DNS Flashcards
Domain Name System (DNS)
A global hierarchy of distributed name server databases that contain information on domains and hosts within those domains.
Top-level domains (TLDs)
*Generic (.com, .org, .net, .info, .biz),
*Sponsored (.gov, .edu),
*Country code (.uk, .ca, .de).
Who operates/manages top-level domains?
DNS is operated by ICANN (icann.org), which also manages the generic TLDs.
Country codes are generally managed by an organization appointed by the relevant government.
Recursive Lookup
DNS query type whereby a server submits additional queries to other servers to obtain the requested information.
The queried server is not authoritative,
Iterative Lookups
DNS query type whereby a server responds with information from its own data store only.
Responds to a query with either the requested record or the address of a name server at a lower level in the hierarchy that is authoritative for the namespace.
Start of Authority (SOA) Record
Identifies the primary authoritative name server that maintains complete resource records for the zone.
Name Server (NS) Record
Identify authoritative DNS name servers for the zone.
Canonical Name (CNAME) Record
(or alias) record is used to configure an alias for an existing address record (A or AAAA).
Mail Exchange (MX) Record
Identify an email server for the domain.
Service (SRV) Record
Contains the service name and port on which a particular application is hosted.
TXT Record
Store any free-form text that may be needed to support other network services.
Pointer (PTR) Record
Maps an IP address to host name (reverse DNS query)
Reverse DNS query
Resolve an IP address to a host name.
Forward lookup zone
Returns an IP address (typical DNS query)
Reverse lookup zone
Returns a hostname from a PTR record (reverse Query)
Port DNS runs on
TCP/UDP 53
Primary DNS Server
Zone records held on the server are editable
Secondary DNS Server
*Holds a read-only copy of the zone.
*Maintained through a process of replication known as a zone transfer from a primary name server
Zone Transfer
Mechanism by which a secondary name server obtains a read-only copy of zone records from the primary server.
Authoritative Server
*Holds complete records for a domain
*Both primary and secondary name servers are authoritative.
Cache-only Servers
*Don’t maintain a zone (primary or secondary)
nut.widget.com
hostname = nut
domain suffix = widget.com
top level domain = .com
nut.widget.com
nut = hostname
widget.com = domain suffix
.com = top level domain
DNSSEC
Uses encrypted digital signatures when passing DNS information between servers to help protect it from poisoning.
DNS Record PTR
Pointer
Correlates an IP address with a domain name
Reverse DNS lookup
Nameserver
Indicates which DNS nameserver has the authority
DNS Record NS
Internal DNS
Allows cloud instances on the same network access each other using internal DNS names.
DNS Latency
Time and delay that occurs whenever users request a particular domain name
