There are many timers in Portal authentication. Which of the following timers can be used to prevent DoS attacks?

Question

Options

• AUser client timer
• BFull-in-heartbeat server heartbeat detection timer
• CPortal server detection timer
• DUser offline retransmission timer

• A
  2% (1)
• B
  11% (5)
• C
  83% (39)
• D
  4% (2)

Explanation

Portal server detection timer (option C) is correct because this timer allows the NAS (Network Access Server) to periodically check whether the Portal server is reachable. When the Portal server fails to respond within the detection interval - which can occur during a DoS attack - the NAS can stop forwarding authentication requests to the server, blocking further attack traffic and protecting the system from being overwhelmed.

The user client timer (A) governs how long the client waits before timing out a portal interaction; it operates on the user side and has no mechanism to detect or block attack traffic at the network level. The full-in-heartbeat server heartbeat detection timer (B) monitors ongoing session health between authenticated users and the server, but it is designed to maintain live sessions rather than to gate incoming authentication attempts. The user offline retransmission timer (D) controls how many times the NAS retransmits a user-logout notification when no acknowledgment is received, which is a session-cleanup function unrelated to attack prevention.

Memory tip: Think of "detection" as the keyword - the Portal server detection timer actively probes the server's status and can cut off traffic when something is wrong, making it the one timer with a defensive, gatekeeping role against DoS scenarios.

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