Cisco IE 4000, Software Configuration Manual

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531
Configuring SNMP
Information About SNMP
Figure 73 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 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.
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 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 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.
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 53 on page 531 to assign an ifIndex value to an interface.
Note: The switch might not use sequential values within a range.
Get-request, Get-next-request,
Get-bulk, Set-request
Network device
Get-response, traps
43581
SNMP Manager
NMS
MIB
SNMP Agent
Table 53 ifIndex MIB Object Values
Interface Type ifIndex Range
SVI 1–4999
EtherChannel 5001–5048
Physical (such as Gigabit Ethernet or SFP-module interfaces) based on type
and port numbers 10000–14500
Null 10501
Loopback and Tunnel 24567 +