Cisco Systems IE 2000 Using SNMP to Access MIB Variables , SNMP Notifications

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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 36 Configuring SNMP
Information About SNMP
Using SNMP to Access MIB Variables
An example of an NMS is the CiscoWorks network management software. CiscoWorks 2000 software
uses the switch MIB variables to set device variables and to poll devices on the network for specific
information. The results of a poll can be displayed as a graph and analyzed to troubleshoot
internetworking problems, increase network performance, verify the configuration of devices, monitor
traffic loads, and more.
As shown in Figure 36-1, the SNMP agent gathers data from the MIB. The agent can send traps, or
notification of certain events, to the SNMP manager, which receives and processes the traps. Traps alert
the SNMP manager to a condition on the network such as improper user authentication, restart s, link
status (up or down), MAC address tracking, and so forth. The SNMP agent also responds to MIB- related
queries sent by the SNMP manager in get-request, get-next-request, and set-request format.
Figure 36-1 SNMP Network
SNMP Notifications
SNMP allows the switch to send notifications to SNMP managers when particular events occur. SNMP
notifications can be sent as traps or inform requests. In command syntax, unless the re is an option in the
command to select either traps or informs, the keyword traps refers to either traps or informs, or both.
Use the snmp-server host command to specify whether to send SNMP notifications as traps or informs.
Note SNMPv1 does not support informs.
Traps are unreliable because the receiver does not send an acknowledgment when it receives a trap, and
the sender cannot determine if the trap was received. When an SNMP manager receives an inform
request, it acknowledges the message with an SNMP response protocol data unit (PDU). If the sender
does not receive a response, the inform request can be sent again. Because they can be resent, informs
are more likely than traps to reach their intended destination.
The characteristics that make informs more reliable than traps also consume more resources in the switch
and in the network. Unlike a trap, which is discar ded as soon as it is sent, an inform request is hel d in
memory until a response is received or the request times out. Traps are sent only once, but an inform
might be resent or retried several times. The retries increase traffic and contribute to a higher overhead
on the network. Therefore, traps and informs require a trade-off between reliability and resources. If it
is important that the SNMP manager receive every notification, use inform requests. If traffic on the
network or memory in the switch is a concern and notification is not required, use traps.
Get-request, Get-next-request,
Get-bulk, Set-request
Network device
Get-response, traps
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SNMP Manager
NMS
MIB
SNMP Agent