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

    upstreamrouter1 [ label="Upstream Router 1\nStateless routing" ];
    upstreamrouter2 [ label="Upstream Router 2\nStateless routing" ];

    router1 [ label="Internal Router 1\nStateful routing" ];
    router2 [ label="Internal Router 2\nStateful routing" ];

    servers [ label="Servers" ]
    internet [ label="Internet" shape=oval ]

    servers->{router1,router2} [ label="Use as default router\nSend packets via either" ]
    {router1,router2}->{upstreamrouter1,upstreamrouter2} [ label="Announce 2001:db8::/64\n via BGP\nUse as default router" ]
    {upstreamrouter1,upstreamrouter2}->internet [ label="Forward packets" ]
    internet->{upstreamrouter1,upstreamrouter2} [ label="Send answers" ]
    {upstreamrouter1,upstreamrouter2}->{router1,router2} [ label="Return anwers from the Internet" ]
    {router1,router2}->servers [ label="Forward the answer" ]

}