The SNMP manager is a system that controls and monitors the activities of network hosts using SNMP. The most common managing system is an NMS. The term NMS can be applied either to a dedicated device used for network management or to the applications used on such a device. Several network management applications are available for use with SNMP and range from simple CLI applications to applications that use GUIs, such as the CiscoWorks2000 products.

The SNMP agent is the software component within a managed device that maintains the data for the device and reports this data, as needed, to managing systems. The agent resides on the routing device (router, access server, or switch). To enable an SNMP agent on a Cisco routing device, you must define the relationship between the manager and the agent.

Note	Although it is possible to configure a Cisco router to be an SNMP agent, this practice is not recommended. Commands that an agent needs to control the SNMP process are available through the Cisco IOS CLI without additional configuration.

A MIB is a virtual information storage area for network management information and consists of collections of managed objects. Within a MIB are collections of related objects defined in MIB modules. MIB modules are written in the SNMP MIB module language, as defined in STD 58, RFC 2578, RFC 2579, and RFC 2580 (see the "MIBs and RFCs" section for an explanation of Request for Comments (RFC) and Standard documents). Individual MIB modules are also referred to as MIBs; for example, the Interfaces Group MIB (IF-MIB) is a MIB module within the MIB on your system.

An SNMP agent contains MIB variables whose values the SNMP manager can request or change through Get or Set operations. A manager can get a value from an agent or store a value in that agent. The agent gathers data from the MIB, the repository for information about device parameters and network data. The agent can also respond to manager requests to get or set data.

The figure below illustrates the communications between the SNMP manager and agent. A manager sends an agent requests to get and set MIB values. The agent responds to these requests. Independent of this interaction, the agent can send the manager unsolicited notifications (traps or informs) to notify the manager about network conditions.

Figure 1

Communication Between an SNMP Agent and Manager

The SNMP get operation is performed by an NMS to retrieve SNMP object variables. There are three types of get operations:

• get--Retrieves the exact object instance from the SNMP agent.
• getNext--Retrieves the next object variable, which is a lexicographical successor to the specified variable.
• getBulk--Retrieves a large amount of object variable data, without the need for repeated getNext operations.

The SNMP set operation is performed by an NMS to modify the value of an object variable.

A key feature of SNMP is its capability to generate unsolicited notifications from an SNMP agent.

• Traps and Informs
  

The ifIndex object (ifEntry 1) is called the Interface Index. The Interface Index is a unique value greater than zero that identifies each interface or subinterface on the managed device. This value becomes the interface index identification number.

The CLI command show snmp mib ifmib ifindex allows you to view the SNMP Interface Index Identification numbers assigned to interfaces and subinterfaces. An NMS is not required.

The ifAlias object (ifXEntry 18) is called the Interface Alias. The Interface Alias is a user-specified description of an interface used for SNMP network management. The ifAlias is an object in the Interfaces Group MIB (IF-MIB) that can be set by a network manager to "name" an interface. The ifAlias value for an interface or subinterface can be set using the description command in interface configuration mode or subinterface configuration mode or by using a Set operation from an NMS. Previously, ifAlias descriptions for subinterfaces were limited to 64 characters. (The OLD-CISCO-INTERFACES-MIB allows up to 255 characters for the locIfDescr MIB variable, but this MIB does not support subinterfaces.) A new CLI command, snmp ifmib ifalias long, configures the system to handle IfAlias descriptions of up to 256 characters. IfAlias descriptions appear in the output of the CLI show interfaces command.

The ifName object (ifXEntry 1) is the textual name of the interface. The purpose of the ifName object is to cross reference the CLI representation of a given interface. The value of this object is the name of the interface as assigned by the local device and is generally suitable for use in CLI commands. If there is no local name or this object is otherwise not applicable, this object contains a zero-length string. No commands introduced by this feature affect the ifName object, but it is discussed here to show its relation to the ifIndex and ifAlias objects.

The show snmp mib command shows all objects in the MIB on a Cisco device (similar to a mibwalk). The objects in the MIB tree are sorted using lexical ordering, meaning that object identifiers are sorted in sequential, numerical order. Lexical ordering is important when using the GetNext operation from an NMS because these operations take an object identifier (OID) or a partial OID as input and return the next object from the MIB tree based on the lexical ordering of the tree.

The event table defines the activities to be performed when an event is triggered. These activities include sending a notification and setting a MIB object. The event table has supplementary tables for additional objects that are configured according to event action. If the event action is set to notification, notifications are sent out whenever the object configured for that event is modified.

The object table lists objects that can be added to notifications based on trigger, trigger test type, or the event that sends a notification. The Event MIB allows wildcarding, which enables you to monitor multiple instances of an object. To specify a group of object identifiers, you can use the wildcard option.

