[mrtg] Re: Help on MRTG polling using MAC address

Rich Adamson radamson at routers.com
Wed Aug 21 16:19:23 MEST 2002


Mrtg uses snmp (a layer-3 protocol), which requires a layer-3 IP address to
function. One way to fake the IP address of each remote device is to set
up permanent ARP table entries in the mrtg machine. This approach assumes 
there are no routers with proxy arp between the mrtg machine and the boxes
that you'd like to poll.

If the mrtg machine is a Windows box, then:
  arp -s   00-aa-00-62-c6-09  .... Adds a static entry.

If the mrtg machine is a Unix box, then "man arp" for the proper syntax
as it varies slightly from one OS to another.

The above approach creates a permanent arp table entry in the mrtg box, and
mrtg would be configured to poll the address (using the above
example). Whatever the actual IP address is of the remote box then becomes

If there is a router between the mrtg box and the remote device, one would
need to create permanent arp table entries in each router as well.


> Now, the problem I'm facing is that I need to setup MRTG wherein I need to poll using MAC 
addresses instead of IP address.
> I am having lots of Linux & Windows servers. I couldn't poll using eth0 cause then I would 
need to run MRTG there on each server. The problem is that IP addresses needs to be changed and 
keep on shifting to other server. So whenever such change occur, I need to change the MRTG 
configuration. Also I can't poll on switch because sometimes re-structuring needs to be done.
> Now since we don't change NICs, they are the only static things which don't change. If anybody 
of you could guide me to any patch/hack available for MRTG which could help me solve my problem, 
that would be highly appreciative.

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