Chapter 10, SNMP

This chapter explains Simple Network Management Protocol (SNMP) as implemented by the CiscoONS15600SDH.

10.1 SNMP Overview

SNMP is an application-layer communication protocol that allows network devices to exchange management information. SNMP enables network administrators to manage network performance, find and solve network problems, and plan network growth.

The ONS15600SDH uses SNMP to provide asynchronous event notification to a network management system (NMS). ONS SNMP implementation uses standard Internet Engineering Task Force (IETF) management information bases (MIBs) to convey node-level inventory, fault, and performance management information for generic read-only management of SDH technologies. SNMP allows limited management of the ONS15600SDH by a generic SNMP manager, for example HP OpenView Network Node Manager (NNM) or Open Systems Interconnection (OSI) NetExpert.

The CiscoONS15600SDH supports SNMP Version 1 (SNMPv1) and SNMP Version 2c (SNMPv2c). The two versions share many features, but SNMPv2c includes additional protocol operations. SNMP Version3 is acceptable, but not required. This chapter describes both versions and explains how to configure SNMP on the ONS15600SDH. Figure10-1 illustrates a basic network managed by SNMP.

10.2 SNMP Basic Components

An SNMP-managed network consists of three primary components: managed devices, agents, and management systems. A managed device is a network node that contains an SNMP agent and resides on an SNMP-managed network. Managed devices collect and store management information and use SNMP to make this information available to management systems that use SNMP. Managed devices include routers, access servers, switches, bridges, hubs, computer hosts, and network elements such as an ONS15600SDH.

An agent is a software module that resides in a managed device. An agent has local knowledge of management information and translates that information into a form compatible with SNMP. The SNMP agent gathers data from the MIB, which is the repository for device parameter and network data. The agent can also send traps, or notifications of certain events, to the manager. Figure10-2 illustrates these SNMP operations.

Figure 10-2 SNMP Agent Gathering Data from a MIB and Sending Traps to the Manager

A management system such as HP OpenView executes applications that monitor and control managed devices. Management systems provide the bulk of the processing and memory resources required for network management. One or more management systems must exist on any managed network. Figure10-3 illustrates the relationship between the three key SNMP components.

10.3 SNMP Support

The ONS15600SDH supports SNMPv1 and SNMPv2c traps and get requests. The SNMP MIBs in the ONS15600SDH define alarms, traps, and status. Through SNMP, NMS applications can query a management agent using a supported MIB. The functional entities include Ethernet switches and SDH multiplexers. To set up SNMP, refer to the CiscoONS15600SDH Procedure Guide.

10.4 SNMP Management Information Bases

A MIB is a hierarchically organized collection of information. Network management protocols such as SNMP access MIBs. MIBs consist of managed objects and are identified by object identifiers.

The ONS15600SDH SNMP agent communicates with an SNMP management application using SNMP messages. Table10-1 describes these messages.

Table 10-1 SNMP Message Types
Operation	Description
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	Replies to a get-request, get-next-request, get-bulk-request, or set-request sent by an NMS.
get-bulk-request	Fills the get-response with up to the max-repetition number of get-next interactions, similar to a get-next-request.
trap	Indicates that an event has occurred. A trap is an unsolicited message sent by an SNMP agent to an SNMP manager.

A managed object (also called a MIB object) is one of any specific characteristics of a managed device. Managed objects consist of one or more object instances (variables). Table10-2 lists the IETF standard MIBs implemented in the ONS15600SDH SNMP Agent.

The ONS15600SDH MIBs are included on the software CD that ships with the ONS15600SDH. Compile these MIBs in the following sequence. If you do not follow the sequence, one or more MIB files might not compile.

If you cannot compile the ONS15600SDH MIBs, contact the Cisco Technical Assistance Center (TAC). For contact information, see the "Obtaining Technical Assistance" section .

