SG300 Monitoring vlan traffic

Hi guy,

I set up my SG300 switch as layer 3 by configuring SVI in it.

now i have multiple users connected to multiple svi i want to monitor each traffic passing thru base on vlan.

I have successfully able to individually graph the port usage via cacti on each interface.

My question is the value of traffic in the svi is zero. Any recommendation on proper tools that can graph the svi on the sg300 i have tried also prtg and same result.

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Thanks,