Co-Existence

In a typical deployment scenario, the management applications and applets are required to communicate with SNMP agents of different versions. Also, they are required to communicate with multi-lingual agents. i.e. SNMP agents which supports all the three SNMP versions.

The multi-lingual SNMP agents support multiple SNMP message versions and co-exist with entities that support only a single SNMP message version. Therefore, management applications with only SNMPv1 or v2c support can communicate with SNMPv3 agents. This is called co-existence support and it is defined in RFC 2576. SNMPv3 agent entities with co-existence support are expected to implement the SNMP-COMMUNITY-MIB. This MIB contains objects for mapping between community strings and version-independent SNMP message parameters.

In a multi-lingual environment, the SNMPv3 agent with co-existence support is configured to respond to requests sent by all managers, irrespective of their versions. When the SNMPv3 agent receives a request of type v1/v2c, it checks for the co-existence support. If supported, it authenticates the request and sends the response in v1/v2c type.

Authenticating SNMPv1/v2c Requests

SNMPv1/v2c management applications and applets communicating to SNMPv3 agent with co-existence support should use the proper community string in the request messages. The SNMPv3 agent with co-existence support uses the community string of SNMPv1/v2c to perform the authentication.

The community string of the manager applications should match with the entry found in SnmpCommunityTable, SnmpTargetAddrTable, and SnmpTargetAddrExtTable maintained by the agent. These tables are initialised by the agent. After the authentication, the request is processed as SNMPv3 request by the agent. While responding, it is converted to v1/v2c response and sent back to the manager.

Remote Configuration

The community table information in the agent can be configured by the SNMPv3 manager. Following are the steps to configure the agent from the manager.

• Load the community MIB that contains all the tables to configure the community details.

• Add an entry from the manager to SnmpCommunityTable, SnmpTargetAddrTable, and SnmpTargetAddrExtTable of the community MIB. This can be done by any of the following options.

• Send SET requests for adding entries to the table.

• Perform a multi variable set.

• Using the SNMP TablePanel of the MibBrowser.

This is similar to adding a row to a table as explained in the Table Handling in Applications section.