[c-nsp] Total bandwidth usage

[Bill Wichers]

> Hi,
>    We are currently looking into usage based charges for our customers as
> an
> alternative option. Are there any free application thats is able to get
> total
> bandwidth usage (daily/weekly/monthly etc reports) which are port based?
> MRTG
> only gets bandwidth utilization rate and not the exact total utilization.
> I
> have a few questions:

MRTG actually keeps track of the value of the byte counter of a port
between samples, so it most certainly *does* keep track of "total
utilization" (but not forever, there are history limitations). You just
need to write a script that can pull the data out and present it in some
form other than rate-based traffic graphs. I'm sure the MRTG list (hint)
could tell you all about it. I've successfully used a a PHP script called
"MRTG Total Traffic Generator" in the past.

> - If an application monitors total utilization for a number of ports on
>   different devices wouldn't it be cpu, memory and bandwidth intensive?

You need a *lot* of ports to watch before you'll challenge recent
hardware. Thousands of ports...

> - Are there any application that gathers bandwidth usage on intervals? If
> yes
> wouldn't it be a problem if the interface counters are reseted?

Lots of things can do that. MRTG, Cisco Works, all kinds of network
management software, etc. Most port counters are just 32 or 64 bit binary
counters, and when they reset they just go from '111...111' to
'000...000'. Since all you care about is the absolute difference between
the two values (which is equal to the number of bytes through a port since
the last sample), the reset doesn't matter since you still have a valid
byte count. The only thing that can be a problem is if the counter resets
*more than once* in *one sample interval*. This is usually only a problem
with 32 bit counters on OC3+ interfaces that are capable of moving more
bytes in a 5-minute sample than a 32 bit counter is capable of counting
(about 114Mb/s is the limit). Those interfaces usually have 64 bit
counters available too which will solve that problem.

     -Bill

*****************************
Waveform Technology
Systems Engineer