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Difficulty: HardCommon Ports and Protocols

An enterprise network administrator is configuring firewall rules for a newly deployed subnet containing critical infrastructure servers. The servers must synchronize their system clocks against an internal stratum 1 time authority and allow the central network management system (NMS) to regularly poll system operational metrics via Simple Network Management Protocol (SNMP). Which TWO protocol and transport layer port combinations must be permitted through the firewall to support these services?

  1. UDP port 123 for Network Time Protocol (NTP) clock synchronizationAnswer
  2. UDP port 161 for SNMP manager-to-agent metric polling queriesAnswer
  3. C
    TCP port 123 for Network Time Protocol (NTP) clock synchronization
  4. D
    UDP port 514 for SNMP manager-to-agent metric polling queries

Answer

UDP port 123 for Network Time Protocol (NTP) clock synchronization and UDP port 161 for SNMP manager-to-agent metric polling queries.
The scenario requires configuring firewall rules for clock synchronization and SNMP metric polling. Network Time Protocol (NTP) operates on UDP port 123 to synchronize clocks with minimal latency. Simple Network Management Protocol (SNMP) manager-to-agent requests and polling operate over UDP port 161. Permitting both UDP 123 and UDP 161 satisfies both operational requirements.

Step-by-Step Solution

1
Identify the required network service for system clock synchronization and its default port/protocol.
Network Time Protocol (NTP) operates over UDP port 123.
NTP requires light connectionless overhead to accurately calculate offset and round-trip delay.
2
Identify the required network service for polling device metrics from a central Network Management System (NMS).
SNMP polling queries from manager to agent operate over UDP port 161.
SNMP uses UDP port 161 for request/response messages (GetRequest, SetRequest) sent by management consoles to managed agents.
3
Evaluate candidate options to select the matching UDP port assignments.
Select UDP port 123 and UDP port 161.
Both NTP and SNMP polling utilize UDP as their transport protocol rather than TCP or alternative service ports.

Key Concept

Standard UDP Port Assignments for Management and Infrastructure Services (NTP and SNMP)
Estimated Time:1m 30s
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Topics

Common Ports and Protocols

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