[mrtg] snmp v3 bug with low-speed interfaces

Daniel J McDonald dan.mcdonald at austinenergy.com
Mon Apr 17 17:54:47 MEST 2006

On certain Cisco platforms, the ifHCInOctets counters are not populated
for certain low-speed interfaces.  This poses a dilemma for snmp v3
users.  The current scheme  for snmp v2 relies on cfgmaker to determine
if the ifHCInOctets counters exist, and if not changes the snmp version
to "1" instead of 2.  But snmp v3 provides not only different counters,
but also different authentication methods, so a simple fallback to a
different version of snmp is not sufficient.

Possible approaches to fix this:
1.  Check every query of ifHCInOctets for "NoSuchInstance" and fall back
at run-time within MRTG_lib.pm
2.  Create a separate flag in the interface config to query low-speed
3.  change the line generated by cfgmaker to read something like:
Target[slowrouter_Se0_1_0]: ifInOctets#Se0/1\:0&ifOutOctets#Se0/1:0:public at slowrouter::2:1:1:3

Which fix should I work towards?

Daniel J McDonald, CCIE #2495, CNX, CISSP #78281
Austin Energy

gpg Key: http://austinnetworkdesign.com/pgp.key
Key fingerprint = B527 F53D 0C8C D38B DCC7  901D 2F19 A13A 22E8 A76A

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