| 12.7 |  | SNMP |
| 12.7.1 |  | SNMP overview |

| SNMP overview This section explains how to use SNMP to monitor the PIX Security Appliance and how to permit SNMP to pass through the PIX Security Appliance for the management and monitoring of other network devices. SNMP is an application-layer protocol designed to facilitate the exchange of management information between network devices. By using SNMP-transported data, such as packets per second and network error rates, network administrators can remotely manage and monitor network devices. As shown in Figure , devices managed by SNMP send information to a management server from which an administrator manages and monitors the device .

SNMP can be used to monitor system events on the PIX Security Appliance. For security reasons, however, information on the PIX Security Appliance cannot be changed with SNMP. Administrators can also enable SMTP through the PIX Security Appliance so that any device can be managed and monitored by a management server on a PIX Security Appliance interface other than that on which it resides.

SNMP is a request and response protocol. The following SNMP operations rely on Management Information Bases (MIBs), which are explained in the next section:

- Get enables the Network Management Station (NMS) to retrieve an object instance from an agent.
- GetNext enables the NMS to retrieve the next object instance from a table or list within an agent.
- GetBulk is used in place of the GetNext operation to simplify acquiring large amounts of related information.
- Set enables the NMS to set values for object instances within an agent.
- Trap is used by the agent to asynchronously inform the NMS of an event.
- Inform enables one NMS to send trap information to another.

Cisco SNMP agents communicate successfully with all SNMP-compliant NMSs, including the Sun Microsystems SunNet Manager, the IBM NetView/6000, and the Hewlett-Packard OpenView.

SNMP key terms
In order to understand SNMP support in the PIX Security Appliance, it is important to understand the SNMP-related terminology discussed in Figure .

SNMP example
In Figure , the NMS uses a Get operation to request management information contained in an agent on host 172.18.0.15. Within the Get request, the NMS includes a complete Object Identifier (OID) so that the agent knows exactly what is being sought. The response from the agent contains a variable binding containing the same OID and the data associated with it. The NMS then uses a Set request to tell the agent to change a piece of information. In an unrelated communication, host 172.16.0.2 sends a trap to the NMS because some urgent condition has occurred.