Port forwarding to VPN Client

[Jonnny]

Hello everybody,

I have a doubt in forwarding the traffic of a software port with destination to a VPN Client (sorry for the noob question).

I found these commands, but I wanted to know if it's the right/safe thing to do.

iptables -t nat -A PREROUTING -i INTERFACE -p udp --dport PORT -j DNAT --to-destination IP_ADDRESS
iptables -t nat -A PREROUTING -i INTERFACE -p tcp --dport PORT -j DNAT --to-destination IP_ADDRESS

INTERFACE = tun13 (eg. interface 3 of OpenVPN Client)
PORT = 3440 (eg. port defined in software)
IP_ADDRESS = 192.168.1.10 (eg. IP of device where installed the software)

If this port is already defined in the GUI (WAN --> Virtual Server / Port Forwarding), it would be better to remove it, correct?

Finally, if the Killswitch option is enable on the VPN Client, will traffic be blocked if the VPN connection fails?

Thanks.