Understanding Simple Network Management Protocol
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Table Of Contents
Understanding Simple Network Management Protocol
About Simple Network Management Protocol Support
SNMP Community Strings and Users
SNMP Management Information Base (MIB)
Understanding Simple Network Management Protocol
May 19, 2009
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About Simple Network Management Protocol Support
About Simple Network Management Protocol Support
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SNMP Basics
SNMP, an application layer protocol, facilitates the exchange of management information among network devices, such as nodes, routers, and so on. As part of the TCP/IP protocol suite, SNMP enables administrators to remotely manage network performance, find and solve network problems, and plan for network growth.
You use Cisco Unified Serviceability to configure SNMP-associated settings, such as community strings, users, and notification destinations for V1, V2c, and V3. Likewise, in the SNMP configuration windows, you can apply the settings to all nodes in the cluster.
An SNMP-managed network comprises three key components: managed devices, agents, and network management systems.
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The first node in the Cisco Unified Communications Manager cluster acts as the managed device.
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Cisco Unified Communications Manager uses a master agent and subagent components to support SNMP. The master agent acts as the agent protocol engine and performs the authentication, authorization, access control, and privacy functions that relate to SNMP requests. Likewise, the master agent contains a few MIB variables that relate to MIB-II. The master agent also connects and disconnects subagents after the subagent completes necessary tasks. The SNMP master agent listens on port 161 and forwards SNMP packets for Vendor MIBs.
The Cisco Unified Communications Manager subagent interacts with the local Cisco Unified Communications Manager only. The Cisco Unified Communications Manager subagents send trap and information messages to the SNMP Master Agent, and the SNMP Master Agent communicates with the SNMP trap receiver (notification destination).
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SNMP version 1 Support
SNMP version 1 (SNMPv1), the initial implementation of SNMP that functions within the specifications of the Structure of Management Information (SMI), operates over protocols, such as User Datagram Protocol (UDP) and Internet Protocol (IP).
The SNMPv1 SMI defines highly structured tables (MIBs) that are used to group the instances of a tabular object (that is, an object that contains multiple variables). Tables contain zero or more rows, which are indexed, so SNMP can retrieve or alter an entire row with a supported command.
With SNMPv1, the NMS issues a request, and managed devices return responses. Agents use the Trap operation to asynchronously inform the NMS of a significant event.
In Cisco Unified Serviceability, you configure SNMP v1 support in the V1/V2c Configuration window.
Related Topics
Configuring SNMP V1/V2c in Cisco Unified Serviceability
SNMP version 2c Support
As with SNMPv1, SNMPv2c functions within the specifications of the Structure of Management Information (SMI). MIB modules contain definitions of interrelated managed objects. The operations that are used in SNMPv1 are similar to those that are used in SNMPv2. The SNMPv2 Trap operation, for example, serves the same function as that used in SNMPv1, but it uses a different message format and replaces the SNMPv1 Trap.
The Inform operation in SNMPv2c allows one NMS to send trap information to another NMS and to then receive a response from the NMS.
In Cisco Unified Serviceability, you configure SNMP v2c support in the V1/V2c Configuration window.
Related Topics
Configuring SNMP V1/V2c in Cisco Unified Serviceability
SNMP version 3 Support
SNMP version 3 provides security features such as authentication (verifying that the request comes from a genuine source), privacy (encryption of data), authorization (verifying that the user allows the requested operation), and access control (verifying that the user has access to the objects requested.) To prevent SNMP packets from being exposed on the network, you can configure encryption with SNMPv3.
Instead of using community strings like SNMP v1 and v2, SNMP v3 uses SNMP users.
In Cisco Unified Serviceability, you configure SNMP v3 support in the V3 Configuration window.
Related Topics
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SNMP Services
To support SNMP, you must use the following services, which display in the Service Activation and/or Control Center windows in Cisco Unified Serviceability.
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Caution
Related Topics
Understanding Feature and Network Services in Cisco Unified Serviceability
SNMP Community Strings and Users
Although SNMP community strings provide no security, they authenticate access to MIB objects and function as embedded passwords. You configure SNMP community strings for SNMP v1 and v2c only.
SNMP v3 does not use community strings. Instead, version 3 uses SNMP users. These users serve the same purpose as community strings, but users provide security because you can configure encryption or authentication for them.
In Cisco Unified Serviceability, no default community string or user exists.
Related Topics
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SNMP Traps and Informs
An SNMP agent sends notifications to NMS in the form of traps or informs to identify important system events. Traps do not receive acknowledgments from the destination whereas informs do receive acknowledgments. You configure the notification destinations by using the SNMP Notification Destination Configuration windows in Cisco Unified Serviceability.
For SNMP notifications, traps are sent immediately if the corresponding trap flags are enabled. In the case of the syslog agent, the alarms and system level log messages are sent to syslog daemon for logging. Also, some standard third-party applications send the log messages to syslog daemon for logging. These log messages are logged locally in the syslog files and are also converted into SNMP traps/notifications.
The following SNMP trap/inform message is sent to a configured trap destination:
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Tip
You configure the SNMP trap destination by choosing SNMP > V1/V2 > Notification Destination or SNMP > V3> Notification Destination in Cisco Unified Serviceability.
Table 12-1 comprises information about Cisco Unified Presence trap/inform parameters that you configure on the Network Management System (NMS). You can configure the values in the table below by issuing the appropriate commands on the NMS, as described in the SNMP product documentation that supports the NMS.
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SNMP Management Information Base (MIB)
SNMP allows access to Management Information Base (MIB), which is a collection of information that is organized hierarchically. MIBs comprise managed objects, which are identified by object identifiers. A MIB object, which contains specific characteristics of a managed device, comprises one or more object instances (variables).
