[mrtg] Bandwidth/Max Speed misreported

Tim Donnelly tim at coalliance.org
Tue Nov 27 19:31:43 CET 2007

On Tue, 2007-11-27 at 10:48 -0700, Tim Donnelly wrote:
> On Tue, 2007-11-27 at 09:11 -0700, Tim Donnelly wrote:
> >> >
> >> >More to the point, cfgmaker blithely reports whatever the host claims 
> >> >as
> >> it's speed from either the ifSpeed or the ifHCSpeed OID.  If you 
> >> >manually walk the switch, do you get sensible values in those two
> >> 
> >> I'm going to admit ignorance here, but how would I manually walk the 
> >> interface?
> >Assuming you have Net-SNMP:
> >snmpwalk -v1 -c public therouter.example.com ifSpeed snmpwalk -v2c -c
> public therouter.example.com ifHCSpeed
> Thanks Dan,
> The results I got are below:
> IF-MIB::ifSpeed.1 = Gauge32: 10000000
> IF-MIB::ifSpeed.2 = Gauge32: 100000000

weren't you looking for gigabit?

Are you certain you have the correct instance?
snmpwalk -v1 -c public therouter.example.com ifName

> IF-MIB::ifSpeed.3 = Gauge32: 0
> IF-MIB::ifSpeed.4 = Gauge32: 0
> IF-MIB::ifSpeed.5 = Gauge32: 0
> IF-MIB::ifSpeed.6 = Gauge32: 0
> It would appear that snmp is giving the correct values, but MRTG is
> just displaying them wrong?

I was looking for gig speeds, yes.  Running the ifName command gives me no
output on one of my servers (janus), and the following on the other that is
showing wrong in MRTG (grdb):

IF-MIB::ifName.1 = STRING: lo
IF-MIB::ifName.2 = STRING: eth0
IF-MIB::ifName.3 = STRING: eth1
IF-MIB::ifName.4 = STRING: sit0

The ifSpeed for that server give me:

IF-MIB::ifSpeed.1 = Gauge32: 10000000
IF-MIB::ifSpeed.2 = Gauge32: 100000000
IF-MIB::ifSpeed.3 = Gauge32: 0
IF-MIB::ifSpeed.4 = Gauge32: 0

Running the ethtool command on grdb produces the following:

Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: g
        Wake-on: d
        Link detected: yes

So snmp is reporting the eth0 is only 100Mb/s and ethtool says it is
1000Mb/s.  I'm inclined to believe ethtool because the switch the this
server is connected to shows that it is operating at 1000Mb/s.  But I am
still confused as to where the inconsistencies lie.  That and not getting
any response back from janus when I run the ifName walk.

Thanks for your help.

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