users.

$($e$)$ What is the purpose of the identification field on a DNS protocol message?

$($f$)$ What is an authoritative DNS server?