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 Versions
Cisco IOS XR software supports the following versions of SNMP:
•
Simple Network Management Protocol Version 1 (SNMPv1)
•
Simple Network Management Protocol Version 2c (SNMPv2c)
•
Simple Network Management Protocol Version 3 (SNMPv3)
Both SNMPv1 and SNMPv2c use a community-based form of security. The community of managers able to
access the agent MIB is defined by an IP address access control list and password.
SNMPv2c support includes a bulk retrieval mechanism and more detailed error message reporting to
management stations. The bulk retrieval mechanism supports the retrieval of tables and large quantities of
information, minimizing the number of round-trips required. The SNMPv2c improved error handling support
includes expanded error codes that distinguish different kinds of error conditions; these conditions are reported
through a single error code in SNMPv1. Error return codes now report the error type. Three kinds of exceptions
are also reported: no such object exceptions, no such instance exceptions, and end of MIB view exceptions.
SNMPv3 is a security model. A
security model
is an authentication strategy that is set up for a user and the
group in which the user resides. A
security level
is the permitted level of security within a security model. A
combination of a security model and a security level will determine which security mechanism is employed
when an SNMP packet is handled. See
for a list of security levels available in SNMPv3. The SNMPv3
feature supports RFCs 3411 to 3418.
You must configure the SNMP agent to use the version of SNMP supported by the management station. An
agent can communicate with multiple managers; for this reason, you can configure the Cisco IOS-XR software
to support communications with one management station using the SNMPv1 protocol, one using the SNMPv2c
protocol, and another using SMNPv3.
Comparison of SNMPv1, v2c, and v3
SNMP v1, v2c, and v3 all support the following operations:
•
get-request
—
Retrieves a value from a specific variable.
•
get-next-request
—
Retrieves the value following the named variable; this operation is often used to
retrieve variables from within a table. With this operation, an SNMP manager does not need to know
the exact variable name. The SNMP manager searches sequentially to find the needed variable from
within the MIB.
•
get-response
—
Operation that replies to a get-request, get-next-request, and set-request sent by an NMS.
System Management Configuration Guide for Cisco NCS 5000 Series Routers, IOS XR Release 6.2.x
21
Implementing SNMP
SNMP Versions
