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Description |
SNMP facilitates communication between a managed device (an SNMP agent, e.g. a router), and an SNMP manager or management application (used by a network manager). Communication is via SNMP protocol data units (PDUs), and essentially four kinds of operations are permitted between managers and agents. These are :
This section provides a detailed description of the SNMP Main Screen layout. It provides the user step-by-step instructions to use each of the Main Screen components.
The SNMP Main Screen is as shown in Figure 1.
The following are the Main Screen components :
Community - is a grouping
of agents and managers. There can be many such communities. Each community
is represented by a name. In Figure 1, publicis
the community name(default and widely used) which represents a set of
managers and agents.
Object - An Object is a network resource managed by the network manager. Following is a brief description of a sample of Objects :
Refer to Figure 2 for a drop-down list of Objects.
To Create New Objects
To Delete an Object
To Modify an Existing Object
Note
: The Objects are stored in an Object file which must have a .snm
extension. While Adding/Deleting/Editing an Object, when the OK button is
selected, if the Object file has not been specified previously (using the
property sheet for the component), the Object File dialog boxas
shown in Figure 4 appears.
An Agent is a processing entity which belongs to one or more communities .
To Create a New Agent
To Delete an Agent
To Modify an Existing Agent
Note
: The Agents are stored in an Agents file which must have a .snm
extension. While Adding/Deleting/Editing an Agent, when the OK
button is selected, if the Agent file has not been specified previously
(using the property sheet for the component), the Agents File dialog box
as shown in Figure 6 appears.
The Main Screen contains four buttons: GetRequest, GetNextRequest, SetRequest and Clear Log button for the main operations.
GetRequest gets the status of the specified Object from the specified Agent. e.g. to know how long the Agent has been up and running.
GetNextRequest - This button is used to get the value of an Object which is lexicographically next in the Management Information Base in the Agent. e.g. the button could be used to get the entries of a table-entry one-by-one. If the System table contains SysDescr, SysObjectID, SysUpTime, SysContact, etc., each time GetNext button of Response - GetNextRequest dialog box is clicked the respective details are displayed. An entire table can be traversed by using GetNextRequest button.
When the GetNextRequest button is clicked the Response - GetNextRequest dialog box as shown in Figure 7 appears. The Response - GetNextRequest dialog box contains the response area, which displays the requested information. When the OK button is clicked the Response - GetNextRequest dialog box is closed. When GetNext button is clicked the lexicographically next Object in the MIB is retrieved and displayed.
SetRequest can be used to change an existing Objects value, e.g. to change the system name :
Clear Log can be used to
clear the contents of the response area.
Response area displays all the requested information. The Response area also logs status information in the form of errors received from an Agent. The Response area can be cleared by clicking the Clear Log button.
When the request is valid, the response is as shown in Figure 9.
When the request is invalid the response is as shown in Figure 10.
If the SNMP agent sends an unknown object identifier (not present in the Objects file), then the GetNext operation fails the message as shown in Figure 11 is displayed.
The SNMP Agent uses traps to report extraordinary events to the Network Manager. It is an asynchronous notification. When a Trap is received a Trap Response dialog box as shown in Figure 12 appears.
Enterprise OID - It contains the type of object generating the trap
Sending Agent - Value of the agents network address
Generic Trap - Contains information about certain unusual events, for e.g. "Generic Trap : Authentication failure" means that the manager is not authenticated to access the Agent
Specific Trap - Enterprise specific trap which is specific to set of Agents and Managers
Time Stamp - The value of the SystemUpTime on Agent side
Some other information about the Trap
Information OID - The Object Identifier carrying the information
Information Value - The Information OIDs
Value