[mrtg] Find out router's address

[Tolga]

Hi,

I've been trying to make MRTG work for me for days now, to no avail. I 
can't find out the router's address. I've tried my own IP, the gateway 
IP so far. They all return:

SNMPWALK Problem for 1.3.6.1.2.1.1 on public at x.x.x.x::::::v4only
  at /usr/bin/cfgmaker line 918
WARNING: Skipping public at x.x.x.x: as no info could be retrieved.

How to find out the information I need?

Regards,