A script to set up IPv6 router advertisment proxy for single peer

setup_ipv6_hacky_router.sh

#!/bin/bash

set -e
if [ -z "$2" ]; then
    echo "Script to set up router advertising proxy for one peer"
    echo "Usage: setup_ipv6_hacky_router UPLINK DOWNLIK"
    echo "Example: setup_ipv6_hacky_router eth0 wlan0"
    exit 1
fi

UPLINK=$1
DOWNLINK=$2


echo "Trying to forward stateless-configured IPv6 from $UPLINK to $DOWNLINK"
echo "0. Checking prerequisites"

tcpdump -h 2>&1 | grep -q version
radvdump -h 2>&1 | grep -q usage
radvd -v 2>&1 | grep -q Version;
npd6 --version 2> /dev/null > /dev/null

echo "1. Turning on forwarding on $UPLINK and $DOWNLINK"

echo 2 > /proc/sys/net/ipv6/conf/$UPLINK/accept_ra
echo 1 > /proc/sys/net/ipv6/conf/$UPLINK/forwarding
echo 1 > /proc/sys/net/ipv6/conf/$DOWNLINK/forwarding

T=/tmp/hackyipv6
mkdir -p "$T"
cd "$T"

echo "2. Getting radvd configuration from $UPLINK and fixing it for $DOWNLINK"
# FIXME: exits on the second dump from radvdump, not the first
radvdump | perl -ne "
    s@interface $UPLINK@interface $DOWNLINK@; 
    s@^.*RtrAdvInterval.*\$@    MaxRtrAdvInterval 5;@;
    print; 
    exit 0 if /End of interface definition/;
    " > radvd.conf

echo "3. Starting radvd"
radvd -p radvd.pid -n -C radvd.conf -m stderr &
RADVPID=$!

trap "kill $RADVPID" EXIT

echo "4. Determining peer's IPv6"
# 02:39:04.127632 IP6 2001:470:7bd6:e105:88af:83ff:fed9:c835 > 2600::: ICMP6, echo request, seq 1, length 64
PEER="$(tcpdump -i $DOWNLINK -c 1  -n  'ip6 and not net fe00::/7' 2> /dev/null | perl -ne '/IP6 ([^ .]{4,})[ .]/ and print "$1\n"')"
PREFIX=${PEER/:*/}:
echo "PEER=$PEER PREFIX=$PREFIX"

echo "5. Adding a route for the peer"
ip -6 route add $PEER/128 dev $DOWNLINK || true

echo "6. Starting npd for the peer"
cat > npd6.conf <<EOF
prefix=$PREFIX
interface = $UPLINK

listtype = white
addrlist = $PEER

collectTargets = 100
linkOption = false
ignoreLocal = true
routerNA = true
maxHops = 255
pollErrorLimit = 20
EOF
npd6 -f -c $T/npd6.conf -l - &
NPD6PID=$!

trap "kill $RADVPID $NPD6PID" EXIT

sleep 2
echo "Finished. Sleeping and terminating services on exit"
echo "(Note: $UPLINK's and $DOWNLINK's forwarding mode and a route to $PEER will not be cleaned up)"
sleep infinity