IF-MIBs

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To use the Interface Group MIB and Ethernet-like Interface MIB described in this document, you must configure SNMP on your system. It is assumed you will be using Cisco IOS or a network management system (NMS) such as CiscoWorks to monitor the performance of your network. For information on these topics, see the documents listed in the "Related Documents" section or the documentation that came with your network management application.

The IF-MIB complies with RFC 2233 and provides SNMP support for subinterfaces. Additionally, you can configure SNMP to use either the existing Cisco implementation of linkUp or linkDown traps or the IF-MIB implementation consistent with IETF standards. Refer to RFC 2233 for information about linkUp and linkDown traps.

Starting with Cisco IOS Release 12.1(2)T/12.0(21)S3, you can configure your router to begin using the new RFC 2233 IETF standards-based implementation by using the snmp-server trap link ietf command. This command enables notification support for subinterfaces and is disabled by default to allow you to continue using the earlier Cisco implementation of linkUp/linkDown traps if you so choose.

However, please note that when using the earlier Cisco object definitions, an arbitrary value is used for the locIfReason object in linkUp/linkDown traps for subinterfaces, which may give you unintended results. This is because the locIfReason object is not defined for subinterfaces in the current Cisco implementation, which uses OLD-CISCO-INTERFACES-MIB.my.

If you do not enable this functionality, the link trap varbind list will consist of {ifIndex, ifDescr, ifType, locIfReason}. After you enable this functionality with the snmp-server trap link ietf command, the varbind list will consist of {inIndex, ifAdminStatus, ifOperStatus, if Descr, ifType}. The locIfReason object will also be conditionally included in this list depending on whether meaningful information can be retrieved for that object. A configured subinterface will generate retrievable information. On non-HWIDB interfaces, there will be no defined value for locIfReason , so it will be omitted from the trap message.

Other updates to the IF-MIB module have also been made to comply with RFC2233. These changes include the addition of the ifCounterDiscontinuityTime object, and the addition of basic support for ifTableLastChange. Updated Online Insertion and Removal (OIR) drivers are planned in a future release for full ifTableLastChange support.

• Benefits of the IF-MIB

1.    enable

2.    configure terminal

3.    snmp-server trap link ietf

4.    end

• Verifying IETF-Compliant Link Traps for SNMP

The following example shows the SNMP related output before the IETF-compliant implementation is enabled, a configuration session in which it is enabled, and the changed output after the configuration:

Router# 
more system:running config
. . .
snmp-server engineID local 00000009000000A1616C2056
snmp-server community public RO
snmp-server community private RW
. . .
Router# 
conf term
 
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# 
snmp-server trap link ietf
 
Router(config)# 
end
Router#
 more system:running config
. . .
snmp-server engineID local 00000009000000A1616C2056
snmp-server community public RO
snmp-server community private RW
snmp-server trap link ietf
. . .

To enable/disable link traps for a particular interface:

7609_supBXL_45(config-if)#snmp trap link-status ?
  permit  Permit the following capability
  <cr>
7609_supBXL_45(config-if)#

To enable link up/down traps during switchover:

7609_supBXL_45(config)#snmp-server trap link ?
  ietf        Use IETF standard for SNMP traps
  switchover  Enable link up/down traps during switchover 

• Configuring the Router to Use SNMP