uplink traffic on a switch

[IT Csar]

To analyze the internet bandwidth usage in a company, I mirrored uplink port on a main switch, and connected box running ntop. This setup delivered clear picture on uplink traffic, however I am getting some of the NFS traffic sourced/destined to internal network. I would expect NFS packets should never travel on uplink (may be broadcast, ARP, DHCP, but not NFS) to the router/gateway. Should main switch route NFS internal traffic w/out sending them all the way to router and back?

Thanks