Operations Manager can detect network devices using the protocol SNMP. Detected devices are monitored to varying degrees, depending on the additional Management Packs used, and can be quite complex in nature. However, you have to start with device detection. Apart from cases of bad configuration, enabled network filtering or lack of SNMP protocol support, there are also cases when the lack of OIDs required during the detection process can even prevent the device from being detected. Of course, the absence of an OID is not the same as the absence of the value of a given OID.
To see what OIDs it is asking for Network Discovery It is enough to prepare an experimental setup containing, in addition to a running Operations Manager server, some SNMP-enabled network device (such as a network printer) or an SNMP simulator, which we must first "feed" with OID values.
When configuring the Network Discovery process, we specify which IP addresses are to be investigated:
Just before the wizard finishes, it's a good idea to run a program that captures network traffic. Such network traffic capture reveals that the following OIDs are queried at the beginning of the SNMP dialogue:
These OIDs are quite basic in nature and can be described as follows:
OID | Name | MIB | Comments |
1.3.6.1.2.1.1.1.0 | sysDescr | RFC1213-MIB | Description (string of printable characters) |
1.3.6.1.2.1.1.2.0 | sysObjectID | RFC1213-MIB | Identifier (OID) of the device type, used for identification by MP packets |
1.3.6.1.2.1.1.4.0 | sysContact | RFC1213-MIB | Contact to the device manager, e.g. email address |
1.3.6.1.2.1.1.5.0 | sysName | RFC1213-MIB | Typically, the name FQDN |
1.3.6.1.2.1.1.6.0 | sysLocation | RFC1213-MIB | Description of the device location |
Once the basic information that a device provides is obtained, a series of queries (SNMP get-next commands) for network interfaces follows. This information comes from an SNMP table called ifTable (MIB: RFC1213-MIB, root OID: .1.3.6.1.2.1.2.2).
An excerpt from the ifTable is shown below: