At 11:26 PM 1/15/98 -0500, Stephen Balbach wrote:
>Pulling the IfOctets of total bytes, the stats seems to mysteriously reset
>to 0 on occasion. No reboots, etc.. throws the count off and makes one
>wonder how reliable the 'total bytes' stats are.
Stephen,
The IfInOctets/IfOutOctets objects are just raw counters of the number of
bytes in/out of a given interface. In SNMP v1, the values of counters are
limited to 4 bytes in length, which gives a maximum of 2^32-1 or
4,294,967,295. When the counter reaches this value, it has no other choice
except to wrap around to zero. This shouldn't cause a problem, though,
since a single value of IfInOctets/IfOutOctets is meaningless by itself.
It only becomes meaningful when you have 2 or more data points so you can
find a difference over some time interval. The only issue is to make sure
your polling interval is small enough so the counters don't wrap multiple
times in a single poll interval.
>What is the best method of getting reliable cisco usage stats, on a 5
>minute basis, over a long period. Prefer SNMP because of the low resource
>overhead vs. an expect script. Unable to find a SNMP variable that shows
>the 5-minute average as seen in 'sh int'.
Not sure how you are doing your billing, but if you are billing for actual
usage, this may not be what you want. Remember that the 5-minute stats
(locIfInBitsSec/locIfOutBitsSec) are "a weighted 5-minute exponentially
decaying average of interface input/output bits per second."
One more thing, don't forget that serial interfaces are full duplex. To
get an accurate view of utilization, you need to look at inbound & outbound
traffic.
Randy
http://www.clark.net/pub/rbenn/cisco.html
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