#!/bin/bash
# ipv6-dhclient-script - https://github.com/outime/ipv6-dhclient-script/

INTERFACE=$1
BLOCK_ADDR=$2
BLOCK_SUBNET=$3
BLOCK_DUID=$4

DEFAULT_INTERFACE=`ip route get 8.8.8.8 | awk '{print $5; exit}'`

write_from_template () {
    sed -e "s/{{INTERFACE}}/$INTERFACE/g" -e "s/{{BLOCK_ADDR}}/$BLOCK_ADDR/g" -e "s/{{BLOCK_SUBNET}}/$BLOCK_SUBNET/g" -e "s/{{BLOCK_DUID}}/$BLOCK_DUID/g" templates/$1 >> $2
}

err_exit () {
    echo "$1" >&2
    exit 1
}

if [[ "$(id -u)" != 0 ]]; then
    err_exit "Sorry, you need to run this as root."
fi

if [[ -e /etc/debian_version ]]; then
    RELEASE=$(cat /etc/debian_version)
    DISTRO="Debian"
elif [[ -f /etc/centos-release ]]; then
    RELEASE=$(rpm -q --queryformat '%{VERSION}' centos-release)
    DISTRO="CentOS${RELEASE}"
else
    err_exit "This distribution type or version is not supported."
fi

while :
do
clear
    if ! [[ -f /proc/net/if_inet6 ]]; then
        err_exit "Seems that IPv6 is not supported by your kernel or the module is not loaded (is it blacklisted?)."
    fi

    echo "WARNING: Network will restart at the end of this script so any existing connections will be dropped!"
    
    while [[ $INTERFACE = "" ]]; do
        read -e -p "Interface where IPv6 will be enabled: " -i $DEFAULT_INTERFACE INTERFACE
    done

    CURRENT_IPV6=$(ip addr show dev $INTERFACE | sed -e's/^.*inet6 \([^ ]*\)\/.*$/\1/;t;d')
    if [[ $? -eq 0 ]]; then
        echo "You have the following IPv6 addreses configured for $INTERFACE:"
        echo "$CURRENT_IPV6"
        read -e -p "Continue? [Y/n]: " -i "Y" SKIP
        if ! [[ $SKIP =~ ^([yY][eE][sS]|[yY])$ ]]; then
            exit 1
        fi
    fi
    
    while [[ $BLOCK_ADDR = "" ]]; do # to be replaced with regex
        read -p "Your IPv6 block address (e.g. 2001:bb8:3e23:200::): " BLOCK_ADDR
    done
    
    while ! [[ $BLOCK_SUBNET =~ ^[0-9]+$ ]]; do
        read -p "Subnet for your block (e.g. if it's /56, input 56): " BLOCK_SUBNET
    done

    while [[ $BLOCK_DUID = "" ]]; do # to be replaced with regex
        read -p "Associated DUID (e.g. 00:03:00:00:34:b0:0c:47:4a:0e): " BLOCK_DUID
    done

    echo "Working..."

    if [[ $DISTRO = "Debian" ]]; then
        write_from_template Debian/etc_network_interfaces /etc/network/interfaces
    elif [[ $DISTRO = "CentOS6" ]]; then
        write_from_template CentOS6/etc_init.d_ipv6-dhclient /etc/init.d/ipv6-dhclient
        chmod +x /etc/init.d/ipv6-dhclient
    elif [[ $DISTRO = "CentOS7" ]]; then
        write_from_template CentOS7/etc_systemd_system_ipv6-dhclient.service /etc/systemd/system/ipv6-dhclient.service
    fi

    write_from_template etc_dhcp_dhclient6.conf /etc/dhcp/dhclient6.conf

    if [[ $DISTRO = "Debian" ]]; then
        sysctl -w net.ipv6.conf.$INTERFACE.autoconf=0
        write_from_template Debian/etc_sysctl.conf /etc/sysctl.conf
        ifdown $INTERFACE && ifup $INTERFACE
        if [ $? -ne 0 ]; then
            ifup $INTERFACE  # see https://git.io/vbKYM
        fi
    elif [[ $DISTRO = "CentOS6" ]]; then
        chkconfig --add ipv6-dhclient
        service ipv6-dhclient start
    elif [[ $DISTRO = "CentOS7" ]]; then
        systemctl enable ipv6-dhclient
        systemctl restart ipv6-dhclient
    fi

    if [[ $DISTRO != "Debian" ]] || [[ $DISTRO = "Debian" && $VERSION != "6*" ]]; then  # TODO: Support for loading IPv6 rules on boot for Debian Squeeze
        echo "Would you like to limit DHCP client traffic to prevent accidental UDP flood towards your provider?"
        echo "This will enable iptables, add a few rules and load them on boot along with other existing rules."
        if [[ $DISTRO = "Debian" ]]; then echo "This will install an additional package (iptables-persistent)."; fi
        read -e -p "Limit traffic? [Y/n]: " -i "Y" SKIP
        if [[ $SKIP =~ ^([yY][eE][sS]|[yY])$ ]]; then
            ip6tables -A OUTPUT -p udp --dport 547 -m limit --limit 10/min --limit-burst 5 -j ACCEPT
            ip6tables -A OUTPUT -p udp --dport 547 -j DROP
            if [[ $DISTRO = "Debian" ]]; then
                ip6tables-save > /etc/iptables/rules.v6
                apt update -q && apt install -y iptables-persistent
            elif [[ $DISTRO = "CentOS*" ]]; then
                ip6tables-save > /etc/sysconfig/ip6tables
                chkconfig iptables on
            fi
        fi
    fi

    echo "Testing IPv6 connectivity..."
    IPV6_TEST=$(ping6 -c 8 ipv6.google.com | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')
    if [[ $IPV6_TEST > 0 ]]; then
        echo "Success!"
    else
        err_exit "Something went wrong :("
    fi
done