Simple utility script that allows you to route incoming TCP traffic on one port to another.

port-route

#!/bin/bash
#
# port-route -- route one port's traffic to another.
#
# Simple utility that wraps `iptables` to enable routing TCP
# traffic of one port to another.
#
# Usage:
#
#  port-route <up|down|show> <source port> <destination port>
#
# Examples:
#
#  port-route up 23 22 <-- route incoming telnet traffic to ssh
#  port-route up 80 22 <-- route incoming HTTP traffic to ssh
#  port-route down 80 22 <-- remove the HTTP -> ssh routing
#
# @author emiller
# @date   2013-09-30
#

function usage() {
  echo "usage: `basename $0` <up|down|show> [src port] [dest port]"
  [ -z "$1" ] || echo $1

  exit 1
}

act=$1
src=$2
dst=$3

if [[ ! -z "$act" && "$act" != "show" ]]; then
  [ -z "$src" ] && usage "missing source port"
  [ -z "$dst" ] && usage "missing destination port"
fi

case $act in
  up)
    echo "enabling port route $src -> $dst"
    opts="-A PREROUTING"
    ;;

  down)
    echo "disabling port route $src -> $dst"
    opts="-D PREROUTING"
    ;;

  show)
    sudo iptables -t nat --list
    exit
    ;;

  *)
    usage
    ;;
esac

sudo iptables -t nat $opts -p tcp --dport $src -j REDIRECT --to-ports $dst