Small script that I use to remap DNS queries on certain portions of my internal network on my ASUSWRT-based router

reroutedns

#!/bin/sh

APPS_MOUNTED_PATH=`nvram get apps_mounted_path`
APPS_INSTALL_FOLDER=`nvram get apps_install_folder`
APPS_INSTALL_PATH=$APPS_MOUNTED_PATH/$APPS_INSTALL_FOLDER
CONFIG="$APPS_INSTALL_PATH/etc/reroutedns.conf"

. "$CONFIG"
COMMAND="PREROUTING -t nat -m iprange --src-range $IP_RANGE -p udp --dport 53 -j DNAT --to-destination $TARGET_IP"

echo $COMMAND

interrupt()
{
        exit 0
}

cleanup()
{
        echo "cleanup"
        iptables -D $COMMAND
}

trap interrupt SIGINT SIGTERM
trap cleanup EXIT

while true ; do
        iptables -C $COMMAND 2> /dev/null
        if [ $? -eq 1 ]; then
                iptables -A $COMMAND
        fi
        sleep 30 &
        wait
done

reroutedns.conf

IP_RANGE="192.168.1.<first>-192.168.1.<last>"
TARGET_IP="<target dns server>"

reroutedns.control

Package: reroutedns
Architecture: arm
Priority: optional
Section: net
Version: 1.0
OptionalUtility: 1.0.0.1+
Maintainer: ASUS
Suggests:
Conflicts:
Enabled: yes

S50reroutedns

APPS_MOUNTED_PATH=`nvram get apps_mounted_path`
APPS_INSTALL_FOLDER=`nvram get apps_install_folder`
APPS_INSTALL_PATH=$APPS_MOUNTED_PATH/$APPS_INSTALL_FOLDER

case "$1" in
        start|force-reload|restart)
                killall -SIGTERM reroutedns
                cd /opt/bin
                ./reroutedns &
        ;;
        stop)
                killall -SIGTERM reroutedns
        ;;
        *)
                exit 1
        ;;
esac