In SNMP, managers and agents have distinct roles that form the foundation of network monitoring: managers are the central control points that request and collect information, while agents are the software components that run on monitored devices (like routers, switches, or servers) and respond to these requests by providing data about their device's status, performance, and configuration. Think of it like a reporter (the manager) gathering information by asking questions to various sources (the agents) - the manager initiates the conversations by sending queries to port 161 on the monitored devices, and the agents respond with the requested information, while also having the ability to send unsolicited urgent notifications (called traps) back to the manager on port 162 when important events occur.
SNMP (Simple Network Management Protocol) actually uses two main ports, and understanding their different purposes helps explain why 161 is the default for agents:
Port 161 is the default port that SNMP agents listen on for incoming requests from SNMP managers. Think of this like a front desk at a hotel - it's where agents wait to receive and respond to queries about the system's status, configuration, or performance metrics.
Port 162, in contrast, is used for SNMP traps, which are unsolicited messages sent from agents to managers to alert them about significant events. This is more like an emergency notification system that proactively sends out alerts.
To use an analogy: If you think of SNMP as a building management system, port 161 is like the main reception desk where staff (agents) wait to answer questions from management (managers), while port 162 is like the alarm system that automatically notifies security (managers) when something requires attention.
> 443 is the default port for HTTPS (secure web traffic)
> 514 is commonly used for Syslog (system logging)