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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, and 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, and 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.
Management Information Base
Agents store information in a hierarchical database called the Structure of
Management Information (SMI). The SMI resembles a file system. Information is
stored in individual files that are hierarchically arranged in the database. The individual
files that store the information are known as Management Information Bases (MIBs).
Each MIB contains nodes of information that are stored in a tree structure. Information
branches down from a root node to individual leaves in the tree, and the individual
leaves comprise the information that is queried by managers for a given MIB. The
nodes of information are identified by an object ID (OID). The OID is a dotted integer
identifier (1.3.6.1.2.1.2, for instance) or a subtree name (such as interfaces) that
corresponds to an indivisible piece of information in the MIB.
MIBs are either standard or enterprise-specific. Standard MIBs are 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 Web site, http://www.ietf.org, and
compile them into your NMS, if necessary.
For a list of standard and enterprise-specific supported MIBS, see the JUNOS Network
Management Configuration Guide.
Enterprise-specific MIBs are 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.
To download enterprise MIBs for a Services Router, go to
http://www.juniper.net/techpubs/software/index_mibs.html.
SNMP Communities
You can grant access to only specific SNMP managers for particular SNMP agents by
creating SNMP communities. The community is assigned a name that is unique on
the host. All SNMP requests that are sent to the agent must be configured with the
same community name. When multiple agents are configured on a particular host,
the community name process ensures that SNMP requests are sorted to only those
agents configured to handle the requests.
Additionally, communities allow you to specify one or more addresses or address
prefixes to which you want to either allow or deny access. By specifying a list of
48 ■ SNMP Architecture
J-series™ Services Router Administration Guide