[AGENT++] Percent of available bandwith, ifinoctets and ifoutoctets

[Arunas Mazeika]

	Hello, I just found out something that is bordering me and it’s
concerning to a formula that I found in the O’REILLY ESSENTIAL SNMP.
It’s the Percent of available bandwidth utilized on an interface
formula:

(Received byte rate + Transmitted byte rate)*800
-------------------------------------------------
                  Interface link speed

	This is valid only for half duplex interfaces. This equation
seems fine to me, the problem is when they translate it to this:

(1.3.6.1.2.1.2.2.1.10 + 1.3.6.1.2.1.2.2.1.16)*800
-------------------------------------------------
	        1.3.6.1.2.1.2.2.1.5

	The two Oid’s in the numerator correspond to both ifinoctets and
ifoutoctets and both are incremental counters that multiplied by 8
provide the amount of bits counted since the agent started, not a bit
rate like it should be, I’m wasn’t surprised when I got an utilization
of 13000%. Please somebody correct me if I’m wrong. The thing that
should be done, I think, is to get the difference of each one ifinoctets
and ifoutoctets in a period of time [(ifinoctets1-ifinoctets2)*8/(period
of time in seconds)] same for ifoutoctets, it would be perfect if agents
could do this each 1 sec. For example I’m testing this with the windows
2000 agent and it does refresh the mib like each 5 seconds, so the only
thing that could be done here is to get an average of the bit rate for
both, if there is a better and more precise way to accomplish this I
would appreciate some suggestions, thanks a lot.

Arunas Mazeika