[mrtg] Re: SNMP Errors

Dan Ratzlaff dratzlaff at mhceck.org
Tue Dec 17 19:21:27 MET 2002

I am having a similar problem, but only with certain devices and only part of the time.

I have been monitoring a Cisco router and several Linux firewalls via MRTG 2.9.22 for some time with no problems.  Now I'm trying to set up monitoring for our new managed switches.

snmpwalk works fine on these switches no matter what.  But mrtg and cfgmaker will only work approx 33% of the time.  The other 66% it reports timeouts talking to the switch.

But tcpdump running on the MRTG machine clearly shows the SNMP request going out, and the response coming in from the switch.  But for some reason mrtg or cfgmaker isn't getting the packets.  And I also see arp requests being sent out quite frequently while mrtg/cfgmaker is attempting the SNMP gets.

And the other three boxes I'm monitoring don't have any problems at all!

This is on RedHat Linux 7.1, kernel 2.4.9-34, mrtg-2.9.22

Anyone have a clue??
Dan Ratzlaff
Network Administrator
Mental Health Center of East Central Kansas
(620) 343-2111 x271
dratzlaff at mhceck.org

On Mon, Dec 16, 2002, Alex van den Bogaerdt wrote:
>On Mon, Dec 16, 2002 at 09:59:39AM -0500, Alan Rader wrote:
>> If anyone has any insight on the below, I would appreciate it.  I have no
>> clue and can't figure out why it just stopped.  I get the same error when
>> trying cfgmaker on ver 2.9.7 and 2.9.22, so I don't think it is mrtg itself.
>> But I am able to get info from my router via getif?
>Perhaps MRTG and getif use another source port number and you
>have a firewall somewhere inbetween (maybe on the mrtg host) that
>does allow udp161<->udp161 and doesn't allow udp<random> <->udp161?
>You could try tcpdump to see what's going on.

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