Port forwarding

[Nigelsp]

I have a docker application that is using the network connection provided by the open-vpn client. My application needs to receive udp packets on port 42000. The connection is working fine , other than udp packets on 42000 are not reaching the application.

I cannot seem to open port 42000 using the -p 42000;udp option.

I start the openvpn client with:
docker run -it --cap-add=NET_ADMIN --device /dev/net/tun --name open-vpn --dns 8.8.4.4 -p 42000:42000/udp -v /root/Documents/openvpn:/vpn -d dperson/openvpn-client -r 192.0.2.0/24 -p 42000;udp

the openvpn client responds with bash: udp: command not found...

How should I be opening this port?

[SiestaCat]

This working for me:

services:
  openvpn_client:
    image: dperson/openvpn-client
    cap_add:
      - NET_ADMIN
    volumes:
      - ./client.ovpn:/vpn/client.conf
    command: "-c /vpn/client.conf"
    devices:
      - /dev/net/tun:/dev/net/tun
  web:
    image: my_image
    network_mode: "service:openvpn_client"

In the openvpn server (APT Distro), assuming web docker compose service is listening 8080 port and 2.2.2.2 is the public server ip address, and the openvpn subnet is 10.8.0.0 (cat /etc/openvpn/server.conf):

apt install iptables-persistent -y
iptables -t nat -A PREROUTING -p tcp -d 2.2.2.2 --dport 8080 -j DNAT --to-destination 10.8.0.2:8080
iptables -A FORWARD -p tcp -d 10.8.0.2 --dport 8080 -j ACCEPT
netfilter-persistent save

Open http://2.2.2.2:8080

Should work.

[Nigelsp]

Thanks for the reply. Im still having no joy :-(
Im using the official openvpn server docker image. Openserver has a web ui that handles port forwarding but Im guessing this assumes its not in a container

Ive added
iptables -t nat -A PREROUTING -d 209.250.230.194 -p udp --dport 42000 -j DNAT --to-dest 192.0.2.2:42000
iptables -t filter -A INPUT -p tcp -d 209.250.230.194 --dport 42000 -j ACCEPT
iptables -A FORWARD -p udp -d 192.0.2.2 --dport 42000 -j ACCEPT

209.250.230.194 is the public ip, and 192.0.2.2 is the fixed address of the container using the vpn (ie the tun0 ip)

still no packets getting through