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Difficulty: MediumCommon Ports and Protocols

A network monitoring engineer is configuring internal firewall rules to allow enterprise routers and switches to send unsolicited asynchronous event notifications (traps) to a centralized Network Management System (NMS). Which transport protocol and destination port must be permitted through the firewall for the NMS collector to receive these incoming trap messages?

  1. UDP port 162Answer
  2. B
    UDP port 161
  3. C
    TCP port 162
  4. D
    TCP port 161

Answer

UDP port 162 is the standard protocol and port used by Network Management System (NMS) collectors to receive SNMP Trap and Inform notifications from network agents.
Simple Network Management Protocol (SNMP) agents send unsolicited notification messages, known as Traps or Informs, to an NMS manager station over UDP port 162. UDP is chosen for its minimal protocol overhead during alert generation.

Step-by-Step Solution

1
Identify the specific SNMP operational communication flow described in the scenario.
The scenario specifies agent-initiated, unsolicited event notifications (traps) sent to an NMS collector.
Standard SNMP polling (GET/SET) and SNMP notifications (TRAP/INFORM) operate on different destination port numbers.
2
Determine the transport protocol used by SNMP messaging.
SNMP utilizes UDP due to its low overhead and connectionless nature.
Connectionless transport prevents management traffic from blocking device resources during network events.
3
Map the trap event direction to the standardized UDP port number.
SNMP Traps target UDP port 162 on the NMS receiver, whereas SNMP Manager queries target UDP port 161 on agents.
Distinguishing port 161 (polling listener on agents) from port 162 (trap listener on NMS) ensures correct firewall ACL directionality.

Key Concept

SNMP Port Differentiation (Polling UDP 161 vs. Traps UDP 162)
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Topics

Common Ports and Protocols

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