Snmp Notifications - Cisco NCS 6000 Series Configuration Manual

Implementing SNMP
objects, defined in MIB modules. MIB modules are written in the SNMP MIB module language, as defined
in STD 58, RFC 2578, RFC 2579, and RFC 2580. Note that individual MIB modules are also referred to as
MIBs; for example, the Interfaces Group MIB (IF-MIB) is a MIB module within the MIB on your system.
The SNMP agent contains MIB variables whose values the SNMP manager can request or change through
Get or Set operations. A manager can get a value from an agent or store a value into that agent. The agent
gathers data from the MIB, the repository for information about device parameters and network data. The
agent can also respond to manager requests to get or set data.
Figure 1: Communication Between an SNMP Agent and Manager, on page 63
relationship between the SNMP manager and agent. A manager can send the agent requests to get and set
MIB values. The agent can respond to these requests. Independent of this interaction, the agent can send
unsolicited notifications (traps) to the manager to notify the manager of network conditions.
Figure 1: Communication Between an SNMP Agent and Manager

SNMP Notifications

A key feature of SNMP is the ability to generate notifications from an SNMP agent. These notifications do
not require that requests be sent from the SNMP manager. On Cisco IOS XR software, unsolicited
(asynchronous) notifications can be generated only as traps. Traps are messages alerting the SNMP manager
to a condition on the network. Notifications can indicate improper user authentication, restarts, the closing of
a connection, loss of connection to a neighbor router, or other significant events.
Note Inform requests (inform operations) are supported in Cisco IOS XR software from release 4.1 onwards. For more info
http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r5-3/sysman/command/reference/b-sysman-cr53x
Traps are less reliable than informs because the receiver does not send any acknowledgment when it receives
a trap. The sender cannot determine if the trap was received. An SNMP manager that receives an inform
request acknowledges the message with an SNMP response protocol data unit (PDU). If the manager does
not receive an inform request, it does not send a response. If the sender never receives a response, the inform
request can be sent again. Thus, informs are more likely to reach their intended destination.
However, traps are often preferred because informs consume more resources in the router and in the network.
Unlike a trap, which is discarded as soon as it is sent, an inform request must be held in memory until a
response is received or the request times out. Also, traps are sent only once, and an inform may be retried
several times. The retries increase traffic and contribute to a higher overhead on the network. Thus, traps and
inform requests provide a trade-off between reliability and resources.
System Management Configuration Guide for the Cisco NCS 6000 Series Router, Release 5.0.x
SNMP Notifications
illustrates the communications
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