[mrtg] Re: IP unnumbered and ifIndex

Tim Schuh tschuh at verio.net
Wed Aug 4 17:50:04 MEST 1999

Vivien LAM wrote:
> As stated in the "config.txt" of v2.8.6:
>      * Sometimes SNMP interface index can change, like when new
>        interfaces are added or removed. This can cause all Target entries
>        in your config file to become wrong by offset, causing MRTG to
>        graphs wrong instances etc.  MRTG supports IP address instead of
>        ifindex in target definition....
> However, since the routers I wanted to monitor is using "IP unnumbered" on
> the interface and also the ifIndex will also be changed, it's likely that
> there is no way for mrtg to take a "index" to recognize the interface when
> it execute.

As the config.txt notes, your ifIndexes will change IF you add or
remove interfaces AND reload the router.  We use ip unnumbered quite
extensively on our customer aggregation routers and sometimes have to
change the hardware configuration to accomidate new customers.  The
ifIndexes stay the same until the router is reloaded.  At that time I
must rebuild my config and index web pages.  For that reason I'm
developing a system that will only care about the ifDescr and any
other field I define.  Mine will be closer to rrdtool and cricket than
MRTG by the time it's finished.


Tim Schuh
Network Systems
Verio Central

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