[mrtg] MRTG and Gigabit and 10GB

Daniel J McDonald dan.mcdonald at austinenergy.com
Thu Nov 8 14:09:09 CET 2007

On Thu, 2007-11-08 at 09:39 +0000, John Cushnie wrote:
> Hi,

> Also where do the Max speeds reported for the interface come from?

I just re-read the source code.  If you are using snmp version 2 or 3,
then ifHighSpeed is consulted if ifSpeed is zero, undefined, or 2**32 -
1.  If you are using snmp version 1, then ifSpeed is used without any
similar checks.

However, it would be theoretically possible to use snmp version 1, even
with a 10G interface, if Interval: were set low enough.  However, I
think you need an  interval of .8 seconds.  But it would be possible to
have an interface with a speed greater than 4Gb/s (maybe some sort of
GigEtherChannel) that could polled with snmp v1.

I think a better patch would be to:
1. Always check ifHighSpeed, even if snmpv1 is used.
2. Warn if the maximum speed exceeds the limits of 32 bit counters for
the interval selected.

> 1GB is reporting 125.0 MB/sec
> 10GB is reporting 536.9MB/sec

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

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