Four types of SNMP messages are defined:
- A
get request returns the value of a named
object. Specific values can be fetched to determine the performance and state
of the device, without logging into the device or establishing a TCP connection
with the device.
- A
get-next request returns the next name
(and value) of the next object supported by a network device is given a valid
SNMP name. This request allows network managers to review all SNMP values of a
device to determine all names and values that an operant device supports.
- A
set request sets a named object to a
specific value. This request provides a method of configuring and controlling
network devices through SNMP to accomplish activities such as disabling
interfaces, disconnecting users, and clearing registers.
- A
trap message is generated asynchronously
by network devices, which can notify a network manager of a problem apart from
any polling of the device. This typically requires each device on the network
to be configured to issue SNMP traps to one or more network devices that are
awaiting these traps. The four message types are all encoded into messages
referred to as Protocol Data Units (PDUs), which are interchanged with SNMP
devices.
