You can quickly and easily enable SNMP on a Sonicwall for monitoring purposes. The instructions below are for SonicOS Enhanced, and has been tested on a NSA 2600 (although configuration should be similar on other models).
Log on to the Sonicwall through the web interface.
In the menu on the left, navigate to System → SNMP.
Check the Enable SNMP check box and click Accept.
Click the Configure button and verify/change the Get Community Name. By default, it is set to public. If you made changes, click OK.
By default, SNMP does not listen on any interface, so what's left is to enable it on one or more interfaces, depending on which interfaces, SNMP is required. Navigate to Network → Interfaces. For each of the interfaces where SNMP needs to be accessible on, click the Configure () icon.
Check the SNMP checkbox, and click OK.
Note that this also automatically creates the proper firewall rules.