WAN Link Util!!!

1998-10-14 18:40:59
Subject: WAN Link Util!!!
From: Leslie Clark <lclark AT US.IBM DOT COM>
To: nv-l AT lists.tivoli DOT com
Date: Wed, 14 Oct 1998 18:40:59 -0400
Here's a cut/paste from my notebook, as it was explained to me by
someone who I'm pretty sure knew what he was talking about:

 For lans, measure both send and receive, since data only flows in one
 direction at a time (half-duplex):

LANIf%Util \
"% interface utilization from                          \
((ifInOctets + ifOutOctets) * 8 * 100) / ifSpeed"      \
                            .     \
                            . +   \
                            8 * 100 *                  \
                            . /

For WANs, measure separately, since data flows both ways at once

WANIf%RecvUtil -
"% interface utilization from                          \
(ifInOctets * 8 * 100) / ifSpeed"                      \
                            .     \
                            8 * 100 *                  \
                            . /

WANIf%SendUtil -
"% interface utilization from                          \
(ifOutOctets * 8 * 100) / ifSpeed"                     \
                            .     \
                            8 * 100 *                  \
                            . /

 A 56kb line can send 56kb and receive 56kb at the same time. So in one
 sense its capacity is 112kb, but not really, since neither can use more
 than 56kb. Two methods:
 1) Take the highest: util = max(wansend,wanrecv)
 This tells you how close you are to the limit, regardless of the
 direction that is being a pig.
 2) Take the average or double the speed:
 This gives effective util of entire link, but is deceptive about how
 close you are to capacity. Eg 99% send and 21% receive would show as
 60% util, but you are really maxxed on the send side.

Hope this help...


Leslie Clark
IBM Global Services - Network & Systems Management - Detroit
(248) 552-4968 TL/896-4968

---------------------- Forwarded by Leslie Clark/Southfield/IBM on 10-14-98
06:22 PM ---------------------------
Please respond to simon AT nettrack.com DOT au
Subject: WAN Link Util!!!


I was looking at the following formula which I have seen
mentioned many times for WAN links:

        max(inOct,outOct) *8 *100/ifSpeed

What does this mean?   Are we taking the highest value
of the two and thresholding on it?    If someone could
explain a bit more than the standard "you need to
accomodate the fact that WAN links are Full Duplex" I would
really appreciate it..   I want to collect and threshold
Utilisation on Cisco serial  WAN interfaces, but the concerns
I have with the above formula are:-

        1. How do I put it into mibExpr.conf?
        2. What is the above formula trying to do?  I looks like it is
            taking the larger of the two and performing a util
            calculation using it and the "ifSpeed" interface value.


Simon Long

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