DNS

Question 1

Which record types does route 53 support ?

Answer 1

A (address record)
AAAA (IPv6 address record)
CNAME (canonical name record)
CAA (certification authority authorization)
MX (mail exchange record)
NAPTR (name authority pointer record)
NS (name server record)
PTR (pointer record)
SOA (start of authority record)
SPF (sender policy framework)
SRV (service locator)
TXT (text record)
\+ alias records,

Question 2

What is DNS ?

Answer 2

DNS is a global system for translating IP addresses to human-readable domain names

Question 3

How DNS works ?

Answer 3

When a user tries to access a web address like “example.com”, their web browser or application performs a DNS Query against a DNS server, supplying the hostname.
The DNS server takes the hostname and resolves it into a numeric IP address, which the web browser can connect to.

Question 4

What are doing DNS Resolver ?

Answer 4

DNS Resolver is responsible for checking if the hostname is available in local cache, and if not, contacts a series of DNS Name Servers, until eventually it receives the IP of the service the user is trying to reach, and returns it to the browser or application. This usually takes less than a second.

Question 5

How many DNS query types exist ?

Answer 5

There are three DNS query types :

• Recursive query
• Iterative query
• Non-recursive query

Question 6

What is a recursive query ?

Answer 6

In a recursive query, a DNS client provides a hostname, and the DNS Resolver “must” provide an answer—it responds with either a relevant resource record, or an error message if it can’t be found. The resolver starts a recursive query process, starting from the DNS Root Server, until it finds the Authoritative Name Server (for more on Authoritative Name Servers see DNS Server Types below) that holds the IP address and other information for the requested host

Question 7

What is Iterative query ?

Answer 7

In an iterative query, a DNS client provides a hostname, and the DNS Resolver returns the best answer it can. If the DNS resolver has the relevant DNS records in its cache, it returns them. If not, it refers the DNS client to the Root Server, or another Authoritative Name Server which is nearest to the required DNS zone. The DNS client must then repeat the query directly against the DNS server it was referred to.

Question 8

What is Non-recursive query ?

Answer 8

A non-recursive query is a query in which the DNS Resolver already knows the answer. It either immediately returns a DNS record because it already stores it in local cache, or queries a DNS Name Server which is authoritative for the record, meaning it definitely holds the correct IP for that hostname. In both cases, there is no need for additional rounds of queries (like in recursive or iterative queries). Rather, a response is immediately returned to the client.

Question 9

How many types of DNS servers ?

Answer 9

3 Types of DNS Servers :

• DNS Resolver
• DNS Root Server
• Authoritative root server

Question 10

What is a DNS Resolver

Answer 10

A DNS resolver (recursive resolver) is designed to receive DNS queries, which include a human-readable hostname such as “www.example.com”, and is responsible for tracking the IP address for that hostname.

Question 11

What is Root servers ?

Answer 11

The root server is the first step in the journey from hostname to IP address. The DNS Root Server extracts the Top Level Domain (TLD) from the user’s query — for example, www.example.com — and provides details for the .com TLD Name Server. In turn, that server will provide details for domains with the .com DNS zone, including “example.com”.

There are 13 root servers worldwide, indicated by the letters A through M, operated by organizations like the Internet Systems Consortium, Verisign, ICANN, the University of Maryland, and the U.S. Army Research Lab.

Question 12

What is authoritative server ?

Answer 12

Higher level servers in the DNS hierarchy define which DNS server is the “authoritative” name server for a specific hostname, meaning that it holds the up-to-date information for that hostname.

The Authoritative Name Server is the last stop in the name server query—it takes the hostname and returns the correct IP address to the DNS Resolver (or if it cannot find the domain, returns the message NXDOMAIN).

Question 13

A Record ?

Answer 13

Address Mapping record (A Record)—also known as a DNS host record, stores a hostname and its corresponding IPv4 address.

Question 14

AAAA Record ?

Answer 14

Stores a hostname and its corresponding IPv6 address.

Question 15

CNAME Record

Answer 15

Points at other URLs => Can be used to alias a hostname to another hostname.

Question 16

MX Record

Answer 16

Specifies an SMTP email server for the domain, used to route outgoing emails to an email server.

Question 17

NS Record

Answer 17

Specifies that a DNS Zone, such as “example.com” is delegated to a specific Authoritative Name Server, and provides the address of the name server.

Question 18

PTR Record

Answer 18

Allows a DNS resolver to provide an IP address and receive a hostname (reverse DNS lookup).

Question 19

CERT Record

Answer 19

Stores encryption certificates—PKIX, SPKI, PGP, and so on.

Question 20

SRV Record

Answer 20

A service location record, like MX but for other communication protocols.

Question 21

TXT Record

Answer 21

Typically carries machine-readable data such as opportunistic encryption, sender policy framework, DKIM, DMARC, etc.

Question 22

SOA Record

Answer 22

This record appears at the beginning of a DNS zone file, and indicates the Authoritative Name Server for the current DNS zone, contact details for the domain administrator, domain serial number, and information on how frequently DNS information for this zone should be refreshed.

Question 23

Which DNS record type is generally used to point Route 53 record sets at AWS logical resources ?

Answer 23

Alias records let you route traffic to selected AWS resources, such as CloudFront distributions and Amazon S3 buckets.