Port-mirroring would work for any traffic that traversed the smart switch ... I actually tried that at one point, but it's somewhat limited:
> If the smart switch is on the LAN side of the router, then I only see traffic from wired devices on the LAN and miss anything from wireless clients.
> If the smart switch is on the WAN side of the router, then I see any traffic destined for the Internet, but now the Pi has to account for NAT (everything coming back from DNS has a destination of my router's WAN interface).
> If the smart switch is on the LAN side of the router, then I only see traffic from wired devices on the LAN and miss anything from wireless clients.
> If the smart switch is on the WAN side of the router, then I see any traffic destined for the Internet, but now the Pi has to account for NAT (everything coming back from DNS has a destination of my router's WAN interface).