digraph G {
    node [ shape=box ]
    rankdir=LR;

    backupserver [ label="ungleich\nIPv6 Backup" ];

    server1  [ label="Server (IPv4)" ];
    server2  [ label="Server (IPv6)" ];
    server3  [ label="Server (Dualstack)" ];

    clientv4 [ label="IPv4 client" ];
    clientv6 [ label="IPv6 client" ];

    backupserver->{server1,server2,server3}

    clientv4->backupserver [ label="Not accessible" ];
    clientv6->backupserver [ label="Accessible (can be restricted)" ];


}