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

    rankdir="LR";


    ipv6 [ label="IPv6" ]
    icmp6 [ label="ICMP6" ]
    icmp6ns [ label="ICMP6 Neigbor Advertisement" ]
    icmp6nsll [ label="ICMP6 Link layer option" ]
    icmp6other [ label="Option field 1" ]
    icmp6other2 [ label="Option field 2" ]
    icmp6othern [ label="Option field n" ]

    ipv6->icmp6->icmp6ns->icmp6nsll->icmp6other->icmp6other2;

    icmp6other2->icmp6othern [ style="dotted" ];

}