I am monitoring some Colubris devices with NPM at my hotspots, in particular I am interested of how much bandwidth gets used by die different VLANS I have configured on the device itself
VLAN1 = Management Traffic (to get to the site remotely etc)
VLAN2 = Wireless Access (for the clients)
VLAN3 = Fixed Access (for the clients)
Then I also monitor the actual physical ports on these devices
eth0 - wan
eth1 - lan
wlan - wireless
Now, how it has always worked is that the total bytes that went through eth0 was the combined bytes of VLAN1, 2 and 3
Oddly enough, I can't see any utilization of the virtual ports (VLANS). I noticed it some time ago, but got busy with other network operations and haven't had time to make this post, so I can't say for sure when it started (maybe after I upgraded to Engine Version 9.1.0 - SolarWinds Orion Network Performance Monitor 9.1 SP5)
You may want to double check the monitored interfaces by doing a "List Resources".
If you are in maintenance you can also take advantage of th newly integrated Wireless component which will collect additional statistics from devices which support the ieee802dot11 mib.
Hope that helps!