The trigger table defines conditions to trigger events. The trigger table lists the objects to be monitored and associates each trigger with an event. An event occurs when a trigger is activated. To create a trigger, you should configure a trigger entry in the mteTriggerTable of the Event MIB. This trigger entry specifies the object identifier of the object to be monitored. Each trigger is configured to monitor a single object or a group of objects specified by a wildcard (*). The Event MIB process checks the state of the monitored object at specified intervals.

The trigger table has supplementary tables for additional objects that are configured based on the type of test performed for a trigger. For each trigger entry type such as existence, threshold, or Boolean, the corresponding tables (existence, threshold, and Boolean tables) are populated with the information required to perform the test. The Event MIB allows you to set event triggers based on existence, threshold, and Boolean trigger types. When the specified test on an object returns a value of true, the trigger is activated. You can configure the Event MIB to send out notifications to the interested host when a trigger is activated.

Absolute sampling uses the value of the MIB object during sampling.

Delta sampling is used for expressions with counters that are identified based on delta (difference) from one sample to the next. Delta sampling requires the application to do continuous sampling, because it uses the value of the last sample.

Changed sampling uses the changed value of the object since the last sample.

• An established SNMP community string that defines the relationship between the SNMP manager and the agent.
• A host defined to be the recipient of SNMP notifications.

1.    enable

2.    configure terminal

3.    snmp-server view view-name oid-tree {included | excluded}

4.    no snmp-server view view-name oid-tree {included | excluded}

5.    exit

6.    show snmp view

Router> enable
Router# configure terminal
Router(config)# snmp-server view test system 1.0 included
Router(config)# exit
Router# show snmp view
test system.1.0 - included nonvolatile active
*ilmi system - included permanent active
*ilmi atmForumUni - included permanent active
v1default iso - included permanent active
v1default internet - included permanent active
v1default snmpUsmMIB - excluded permanent active
v1default snmpVacmMIB - excluded permanent active
v1default snmpCommunityMIB - excluded permanent active
v1default ciscoIpTapMIB - excluded permanent active
v1default ciscoMgmt.395 - excluded permanent active
v1default ciscoTap2MIB - excluded permanent active

1.    enable

2.    configure terminal

3.    snmp-server community string [view view-name] [ro | rw] [ipv6 nacl] [access-list-number]

4.    no snmp-server community string

5.    exit

6.    show snmp community

Router> enable
Router# configure terminal
Router(config)# snmp-server community public ro
Router(config)# snmp-server community private rw
Router(config)# exit
Router# show snmp community
Community name: private
Community Index: private
Community SecurityName: private
storage-type: nonvolatile        active
Community name: public
Community Index: public
Community SecurityName: public
storage-type: nonvolatile        active

1.    enable

2.    configure terminal

3.    snmp-server host host-id [traps | informs] [version {1| 2c | 3 [auth | noauth | priv]}] community-string [udp-port port-number] [notification-type]

4.    exit

5.    show snmp host

Router> enable
Router# configure terminal
Router(config)# snmp-server host 10.2.28.1 inform version 2c public
Router(config)# exit
Router# show snmp host

Notification host: 10.2.28.1 udp-port: 162   type: inform
user: public    security model: v2c
traps: 00001000.00000000.00000000

1.    enable

2.    configure terminal

3.    snmp-server group [groupname {v1 | v2c | v3 [auth | noauth | priv]}] [read readview] [write writeview] [notify notifyview] [access access-list]

4.    exit

5.    show snmp group

Router# show snmp group
groupname: ILMI                             security model:v1 
readview : *ilmi                            writeview: *ilmi 
notifyview: <no notifyview specified> 
row status: active
groupname: ILMI                             security model:v2c 
readview : *ilmi                            writeview: *ilmi 
notifyview: <no notifyview specified> 
row status: active
groupname: group1                           security model:v3 auth
readview : v1default                        writeview: <no writeview specified> 
notifyview: <no notifyview specified>
row status: active                          access-list:lmnop
groupname: public                           security model:v1 
readview : <no readview specified>          writeview: <no writeview specified> 
notifyview: <no notifyview specified>
row status: active

1.    enable

2.    configure terminal

3.    snmp-server user username groupname [remote ip-address [udp-port port]] {v1 | v2c | v3 [encrypted] [auth {md5 | sha} auth-password]} [access access-list]

4.    exit

5.    show snmp user [username]

Router# show snmp user user1
User name: user1 
Engine ID: 00000009020000000C025808 
storage-type: nonvolatile       active access-list: 10
Rowstatus: active 
Authentication Protocol: MD5
Privacy protocol: None
Group name: group1 

