Oracle SNMP Support Reference Guide
How SNMP Communications Are Performed
SNMP is based on connectionless communication between the framework and the managed nodes. Because most management information does not demand reliable delivery, SNMP packets are transmitted from one node to a well-known address of another node, but no verification of successful delivery is made. The penalty for the light-weight, connectionless SNMP communication is paid by the management applications, which need to verify that SNMP transactions get completed successfully within a reasonable amount of time. If SNMP packets get lost in the network, the application cancels the associated transaction and possibly re-initiates it.
The most popular SNMP implementation uses the User Datagram Protocol (UDP) over the Internet Protocol (IP), although implementations also exist over other protocols, such as Novell's Internetwork Packet Exchange (IPX) and Apple's AppleTalk.