Chapter 11, SNMP

This chapter explains Simple Network Management Protocol (SNMP) as implemented by the Cisco ONS 15327.

11.1 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 ONS 15327 uses SNMP to provide asynchronous event notification to a network management system (NMS). ONS SNMP implementation uses standard Internet Engineering Task Force (IETF) MIBs to convey node-level inventory, fault, and performance management information for generic read-only management of DS-1, DS-3, SONET, and Ethernet technologies. SNMP allows limited management of the ONS 15327 by a generic SNMP manager, for example, HP OpenView Network Node Manager (NNM) or Open System Interconnection (OSI) NetExpert.

The Cisco ONS 15327 supports SNMP Version 1 (SNMPv1) and SNMP Version 2c (SNMPv2c). Both versions share many features, but SNMPv2c includes additional protocol operations. This chapter describes both versions and explains how to configure SNMP on the ONS 15327. Figure 11-1 illustrates a basic network managed by SNMP.

11.2 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 ONS 15327.

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 manager gathers data from the SNMP agent using a Management Information Base (MIB), which is a textual (ASN.1) representation of management information such as device parameters and network data. The agent can also send traps, or notification of certain events, to the manager. Figure 11-2 illustrates these SNMP operations.

Figure 11-2 SNMP agent gathering data from an MIB and sending traps to the manager

A management system such as HP OpenView NNM 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. Figure 11-3 illustrates the relationship between the three key SNMP components.

11.3 SNMP Support

The ONS 15327 supports SNMPv1 and SNMPv2c traps and get requests. The SNMP MIBs in the ONS 15327 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 SONET multiplexers. The ONS 15327 also supports set requests for the System Group in MIB-II and the Statistics, History and Alarm groups in the Remote Monitoring (RMON) MIB.

11.4 SNMP MIBs

A MIB is a hierarchically-organized collection of information. Network management applications gain access to MIBs and then the NMSs run SNMP queries on the MIB objects supported by the SNMP agent to gather management information. MIBs consist of managed objects and are identified by object identifiers.

The ONS 15327 SNMP agent communicates with an SNMP management application using SNMP messages. Table 11-1 describes these messages.

Table 11-1 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	Reply to a get-request, get-next-request, get-bulk-request, or set-request sent by an NMS.
get-bulk-request	Similar to a get-next-request, but this operation fills the get-response with up to the max-repetition number of get-next interactions.
trap	Unsolicited message sent by an SNMP agent to an SNMP manager indicating that an event has occurred.

A managed object (sometimes called a MIB object) is one of any specific characteristics of a managed device. Managed objects consist of one or more object instances (variables). Table 11-2 lists the IETF standard MIBs implemented in the ONS 15327 SNMP Agent.

The ONS 15327 MIBs are included on the software CD that ships with the ONS 15327. Compile these MIBs in the following order. If you do not follow the sequence shown, one or more MIB files might not compile.

If you cannot compile the ONS 15327 MIBs, call the Technical Assistance Center (TAC) at 1-877-323-7368.

Table 11-2 IETF Standard MIBs Implemented in the ONS 15327 SNMP Agent
RFC#	Module Name	Title/Comments
1213 +1907	RFC1213-MIB, SNMPV2-MIB	MIB-II from RFC1213 with enhancement from RFC1907 for SNMPv2
1493	BRIDGE-MIB	Bridge/Spanning Tree (SNMPv1 MIB)
1757	RMON-MIB	RMON Ethernet
2737	ENTITY-MIB	Entity MIB using SMI v2 (version II)
2233	IF-MIB	Interface evolution (enhances MIB-II)
2358	Etherlike-MIB	Ethernet-like interface (SNMPv2 MIB)
2495	DS1-MIB	DS-1/E1
2496	DS3-MIB	DS-3/E3
2558	SONET-MIB	SONET
2674	P-BRIDGE-MIB, Q-BRIDGE-MIB	P-Bridge and Q-Bridge MIB

11.5 SNMP Traps

The ONS 15327 can receive SNMP requests from a number of SNMP managers and send traps to eleven trap receivers. The ONS 15327 generates all alarms and events as SNMP traps.

