BREB Junior Assistant Manager (ICT) Exam: 2021প্রশ্ন ও সমাধান

Answer:

A firewall is a network security system — hardware, software, or both — that monitors and controls incoming and outgoing network traffic based on a defined set of security rules, acting as a barrier between a trusted internal network (LAN) and an untrusted external network (the Internet).

• It works by inspecting packets (source/destination IP, port, protocol) and allowing or blocking them according to a configured rule set (an Access Control List).
• Types: packet-filtering firewall (checks headers only), stateful inspection firewall (tracks connection state), and application-layer/proxy firewall (inspects actual application data, e.g., HTTP content).
• Purpose: prevent unauthorized access and block malicious traffic (malware, port scans, intrusion attempts) while still allowing legitimate business traffic through.

LAN network with a firewall:

graph LR
    subgraph Internal_LAN[Internal LAN]
        PC1[Workstation 1]
        PC2[Workstation 2]
        SRV[File / Print Server]
        SW[Switch]
        PC1 --- SW
        PC2 --- SW
        SRV --- SW
    end
    SW --- FW[Firewall]
    FW --- R[Router / Modem]
    R --- NET((Internet))

• All traffic between the internal LAN and the Internet must pass through the firewall — the switch connects internal devices, the firewall filters what crosses the boundary, and the router forwards allowed traffic on to the ISP/Internet.
• Only traffic matching allowed rules (e.g., outbound HTTP/HTTPS, permitted inbound ports) passes through; everything else is dropped and logged.

Exam takeaway: a firewall sits at the boundary between a trusted LAN and the untrusted Internet, filtering traffic by rule (packet-filtering, stateful, or application-layer) to block unauthorized access while permitting legitimate communication.