Messages in this thread | ![/](/images/icornerl.gif) | | From | Leif Sawyer <> | Subject | RE: IP Acounting Idea for 2.5 | Date | Mon, 16 Apr 2001 15:52:39 -0800 |
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> From: Ian Stirling [mailto:root@mauve.demon.co.uk] > > Manfred Bartz responded to > > > Russell King <rmk@arm.linux.org.uk> who writes: > <snip> > > > You just illustrated my point. While there is a reset capability > > > people will use it and accounting/logging programs will get wrong > > > data. Resetable counters might be a minor convenience > when debugging > > > but the price is unreliable programs and the loss of the > ability of > > > several programs to use the same counters. > > > > You of course, are commenting from the fact that your > applications are > > stupid, written poorly, and cannot handle 'wrapped' data. Take MRTG > <snip> > > Similarly, if my InPackets are at 102345 at one read, and > 2345 the next > > read, > > and I know that my counter is 32 bits, then I know i've > wrapped and can do > > I think the point being made is that if InPackets are at > 102345 at one read, > and 2345 the next, and you know it's a 32 bit counter, it's completely > unreliable to assume that you have in fact recieved 4294867295 > packets, if the counter can be zeroed. > You can say nothing other than at least 2345 packets, at most > 2345+n*2^32 have been got since you last checked.
Ah, yes.. I seem to have misplaced a bit of text in my reply.
The continuation of thought:
How the application derives the status of a wrapped counter or a zero'ed counter is dependant on the device being monitored.
Yes, you have to know what your interface is capable of (maxbytes/sec) so that you can do a simple calculation where:
maximum_throughput = maxbytes_sec * (time_now - time_last_read)
and if your previous good counter + the maximum throughput wraps the counter, you have a good chance that you've simply wrapped.
If not, then you can assume that your counters were cleared at some point, log the data you've got, and keep moving forward.
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