SNMP messages

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

SNMP messages

When simple network management protocol (SNMP) management programs send requests to a network device, the agent software on that device receives the requests and retrieves information from MIBs. The agent then sends the requested information back to the initiating SNMP management program. To perform these tasks, the agent uses the following message types:

SNMP Message	Description
Get	The basic SNMP request message. Sent by an SNMP management system, it requests information about a single MIB entry on an SNMP agent. For example, the amount of free drive space.
Get-next	An extended type of request message that can be used to browse the entire tree of management objects. When processing a Get-next request for a particular object, the agent returns the identity and value of the object which logically follows the object from the request. The Get-next request is useful for dynamic tables, such as an internal IP route table.
Set	If write access is permitted, this message can be used to send and assign an updated MIB value to the agent.
Getbulk	Requests that the data transferred by the host agent be as large as possible within given restraints of message size. This minimizes the number of protocol exchanges required to retrieve a large amount of management information. The maximum message size should not be larger than the path maximum transmission unit (MTU), the largest frame size allowed for a single frame on your network, or fragmentation can occur.
Trap	An unsolicited message sent by an SNMP agent to an SNMP management system when the agent detects that a certain type of event has occurred locally on the managed host. The SNMP management console that receives a trap message is known as a trap destination. For example, a trap message might be sent on a system restart event.

Four of these message types are simple request-reply protocols where SNMP uses User Datagram Protocol (UDP). This means that a request from the management system might not arrive at the agent, and the agent's reply might not make it back to the management system. Because SNMP is a connectionless network protocol, SNMP messages are not guaranteed to arrive at their destinations.

You can use Internet Protocol security (IPSec) to secure traffic between SNMP management systems and agents. For more information, see Securing SNMP messages with IPSec.