DNS stands for Domain Name System.
It translates human-friendly domain names (e.g., www.example.com) into IP addresses (e.g., 192.168.1.1) that computers use to identify each other on the network.

Humans remember names better, but computers communicate using IP addresses.
DNS acts as the phonebook of the internet, mapping domain names to IP addresses.

Step 1: User enters a domain name in the browser (e.g., www.google.com).
Step 2: The browser checks its cache for the IP address.
- Cache can be local (browser, OS) or ISP-level.
Step 3: If not found, the query goes to a DNS resolver (provided by ISP).
Step 4: The resolver asks:
- Root DNS Server → Finds the top-level domain (TLD) server (e.g., .com).
- TLD Server → Finds the domain’s authoritative DNS server (e.g., for google.com).
- Authoritative DNS Server → Returns the IP address for the domain.
Step 5: Browser connects to the IP and loads the website.

A Record: Maps domain to IPv4 address.
AAAA Record: Maps domain to IPv6 address.
CNAME Record: Alias for another domain (e.g., blog.example.com → example.com).
MX Record: Handles email routing.

MCQ

What does DNS stand for?
a) Domain Network Service
b) Domain Name System
c) Data Name Server
d) Domain Numbering Service
Answer: b) Domain Name System
What is the primary purpose of DNS?
a) Encrypt data transmitted over the internet
b) Convert IP addresses to domain names
c) Map domain names to IP addresses
d) Create new domain names
Answer: c) Map domain names to IP addresses
Which protocol is used by DNS for most of its operations?
a) HTTP
b) FTP
c) UDP
d) SMTP
Answer: c) UDP
Which port is used by DNS for standard queries?
a) 25
b) 80
c) 53
d) 443
Answer: c) 53

What is the first step in the DNS resolution process?
a) Querying the TLD server
b) Checking the local cache
c) Querying the authoritative server
d) Querying the root server
Answer: b) Checking the local cache
What is the role of a root server in DNS?
a) Provides the final IP address for the domain
b) Resolves domain names directly
c) Directs the resolver to the TLD server
d) Stores DNS records permanently
Answer: c) Directs the resolver to the TLD server
Which server provides the final IP address for a domain name?
a) Root Server
b) Recursive Resolver
c) TLD Server
d) Authoritative DNS Server
Answer: d) Authoritative DNS Server
Which DNS record type maps a domain name to an IPv4 address?
a) A Record
b) AAAA Record
c) MX Record
d) CNAME Record
Answer: a) A Record
Which DNS record type maps a domain name to an IPv6 address?
a) A Record
b) AAAA Record
c) TXT Record
d) CNAME Record
Answer: b) AAAA Record

What does an MX record in DNS specify?
a) A mail exchange server for emails
b) An alias for another domain
c) The TTL of the DNS query
d) A backup server for DNS
Answer: a) A mail exchange server for emails
What is a CNAME record used for?
a) Maps a domain name to an alias of another domain
b) Translates domain names to IP addresses
c) Specifies mail servers
d) Maps a domain name to an IPv6 address
Answer: a) Maps a domain name to an alias of another domain
Which DNS record contains metadata like SPF and DKIM for emails?
a) TXT Record
b) NS Record
c) SRV Record
d) AAAA Record
Answer: a) TXT Record
What does an NS record indicate in DNS?
a) The authoritative name servers for a domain
b) The mail servers for a domain
c) The alias for a domain
d) The TTL for a DNS query
Answer: a) The authoritative name servers for a domain

Which type of query does the DNS resolver make to the root server?
a) Recursive Query
b) Iterative Query
c) Direct Query
d) Reverse Query
Answer: b) Iterative Query
What is the TTL (Time to Live) in DNS?
a) The time DNS records remain valid in cache
b) The total time taken for DNS resolution
c) The time taken by DNS queries to propagate
d) The lifetime of DNS servers
Answer: a) The time DNS records remain valid in cache
What is reverse DNS lookup?
a) Resolving a domain name to an IP address
b) Resolving an IP address to a domain name
c) Finding the TTL of a DNS record
d) Querying a secondary DNS server
Answer: b) Resolving an IP address to a domain name
Which of the following is a potential DNS attack?
a) DNS Amplification Attack
b) DNS Spoofing
c) DNS Cache Poisoning
d) All of the above
Answer: d) All of the above
What is DNS Spoofing?
a) Blocking DNS queries
b) Faking a DNS response to redirect traffic to malicious sites
c) Overloading DNS servers
d) Encrypting DNS records
Answer: b) Faking a DNS response to redirect traffic to malicious sites

Which protocol enhances DNS security by adding authentication to DNS records?
a) DNSSEC
b) HTTPS
c) SNMP
d) SSH
Answer: a) Domain Name System Security Extensions (DNSSEC) is a set of specifications that add security to the Domain Name System (DNS) protocol.
What does DNSSEC provide?
a) Confidentiality
b) Integrity and Authentication
c) Encryption
d) Data Compression
Answer: b) Integrity and Authentication
Which of the following is used to encrypt DNS queries?
a) DNS over HTTP (DoH)
b) DNS over TLS (DoT)
c) Both a and b
d) None of the above
Answer: c) Both a and b

What happens if the authoritative DNS server for a domain is unavailable?
a) The domain becomes inaccessible
b) TLD server handles the query
c) The query is redirected to a root server
d) The resolver retries indefinitely
Answer: a) The domain becomes inaccessible
Which tool can be used to test DNS resolution?
a) ping
b) nslookup
c) traceroute
d) netstat
Answer: b) nslookup
What is a recursive DNS query?
a) The resolver fetches the final IP address for the client
b) The client queries each DNS server sequentially
c) The resolver only points to the root server
d) A query to find reverse DNS records
Answer: a) The resolver fetches the final IP address for the client
What is the default DNS hierarchy?
a) Root → Recursive Resolver → TLD → Authoritative Server
b) Root → TLD → Authoritative Server → Recursive Resolver
c) Recursive Resolver → Root → TLD → Authoritative Server
d) Root → TLD → Recursive Resolver → Authoritative Server
Answer: c) Recursive Resolver → Root → TLD → Authoritative Server

Role of DNS in Domain Name Resolution