DNS 101

Question 1

What is DNS

Answer 1

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…

Question 2

How many bits in an IPv4 address?

Answer 2

32

Question 3

How many IPv4 addresses can exist?

Answer 3

over 4 billion.

4,294,967,296 to be exact.

Question 4

How many bits in an IPv6 address?

Answer 4

128

Question 5

How many IPv6 addresses can exist?

Answer 5

340 undecillion addresses.

That’s 340, followed by 36 zeroes.

Question 6

What is a Top Level Domain?

Answer 6

the last word after the last dot in a domain name

.guru

Question 7

What is the second level domain?

Answer 7

the word before the last dot.

acloud.guru

Question 8

In this following example, which is top level, and which is the second level?
buystuff.com

Answer 8

buystuff = second level
.com = top level

Question 9

In this following example, which is top level, and which is the second level?
.co.uk

Answer 9

.co = second level
.uk = top level

Question 10

Who manages and controls top level domains?

Answer 10

IANA - Internet Assigned Numbers Authority

www.iana.org

Question 11

What is the name of the database controlled by IANA

Answer 11

Root zone database

Question 12

If you want to see all the available top level domains, where can you go?

Answer 12

http://www.iana.org/domains/root/db

Question 13

what is a domain registrar?

Answer 13

An authority that can assign names directly under one or more top-level domains.

Question 14

Where are domain names registered to?

Answer 14

InterNIC, a service of ICANN.

Question 15

What is ICANN?

Answer 15

A service that enforces the uniqueness of domain names across the internet.

Question 16

What is the database where domain names are registered?

Answer 16

The WhoIS database

Question 17

Examples of domain registrars

Answer 17

AWS Route 53, GoDaddy, 123-reg-co-uk

Question 18

Each DNS record contains what kind of entry?

Answer 18

Start of Authority (SOA)

Question 19

What information is contained in a Start of Authority

Answer 19

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

Question 20

What is an NS Record?

Answer 20

Used by Top Level domains to direct traffic to the content DNS server which contains the authoritative DNS record

Question 21

What is an A record?

Answer 21

The fundamental DNS record that translates the domain name to the IP address.

Question 22

What does the “A” in A Record stand for?

Answer 22

Address

Question 23

What is a DNS TTL?

Answer 23

The length of time the record is cached. The longer the TTL, the longer DNS changes take to propogate.

Question 24

What is a CNAME?

Answer 24

Used to resolve one domain name to another.

Question 25

What is an Alias record?

Answer 25

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.

Question 26

Can CNAMEs be used for apex records?

Answer 26

No

Question 27

True or False: Elastic Load Balancers do not have a predefined IPv4 address?

Answer 27

True. You will always resolve to them using the DNS name.

Question 28

Given the choice, should you always choose Alias over CNAME records?

Answer 28

Yes.

Question 29

True or False: Alias records save time because changes to the records are recognized automatically without requiring any changes to the hosted zone?

Answer 29

True.