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GATE 2011 CS (CS1) – Question 12

Computer Networks · Principles of Layering · 1 mark · Multiple choice

A layer-four firewall can inspect protocol headers through the transport layer. Which can it NOT do?

  1. Block all HTTP traffic between 9 PM and 5 AM
  2. Block all ICMP traffic
  3. Block incoming traffic from one IP while allowing outgoing traffic to that IP
  4. Block TCP traffic from a particular user on a multiuser system between 9 PM and 5 AM

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Correct answer: (D) Block TCP traffic from a particular user on a multiuser system between 9 PM and 5 AM

Explanation

IP/protocol/port fields and connection direction allow the first three conventional filters. A transport-layer header does not identify the human user behind a TCP connection on a shared machine, so a user-specific rule needs additional authentication or application information. Thus D; HTTP filtering here assumes its conventional port.

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