While doing shadowing across firewall by default people guess 1494/2598 but that is not the case. Shadowing is tested RPD over RDP /RDP over ICA and both have different result.
We captured wireshark trace and found that 139 and 445 which is not responding to send sync.
Once we opened above port shadowing started working. So for shadowing to work across firewall we need to open port 139/445/1494/2598