[mrtg] Re: problem with interfaces

Greg.Volk at edwardjones.com Greg.Volk at edwardjones.com
Mon Jun 17 21:34:13 MEST 2002

> I'm not sure you can do anything about it on a switch...  For a router,
> if the interface changes and you are specifying interfaces via ip, MRTG
> will search for the new interface number automagically...
> I've had to write lots of code to fix problems like this and it still
> only gets fixed once every 24 hours...  *sigh*

I use 'cfgmaker --ifref=descr' to get around this and it usually
works. Most well behaved cisco switches (IOS) will default the 
interface description to the port name (e.g. fastethernet1_3). 
If someone sets the description to something else, cfgmaker
will need to be rerun, but all the other ports will stay the
same unlike with musical-instance numbers. 

Now, on a catos based switch, I have to use '--ifref=name' because
on certain versions of catos an empty description field will 
generate an empty interface reference. (This is definitely true
for OC3 interfaes in a flexwan blade). But AFAIK, catos treats
the names in a consistant manner, whether or not someone has
specified the port name in the actual switch config.

The above stuff is only helpful if you regularly regenerate
your mrtg configs, as things can get out of date and break 
pretty quickly in even a slowly changing environment. Even if
your not running on a cisco, it's worth trying '--ifref=descr'.
You may need to set the descriptions prior to running cfgmaker,
and if you stuff doesn't support description fields try setting
names for each port, and then running cfgmaker with '--ifref=name'.

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