This question was originally posted on DCIM Support by Christian Riis on 2015-02-18
I am trying to validate my network capacity calculations, in a simple data center with two racks, each of them have a patch panel in position 42 and a layer-2 switch in position 41:
From the capacity pie chart I can see that I have used 4% out of 24 ports available, approximately equal to 1 port. Thus I should have 23 ports available.
Now, if I look at the two racks in my data center, I would expect that I have only 22 ports available:
... since each switch has a used connection. In the left rack it is an "incoming" connection (from the server), in the right rack it is an "out-going" connection (to the layer 1 patch panel).
Each of the switches has 11 free ports that can be used for server equipment. Therefor I would expect the capacity pie chart to show a network utilization of approx. 8% (2 used ports out of 24 non-layer-1 ports).
In a larger data center this offset quickly scales to significant values.
Is the omission of connections to layer-1 equipment in the utilization calculation by intention?
This answer was originally posted on DCIM Support by Torben Nielsen on 2015-02-20
I looked into this, and it seems that for a port to count as used, it needs to be part of a complete route. A route does not terminate in a patch panel, so the starting port is not counted as used until the route is completed - i.e. something is plugged into the other side of the patch panel. I believe this is working as intended.
There does, however, seem to be a special case for routes between layer 2 and/or layer 3 network equipment - ports used in these routes are not counted as used. I will need to investigate further, whether there is a reason for this, or if this is unintended.
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