Delegate IPv6 PD from Remote Router

00-installer-config.yaml.template

# This is the network config written by 'subiquity'
network:
  ethernets:
    enp2s0:
      accept-ra: no
      addresses:
      - 192.168.1.2/24
      - $IPV6_ADDR
      gateway4: 192.168.1.1
      gateway6: fe80::8ede:f9ff:feb7:2dbc
      nameservers:
        addresses:
        - 192.168.1.1
        search: []
  version: 2

radvd.conf.template

interface enp2s0 {
  AdvSendAdvert on;
  prefix $IPV6_PD {
    AdvAutonomous on;
  };
  RDNSS fe80::2e0:70ff:fe86:cebb {};
};

update_pd.sh

#!/bin/bash

CURRENT_IPV6_PD=$(ip -6 addr | grep -Po '[\da-z:]+::c9b/64' | sed 's/::c9b\/64/::\/60/g')
ROUTER_IPV6_PD=$(ssh root@192.168.1.1 "ip -6 addr | grep -Po '[\da-z:]+/60' | sed 's/::1/::/g'")

echo "Current: $CURRENT_IPV6_PD, Router: $ROUTER_IPV6_PD"

if [ ! -z "$ROUTER_IPV6_PD" ] && [ "$ROUTER_IPV6_PD" != "$CURRENT_IPV6_PD" ]; then
    echo "New IPv6 prefix detected: $ROUTER_IPV6_PD"

    export IPV6_ADDR=$(echo $ROUTER_IPV6_PD | sed "s/::\/60/::c9b\/64/g")
    envsubst < /etc/netplan/00-installer-config.yaml.template > /etc/netplan/00-installer-config.yaml
    netplan apply

    export IPV6_PD="$ROUTER_IPV6_PD"
    envsubst < /etc/radvd.conf.template > /etc/radvd.conf
    systemctl restart radvd
fi