--- title: "Intranet vs Internet, firewall, content filtering" subject: "Internet and Intranet" chapter: 1 key: "semester_8/internet_and_intranet:intranet-internet-benefits-firewall" source: https://www.bctengineer.com/q/semester_8/internet_and_intranet/intranet-internet-benefits-firewall site: BCT Engineering --- # Intranet vs Internet, firewall, content filtering Internet and Intranet · Chapter 1: Introduction - Asked in: 2072 Asoj, 4+6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/internet_and_intranet/intranet-internet-benefits-firewall - Whole chapter: https://www.bctengineer.com/md/semester_8/internet_and_intranet/chapter-1 ## Question Compare intranet and internet in terms of benefits and drawbacks. Discuss in detail about firewall and content filtering. ## Short answer Intranet offers secure, private, fast internal sharing with low cost but is limited to the organization and needs maintenance. A firewall filters traffic between intranet and internet based on rules (packet, stateful, proxy). Content filtering blocks unwanted material by URL, keyword, or file-type to enforce policy and block malware. ## Answer #### Intranet vs Internet: benefits and drawbacks | | Intranet | Internet | |---|---|---| | Benefits | Secure, private; fast LAN speed; internal sharing of files, policies, applications; central control and low cost for communication; easy to customise | Global reach; huge information; e-commerce, e-mail, social media; low-cost communication; open services | | Drawbacks | Limited to the organisation; needs setup, maintenance and skilled staff; needs a gateway for Internet access; can be misused by insiders | Security risks (malware, hacking, phishing); no central control; unreliable content; privacy loss; depends on ISP | #### Firewall A **firewall** is hardware or software placed between a trusted network (intranet) and an untrusted network (Internet) that allows or blocks traffic according to security rules. ```text Internet --- [Firewall] --- Intranet (LAN) | DMZ: web, mail, DNS servers ``` **Types** 1. **Packet-filtering firewall:** checks source/destination IP, port and protocol against an ACL. Fast but does not track connections. 2. **Stateful inspection firewall:** keeps a table of active connections and allows only valid replies. 3. **Application-level gateway / proxy firewall:** acts as an intermediary for a particular application (HTTP, FTP), hides internal hosts and inspects the content. 4. **Next-generation firewall (NGFW):** adds deep packet inspection, intrusion prevention, application control and user identity. **Functions:** block unauthorised access, hide internal addresses (NAT), log traffic, create a DMZ for public servers, support VPN. Example rule: allow TCP 80/443 from the LAN to any; allow TCP 25 only to the mail server; deny all other inbound traffic. **Limitations:** cannot stop insider attacks, malware carried on USB or inside allowed traffic, or attacks that bypass the firewall. #### Content filtering **Content filtering** screens web pages, e-mail and downloads and blocks material that breaks the organisation's policy. Methods: - **URL/category filtering:** block websites by address list or category (adult, gambling, social media). - **Keyword filtering:** block pages or mail with certain words. - **File-type/MIME filtering:** block executables or large media downloads. - **Antivirus and spam filtering:** scan attachments and mail. - **DNS filtering:** refuse to resolve harmful domains. - **Implemented** in a proxy server (e.g. Squid with ACLs), in firewall/UTM devices or in cloud security services. Purposes: protect against malware, enforce an acceptable-use policy, save bandwidth, increase productivity, and meet legal requirements. Limitations are over-blocking, evasion through VPNs and difficulty with encrypted HTTPS traffic. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a stateful inspection firewall differ from a packet-filtering firewall? A. It only checks port numbers B. It keeps a table of active connections and allows only valid replies, whereas a packet filter checks IP, port and protocol against an ACL without tracking connections C. It works only at the application layer D. It cannot use ACLs Answer: B. Packet filters are fast but stateless; stateful firewalls track connections. (Key point: Packet-filter vs stateful firewall) 2. What does an application-level gateway (proxy) firewall do? A. Acts as intermediary for a specific application, hides internal hosts and inspects content B. Only forwards packets by IP C. Replaces the DNS server D. Blocks all traffic by default with no inspection Answer: A. A proxy firewall stands between client and server for applications like HTTP and FTP. (Key point: Proxy firewall) 3. What is the purpose of a DMZ? A. To store user passwords B. To speed up the LAN C. To host public servers (web, mail, DNS) separated from the internal intranet D. To block all outside traffic Answer: C. A DMZ places public-facing servers in a separate zone off the firewall. (Key point: DMZ purpose) 4. Which threat can a firewall NOT stop? A. Packets to a closed port B. Traffic from a denied IP C. Direct inbound telnet D. Insider attacks and malware carried on USB or inside allowed traffic Answer: D. Firewalls only control traffic crossing them, so insiders and allowed traffic can bypass them. (Key point: Firewall limitations) 5. Which is a content filtering method? A. Routing by OSPF B. URL/category filtering that blocks sites by address list or category C. Assigning private IPs D. Increasing link bandwidth Answer: B. Content filtering uses URL, keyword, file-type, antivirus/spam and DNS filtering, often in a proxy. (Key point: Content filtering methods) ## Related in Internet and Intranet - [Content filtering vs packet filtering](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Acontent-filtering-packet-filtering) — Internet and Intranet, chapter 5 - [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 - [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 - [Short note: Content filtering](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Anote-content-filtering) — Internet and Intranet, chapter 5 - [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 - [Short note: Firewall types, bastion host](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Anote-firewall-bastion-host) — Internet and Intranet, chapter 5 ## Related in other subjects - [How packet filtering firewall works](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Apacket-filtering-firewall) — Computer Networks and Security, chapter 8 - [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 - [Case study: feasibility, drawbacks, convincing](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-2072kartik-feasibility) — Instrumentation II, chapter 10