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clients, you can control exactly which SNMP managers have access to a particular
agent.
SNMP Traps
The get and set commands that SNMP uses are useful for querying hosts within a
network. However, the commands do not provide a means by which events can
trigger a notification. For instance, if a link fails, the health of the link is unknown
until an SNMP manager next queries that agent.
SNMP traps are unsolicited notifications that are triggered by events on the host.
When you configure a trap, you specify the types of events that can trigger trap
messages, and you configure a set of targets to receive the generated messages.
SNMP traps enable an agent to notify a network management system (NMS) of
significant events. You can configure an event policy action that uses system log
messages to initiate traps for events. The traps enable an SNMP trap-based application
to be notified when an important event occurs. You can convert any system log
message that has no corresponding traps into a trap. This feature helps you to use
NMS traps rather than system log messages to monitor the network.
Spoofing SNMP Traps
You can use the request snmp spoof-trap operational mode command to mimic SNMP
trap behavior. The contents of the traps (the values and instances of the objects
carried in the trap) can be specified on the command line or they can be spoofed
automatically. This feature is useful if you want to trigger SNMP traps from routers
and ensure they are processed correctly within your existing network management
infrastructure, but find it difficult to simulate the error conditions that trigger many
of the traps on the router. For more information, see the JUNOS System Basics and
Services Command Reference.
SNMP Health Monitor
The SNMP health monitor feature uses existing SNMP remote monitoring (RMON)
alarms and traps to monitor a select set of Services Router characteristics (object
instances) like the CPU usage, memory usage, and file system usage. The health
monitor feature also monitors the CPU usage of the J-series Services Router forwarding
process (also called a daemon)—for example, the chassis process and forwarding
process microkernel. You can configure the SNMP health monitor options rising
threshold, falling threshold, and interval using the SNMP Quick Configuration page.
A threshold is a test of some SNMP variable against some value, with a report when
the threshold value is exceeded. The rising threshold is the upper threshold for a
monitored variable. When the current sampled value is greater than or equal to this
threshold, and the value at the last sampling interval is less than this threshold, the
SNMP health monitor generates an alarm. After the rising alarm, the health monitor
cannot generate another alarm until the sampled value falls below the rising threshold
and reaches the falling threshold.
The falling threshold is the lower threshold for the monitored variable. When the
current sampled value is less than or equal to this threshold, and the value at the last
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Chapter 3: Configuring SNMP for Network Management