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Calculate Bandwidth for a CISCO interface using SNMP

Using SNMP to interrogate Cisco firewalls. I am trying to
create NMS reporting on a CISCO ASA firewall interface "OUTSODE"
I have the OID's and can interogate and get a value returned.
The OID's I need are :=
# = interface number
Once I get a value returned I have been performing the following
(<interfaces.ifTable.ifEntry.ifInOctets.> * 8) / 1024 then divide by 1024

Although this returns a vlaue, the value is larger than 100Mb which
is the interface's max speed. I have reduced the polling frequency to
1 min.
Can anyhelp me with what I need to do to get a proper and more
meanigful value.

1 Solution
interfaces.ifTable.ifEntry.ifInOctets.# is total bytes without a time dimenstion. If you want to use the method you are describing, for each of your traffic directions I'd suggest doing your poll (call it CurrPoll), keeping the last poll (call it LastPoll), and as accurately as possible track the time between your polls (as SecondsBetwPolls). Then have your monitor app use this algorithm:
((CurrPoll - LastPoll)*8)/SecondsBetwPolls
yielding for you a fairlyaccurate number on bits per second.
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