[mrtg] WAN Speed

Jay Hennigan jay at west.net
Wed Jul 9 05:28:34 CEST 2014

On 7/8/14 2:36 PM, Tyler, Rodney wrote:
> I have setup mrtg to monitor traffic 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, but we need to verify what we are actually getting. 
> I  have come to realize that simply monitoring the WAN interface gives
> me a nice graph and actual kB/s (or MB/s) data passed, as shown below;
> however, the percentages are based on my Maxbytes value that is based on
> what the ISP says we are getting (100Mpbs or 12.5MB/s).  In other words,
> I can change the percentages by adjusting MaxBytes.  Is there any way to
> use mrtg to verify the available bandwidth over the WAN, or do I need a
> different tool?

MRTG will show historical utilization but not capacity.  On a heavily
used link you can sometimes infer capacity based on the shape of the
graph but it is not definitive (and by then it's likely time to upgrade).

One tool to consider is iperf.



Iperf requires a pair of devices running the code, one at each end of
the link to be measured.

Also search for bandwidth-delay-product and LFN (Long fat network) for
caveats and gotchas, particularly if the two campuses are some distance
apart resulting in propagation delay.

Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV

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