356 V6100 and V7122 User Guide Trap - A message generated asynchronously by network devices. It is an unsolicitedmessage from an agent to the manager.Each of these message types fulfills a particular requirement of Network Managers: Get Request - Specific values can be fetched via the ‘get’ request to determine theperformance and state of the device. Typically, many different values and parameterscan be determined via SNMP without the overhead associated with logging into thedevice, or establishing a TCP connection with the device. Get Next Request - Enables the SNMP standard network managers to ‘walk’ through allSNMP values of a device (via the ‘get-next’ request) to determine all names and valuesthat an operant device supports. This is accomplished by beginning with the first SNMPobject to be fetched, fetching the next name with a ‘get-next’, and repeating thisoperation. Set Request - The SNMP standard provides a method of effecting an action associatedwith a device (via the ‘set’ request) to accomplish activities such as disabling interfaces,disconnecting users, clearing registers, etc. This provides a way of configuring andcontrolling network devices via SNMP. Trap Message - The SNMP standard furnishes a mechanism by which devices can‘reach out’ to a Network Manager on their own (via a ‘trap’ message) to notify or alert themanager of a problem with the device. This typically requires each device on the networkto be configured to issue SNMP traps to one or more network devices that are awaitingthese traps.The above message types are all encoded into messages referred to as Protocol Data Units(PDUs) that are interchanged between SNMP devices.SNMP MIB ObjectsThe SNMP MIB is arranged in a tree-structured fashion, similar in many ways to a diskdirectory structure of files. The top level SNMP branch begins with the ISO ‘internet’directory, which contains four main branches: The ‘mgmt’ SNMP branch - Contains the standard SNMP objects usually supported (atleast in part) by all network devices. The ‘private’ SNMP branch - Contains those ‘extended’ SNMP objects defined bynetwork equipment vendors. The ‘experimental’ and ‘directory’ SNMP branches - Also defined within the ‘internet’ rootdirectory, these branches are usually devoid of any meaningful data or objects.
