DNS 101 Flashcards
What is DNS
It’s the internet’s phone book. It translates URL addresses to IP addresses. For example, http://acloud.guru to 82.124.53.1. In this analogy, the URL address is a business name, and the IP address is their phone number. If you’ve ever seen a phone book…
How many bits in an IPv4 address?
32
How many IPv4 addresses can exist?
over 4 billion.
4,294,967,296 to be exact.
How many bits in an IPv6 address?
128
How many IPv6 addresses can exist?
340 undecillion addresses.
That’s 340, followed by 36 zeroes.
What is a Top Level Domain?
the last word after the last dot in a domain name
.guru
What is the second level domain?
the word before the last dot.
acloud.guru
In this following example, which is top level, and which is the second level?
buystuff.com
buystuff = second level .com = top level
In this following example, which is top level, and which is the second level?
.co.uk
.co = second level .uk = top level
Who manages and controls top level domains?
IANA - Internet Assigned Numbers Authority
www.iana.org
What is the name of the database controlled by IANA
Root zone database
If you want to see all the available top level domains, where can you go?
http://www.iana.org/domains/root/db
what is a domain registrar?
An authority that can assign names directly under one or more top-level domains.
Where are domain names registered to?
InterNIC, a service of ICANN.
What is ICANN?
A service that enforces the uniqueness of domain names across the internet.
What is the database where domain names are registered?
The WhoIS database
Examples of domain registrars
AWS Route 53, GoDaddy, 123-reg-co-uk
Each DNS record contains what kind of entry?
Start of Authority (SOA)
What information is contained in a Start of Authority
Name of the server that supplied the zone data
The administrator of the zone
The current version of the zone
the TTL in seconds on resource records
What is an NS Record?
Used by Top Level domains to direct traffic to the content DNS server which contains the authoritative DNS record
What is an A record?
The fundamental DNS record that translates the domain name to the IP address.
What does the “A” in A Record stand for?
Address
What is a DNS TTL?
The length of time the record is cached. The longer the TTL, the longer DNS changes take to propogate.
What is a CNAME?
Used to resolve one domain name to another.
What is an Alias record?
Similar to CNAME, an alias is also used to map resource record sets in your hosted zone to Elastic Load Balancer, CloudFront, or S3 web hosting buckets.
Can CNAMEs be used for apex records?
No
True or False: Elastic Load Balancers do not have a predefined IPv4 address?
True. You will always resolve to them using the DNS name.
Given the choice, should you always choose Alias over CNAME records?
Yes.
True or False: Alias records save time because changes to the records are recognized automatically without requiring any changes to the hosted zone?
True.
