Ponits in DNS

Auhoritative DNS Server: it is responsible of a specific name space and it know there is an entry or ther is no such entry

Non Authorititive DNS Server: they use either the cache or forwarder for DNS resoluton

Forwarders: A forwarder is a DNS Server to which other DNS Servers forward queries

2 types of forwardes

1) Standard: all the queries will forward to an another dns server and that server will resolve the domain name on behalf of this dns server

2)Conditional: in this type of forwarding, all the dns query other than 1 or more domain names will be forwarded to another DNS server

DIffernet types of DNS Zones

1)Standard primary :which is the master zone and it is read/write option

2)Secondary : Which is the read only copy of primary zone

3)Stub zone : only have information about other DNS Server. It only have the below entries.

A copy of the SOA record for the zone.

Copies of NS records for all name servers authoritative for the zone.

Copies of A records for all name servers authoritative for the zone.

That's it--no CNAME records, MX records, SRV records, or A records for other hosts in the zone

Aging and scavenging : it uses to keep DNS database updated by removing outdated records

Aging : Determids when a stale record should removed from a DNS database

Scavenging : removes outdated or extinct names from a database

Parameter

 DNS -Parameters :

1) No-Refresh Interval -default is 7 days

refresh interval -default is 7 days