DNS & DHCP & NTP Flashcards
DNS Record: A/AAAA
A: Address record maps hostname to IPv4
AAAA: Address record maps hostname to IPv6
DNS Record: CNAME
Canonical name is an alias for existing record
diontraining.com = www.diontraining.com
DNS Record: MX
Mail exchange record maps domain name to email server
DNS Record: NS
Denotes the authoritative name server for domain
DNS Record: PTR
Pointer record; used for reverse DNS lookups
DNS Record: SRV
Service Record
Used to specify a host & port for a specific service
Can specify a port along with our IP address
DNS Record: TXT
Designed initially to hold human readable code.
Now used to hold machine readable data
(DKIM: DomainKeys Indentified Email, SPF: Sender Policy Framework)
DNS Resolver (DNS Cache)
Temporary database that remembers the answers it received from the DNS server
Recursive Lookup: DNS Server will hunt it down & report back to your resolver
Iterative Lookup: DNS resolve will continually query DNS servers until it finds the one with the IP for the domain
DNS Zone Transfer
The process of sending DNS records data from the primary nameserver to a secondary name server.
Uses TCP to verify data is successfully sent by primary server & received by secondary server.
TTL (DNS)
Time to Live:
Tells the DNS resolver how long to cache a query before requesting a new one
In things like traceroute, it’s the number of hops until the packet is dropped.
Internal DNS
Allows cloud instances on the same network access each other using internal DNS names.
External DNS
Records created around the domain names we purchase from a central authority and use on the public internet.
DHCP
Provides an IP address to every machine on the network & eliminates configuration errors
IP, Subnet Mask, Default Gateway, DNS Server
UDP Port 67/68
DHCP: Scope
A list of valid IP addresses available for assignment/lease to a client computer or endpoint device on a given subnet
DHCP: Reservation
Excludes some IP addresses from being handed out to devices unless they meet a certain condition
DHCP: D-O-R-A Process
Discover, Offer, Request, Acknowledge
DHCP Relay
Any host that forwards DHCP packets between clients & servers
Used when the client device & DHCP server are not located on the same subnet/network
DHCP: Scope Options
Subnet mask
Default gateway
DNS server
Lease time
DHCP: IP Helper
Forwards several different kinds of UDP broadcasts across the router & can be used in conjunction with DHCP relay
NTP
Synchronizes clocks between systems communicating over a packet-switched, variable-latency data network.
UDP Port 123
NTPv4 (2010): Most current version
DNS: Top Level Domains
Organizational Hierarchy:
.com
.net
.org
Geographic Hierarchy:
.uk
.fr
.it
DNS: Second Level Domains
The site directly below the top level domain
Ex: diontraining.com
DNS: Subdomains
Ex: chat.diontraining.com
DNS: Host Level
The lowest & most detailed level in DNS hierarchy
Refers to a specific machine
NTP
Synchronizes clocks between systems communicating over a packet-switched, variable-latency data network.
UDP Port 123
NTP: Stratum
NTP Uses a hierarchal, semi-layered system of time sources.
Each layer of the hierarchy is a stratum. (Max: 15)
Stratum 0: Reference clocks
Stratum 1: First NTP servers (within usecs of Strat 0)
Stratum 2: Queries multiple Stratum 1 servers
Stratum 3: Pattern continues as you go up stratums
DNS Record: SOA
Indicates which Domain Name Server (DNS) is the best source of information for the specified domain
