--- title: "Need and services of DNS" subject: "Internet and Intranet" chapter: 3 key: "semester_8/internet_and_intranet:dns-need-services" source: https://www.bctengineer.com/q/semester_8/internet_and_intranet/dns-need-services site: BCT Engineering --- # Need and services of DNS Internet and Intranet · Chapter 3: Protocols and Client/Server Applications - Asked in: 2069 Bhadra (old course), 10 marks - Video: [How a DNS Server (Domain Name System) works.](https://www.youtube.com/watch?v=mpQZVYPuDGU) — PowerCert Animated Videos - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/internet_and_intranet/dns-need-services - Whole chapter: https://www.bctengineer.com/md/semester_8/internet_and_intranet/chapter-3 ## Question Discuss the need of Domain Name Systems (DNS) in an Internet / Intranet environment. Also explain the service provided by DNS. ## Short answer DNS translates human-readable names to IP addresses, enabling scalability and flexibility. Services include forward and reverse resolution, host aliasing (CNAME), mail server identification (MX), load distribution, and caching for efficiency. ## Answer #### Need of DNS Hosts on the Internet are identified by IP addresses (e.g. 142.250.190.78) which are hard for people to remember, while humans prefer names such as `www.example.com`. The **Domain Name System (DNS)** is a distributed, hierarchical database and an application layer protocol (UDP/TCP port 53) that translates host names to IP addresses and back. Why it is needed in an Internet or Intranet: - **Human-friendly names.** Users remember names, not 32-bit/128-bit numbers. - **Flexibility.** If a server moves to a new IP address, only the DNS record changes; users keep using the same name. - **Scalability.** One central hosts file (HOSTS.TXT) cannot scale to millions of hosts. DNS spreads the data over many servers. - **Required by other services.** Web, e-mail (MX records), FTP and proxy all depend on name resolution. In an intranet, names such as `intranet.company.local` or `mail.company.local` make internal services easy to reach. - **Load distribution and redundancy.** One name can map to several IPs. #### Hierarchy ```text . (root) +-------+-------+ com org np | | google edu.np | | www ioe ``` Root servers -> TLD servers (.com, .np) -> authoritative servers of each organisation. Local (recursive) DNS servers of an ISP or company resolve queries for clients and cache answers. #### Services provided by DNS 1. **Host name to IP address translation** (forward lookup, A/AAAA records) and **IP to name** (reverse lookup, PTR records). 2. **Host aliasing.** A canonical name can have many aliases (CNAME), e.g. `www.example.com` -> `web1.example.com`. 3. **Mail server aliasing.** MX records identify the mail server of a domain, so addresses like `user@example.com` work. 4. **Load distribution.** A busy site may have several IPs for one name; DNS rotates the order of the list (round robin). 5. **Name server records (NS)** delegate a zone to its authoritative servers. 6. **Caching.** Servers cache answers for a TTL, reducing delay and traffic. 7. **Other records:** TXT (SPF, verification), SRV (service location), SOA (zone parameters). Resolution can be **recursive** (server does the whole job for the client) or **iterative** (server returns a referral to the next server). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main reason DNS is needed? A. To encrypt web traffic B. To translate human-friendly host names to IP addresses and back C. To assign IP addresses to hosts dynamically D. To route packets between networks Answer: B. People remember names, not numeric IPs, so DNS maps names to addresses (and reverse). (Key point: Need for DNS) 2. Why did DNS replace a single central HOSTS.TXT file? A. A single file cannot scale to millions of hosts; DNS distributes data over many servers B. HOSTS.TXT cannot store IP addresses C. DNS is faster only because it uses TCP D. HOSTS.TXT is encrypted Answer: A. One central file does not scale; DNS is a distributed, hierarchical database. Also, a changed server IP only needs a DNS record update. (Key point: Scalability and flexibility) 3. Which record type identifies the mail server of a domain, and which gives host aliasing? A. PTR for mail, A for alias B. NS for mail, TXT for alias C. MX for mail, CNAME for alias D. SOA for mail, MX for alias Answer: C. MX records name the domain's mail server and CNAME maps an alias to a canonical name. (Key point: MX and CNAME records) 4. What distinguishes recursive from iterative DNS resolution? A. Recursive uses UDP, iterative uses TCP B. In recursive the server does the whole job for the client; in iterative it returns a referral to the next server C. Iterative caches answers, recursive does not D. Recursive only works for reverse lookups Answer: B. A recursive query makes the server resolve fully; an iterative one returns a referral for the client to follow. (Key point: Recursive vs iterative) ## Related in Internet and Intranet - [Internet vs Intranet and DNS need](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Ainternet-intranet-compare-dns) — Internet and Intranet, chapter 1 - [Intranet vs Internet, firewall, content filtering](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aintranet-internet-benefits-firewall) — Internet and Intranet, chapter 1 - [Intranet, Internet, Extranet comparison and resources](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aintranet-internet-extranet-compare) — Internet and Intranet, chapter 1 - [Intranet vs Internet and intranet protocols](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aintranet-vs-internet-protocols) — Internet and Intranet, chapter 1 ## Related in other subjects - [Name service and name resolution](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aname-service-types) — Distributed System, chapter 2 - [Internet, intranet and extranet use](https://www.bctengineer.com/question.md?key=semester_8%2Finformation_system%3Ainternet-intranet-extranet) — Information System, chapter 1 - [Short note: Internet / Intranet](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Ashort-note-internet-intranet) — Basic Electronics Engineering, chapter 5 - [DNS and its working mechanism](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Adns-working) — Distributed System, chapter 2, asked 3×