### DHCP option 108
kea dhcp を使用。
option-data に　"v6-only-preferred"　を追加。

    "option-data": [
        { "name":"v6-only-preferred", "data": "3600" }
    ]

この機能はこちらのPRで追加されたっぽい。https://gitlab.isc.org/isc-projects/dhcp/-/issues/132

### RA
https://github.com/radvd-project/radvd
radvd を ソースからビルド。 (途中でいろいろdependancyを入れる必要ありかも)

(途中でいろいろdependancyを入れる必要あるかもしれないものたち。もしかしたらいらないものもあるかも）

sudo apt-get install -y build-essential autoconf pkg-config check autoconf-archive libbsd-dev yacc flex

Added in this PR: https://github.com/radvd-project/radvd/pull/179

git clone https://github.com/radvd-project/radvd
cd radvd
./autogen.sh
configure --prefix=/usr/local --sysconfdir=/etc --mandir=/usr/share/man
make
sudo make install
radvd --version

$ cat /etc/radvd.conf
interface ens192
{
    AdvSendAdvert on;
    MinRtrAdvInterval 3;
    MaxRtrAdvInterval 10;
    AdvDefaultLifetime 1800;

    prefix 2400:5320:0:4300::/64
   {
        AdvOnLink on;
         AdvAutonomous on;
  	AdvValidLifetime 1800;
  	AdvPreferredLifetime 1800;
     };

    route 64:ff9b::/96
    {
        AdvRoutePreference high;
        AdvRouteLifetime 1800;
    };

    nat64prefix 64:ff9b::/96
   {
        AdvValidLifetime 1800;
   };

    RDNSS 2400:5320:0:4210:202:236:88:195
    {
        AdvRDNSSLifetime 1800;
    };
};

### jool

install and start jool

sudo apt install jool-dkms jool-tools
sudo modprobe jool
sudo jool instance add "ipv6mostly" --netfilter --pool6 64:ff9b::/96
sudo iptables -t mangle -A PREROUTING -j JOOL

To make sure it starts up at reboot`jool.service` file.

$ cat /etc/systemd/system/jool.service
[Unit]
Description=Start Jool at system boot

[Service]
ExecStart=/bin/bash -c 'modprobe jool && jool instance add "ipv6mostly" --netfilter --pool6 64:ff9b::/96 && iptables -t mangle -A PREROUTING -j JOOL'

[Install]
WantedBy=multi-user.target

After saving the service file, reload the systemd daemon with:

sudo systemctl daemon-reload

Then, enable your service with:

sudo systemctl enable jool