i want to explain how we can add Loopback to work with Dynamips ( another interface).

First Step
add a new loopback with the " Add new hadware " from your control panel.



















second Step

copy your network id from " network device list"



Third Step

create this configuratio

كود:
autostart = False

[mycomp]


[[3640]]
image = c:\Program Files\Dynamips\images\c3640-i-mz.120-28a.BIN
#npe = npe-400
ram = 160


[[ROUTER R1]] 
console = 2001 
model = 3640
s1/0 = R2 s1/0
f0/0 = SW1 1

[[ROUTER R2]] 

[[ethsw SW1]]
1 = access 1
2 = access 1 NIO_gen_eth:\Device\NPF_{513633F8-417A-49D6-A9C0-E0CDE1279388}
Fourth Step

start dynamips and configure ip address on R1 in E0 with 192.168.1.1 /24 ( example ) and configure your Loopback with the same subnet.
after that try to Ping it.