The Simple Network Management Protocol (SNMP) extension agent resides in each Cisco Unified Presence node. Cisco Unified Presence supports the following MIBs.
CISCO-CDP-MIB
Use the Cisco Unified Presence CDP subagent to read the Cisco Discovery Protocol MIB, CISCO-CDP-MIB. This MIB enables Cisco Unified Presence to advertise itself to other Cisco devices on the network.
The CDP subagent implements the CDP-MIB. The CDP-MIB contains the following objects:
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SYSAPPL-MIB
Use the System Application Agent to get information from the SYSAPPL-MIB, such as installed applications, application components, and processes that are running on the system.
System Application Agent supports the following object groups of SYSAPPL-MIB:
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MIB-II
Use MIB2 agent to get information from MIB-II. The MIB2 agent provides access to variables that are defined in RFC 1213, such as interfaces, IP, and so on, and supports the following groups of objects:
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HOST-RESOURCES MIB
Use Host Resources Agent to get values from HOST-RESOURCES-MIB. The Host Resources Agent provides SNMP access to host information, such as storage resources, process tables, device information, and installed software base. The Host Resources Agent supports the following groups of objects:
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CISCO-SYSLOG-MIB
The system supports trap functionality only. The Cisco Syslog Agent supports only the following objects of CISCO-SYSLOG-MIB:
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CISCO-CCM-MIB
Simple Network Management Protocol (SNMP) tables contain information such as IP address, registration status, and model type.
To view the support lists for the CISCO-CCM-MIB, go to the following link:
ftp://ftp.cisco.com/pub/mibs/supportlists/callmanager/callmanager-supportlist.html
The following list of tables exists in the CISCO-CCM-MIB:
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For the Cisco Unified IP Phone, the number of registered phones in ccmPhoneTable should match Cisco Unified Communications Manager/RegisteredHardware Phones perfmon counter. The ccmPhoneTable includes one entry for each registered, unregistered, or rejected Cisco Unified IP Phone.
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The ccmCTIDeviceTable stores each CTI device as one device. Based on the registration status of the CTI Route Point or CTI Port, the ccmRegisteredCTIDevices, ccmUnregisteredCTIDevices, and ccmRejectedCTIDevices counters in the Cisco Unified Communications Manager MIB get updated.
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The CCMSIPDeviceTable stores each SIP trunk as one device.
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The ccmH323DeviceTable contains the list of H323 devices for which the local Cisco Unified Communications Manager contains information. For H.323 phones or H.323 gateways, the ccmH.323DeviceTable contains one entry for each H.323 device. (The H.323 phone and gateway do not register with Cisco Unified Communications Manager. Cisco Unified Communications Manager generates the H.323Started alarm when it is ready to handle calls for the indicated H.323 phone and gateway.) The system provides the gatekeeper information as part of the H323 trunk information.
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For Cisco uOne, ActiveVoice, the ccmVoiceMailDeviceTable has one entry for each voice-messaging device. Based on the registration status, the ccmRegisteredVoiceMailDevices, ccmUnregisteredVoiceMailDevices, and ccmRejectedVoiceMailDevices counters in the Cisco Unified Presence MIB get updated.
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The ccmRegisteredGateways, ccmUnregistered gateways, and ccmRejectedGateways keep track of the number of registered gateway devices or ports, number of unregistered gateway devices or ports, and number of rejected gateway devices or ports, respectively.
Cisco Unified Communications Manager generates alarms at the device or port level. The ccmGatewayTable, based on CallManager alarms, contains device- or port-level information. Each registered, unregistered, or rejected device or port has one entry in ccmGatewayTable. The VG200 with two FXS ports and one T1 port has three entries in ccmGatewayTable. The ccmActiveGateway and ccmInActiveGateway counters track number of active (registered) and lost contact with (unregistered or rejected) gateway devices or ports.
Based on the registration status, ccmRegisteredGateways, ccmUnregisteredGateways, and ccmRejectedGateways counters get updated.
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The table contains a list of all media devices which have tried to register with the local CallManager at least once.
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Related Topics
Vendor-Specific MIBs
The following MIBs exist on various Cisco MCS, depending on vendor and model number. To query these MIBS, you can use the standard MIB browsers that are developed by the hardware vendors; for example, HP Systems Insight Manager (SIM) and IBM Director Server+Console. For information about using the MIB browsers, refer to the documentation that the hardware vendor provides.
To review the vendor-specific MIB information, see the following tables:
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SNMP Configuration Checklist
Table 12-4 provides an overview of the steps for configuring SNMP.
Table 12-4 SNMP Configuration Checklist
Step 1
Install and configure the SNMP NMS.
SNMP product documentation that supports the NMS
Step 2
In the Control Center—Network Services window, verify that the system started the SNMP services.
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Step 3
If you are using SNMP v1/v2c, configure the community string.
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If you are using SNMP v3, configure the SNMP user.
Step 5
Configure the notification destination for traps or informs.
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Step 6
Configure the system contact and location for the MIB2 system group.
Step 7
Restart the Master Agent service.
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Step 8
On the NMS, configure the Cisco Unified Communications Manager trap parameters.
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Troubleshooting SNMP
Review this section for troubleshooting tips.
Make sure that all of the feature and network services are running.
Problem
This condition means that the community string or the snmp user is not configured on the system or they do not match with what is configured on the system. By default, no community string or user is configured on the system.
Solution
Check whether the community string or snmp user is properly configured on the system by using the SNMP configuration windows.
Problem
This condition means that the notification destination is not configured correctly on the system.
Solution
Verify that you configured the notification destination properly in the Notification Destination (V1/V2c or V3) Configuration window.
Related Topics
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