Week 4 Flashcards
Domain Name System (DNS)
A global and highly distributed network service that resolves strings of letters into IP addresses for you
Domain name
Term used for something that can be resolved by DNS
What are the five primary types of DNS servers?
Caching name servers Recursive name servers Root name servers TLD name servers Authoritative name servers
Caching and recursive name servers
Purpose is to store known domain name lookups for a certain amount of time
Recursive name servers
Perform full DNS resolution requests
TTL (Time to live)
A value, in seconds, that can be configured by the owner of a domain name for how long a name server is allowed to cache an entry before it should discard it and perform a full resolution again
Steps of a full recursive resolution
- Recursive name server contacts a root name server (there’s 13 authority root servers in total)
- Root server responds with the TLD name that should be queried
- Then the recursive name server contacts an appropriate TLD server
- TLD server responds with the authoritative name server the recursive name server should contact
- The recursive name server contacts the given name server
- The name server gives the IP of the website being looked up
Anycast
A technique that’s used to route traffic to different destinations depending on factors like location, congestion, or link health
Does the DNS lookup use UDP or TCP?
UDP
An A Record
Used to point a certain domain name at a certain IPv4 IP address
CNAME record
Used to redirect traffic from one domain name to another
Mail exchange
Used to direct email to the correct server
TLD
Top level domain
Last part of a domain name
.com
.org
And so on
Domain
Used to refer to the second part of a domain name
Subdomain
A.K.A the host name
Fully qualified domain name
When you combine the subdomain, domain, and TLD together
Registrar
A company with an agreement with ICANN that allows them to sell unregistered domain names
How many levels can DNS support in a fully qualified domain name?
127
DNS zones
Allow for easier control over multiple levels of a domain
Zone files
Simple configuration files that declare all resource records for a particular zone
Start of Authority (SOA)
Declares the zone and the name of the name server that is authoritative for it
NS records
Indicate other name servers that might also be responsible for this zone
Reverse lookup zone files
These let DNS resolves ask for an IP and get the FQDN associated with it returned
Pointer resource record
Resolves an IP to a name
Dynamic Host Configuration Protocol (DHCP)
An application layer protocol that automates the configuration process of hosts in a network
Dynamic Allocation
A range of IP addresses is set aside for client devices and one of these IPs is issued to these devices when they request one
Automatic allocation
A range of IP addresses is set aside for assignment purposes
Fixed allocation
Requires a manually specified list of MAC addresses and their corresponding IPs
Network time protocol (NTP) servers
Used to keep all computers on a network synchronized in time
DHCP discovery
The process by which a client configured to use DHCP attempts to get network configuration information
4 steps of DHCP discovery
- Server discovery broadcast
- DHCP Server sends an IP offer
- Client sends a request to say it would like that IP address given in the offer
- Server sends an acknowledgement back to the client
Now the client has an IP address
What ‘re the port numbers of an “IP-less” client and the DHCP server?
68 for the source and 67 for the destination
Network Access Translation
A technique that translates one IP address into another.
It allows a gateway, usually a router or firewall, to rewrite the source IP of an outgoing IP datagram while retaining the original IP in order to rewrite it into the response.
Port preservation
A technique where the same port a client uses, the router uses when using NAT to mask the client IP
Port forwarding
A technique where specific destination ports can be configured to always be delivered to specific nodes
Virtual Private Network
A technology that allows for the extension of a private or local network to hosts that might not be on that local network
Proxy service
A server that acts on behalf of a client in order to access another service
Reverse Proxy
A service that might appear to be a single server to external clients, but actually represents many servers living behind it.