1.    enable

2.    configure terminal

3.    snmp-server manager

4.    snmp-server manager session-timeout seconds

5.    exit

6.    show snmp

7.    show snmp sessions [ brief ]

8.    show snmp pending

Router# show snmp
Chassis: 01506199
37 SNMP packets input
    0 Bad SNMP version errors
    4 Unknown community name
    0 Illegal operation for community name supplied
    0 Encoding errors
    24 Number of requested variables
    0 Number of altered variables
    0 Get-request PDUs
    28 Get-next PDUs
    0 Set-request PDUs
78 SNMP packets output
    0 Too big errors (Maximum packet size 1500)
    0 No such name errors
    0 Bad values errors
    0 General errors
    24 Response PDUs
    13 Trap PDUs
SNMP logging: enabled
    Logging to 172.17.58.33.162, 0/10, 13 sent, 0 dropped.
SNMP Manager-role output packets
    4 Get-request PDUs
    4 Get-next PDUs
    6 Get-bulk PDUs
    4 Set-request PDUs
    23 Inform-request PDUs
    30 Timeouts
    0 Drops
SNMP Manager-role input packets
    0 Inform response PDUs
    2 Trap PDUs
    7 Response PDUs
    1 Responses with errors
SNMP informs: enabled
    Informs in flight 0/25 (current/max)
    Logging to 172.17.217.141.162
        4 sent, 0 in-flight, 1 retries, 0 failed, 0 dropped
    Logging to 172.17.58.33.162
        0 sent, 0 in-flight, 0 retries, 0 failed, 0 dropped

Router# show snmp sessions
Destination: 172.17.58.33.162, V2C community: public
  Round-trip-times: 0/0/0 (min/max/last)
  packets output
    0 Gets, 0 GetNexts, 0 GetBulks, 0 Sets, 4 Informs
    0 Timeouts, 0 Drops
  packets input
    0 Traps, 0 Informs, 0 Responses (0 errors)
Destination: 172.17.217.141.162, V2C community: public, Expires in 575 secs
  Round-trip-times: 1/1/1 (min/max/last)
  packets output
    0 Gets, 0 GetNexts, 0 GetBulks, 0 Sets, 4 Informs
    0 Timeouts, 0 Drops
 packets input
    0 Traps, 0 Informs, 4 Responses (0 errors)

Router# show snmp pending
req id: 47, dest: 172.17.58.33.161, V2C community: public, Expires in 5 secs
req id: 49, dest: 172.17.58.33.161, V2C community: public, Expires in 6 secs
req id: 51, dest: 172.17.58.33.161, V2C community: public, Expires in 6 secs
req id: 53, dest: 172.17.58.33.161, V2C community: public, Expires in 8 secs

To monitor SNMP trap activity in real time for the purposes of troubleshooting, use the SNMP debug commands, including the debug snmp packet EXEC command. For documentation of SNMP debug commands, see the Cisco IOS Debug Command Reference.

1.    enable

2.    configure terminal

3.    snmp-server user username groupname [remote host [udp-port port] {v1 | v2c | v3 [encrypted] [auth {md5 | sha} auth-password]} [access access-list]

4.    snmp-server group groupname {v1 | v2c | v3 {auth | noauth | priv}} [read readview] [write writeview] [notify notifyview] [access access-list]

5.    snmp-server host host [traps | informs] [version {1 | 2c | 3 [auth | noauth | priv]}] community-string [notification-type]

6.    snmp-server enable traps [notification-type [notification-options]]

1.    enable

2.    configure terminal

3.    snmp-server trap-source interface

4.    snmp-server queue-length length

5.    snmp-server trap-timeout seconds

6.    snmp-server informs [retriesretries] [timeoutseconds] [pendingpending]

1.    enable

2.    configure terminal

3.    snmp-server enable traps snmp [authentication] [linkup] [linkdown] [warmstart] [coldstart]

4.    interface type slot / port

5.    no snmp-server link-status

6.    exit

7.    exit

1.    enable

2.    configure terminal

3.    snmp mib notification-log default

4.    snmp mib notification-log globalageout seconds

5.    snmp mib notification-log globalsize size

6.    exit

7.    show snmp mib notification-log

Router# show snmp mib notification-log
 
GlobalAgeout 20, GlobalEntryLimit 600
Total Notifications logged in all logs 0
Log Name"", Log entry Limit 600, Notifications logged 0
Logging status enabled
Created by cli

Before You Begin

The configuration tasks described in this section assume that you have configured SNMP on your routing device and are using SNMP to monitor network activity using the Cisco IOS CLI and/or an NMS application.

