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Resource Record (RR):
Defines the DNS data types stored in the DNS database. Common types of RRs include:
SOA (Start of Authority): Provides information about the domain and zone.
A: Maps a domain name to an IPv4 address.
AAAA: Maps a domain name to an IPv6 address.
MX: Specifies the mail server for the domain.
NS: Indicates the authoritative name servers for the domain.
PTR: Used for reverse DNS lookups, mapping an IP address to a domain name.
CNAME: Creates an alias for a domain name.
An RR consists of the following fields: NAME, TYPE, CLASS, TTL (Time to Live), RDLENGTH, and RDATA.
Stub DNS Resolver:
A simple DNS resolver typically used by client devices or applications. Stub resolvers issue DNS queries to DNS recursive resolvers for both internal and publicly registered domain information.
DNS Recursive Resolver:
A DNS server that processes client DNS queries by querying authoritative DNS servers for the necessary RR information and returning answers to the DNS client. These resolvers are usually internal to an organization and should only allow DNS queries from internal clients.
Open DNS Recursive Resolvers:
DNS recursive resolvers that accept queries from any IP address and are accessible over the Internet. Public examples include Google DNS (8.8.8.8) and Cisco OpenDNS (208.67.222.222 and 208.67.220.220). They can be targeted by attackers for reflection or amplification DDoS attacks, necessitating careful management and monitoring by organizations.
Authoritative DNS Server:
Responsible for all RRs of a domain, returning answers to DNS queries using information stored locally. Authoritative DNS servers provide responses to recursive resolvers and are accessible over the Internet, generally allowing queries from any IP address.
Zones:
The DNS name space is partitioned into zones to simplify database management. A zone is a contiguous portion of the domain name space for which administrative responsibility has been delegated to a single manager. Zones are the authoritative source for information about the domains they contain.
Zone File:
A text file that describes a DNS zone, containing a list of the zone's resource records.
This terminology provides a foundational understanding of how DNS operates, the roles of various servers, and the organization of the DNS database.