SNMP Architecture and SNMP MIBs Overview

SNMP Architecture

A typical SNMP implementation includes three components:

Network Management System (NMS)—A combination of hardware (devices) and software (the SNMP manager) used to monitor and administer a network. The manager polls the devices on your network as you specify for information about network connectivity, activity, and events.
Managed device—A managed device (also called a network element) is any device on a network managed by the NMS. Routers and switches are common examples of managed devices.
SNMP agent—The SNMP agent is the SNMP process that resides on the managed device and communicates with the NMS. The SNMP agent exchanges network management information with the SNMP manager software running on an NMS, or host. The agent responds to requests for information and actions from the manager. The agent also controls access to the agent’s MIB, the collection of objects that can be viewed or changed by the SNMP manager.

This topic contains the following sections:

SNMP MIBs
SNMP Manager and Agent Authentication and Communication
SNMP Traps and Informs

SNMP MIBs

You can store SNMP data in a highly structured, hierarchical format known as a Management Information Base (MIB). A MIB defines managed objects in a network device.

The MIB structure is based on a tree structure and defines a grouping of objects into related sets. Each object in the MIB is associated with an object identifier (OID), which names the object. The “leaf” in the tree structure is the actual managed object instance, which represents a resource, event, or activity that occurs in your network device.

MIBs are either standard or enterprise-specific. For more information, see Table 1.

Table 1: Standard and Enterprise-specific MIBs
Standard MIBs	Enterprise-specific MIBs
Created by the Internet Engineering Task Force (IETF) and documented in various RFCs. Depending on the vendor, many standard MIBs are delivered with the NMS software. You can also download the standard MIBs from the IETF website, www.ietf.org, and compile them into your NMS, if necessary.	Developed and supported by a specific equipment manufacturer. If your network contains devices that have enterprise-specific MIBs, you must obtain them from the manufacturer and compile them into your network management software.
For a list of standard supported MIBs, see Standard SNMP MIBs Supported by Junos OS.	For a list of Juniper Networks enterprise-specific supported MIBs, see Enterprise-Specific SNMP MIBs Supported by Junos OS.

SNMP Manager and Agent Authentication and Communication

SNMP uses a basic form of authentication called community strings to control access between a manager and remote agents. Community strings are administrative names used to group collections of devices (and the agents running on them) into common management domains. If a manager and an agent share the same community, they can talk to one another. Many people associate SNMP community strings with passwords and keys because the jobs they do are similar. As a result, SNMP communities are traditionally referred to as strings.

Communication between the agent and the manager occurs in one of the following forms:

Get, GetBulk, and GetNext requests—The manager requests information from the agent; the agent returns the information in a Get response message.
Set requests—The manager changes the value of a MIB object controlled by the agent; the agent indicates status in a Set response message.
Traps notification—The agent sends traps to notify the manager of significant events that occur on the network device.

SNMP Traps and Informs

Routers can send notifications to SNMP managers when significant events occur on a network device, most often errors or failures. You can send SNMP notifications as traps or inform requests.

SNMP traps are unconfirmed notifications and SNMP informs are confirmed notifications.

SNMP traps are either standard or enterprise-specific. For more information, see Table 2.

Table 2: Standard and Enterprise-specific Traps
Standard Traps	Enterprise-specific Traps
Created by the IETF and documented in various RFCs. The standard traps are compiled into the network management software. You can also download the standard traps from the IETF website, www.ietf.org.	Developed and supported by a specific equipment manufacturer. If your network contains devices that have enterprise-specific traps, you must obtain them from the manufacturer and compile them into your network management software.
For more information about standard traps supported by the Junos OS, see Standard SNMP Traps Supported on Devices Running Junos OS.	For more information about enterprise-specific traps supported by the Junos OS, see Enterprise-Specific SNMP Traps Supported by Junos OS. For information about system logging severity levels for SNMP traps, see Understand SNMP Implementation in Junos OS.

With traps, the receiver does not send any acknowledgment when it receives a trap, and the sender cannot determine if the trap was received. To increase reliability, SNMP informs are supported in SNMPv3. An SNMP manager that receives an inform acknowledges the message with a response. For information about SNMP informs, see Configure SNMP Informs.