Which command is most effective for determining SNMP discovery issues from the backend?

The command that is most effective for determining SNMP discovery issues from the backend is snmpwalk. This command is crucial because it allows for the retrieval of a large amount of information from an SNMP-enabled device. By querying the SNMP agent on the device, snmpwalk can provide a comprehensive list of available SNMP data, including object identifiers (OIDs) and the values they hold.

Using snmpwalk, an administrator can verify if the SNMP service is functioning correctly and whether it is accessible. If there are issues with SNMP discovery, such as incorrect community strings, firewalls blocking SNMP traffic, or misconfigured SNMP settings, snmpwalk will typically fail to retrieve the expected data, thereby highlighting potential issues effectively.

In contrast, while the other options like phSNMPTest and snmptest can be useful for specific SNMP testing scenarios, they do not provide the same level of extensive data retrieval as snmpwalk. Furthermore, ssh is unrelated to SNMP and is mainly used for secure shell access to devices, making it unsuitable for SNMP-related diagnostics. Thus, snmpwalk is the most reliable choice for troubleshooting SNMP discovery problems.