ISP--(via DSL)--+
                |
                |
====MainBuilding|========
                |
            DSLmodem
                |
                V
+-----------------------+
|             NIC1(eth0)|
|                       |
|  LinuxBox(router/NAT) |
|                       |
|             NIC2(eth1)|
+-----------------------+
                      |
                      V
+---------+   +----------+   
|VDSLmodem|<--|LAN switch|
+---------+   | 8ports   |
 |            +----------+ 
 |ordinary     |  |  |  |        
 |telephone    V  V  V  V    
 |wire        pc1pc2pc3pc4   
=|========================
 |
 | ~1km away
 |
=|=========Building2======
 |
 V
+---------+   +----------+   
|VDSLmodem|<--|LAN switch|
+---------+   | 8ports   |
              +----------+ 
               |  |  |  |        
               V  V  V  V    
              pc1pc2pc3pc4