Sniffing A VPN Router

Hello and good day,

I have a Linksys RV016 VPN Router which I am trying to sniff. I would
like to see all of the traffic using Ethereal (or a similar program),
but right now I can only see Broadcast and Multicast traffic, as well
as Unicast to and from my local machine. I have tried plugging into
the uplink port which I hear sometimes works, but does not in this
case. Also, this router has no options to mirror or span ports, which
I guess would have been another solution. Other than replacing this
router with a hub (possible since it is for a dedicated LAN, i.e. no
WAN connection), is there a way for me to sniff all traffic directed
over all ports of this router? Is there a way I can do it with VLANs?
Is there a tool better than Ethereal or one designed for this purpose?

Thank you for your time!

- Jason