A hub comes in very handy here - especially if you can't set up a switchport as a monitoring port. just use a x-over cable to connect the hub to the switch, then attach the NAS and the PC you are running your sniffer on to the hub. Now you will see all traffic between the NAS and everything else.
Calling SD!
I thought I'd followed the above instructions clearly when running Wireshark, but it would appear not because after resolutely remaining at zero relevant hits since the firewall rule* was defined a few days ago, my HomeHub has today blocked over 10,000 NAS attempts to get outside but Wireshark spotted none of them.
Please will you be kind enough to re-describe?
TVM,
XV
*Custom settings to block all WAN traffic to and from the NAS.