How do I find ports used by an host in DMZ?

[lollapalooza]

Hello,
I have a Raspberry in my LAN, acting as VPN server, behind Gargoyle.

As per documentation, the VPN should be using port 1723 only.

Anyway, when I set-up port forwarding for 1723, both protocols, the VPN client does not connect.

If I set-up DMZ to Raspberry IP, the VPN client connects.

Now... obviously I don't want the DMZ to be set-up there, so I'd like to check what ports are in use when VPN client is connected.

How can I "sniff" the ports?

[Lantis]

Status -> Connections and filter for the device?

[lollapalooza]

Absolutely right :-O
I lost a loooong time googling and trying to find out how to sniff packets via CLI, but the solution was far more easy