[mrtg] Re: IP unnumbered and ifIndex

Vivien LAM vivienna at pacific.net.hk
Wed Aug 4 13:07:08 MEST 1999

On Wed, 4 Aug 1999, Alan J. Flavell wrote:
> On Wed, 4 Aug 1999, Vivien LAM wrote:
> > I have problem on using MRTG to monitor the interfaces on some Cisco
> > routers which use "IP unnumbered" on the interfaces.
> > 
> > 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.
> > 
> > Any solution and suggstion?  
> The only solution seems to be: don't use that option.  On the basis of
> what you said, it clearly cannot work.

Thanks for your advice.

> How about the -d option instead?  

In my understanding, -d option only change the word in "Target[XXXX]" but
not those after "Target[]" which is used in the SNMP part.

In the website: http://www.ulg.ac.be/~pirard/Cisco/, a solution is
provided.  It patched the original mrtg and do not use "ifIndex" but
"ifDescr" for the indexing.  I have just tried it and it works fine.  :)

Vivien Lam
Pacific Supernet Ltd.

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