Dns (domain Name Service

DNS (domain name service / domain name system)

 Provide resolution of FQDN (Fully qualified domain name) to IP addresses and resolution of IP address to FQDN  It defines hierarchical name space where each level of name space is divided by a “.”

DNS hierarchical

Query types : 1) Recursive queries 2) Iterative quesies

Recursive queries: Query made from client to dns server, in which server assume full work, dns server returns either complete answer or negative answer Iterative queries: Receiving server may return an answer, or negative response, or referral to other DNS server’s

Authoritative DNS server: An authoritative DNS server will either  Return request to ip address  Or it will return an authoritative “no”

Non authoritative DNS server An non-authoritative dns server will either:  Checks its cache  Use forwarders (Which will be pointing to some another DNS server)  Uses Root hints (13 root server which we have in internet)

ZONES

Forward lookup zone and Reverse lookup zone

1) Forward lookup zone is used to resolve IP address from FQDN 2) Reverse lookup zone is used to resolve FQDN from IP address

ZONE TYPES

1) Standard primary zone: It is master copy of all zone information, we can read information and we can also write information in primary zone

2) Standard secondary It is backup of primary zone, it is read only, it can be used for load balancing, if primary is fail then secondary can resolve query

3) Stub zone It contain only, NS and SOA records, it is used for forwarding queries, if primary zone and secondary zones are failed then stub zone will not resolve queries because it can only forward the queries, it does not have host records

4) Active directory integrated zone It stores information of zone inside active directory database

Types of records: 1) SOA records  First record in any zone file 2) NS records  Identifies DNS server for each zone (e.g. for CAT. COM)

3) Host records:  Resolve hostname (FQDN) to IP address 4) Alias records  Resolve alias name to host name

5) Pointer records:  Resolves IP address to host name 6) Mx records:  It is used by mail server 7) SRV records (Service records)  Resolves names of server providing services