Network topology

       ,----------------------------------------.
       |            Rest of Internet            |
       `-------+--+------------------+--+-------'
               |  |                  |  |
          ,----+--+--.            ,--+--+----.
          | router 1 |            | router 2 |  ...
          `--+-------'            `-------+--'
             |                            |
          ,--+-------.            ,-------+--.
          | switch 1 +------------+ switch 2 |  ...
          `-+------+-'            `-+------+-'
            |      |                |      |
     ,------+-.  ,-+------.  ,------+-.  ,-+------.
     | host 1 |  | host 2 |  | host 3 |  | host 4 |  ...
     `--------'  `--------'  `--------'  `--------'