Table 10-2 IETF Standard MIBs Implemented in the ONS 15600 SNMP Agent
RFC#	Module Name	Title/Comments
1213 +1907	RFC1213-MIB, SNMPV2-MIB	MIB-II from RFC1213 with enhancement from RFC1907 for v2
1253	OSPF-MIB	Open Shortest Path First
1493	BRIDGE-MIB	Bridge/Spanning Tree (SNMPv1 MIB)
2737	ENTITY-MIB	Entity MIB using SMI¹ v2 (version II)
2233	IF-MIB	Interface evolution (enhances MIB-II)
2358	Etherlike-MIB	Ethernet-like interface (SNMPv2 MIB)
2558	SDH-MIB	SDH
2674	P-BRIDGE-MIB, Q-BRIDGE-MIB	P-Bridge and Q-Bridge MIB

¹SMI = Structure of Management Information

10.5 SNMP Traps

The ONS15600SDH can receive SNMP requests from a number of SNMP managers and send traps to ten trap receivers. The ONS15600SDH generates all alarms and events as SNMP traps.

The ONS15600SDH generates traps containing an object ID that uniquely identifies the alarm. An entity identifier uniquely identifies the entity that generated the alarm (slot, port, VC4, etc.). The traps give the severity of the alarm (critical, major, minor, event, etc.) and indicate whether the alarm is service-affecting or non-service-affecting. The traps also contain a date/time stamp that shows the date and time the alarm occurred. The ONS15600SDH also generates a trap for each alarm when the alarm condition clears.

Table 10-3 SNMP Trap Variable Bindings for the ONS 15600 SDH
Number	Name	Description
1	cerent454AlarmTable	This table holds all the currently raised alarms. When an alarm is raised, it appears as a new entry in the table. When an alarm is cleared, it is removed from the table and all the subsequent entries move up by one row.
2	cerent454AlarmIndex	This variable uniquely identifies each entry in an alarm table. When an alarm in the alarm table clears, the alarm indexes change for each alarm listed after the cleared alarm.
3	cerent454AlarmObjectType	This variable provides the entity type that raised the alarm. The NMS should use this value to decide which table to poll for further information about the alarm.
4	cerent454AlarmSlotNumber	This variable indicates the slot of the object that raised the alarm. If a slot is not relevant to the alarm, the slot number is zero.
5	cerent454AlarmPortNumber	This variable provides the port of the object that raised the alarm. If a port is not relevant to the alarm, the port number is zero.
6	cerent454AlarmLineNumber	This variable provides the object line that raised the alarm. If a line is not relevant to the alarm, the line number is zero.
7	cerent454AlarmObjectIndex	Every alarm is raised by an object entry in a specific table. This variable is the index of the objects in each table; if the alarm is interface related, this is the index of the interfaces in the interface table.
8	cerent454AlarmType	This variable provides the exact alarm type.
9	cerent454AlarmState	This variable specifies alarm severity and service-affecting status. Severities are minor, major and critical. Service-affecting statuses are service-affecting and non-service-affecting.
10	cerent454AlarmTimeStamp	This variable gives the time when the alarm occurred.
11	cerent454AlarmObjectName	This variable gives the TL1-style user-visible name which uniquely identifies an object in the system.

Table 10-4 Traps Supported in the ONS 15600 SDH
Trap	From RFC No.	Description
ColdStart	RFC1213-MIB	Agent up, cold start.
WarmStart	RFC1213-MIB	Agent up, warm start.
NewRoot	RFC1493/ BRIDGE-MIB	The sending agent is the new root of the spanning tree.
TopologyChange	RFC1493/ BRIDGE-MIB	A port in a bridge has changed from Learning to Forwarding or Forwarding to Blocking.
EntConfigChange	RFC2037/ ENTITY-MIB	The entLastChangeTime value has changed.
risingAlarm	RFC1757	The SNMP trap that is generated when an alarm entry crosses the rising threshold and generates an event that is configured for sending SNMP traps.
fallingAlarm	RFC1757	The SNMP trap that is generated when an alarm entry crosses the falling threshold and generates an event that is configured for sending SNMP traps.

10.6 SNMP Community Names

You can provision community names for all SNMP requests from the SNMP Trap Destination dialog box (see the "SNMP Support" section ). In effect, SNMP considers any request valid that uses a community name matching a community name on the list of provisioned SNMP trap destinations. Otherwise, SNMP considers the request invalid and drops it.

If an SNMP request contains an invalid community name, the request silently drops and the MIB variable (snmpInBadCommunityNames) increments. All MIB variables managed by the agent grant access to all SNMP requests containing a validated community name.