Snmp Notifications; Snmp Ifindex Mib Object Values - Cisco Catalyst 2975 Software Configuration Manual

Chapter 30 Configuring SNMP
Figure 30-1
SNMP Manager
For information on supported MIBs and how to access them, see

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 there 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.
SNMPv1 does not support informs.
Note
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 re-sent, 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 discarded as soon as it is sent, an inform request is held in
memory until a response is received or the request times out. Traps are sent only once, but an inform
might be re-sent 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.

SNMP ifIndex MIB Object Values

In an NMS, the IF-MIB generates and assigns an interface index (ifIndex) object value that is a unique
number greater than zero to identify a physical or a logical interface. When the switch reboots or the
switch software is upgraded, the switch uses this same value for the interface. For example, if the switch
assigns a port 2 an ifIndex value of 10003, this value is the same after the switch reboots.
The switch uses one of the values in
Table 30-3
Interface Type
SVI
EtherChannel
Loopback
OL-19720-02
SNMP Network
Get-request, Get-next-request,
NMS
Get-bulk, Set-request
Get-response, traps
ifIndex Values
1
Network device
SNMP Agent
Table 30-3 to assign an ifIndex value to an interface:
Catalyst 2975 Switch Software Configuration Guide
Understanding SNMP
MIB
Appendix A, "Supported MIBs."
ifIndex Range
1–4999
5000–5012
5013–5077
30-5