+-----------------------+              +-----------------------+      +-----------------------+
|                       |              |                       |      |      DSL Router       |
|         eth0          |              |          eth0         |      |                       |
|    192.168.200.201 -+-+--------------+--- 192.168.200.202 ---+------+--- 192.168.200.254    |
|                     | |              |                       |      |                       |
|        eth0:1       | |              +-----------------------+      |     (NAT routing)  ---+--- Internet
|    192.168.200.1 ---+ |                  M2                         |                       |
|                       |              +-----------------------+      +-----------------------+
|                       |              |                       |          Router
|         tap0          |              |         eth0          |
|      172.20.0.1    ---+--------------+---  172.20.0.2        |
|                       |              |                       |
+-----------------------+              +-----------------------+
    M1                                     M3


(M1)# route -n
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.200.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0
172.20.0.0      0.0.0.0         255.255.0.0     U     0      0        0 tap0
0.0.0.0         192.168.200.254 0.0.0.0         UG    0      0        0 eth0

(M2)# route -n
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.200.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0
0.0.0.0         192.168.200.254 0.0.0.0         UG    0      0        0 eth0

(M3)# route -n
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
172.20.0.0      0.0.0.0         255.255.255.0   U     0      0        0 eth0
0.0.0.0         172.20.0.1      0.0.0.0         UG    0      0        0 eth0