digraph G {
    node [ shape="box"];


    ipv6 [ label="IPv6" ]
    icmp6 [ label="ICMP6" ]
    icmp6ns [ label="ICMP6 Neigbor Advertisement" ]
    icmp6nsll [ label="ICMP6 Neigbor Solicitation Link layer option" ]
    icmp6other [ label="More option fields" ]

    ipv6->icmp6->icmp6ns->icmp6nsll->icmp6other;

}