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Typically I use the following command to show port utilization percentage:

monitor port 1/1/8 rate interval 5

As an example, this would result in the following output every few seconds:

===============================================================================
Monitor statistics for Port 1/1/8
===============================================================================
                                                   Input                 Output
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
At time t = 0 sec (Base Statistics)
-------------------------------------------------------------------------------
Octets                                    75258450207721         75077561029121
Packets                                     690944243167           685878159990
Errors                                                 1                      0

-------------------------------------------------------------------------------
At time t = 5 sec (Mode: Rate)
-------------------------------------------------------------------------------
Octets                                           1185742                1015941
Packets                                            10264                   8347
Errors                                                 0                      0
Utilization (% of port capacity)                    1.11                   0.94

-------------------------------------------------------------------------------
At time t = 10 sec (Mode: Rate)
-------------------------------------------------------------------------------
Octets                                           1182030                1020105
Packets                                            10231                   8397
Errors                                                 0                      0
Utilization (% of port capacity)                    1.10                   0.95

How is the Utilization (% of port capacity) calculated for a 1000Mbps port?

The solution does NOT appear to be (octets*8)/1E9 for a 1000Mbps port. For example, at t = 5 sec, (1185742 octets * 8)/1E9 * 100% = .95% rather than 1.11 %.

I assume there is something to the math used by Nokia/ALU I am not seeing.

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  • Did you divide the number by the 5 seconds or use 5,000,000,000 bits per 5 seconds?
    – Ron Maupin ♦
    Jul 24, 2018 at 16:29
  • 1
    No, if you divide by 5 seconds you end up with 0.19%. Also, if you adjust "interval 5" to "interval 10" you end up with roughly the same results (depending on intermittent traffic), which leads me to believe the octet and packet values are reported as per 1 second.
    – mkitchen
    Jul 24, 2018 at 16:47

1 Answer 1

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The octet statistics count L2, not L1, so do not include preamble, start of frame delimiter and inter frame gaps, totaling 20B per packet on the wire. Port utilization of course looks at L1. If you add 20B per packet you'll see the calculations are correct. So basically use 8*(octets+packets*20)/capacity instead of 8*octets/capacity.

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  • Actually, the 7705 is a router, hinted at by displaying "packets" instead of "frames". So, it's quite possible that it only counts L3 octets and omits L1 and L2 overhead. If the +packets*20 doesn't provide an accurate result either you should try +packets*38.
    – Zac67 ♦
    Jun 23, 2020 at 11:54

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