Management Information Base Database
Network management can be passive or active. Passive network management involves the collection of statistical data to profile the network activity of each host. Every variable in the Internet-standard Management Information Base (MIB) has a value that can be queried and used for this purpose.
Active network management uses a subset of MIB variables that are designated read-write. When an Simple Network Management Protocol (SNMP) agent is instructed to modify the value of one of these variables, an action is taken on the agent's host as a side effect. For example, a request to set the ifAdminStatus.3 variable to the value of 2 has the side effect of disabling the network adapter card whose ifIndex variable is set to a value of 3.
Requests to read or change variable values are generated by manager applications. Three kinds of requests exist:
| Item | Description |
|---|---|
| get | Returns the value of the specified variable instance. |
| get-next | Returns the value of the variable instance following the specified instance, a get-next request. |
| set | Modifies the value of the specified variable instance. |
Requests are encoded according to the ISO ASN.1 CCITT standard for data representation (ISO document DIS 8825). Each get request contains a list of pairs of variable instances and variable values called the variable binding list. The variable values are empty when the request is transmitted. The values are filled in by the receiving agent and the entire binding list is copied into a response packet for transmission back to the monitor. If the request is a set request, the request packet also contains a list of variable values. These values are copied into the binding list when the response is generated. If an error occurs, the agent immediately stops processing the request packet, copies the partially processed binding list into the response packet, and transmits it with an error code and the index of the binding that caused the error.