About Snmp; Configuring The Master Agent - Red Hat DIRECTORY SERVER 7.1 - ADMINISTRATOR Administrator's Manual

About SNMP

About SNMP
SNMP is a protocol used to exchange data about network activity. With SNMP,
data travels between a managed device and a network management application
(NMS) where users remotely manage the network. A managed device is anything
that runs SNMP, such as hosts, routers, and your Directory Server. An NMS is
usually a powerful workstation with one or more network management
applications installed. A network management application graphically shows
information about managed devices, whether a device is up or down, which and
how many error messages were received, and so on.
Information is transferred between the NMS and the managed device through the
use of two types of agents: the subagent and the master agent. The subagent
gathers information about the managed device and passes the information to the
master agent. Directory Server has a subagent. The master agent exchanges
information between the various subagents and the NMS. The master agent runs
on the same host machine as the subagents it talks to.
You can have multiple subagents installed on a host machine. For example, if you
have Directory Server and a messaging server all installed on the same host, the
subagents for both of these servers communicate with the same master agent.
Values for SNMP attributes, or variables, that can be queried are kept on the
managed device and reported to the NMS as necessary. Each variable is known as
a managed object, which is anything the agent can access and send to the NMS.
All managed objects are defined in a management information base (MIB), which
is a database with a tree-like hierarchy. The top level of the hierarchy contains the
most general information about the network. Each branch underneath is more
specific and deals with separate network areas.
SNMP exchanges network information in the form of protocol data unit (PDUs).
PDUs contain information about variables stored on the managed device. These
variables, also known as managed objects, have values and titles that are reported
to the NMS as necessary. Communication between an NMS and a managed
device takes place either by the NMS sending updates or requesting information
or by the managed object sending a notice or warning, called a trap, when a server
shuts down or starts up.

Configuring the Master Agent

To use the subagent, you must have a Net-SNMP v5.21 master agent running on
your system. You can download the Net-SNMP Master Agent from the
Net-SNMP website (
470 Red Hat Directory Server Administrator's Guide • May 2005
http://www.net-snmp.org
).