Script for dhcp6c to handle IPv6 network prefix translation as described in https://blog.altimos.de/2016/11/isolating-your-home-ipv6-network-with-nptv6-on-edgerouter-lite/

my-npt-dhcp6c-script

#!/bin/bash

INSIDE_PREFIX="fdxx::/64"
OUTSIDE_INTERFACE="eth2"
DUMMY_INTERFACE="dummypd0"
OUTSIDE_PREFIX_FILE="/var/run/my-npt-outside-prefix"

logger -p info -t my-npt "my-npt-dhcp6c-script invoked"

OLD_OUTSIDE_PREFIX=""
if [ -f "$OUTSIDE_PREFIX_FILE" ]; then
  OLD_OUTSIDE_PREFIX=`cat $OUTSIDE_PREFIX_FILE`
fi

# assumes IP on dummy interface ends with ::1/64
NEW_OUTSIDE_PREFIX=`ip -6 -o addr show $DUMMY_INTERFACE | head -n 1 | cut -d\  -f 7 | sed 's,::1/64,::/64,'`

# on prefix change
if [ "$OLD_OUTSIDE_PREFIX" != "$NEW_OUTSIDE_PREFIX" ]; then
  # delete old NPTv6 firewall rule if present
  if [ -n "$OLD_OUTSIDE_PREFIX" ]; then
    logger -p notice -t my-npt "deleting old DHCPv6-PD prefix $OLD_OUTSIDE_PREFIX from NPTv6"

    ip6tables -t nat -D PREROUTING -i $OUTSIDE_INTERFACE -d $OLD_OUTSIDE_PREFIX -j NETMAP --to $INSIDE_PREFIX
    ip6tables -t nat -D POSTROUTING -o $OUTSIDE_INTERFACE -s $INSIDE_PREFIX -j NETMAP --to $OLD_OUTSIDE_PREFIX
    rm $OUTSIDE_PREFIX_FILE
  fi

  # add new NPTv6 firewall rule if new prefix
  if [ -n "$NEW_OUTSIDE_PREFIX" ]; then
    echo -n "$NEW_OUTSIDE_PREFIX" > $OUTSIDE_PREFIX_FILE
    logger -p notice -t my-npt "adding new DHCPv6-PD prefix $NEW_OUTSIDE_PREFIX to NPTv6"

    ip6tables -t nat -A PREROUTING -i $OUTSIDE_INTERFACE -d $NEW_OUTSIDE_PREFIX -j NETMAP --to $INSIDE_PREFIX
    ip6tables -t nat -A POSTROUTING -o $OUTSIDE_INTERFACE -s $INSIDE_PREFIX -j NETMAP --to $NEW_OUTSIDE_PREFIX
  fi
fi

# show debug: ip6tables -S -t raw; ip6tables -S -t nat
# do debug: conntrack -f ipv6 -L; ip6tables -t raw -D OUTPUT -j NOTRACK; ip6tables -t raw -D PREROUTING -j NOTRACK
# to expire and renew prefix: kill -HUP $(cat /var/run/dhcp6c.pid)

exit 0