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Difficulty: MediumSNMP Operations, MIBs, Traps, Informs, and Version Differences

A network engineer is configuring access control lists on an enterprise router to restrict network management traffic. The policy must allow a Network Management System (NMS) server to send SNMP query messages (such as GetRequest) to managed network devices, and also allow managed devices to send asynchronous event notifications (Traps and Informs) back to the NMS server. Which port and protocol combination must be permitted through the security filters to satisfy both operational requirements?

  1. UDP port 161 for SNMP queries sent to managed devices, and UDP port 162 for SNMP notifications sent to the NMS server.Answer
  2. B
    TCP port 161 for SNMP queries sent to managed devices, and TCP port 162 for SNMP notifications sent to the NMS server.
  3. C
    UDP port 162 for SNMP queries sent to managed devices, and UDP port 161 for SNMP notifications sent to the NMS server.
  4. D
    UDP port 161 for both SNMP queries sent to managed devices and SNMP notifications sent to the NMS server.

Answer

UDP port 161 for SNMP queries sent to managed devices, and UDP port 162 for SNMP notifications sent to the NMS server.
Simple Network Management Protocol (SNMP) uses UDP as its transport protocol. Managed devices run an SNMP agent that listens for incoming management requests (GetRequest, GetNextRequest, SetRequest) on UDP port 161. Conversely, the SNMP manager (NMS) listens for incoming asynchronous notification messages (Traps and Informs) on UDP port 162. Therefore, allowing UDP 161 towards managed devices and UDP 162 towards the NMS fulfills both monitoring requirements.

Step-by-Step Solution

1
Identify the transport protocol used by standard SNMP operations.
SNMP utilizes UDP as its transport layer protocol for standard operations.
UDP provides low overhead connectionless transport appropriate for polling and notification delivery.
2
Determine the destination UDP port for agent polling operations (Get, GetNext, Set).
Managed devices (SNMP agents) listen on UDP port 161.
NMS managers send query requests to destination UDP port 161 on target network devices.
3
Determine the destination UDP port for notification messages (Traps and Informs).
NMS trap daemons listen on UDP port 162.
Managed devices send unsolicited Traps or acknowledged Informs to destination UDP port 162 on the management station.

Key Concept

SNMP Transport Layer Ports and Operational Mechanics
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Topics

SNMP Operations, MIBs, Traps, Informs, and Version Differences

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