Monitoring VLANs traffic rate by SNMP

Hello All,

I want to monitor traffic rate of configured VLANs on the BIG-IP LTM V.11.6.0 on Viprion 2400 with B2250 by SNMP. I tried PRTG and Solarwinds NPM but the result was not OK and the returned values was much less than the real traffic. It was OK in the physical interfaces but wrong on the VLANs. Do you know how can I do that? Is there specific OID for the VLANs traffic?

Thank you, Ali