Components

1. SNMP manager – System that controls (set) and monitors (get) network devices. This is usually a network management system (NMS).

2. SNMP agent – System that reports to the manager by responding to manager’s get request or by sending snmp trap to NMS.

3. Management information base (MIB) – Database of SNMP agents.

Version

1 – Uses community string to authenticate between manager and agent, community string is clear text.

2 – Adds getbulk request and inform message. No community string is required.

2c – Combines the goodness of version 1 and 2. In other words, version 2c uses community string to authenticate manager and agent like version 1, and has getbulk and inform message.

3 – Encryption is added for authentication, username and password is required for authenticating manager and agents. version 1 and 2c are clear text community string authentication without username.

Message types

Get – A request sent by manager to agent to request single variable value from agent.

GetNext – A request sent by manager to agent to request the next single variable from agent.

GetBulk – Debut in version 2. Sent by manager to agent to request multiple variable data within one single request.

Response – Sent by agent to manager to reply get and set request from manager.

Set – Sent by manager to agent to modify variable data.

Trap – Unsolicited message sent by agent to manager to report an event.

Inform – Sent among managers to exchange/share MIB data.

Service ports

161 UDP – SNMP message: Get, GetNext, GetResponse, GetBulk, Set, Inform

162 UDP – SNMP trap only. Firewall administrator please note that this udp port is unsolicited.