Setting Common Parameters

The parameters, such as host, port, and community, can be set in the MibBrowser's main window. Applications use the host name or the IP address of the device to communicate with the agent of the device in a particular port number. This remote port number is the UDP port 161. By default, all the SNMP request messages are received in this port.

SNMP mandates that the SNMP agents should accept request messages only if the community string in the message matches its community name. Therefore, the management application should always communicate with the agents along with the associated community name. The default SNMP community names are "public" for read-only (GET) operations and "private" for read-write (SET) operations. The management applications should have provision to include the community names in their request messages. Community strings are used to authenticate SNMP PDUs. Since SNMP packets are usually sent using UDP packets, there is no connection established as in the case of TCP/IP packets. Therefore, when a UDP packet is sent to the agent, the agent validates the packet. It accepts and sends a response if the community string of the PDU is equal to that set on the agent, or else drops the packet. The agent does not change the community name after communicating. Applications typically communicate with the SNMP agents by specifying the community name of the agent.

The default community string is "public" and the default Write Community string is null. When Write Community is null, community itself is used for SET operations. Therefore, applications should explicitly set the Write Community, before they can use it for SET operations.

The other parameters are set in the General tab of the MibBrowser Settings frame. The general settings include the basic protocol options related to SNMP, the display options, and a section for encoding field. The image depicted below shows the General tab of the MibBrowser Settings dialog box.

The various protocol-related options to SNMP are listed in the table below.

The Validate Broadcast Address check box enables you to check the validity of the broadcast address provided. You need to provide the Netmask address to validate the broadcast address. A Netmask is a string of 0's and 1's that hides the network part of the IP address and allows only the host ID to remain.

In the v3 Options section, Context Name and the ContextID are to be provided as additional parameters for an SNMPv3 request. An SNMP context name is a collection of management information accessible by an SNMP entity. An item of management information may exist in more than one context. An SNMP entity potentially has access to many contexts. In other words, if a management information has been defined under certain context by an SNMPv3 entity, any management application can access that information by giving that context name. The ContextID uniquely identifies an SNMP entity that may recognize an instance of a context with a particular context name within an administrative domain.

The next section is the v3Settings section. The following are the security-related parameters for accessing the SNMPv3 agents. You can add, modify, and delete users by clicking the Add, Modify, Delete buttons.

If the security level is "NoAuthNoPriv", no additional parameters are required. If the security level is "AuthNoPriv", the parameters AuthProtocol and AuthPassword are set. If the user security level is "AuthPriv", the privacy password needs to be set in addition to the other parameters.

The v3Settings section has an option for storing the v3 table entries. The v3 table entries can be stored in:

• A serialized file

• A database

Storing Table Entries in a Serialized File

To enable serialization of v3 table entries, select the Save v3 Settings to File option. If this option is selected, the user information is stored in the serialized files namely UserEntry.ser and EngineEntry.ser. When MibBrowser is invoked the next time, the serialized files are de-serialized and the v3 table is updated. The advantage of storing table entries in serialized files is that the operation is faster.

Storing Table Entries in a Database

To store v3 table entries in a database, select the Save v3 Settings to Database option. To use this, the database connection has to be established. Clicking the "Database Settings" button displays the Database Parameters dialog box. The image of the dialog box that appears is given below.

Enter the necessary database parameters in this dialog box, and click the OK button. If the database connection is established successfully, all the user information entered is saved in the database. When the MibBrowser is invoked the next time, v3 details are restored and the v3 table is updated.

The advantages of storing v3 table entries in a database are:

• Scalability - Any number of entries can be maintained in the database.

• Accessibility - All the authenticated users of the database can access the entries.

The last section is the field entry section in which the corresponding fields in the v3 table are displayed for data entry. The various buttons available in the field entry section are Add, Modify, and Delete.

To add an entry, enter the required parameters in the respective fields and click the Add Entry button. Based on the parameters and the security level, Discovery and Time Synchronization are done and USM Table is updated and listed in the v3 table.

To modify an entry, select the entry in the v3 table, modify the required fields, and click the Modify button. Time Synchronization is done and the USM table is updated and listed in the v3 table.

To delete an entry in the v3 table, select the entry in the v3 table and click the Delete button. The entry is removed from the USM table.