Connectivity Issues

OID cannot be found

If the object identifier (OID) is incorrectly formatted or truncated, connection to the object will fail as the OID cannot be found.

The OID is an object identifier consisting of integers separated by decimals indicating a node in a hierarchically organized namespace. The OID structure allows for precise referencing of a data attribute.

For a list of common item references, see Common SNMP Item References. You can also leverage commercially available SNMP browsers to find specific OID devices.

For connectivity failures, check the following:

• Is the first character the OID a decimal? A correctly formatted OID begins with a decimal.

• Is the last character of the OID a 0 (zero)? A final .0 digit indicates a leaf node, typical of most attributes. Some MIB browsers leave this off. Add .0 if connection fails.

  In the following example, using a commonly available MIB browser for illustration purposes, the MIB browser might display the OID in two places. Use the complete OID as the item reference, otherwise reads and writes will fail.

  

Device cannot be reached

In an instance where a well-known device cannot be reached, check the following configuration elements:

1. IP address

   In the Device Selector object, Station parameter, check that the IP address is correct. You can also check the IP address in a commercially available MIB browser. If you are using an MIB browser, the IP address must be the same as that configured in the SNMP Communication Driver configuration.

2. SNMP protocol version. Some devices do not support SNMP v1, and other devices do not support SNMP v2. Adjust the version number in the Device Selector object, Station parameter. You might also need to adjust the version number in your MIB browser to match that configured in the SNMP Communication Driver configuration.

3. Read community and write community if configured. By default, most devices have "public" configured as the read community. Adjust your configuration to test the read community with "public" if not already so configured. If you are using an MIB browser, the communities must match those configured in the SNMP Communication Driver configuration.

   

   Note: You can configure the Station parameter IP address only provided all other values are the defaults. However, we recommend explicitly providing the fully defined Station parameter. For example, SNMP v1 typically is the protocol version found in most PLCs. On Windows devices, however, SNMP v2 is more common.