[mrtg] SNMPWALK Problem for on cross-compiled mrtg (openwrt mipsbe)

Mike Mitchell Mike.Mitchell at sas.com
Fri Jan 22 16:56:54 CET 2010

As the author of SNMP_util.pm I strongly disagree that the problem lies with the SNMP_util module.
The SNMP_util.pm module does not do any SNMP queries on its own, rather it calls Simon Leinen's SNMP_Session module to do all socket I/O.  In private email I suggested Brandon Miller use 16-bit SNMP request IDs (--use-16bit on cfgmaker) and to enable 'avoid_negative_request_ids', but he did not respond.

Mike Mitchell

From: mrtg-bounces at lists.oetiker.ch [mailto:mrtg-bounces at lists.oetiker.ch] On Behalf Of Brandon Miller
Sent: Friday, January 22, 2010 10:32 AM
To: Steve Shipway
Cc: mrtg at lists.oetiker.ch
Subject: Re: [mrtg] SNMPWALK Problem for on cross-compiled mrtg (openwrt mipsbe)

Steve Shipway wrote:

I'm attempting to cross-compile mrtg for openwrt on a mipsbe processor.


SNMPv1_Session (remote host: "" [].161)

community: "public"

request ID: -552632565

PDU bufsize: 8000 bytes

timeout: 2s

retries: 5

backoff: 1)

at /usr/share/mrtg/bin/../lib/mrtg2/SNMP_util.pm line 631

SNMPWALK Problem for on public at<mailto:public at>

at ./cfgmaker line 950


root at OpenWrt:/usr/share/mrtg/lib/mrtg2# snmpwalk -c public -v 1


iso. = STRING: "router"

iso. = OID: iso.

iso. = Timeticks: (46821500) 5 days, 10:03:35.00

iso. = STRING: "test-box"

iso. = STRING: "wrtName"

iso. = STRING: "here"

iso. = INTEGER: 78

Sounds as if the problem lies in the SNMP_util module, which is part of the MRTG installation.  I have no familiarity with your OS but it may be that this module is making some assumptions about SNMP - maybe there are permissions issues on who can listen the UDP responses, for example.

Since snmpwalk works we know the issue is not the agent, but snmpwalk uses different code to SNMP_util.pm.

I'd suggest you direct your investigations to this module, maybe make a small Perl script to use it to make a single SNMP lookup and see if that works?


Thanks for the responses.  I took the easy way out and decided to use a different monitoring tool.  Found that rrd was a pre-compiled package for my openwrt install.  Gave that a try and got it working.

Unfortunately, this project is short-fused and I don't have much time to troubleshoot the mrtg install...even though I got this far :)  I agree, the problem was probably in SNMP_util.pm.  I didn't get too far in examining that or the packet dumps that I captured.  I'm also wondering if running the perl code on a big endian machine vs a little endian machine made a difference?

Thanks again

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