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This chapter provides an overview of the enhanced management feature of the Cisco 4000 Series Integrated Services Router (ISR). This chapter contains the following topics:
A Management and Information Base (MIB) is a database of the objects that can be managed on a device. The managed objects, or variables, can be set or read to provide information on the network devices and interfaces and are organized hierarchically. The MIB consists of collections of managed objects identified by object identifiers. MIBs are accessed using a network management protocol such as SNMP. A managed object (sometimes called a MIB object or an object) is one of a number of characteristics of a managed device, such as a router. Managed objects comprise one or more object instances, which are essentially variables. The Cisco implementation of SNMP uses the definitions of MIB II variables described in RFC 1213.
MIBs can contain two types of managed objects:
System MIB variables are accessible through SNMP as follows:
The enhanced management feature on the Cisco 4000 Series ISR allow you to manage the router through the Simple Network Management Protocol (SNMP). The feature also expands the number of MIBs included with the router. See the “SNMP Overview” section for more information about SNMP and MIBs.
Using the Cisco 4000 Series ISR enhanced management feature, you can:
An object identifier (OID) uniquely identifies a MIB object on a managed network device. The OID identifies the MIB object’s location in the MIB hierarchy, and provides a means of accessing the MIB object in a network of managed devices:
Each number in the OID corresponds to a level of MIB hierarchy. For example, the OID 1.3.6.1.4.1.9.9.xyz represents the. xyz with the location in the MIB hierarchy as follows. Note that the numbers in parentheses are included to help show correspondence to the MIB hierarchy. In actual use, OIDs are represented as numerical values only.
iso(1).org(3).dod(6).internet(1).private(4).enterprises(1).cisco(9).ciscoMgt(9). nn -MIB
You can uniquely identify a managed object, such as ifNumber in the IF-MIB, by its object name (iso.org.dod.internet.mgmt.enterprises.interfaces.ifNumber) or by its OID (1.3.6.1.2.1.2.1).
For a list of OIDs assigned to MIB objects, go to the following URL:
The Simple Network Management Protocol (SNMP) is an application-layer protocol that provides a standardized framework and a common language used for monitoring and managing devices in a network.
The SNMP framework has three parts:
Instead of defining a large set of commands, SNMP places all operations in a get-request, get-next-request, and set-request format. For example, an SNMP manager can get a value from an SNMP agent or set a value in that SNMP agent.
An SNMP agent can notify the SNMP manager when important system events occur, such as the following:
When an agent detects an alarm condition, the agent:
SNMP notifications are sent as either:
The Cisco implementation of SNMP uses the definitions of SNMP traps described in RFC 1215.
When an agent detects an alarm condition, it logs information about the time, type, and severity of the condition and generates a notification message, which it then sends to a designated IP host. SNMP notifications can be sent as either traps or informs. For more information, see “Enabling Notifications” on the Cisco 4000 Series ISR. Use the snmp-server host command to specify whether to send SNMP notifications as traps or informs. See “Monitoring Notifications,” for information about Cisco 4000 Series ISR traps.
Cisco IOS software supports the following versions of SNMP:
– Message integrity—Ensuring that a packet has not been tampered with in transit.
– Authentication—Determining that the message is from a valid source.
– Encryption—Scrambling the contents of a packet to prevent it from being learned by an unauthorized source.
Both SNMPv1 and SNMPv2c use a community-based form of security. The community of managers who are 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-trip transmissions required. 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 report the error type. Three kinds of exceptions are also reported:
SNMPv3 provides security models and security levels:
Table 1-1 describes the security models and levels provided by the different SNMP versions.
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 software to support communications with one management station using the SNMPv1 protocol, one using the SNMPv2c protocol, and another using SMNPv3.
MIB modules are written in the SNMP MIB module language, and are typically defined in RFC documents submitted to the Internet Engineering Task Force (IETF). RFCs are written by individuals or groups for consideration by the Internet Society and the Internet community as a whole. Before being given RFC status, recommendations are published as Internet Draft (I-D) documents. RFCs that have become recommended standards are also labeled as standards (STD) documents. For more information, see the Internet Society website (http://www.internetsociety.org) and IETF website ( http://www.ietf.org).
We provide private MIB extensions with each Cisco system. Cisco enterprise MIBs comply with the guidelines described in the relevant RFCs unless otherwise noted in the documentation.
The following URL provides access to general information about Cisco MIBs. Use the links on this page to access MIBs for download, and to access related information (such as application notes and OID listings).
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
The following Cisco documents provide access to SNMP information developed by the Cisco Technical Assistance Center (TAC):
The following Cisco documents provide information about configuring SNMP: