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Difficulty: HardCommon Ports and Protocols

A network administrator is configuring inbound firewall rules on a security zone interface separating managed infrastructure switches from a central Network Management System (NMS). The switches are configured to send asynchronous, unprompted alert notifications to the NMS whenever a physical interface state changes. Which port and transport layer protocol combination must be permitted on the firewall to allow these unsolicited switch notifications to reach the central management server?

  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 port and protocol required to receive unsolicited Simple Network Management Protocol (SNMP) traps and notifications on an NMS.
Simple Network Management Protocol (SNMP) uses two distinct UDP ports depending on the direction and nature of the communication. When managed network devices send unprompted, asynchronous event alerts (SNMP Traps or InformRequests) to a Network Management System (NMS), the traffic is destined for UDP port 162 on the NMS. Therefore, the perimeter firewall must permit inbound UDP port 162 traffic from the switches to the NMS.

Step-by-Step Solution

1
Identify the protocol and communication direction required by the scenario
The network switches are sending asynchronous, unsolicited event alerts to a central Network Management System (NMS), which corresponds to Simple Network Management Protocol (SNMP) Traps.
Unprompted event notifications initiated by managed agents use SNMP Trap messages.
2
Differentiate between SNMP polling ports and SNMP trap ports
SNMP agent polling (queries initiated by the NMS) uses UDP port 161, whereas SNMP trap messages (alerts initiated by managed devices) are sent to destination UDP port 162 on the NMS collector.
Separating polling requests from event traps prevents trap notifications from interfering with routine request-response polling traffic.
3
Determine the transport protocol requirement
SNMP standard operations utilize UDP for low-overhead, connectionless transport.
UDP provides the required lightweight transport mechanism for SNMP messages without session establishment overhead.

Key Concept

SNMP Port Differentiation (UDP 161 vs UDP 162)
Estimated Time:1m 30s
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Topics

Common Ports and Protocols

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