Messages

Message Class	Description	Messages
Read	Messages sent be the NMS to read information from the managed devices. (ie. What's your current CPU usage %?)	GET GetNext GetBulk
Write	Messages sent by the NMS to change information on the managed devices. (ie. change an IP address)	Set
Notification	Messages sent by the managed devices to alert the NMS of particular event.	Trap Inform
Response	Messages sent in response to a previous message/request.	Response

Read

• Get

  • A request sent from the manager to the agent to retrieve the value of a variable (OID), or multiple variables. The agent will send a Response with the current value of each variable.

• GetNext

  • A request sent from the manager to the agent to discover the available variables in the MIB.

• GetBulk

  • A more efficient version of the GetNext message (introduced in SNMPv2).

Write

• Set

  • A request sent from the manager to the agent to change the value of one or more variables. The agent will send a Response message with the new values.

Notification

• Trap

  • A notification sent from the agent to the manager. The manager does not send a Response message to acknowledge that it received the Trap, so these messages are 'unreliable'.

• Inform

  • A notification message that is acknowledged with a Response message.

  • Originally used for communications between managers, but later updates allow agents to send Inform messages to managers, too.

SNMP Agent -> UDP port 161

SNMP Manager -> UDP port 162