The interface-specific ifIndex persistence command (snmp ifindex persistence) cannot be used on subinterfaces. A command applied to an interface is automatically applied to all subinterfaces associated with that interface.

Testing indicates that approximately 25 bytes of NVRAM storage are used by this feature per interface. There may be some boot delay exhibited on platforms with lower CPU speeds.

Note	After ifIndex persistence commands have been entered, the configuration must be saved using the copy running-config startup-config EXEC mode command to ensure consistent ifIndex values.

1.    enable

2.    configure terminal

3.    snmp-server ifindex persist

4.    no snmp-server ifindex persist

5.    exit

Perform this task to configure ifIndex persistence only on a specific interface.

Tip	Use the snmp ifindex clear command on a specific interface when you want that interface to use the global configuration setting for ifIndex persistence. This command clears any ifIndex configuration commands previously entered for that specific interface.

1.    enable

2.    configure terminal

3.    interface type slot / port

4.    snmp ifindex persist

5.    no snmp ifindex persist

6.    exit

7.    exit

1.    setany -v2c $ADDRESS private mteTriggerEntryStatus.4.106.111.104.110.1 -i 5

2.    setany -v2c $ADDRESS private mteTriggerValueID.4.106.111.104.110.1 -d 1.3.6.1.2.1.2.2.1.10

3.    setany -v2c $ADDRESS private mteTriggerValueIDWildcard.4.106.111.104.110.1 -i 1

4.    setany -v2c $ADDRESS private mteTriggerTest.4.106.111.104.110.1 -o '20'

5.    setany -v2c $ADDRESS private mteTriggerFrequency.4.106.111.104.110.1 -g 60

6.    setany -v2c $ADDRESS private mteTriggerSampleType.4.106.111.104.110.1 -i 2

7.    setany -v2c $ADDRESS private mteTriggerEnabled.4.106.111.104.110.1 -i 1

1.    setany -v2c $ADDRESS private mteEventEntryStatus.4.106.111.104.110.101.118.101.110. 116 -i 5

2.    setany -v2c $ADDRESS private mteEventEnabled.4.106.111.104.110.101.118.101.110.116 -i 1

3.    setany -v2c $ADDRESS private mteEventEntryStatus.4.106.111.104.110.101.118.101.110. 116 -i 1

1.    setany -v2c $ADDRESS private mteTriggerThresholdRising.4.106.111.104.110.1 -i 30

2.    setany -v2c $ADDRESS private mteTriggerThresholdRisingEventOwner.4.106.111.104.110.1 -D "owner"

1.   setany -v2c $ADDRESS private mteTriggerEntryStatus.4.106.111.104.110.1 -i 1

To confirm that the above configuration is working, ensure that at least one of the interfaces gets more than 30 packets in a minute. This should cause a trap to be sent out after one minute.

Use the following commands to monitor Event MIB activity from the Cisco IOS CLI:

1.    enable

2.    configure terminal

3.    snmp mib event sample minimum value

4.    snmp mib event sample instance maximum value

5.    exit

1.    enable

2.    configure terminal

3.    snmp mib event object list owner object-list-owner name object-list-name object-number

4.    object id object-identifier

5.    wildcard

6.    exit

1.    enable

2.    configure terminal

3.    snmp mib event owner event-owner name event-name

4.    description event-description

5.    enable

6.    exit

By configuring an event action, you can define the actions that an application can perform during an event trigger. The actions for an event include sending a notification, setting a MIB object and so on. You can set the event action information to either set or notification. The actions for the event can be configured only in event configuration mode.

The following sections contain the tasks to configure an event action:

• Configuring Action Notification
  
• Configuring Action Set
  

1.    enable

2.    configure terminal

3.    snmp mib event trigger owner trigger-owner name trigger-name

4.    description trigger-description

5.    frequency seconds

6.    object list owner object-list-owner name object-list-name

7.    object id object-identifier

8.    enable

9.    exit

1.    test existence

2.    event owner event-owner name event-name

3.    object list owner object-list-owner name object-list-name

4.    type {present | absent | changed}

5.    startup {present | absent}

6.    exit

1.    test boolean

2.    comparison {unequal | equal | less | lessOrEqual | greater | greaterOrEqual}

3.    value integer-value

4.    object list owner object-list-owner name object-list-name

5.    event owner event-owner name event-name

6.    startup

7.    exit

1.    test threshold

2.    object list owner object-list-owner name object-list-name

3.    rising integer-value

4.    rising event owner event-owner name event-name

5.    falling integer-value

6.    falling event owner event-owner name event-name

7.    delta rising integer-value

8.    delta rising event owner event-owner name event-name

9.    delta falling integer-value

10.    delta falling event owner event-owner name event-name