[rrd-users] Re: Spikes

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Mon Dec 6 01:20:31 MET 1999

> presentation. It appears that the 7500 is doing some double 
> counting of out going packets when it comes under load. 
> Any one else seen this behaviour?

Until recently I had some BVIs on our 7500.  LAN traffic was far more
than WAN traffic and yes, I too was puzzled by some of the figures.
The traffic in on one BVI did not match the traffic out on the other
and there is no way that this could be due to WAN traffic.  This means
that inbound and outbound traffic should have been, roughly, the same.

It did indeed happen when processing large amounts of data (in my case
also a few hours).  On the other hand, I don't think it is caused by
load either as the 7500 is capable of handling much more traffic than
we did at that time.  

I do agree that it seems that traffic is counted twice; perhaps this
happens in both a VIP and a RSP ?

A quick scan in the bug navigator finds to many bugs to choose from.
One of them, id CSCdm60254 could be the one we're looking for, it
says: "The output counters of PA-8T-V35 module on a vip2-40 in a
7500 connected via 2Mb/s to a remote 2501 is incorrect..." etcetera.
The workaround for this specific bug is to disable CEF.

Another one (CSCdi41891) talks about two counters who get both incremented
when only one should be.  In my case this should not be possible as this
bug should be fixed.  OTOH a similar bug is not unthinkable.

Several other bugs exist, more or less the same, such as "ip ping
packets" that causes either a double answers or one answer that is
counted twice (personally I think this looks remarkably the same as
the previous bug).

It seems that counting octets is very hard to do properly.  It fails
on several occasions, not only the 7500.  Some bugs are fixed and
reintroduced (or at least they *look* similar).  As the hardware gets
more and more complex, the number of problems will increase unfortunately.

Time to say "sigh" and carry on doing monitoring on both sides of the link.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
| work                                                         private |
| My employer is capable of speaking therefore I speak only for myself |

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