#1: Redirect traffic from port to port (local) #2: Route all incoming traffic to other host preserving the information about requester's IP address

network-redirections.sh

#!/bin/bash

function get_gateway_interface() {
    route|grep default|awk '{print $8}'
}

# Redirect all incoming traffic to the other port
function redirect_port_to_port() {
    # $1 from port
    # $2 to port
    iptables -t nat -A PREROUTING -i $(get_gateway_interface) -p tcp --dport $1 -j REDIRECT --to-port $2
}

function redirect_port_to_other_host() {
    # $1 port
    # $2 target IP address
    gatewayInterface=$(get_gateway_interface)
    iptables -t nat -A DOCKER -i $gatewayInterface -p tcp --dport $1 -j DNAT --to-destination "$2:$1"
}