digraph G {
    graph [layout=dot fontname="Cantarell,sans-serif"];
    node [shape=Mrecord fontname="Cantarell,sans-serif"];
    edge [fontname="Cantarell,sans-serif"];

    subgraph cluster_kernel {
        label = <<font point-size="20">Linux (kernel mode)</font>>;
        color = "brown";
        nft_nat_postrouting   [label="NFTables 規則 (nat, postrouting)"];
    }

    pkt_in  [label="DNS response 封包輸入"];
    pkt_out [label="DNS response 封包輸出"];

    pkt_in                 -> nft_nat_postrouting  [label=<<font color="red"><b>1</b></font>>];
    nft_nat_postrouting    -> pkt_out              [label=<<font color="red"><b>2</b></font>>];
}