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To use this program to manage an object, the user must first select the object. The screen shot in Exhibit 2 shows that the Ethernet probe at IP address 198.78.46.41 was selected. Exhibit 3 represents the values of object identifiers in the system group of the Ethernet probe. This system group contains seven object identifiers.
Tools such as SimpleView allow a network administrator to retrieve basic SNMP or RMON information. Because there are more than 1,000 vendors that are assigned subtrees under the private enterprises node in the global naming tree (which would make their support difficult, if not impossible, to accomplish via a menu that identifies the name of each object identifier), the sample tool uses a series of SNMP commands to access information in managed objects developed by different vendors.
The Get, Get Next, and Set entries shown in the Manage menu in Exhibit 2 represent three SNMP commands. The Get command is used to request the values of one or more Management Information Base variables. The Get Next command is used to read values sequentially. By selecting the Get Next command, the user can either go directly to a specific tree address (by typing in the address) or, if they do not know the address, browse predefined portions of the global naming tree that locate commonly used objects.
The third SNMP command supported, the Set command, allows the network administrator to update one or more MIB values.
Exhibit 2. Sample of SimpleView Screen.
Exhibit 3. The System Group
Object Identifier | Location | Description |
---|---|---|
sysDescr | 1.3.6.1.2.1.1.1 | A text description about the device. |
sysObjectID | 1.3.6.1.2.1.1.2 | An identifier assigned to the device by its vendor. |
sysUpTime | 1.3.6.1.2.1.1.3 | The time in hundredths of a second since the system was last reinitialized. |
SysContact | 1.3.6.1.2.1.1.4 | The person responsible for the device. |
SysName | 1.3.6.1.2.1.1.5 | An administratively assigned name. |
SysLocation | 1.3.6.1.2.1.1.6 | The physical location of the device. |
SysServices | 1.3.6.1.2.1.1.7 | A coded number that indicates the layer in the ISO model at which the device performs services. |
Notes:
Although the system group must be included in every managed device, the setting of some objects in the system group will depend on the user of the device. The sysContact identifier could be set by the organization using the device. Some organizations will set this identifier while others may elect to leave it at its default Not Set string value.
The location is the object identification number. If the object (e.g., sysUpTime) is a one-of-a-kind object, tools such as SimpleView automatically append a zero (0) to the path address.
Exhibit 4. SimpleView Trap Log Window.
Once a command is executed, SimpleView displays the results in the programs Trap Log. Exhibit 4 shows an entry that occurred as a result of the execution of the Get Next command using a tree address to retrieve the value of the object. Although the time is displayed in hundredths of a second, such tools can also convert that time into days, hours, minutes, and seconds. By issuing several Get Next Commands, the values for sysName and subsequent objects in the group would also be displayed in the Trap Log. Thus, once the user knows an address they can walk through a path using a series of Get Next commands to retrieve subsequent object values.
The global naming tree provides a mechanism for labeling and identifying objects while eliminating the possibility of addressing conflicts. By understanding how to use path addresses in conjunction with object identifier information, network administrators can manage any device that complies with the global naming tree method for identifying objects. The easiest way to retrieve information from proprietary products developed to comply with the global naming tree is for the user to refer to the device user manual to determine the path to different managed objects in the device.
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