Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

Guide That Contains This Content
[+] Expand All
[-] Collapse All

    Setting Up an Interface Numbering Method in the IfTable to Use Contiguous Integers

    Each interface in the ifTable is assigned an ifIndex number. RFC 1213 required that ifIndexes use contiguous integers and that the ifIndex be less than the value of the total number of interfaces (ifNumber). More recent RFCs—1573, 2232, and 2863—removed these restrictions to accommodate interface sublayers. The E Series router implementation of SNMP derives index numbers in 32-bit values that are unique on a given router. This numbering scheme can result in large gaps in the ifIndex.

    Legacy network management software that was designed to work with RFC 1213 implementations expects contiguous integers and can fail when the software encounters large gaps in the ifIndex.

    By default, the router uses a numbering scheme based on RFC 2863. For compatibility with RFC 1213, you can set up the router to use contiguous numbers and to limit the values of the ifIndex and the ifNumber.

    You can use the snmp-server interfaces rfc1213 command to set up the interface numbering method in the IfTable to use contiguous integers, which provides compatibility with versions of SNMP that are based on RFC 1213. This command has the following options:

    • maxIfIndex—Sets the maximum value of the ifIndex field that the system will allocate.
    • maxIfNumber—Sets the maximum number of interfaces allowed in the interface tables.

    Caution: Reducing the value of the maxIfIndex or maxIfNumber causes the router to automatically reboot to factory default settings.

    When the IfIndex and IfNumber maximums are reached, the system logs the event and ignores the creation of additional interfaces, which means that new interfaces are not visible in the interface table.

    To set up the interface numbering method in the IfTable to use contiguous integers:

    • Execute the snmp-server interfaces rfc1213 command in Global Configuration mode.
      host1(config)#snmp-server interfaces rfc1213 55000 100000 WARNING: Execution of this command will cause all configuration settings to revert to factory defaults upon the next system reboot.Proceed with 'snmp interfaces rfc1213'? [confirm]

      Use the no version to return to the default method of interface numbering.

    Published: 2014-08-12