+--------+                  +------------+                +------------+
| ssh    |                  | Hop Server |                | server     |
| client |  _ _ _ ssh _ _ _ | notebook01 |                | notebook02 |
|        | ================ssh========tunnel============> |            |
+--------+  ̅  ̅  ̅  ̅  ̅  ̅  ̅  ̅  +------------+                +------------+