Configuring Reverse Proxy on the Synology DSM 6. Forward port 80 to WebDAV server port 5005

You can Go to Control Panel –> Application Portal
Go to the Reverse Proxy tab and click on “Create”. However, If you try to enter 80 as source port you will receive an error message

This port number is reserved for system use only. Please enter a different number

To forward all traffic from HTTP port 80 to WebDAV server port 5005
I created following file in the /etc/nginx/site-enabled folder

server {
    listen 80;
    server_name yourdomain.com;
    location / {
        proxy_pass http://127.0.0.1:5005;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $remote_addr;
    }
}

Hope this will be helpful