1What problem does DNS solve?
Without DNS, users would have to memorize IP addresses (e.g., 202.48.169.112) instead of typing domain names (e.g., google.com).
2What is an FQDN?
A fully qualified domain name (e.g., www.dell.com), consisting of:
Host (www),
Secondary domain (dell),
Top-level domain (TLD) (.com).
3What is a TLD? Give examples.
A top-level domain (e.g., .com, .org, .edu) at the highest level in the DNS hierarchy.
4What is DNS recursion?
The process where a DNS server queries multiple servers (root → TLD → authoritative) to resolve a domain name into an IP address.
5What is an authoritative DNS server?
The server that holds the final IP address record for a domain (e.g., Dell’s DNS server knows www.dell.com’s IP).
6Why is caching important in DNS?
It stores resolved IP addresses locally, reducing lookup time for future requests.
7What does the root DNS server do?
It directs queries to the appropriate TLD server (e.g., .com, .org).
8What happens if DNS fails?
Users would have to manually enter IP addresses to access websites, making the internet much harder to use.
9What does DNS stand for?
Domain Name System.
10What is the purpose of DNS?
To resolve Fully Qualified Domain Names (FQDNs) into IP addresses.
11In www.teetotalism.com, what is the host?
www
12In www.teetotalism.com, what is the secondary domain?
teetotalism
13In www.teetotalism.com, what is the TL
.com
14What is a root server?
A server at the top of the DNS hierarchy that directs queries to TLD servers.
15What is an authoritative DNS server?
A DNS server that contains the actual IP address for a specific domain.
16What is recursion in DNS?
The process where a DNS server queries other servers step-by-step until it finds the IP.
17What is caching in DNS?
Storing DNS resolution results for faster future lookups.
18What is stored in root hints?
IP addresses of root DNS servers.
19Why is www used so often in hostnames?
It’s a convention for web servers, though any valid host name could be used.
20What happens if your local DNS server has the IP cached?
The IP is returned immediately without querying other servers.
21What are the two most common DNS server software?
BIND (Unix/Linux) and Microsoft DNS (Windows Server).
22Why is .local not recommended for internal domains?
It’s reserved for mDNS (RFC 6762). Use .lan or a subdomain (e.g., internal.example.com).
23What’s the difference between A and AAAA records?
A = IPv4, AAAA = IPv6 (not "quadruple A," though colloquially used).
24What is a CNAME record used for?
Creating aliases (e.g., fred.classroom.local → student1.classroom.local).
25Why are MX records critical for email?
They specify mail servers for a domain, with priority values (lower = higher priority).
26What is the purpose of a PTR record?
Reverse DNS lookup (IP → FQDN), required for spam prevention in email.
27What’s the correct format for a reverse DNS zone?
[reverse-IP].in-addr.arpa (e.g., 200.156.192.in-addr.arpa for 192.156.200.0/24).
28How do SPF and DKIM combat spam?
SPF: Lists allowed mail servers.
DKIM: Uses cryptographic signatures to verify email integrity.
29What is DNS often compared to?
A phone book for the internet.
30What do root servers store?
Information about where to find TLD servers.
31What do TLD servers store?
Details for domains ending in .com, .net, .org, etc.
32What do authoritative name servers store?
The IP address for a specific domain.
33What is the first step when you type www.google.com?
The request goes to the recursive resolver.
34What happens if the recursive resolver doesn’t have the IP cached?
It queries the root server.
35What happens after the root server responds?
The resolver goes to the TLD server.
36What is returned by the TLD server?
Information on the IP address.
37Why is DNS caching important?
To speed up future lookups.
38How do you verify if DNS is the problem when a website fails to load?
Try accessing the site via its IP address. If it works, DNS is the issue.
39What command clears the DNS cache on Windows?
ipconfig /flushdns.
40Why configure both primary and alternate DNS servers?
For redundancy; if the primary fails, the alternate is used automatically.
41What does nslookup example.com 8.8.8.8 test?
Queries example.com specifically on Google’s DNS (8.8.8.8), bypassing local DNS.
42Why might dig or nslookup return limited results?
Many DNS servers restrict zone transfers and detailed queries to prevent abuse.
43What’s a quick way to check DNS resolution without third-party tools?
ping example.com — it resolves the domain to an IP even if the host is down.
44Name two public DNS servers and their IPs.
Google: 8.8.8.8, 8.8.4.4.
Cloudflare: 1.1.1.1.
45What does a SERVFAIL response indicate?
The DNS server encountered an error (e.g., misconfiguration or overload).
46How can you check which DNS server your PC is using?
Run ipconfig /all and look under “DNS Servers.”
47Can you have manual DNS settings alongside DHCP IP configuration?
Yes, Windows allows separate DNS configuration.
48Why are two DNS servers usually configured?
Preferred and Alternate provide fallback if the primary fails.
49How do you view DNS cache on Windows?
ipconfig /displaydns
50How do you clear the DNS cache?
ipconfig /flushdns
51Name a reliable public DNS server
Google DNS: 8.8.8.8 and 8.8.4.4.
52What is nslookup used for?
Testing whether a DNS server can resolve names.
53What is dig used for?
Advanced DNS queries (records, resolution, troubleshooting).
54How can ping help with DNS?
Resolves a hostname to an IP; even if ping fails, name resolution confirms DNS works.
55Outline the steps to troubleshoot a DNS issue.
Identify complaint → confirm DNS failure → check settings → correct DNS → flush cache → test with public DNS → verify with nslookup or dig.