The ONS 15327 generates traps containing an object ID that uniquely identifies the alarm. An entity identifier uniquely identifies the entity that generated the alarm (slot, port, STS, VT, BLSR, STP, 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 ONS 15327 also generates a trap for each alarm when the alarm condition clears.

Each SNMP trap contains eleven variable bindings listed in Table 11-3 for the ONS 15327.

Table 11-3 SNMP Trap Variable Bindings Used in ONS 15327
Number	Name	Description
1	cerentGenericAlarmTable	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 subsequent entries move up by one row.
2	cerentGenericAlarmIndex	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 located subsequent to the cleared alarm.
3	cerentGenericAlarmObjectType	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	cerentGenericAlarmSlotNumber	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	cerentGenericAlarmPortNumber	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	cerentGenericAlarmLineNumber	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	cerentGenericAlarmObjectIndex	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	cerentGenericAlarmType	This variable provides the exact alarm type.
9	cerentGenericAlarmState	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	cerentGenericAlarmTimeStamp	This variable gives the time when the alarm occurred. The value is the number of the ticks that have lapsed since 1/1/1970.
11	cerentGenericAlarmObjectName	This variable gives the TL1-style user-visible name that uniquely identifies an object in the system.

Table 11-4 Traps Supported in the ONS 15327
Trap	From RFC No.	Description
ColdStart	RFC1213-MIB	Agent up, cold start.
WarmStart	RFC1213-MIB	Agent up, warm start.
AuthenticationFailure	RFC1213-MIB	Community string does not match.
NewRoot	RFC1493/ BRIDGE-MIB	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 from Forwarding to Blocking.
EntConfigChange	RFC2037/ ENTITY-MIB	The entLastChangeTime value has changed.
ds1xLineStatusChange	RFC2495/ DS1-MIB	Sent when the value of an instance of dsx1LineStatus changes. The trap can be used by an NMS to trigger polls. When the line status change results from a higher-level line status change (for example, DS-3), no traps for the DS-1 are sent.
dsx3LineStatusChange	RFC2496/ DS3-MIB	Sent when the value of an instance of dsx3LineStatus changes. This trap can be used by an NMS to trigger polls. When the line status change results in a lower-level line status change (ex. DS-1), no traps for the lower-level are sent.
risingAlarm	RFC1757/ RMON-MIB	Generated when an alarm entry crosses the rising threshold and the entry generates an event that is configured for sending SNMP traps.
fallingAlarm	RFC1757/ RMON-MIB	Generated when an alarm entry crosses the falling threshold and the entry generates an event that is configured for sending SNMP traps.

11.6 SNMP Community Names

You can provision community names for all SNMP requests from the SNMP Trap Destination dialog box in CTC. (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.

11.7 SNMP Remote Monitoring

The ONS 15327 incorporates RMON to allow network operators to monitor the ONS 15327 E10/100-4 cards. This feature is not apparent to the typical CTC user, because RMON interoperates with an NMS. However, with CTC you can provision the RMON alarm thresholds. (See the "SNMP Remote Monitoring" section.) CTC also monitors the five RMON groups implemented by the ONS 15327.

ONS 15327 RMON implementation is based on the IETF-standard MIB Request for Comments (RFC) 1757. The ONS 15327 implements five groups from the standard MIB: Ethernet Statistics, History Control, Ethernet History, Alarm, and Event.

11.7.1 Ethernet Statistics Group

The Ethernet Statistics group contains the basic statistics for each monitored subnetwork in a single table named etherstats.

11.7.2 History Control Group

The History Control group defines sampling functions for one or more monitor interfaces. RFC 1757 defines the historyControlTable.

11.7.3 Ethernet History Group

The ONS 15327 implements the etherHistoryTable as defined in RFC 1757, within the bounds of the historyControlTable.

11.7.4 Alarm Group

The Alarm group consists of a single alarm table. This table provides the network performance alarm thresholds for the network management application. With CTC, you can provision the thresholds in the table.

11.7.5 Event Group

The Event group consists of two tables, eventTable and logTable. The eventTable is read-only. The ONS 15327 implements the logTable as specified in RFC 1757.

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