Tracking traffic usage at router or switch port?

[Jason Lee <jason.m.lee () gmail com>]

NANOG Community,

Typically where would you expect a service provider to monitor bandwidth
usage on your circuits? On the physical switch port interface or on the
vlan interface at the router? In some of the field testing I've been doing
there can be a difference in the bandwidth usage on the vlan interface at
the router vs the physical switch port. Is there any particular reason for
using one vs the other? Is there an industry best practice for this?

Thanks,

Jason