[mrtg] MaxBytes Question

Pavel Ruzicka pavouk at pavouk.org
Wed Sep 4 17:30:56 CEST 2013

Hello Rodney!

Easy way is generate configuration for MRTG automatically with "cfgmaker"
for example one per 24 hours.
cfgmaker generates Maxbytes from "ifhighspeed" and "ifspeed" snmp values.
On cisco is this value initially from "bandwidth" which is from speed of

If you want to have right percent values on the graphs, that you can
set it on the interface with command "bandwidth 100000" for 100Mbps.

If you will have more traffic than MaxBytes, that this value will not be visible
on the graph. (I don't remember if MRTG ignore this value before write to the
database file).

best regards,


> I'm new to MRTG and bandwidth monitoring, but I've been asked to setup
> traffic monitoring for a specific Ethernet interface on a Cisco Catalyst
> 6509 that connects two campuses over a fiber WAN link.  The third party
> fiber provider says they are giving us 100Mbps across the fiber, and we
> want to verify if we are getting that, as well as document our throughput
> historically.  I have managed to setup SNMP and MRTG and get successful
> connections, but I'm confused about the MaxBytes, AbsMax, and Unscaled.  As
> I said, the link speed is supposed to be 100Mbit/s (100Mbps).  But our
> interface is connected at 1000Mbps, as shown below from a partial "show
> interface" command:
>   Hardware is C6k 1000Mb 802.3
>   MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
>   Full-duplex, 1000Mb/s, media type is 10/100/1000BaseT
>   Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
>   Queueing strategy: fifo
>   Output queue: 0/40 (size/max)
>   5 minute input rate 544000 bits/sec, 408 packets/sec
>   5 minute output rate 5656000 bits/sec, 595 packets/sec
>      554615327 packets input, 128091215313 bytes, 0 no buffer
>      839477309 packets output, 1079159783816 bytes, 0 underruns
> What should my MaxBytes be set to?  Is it supposed to reflect my 1Gbps
> interface speed or the 100Mbps link speed stated by the vendor?  Do I need
> to set the AbsMax and Unscaled keywords?  Also, what is the best way to
> "clear" the MRTG data collected thus far and start over?  My current graph
> looks like this:

More information about the mrtg mailing list