udhcpc - script isn?t called

[Manuel Sahm]

Hello,

I try to make the udhcpc running.....

I started withplugged cable:

udhcpc -i eth0 -s /etc/init.d/simple.script

then:
udhcpc(v.1.10.2) started
Sending discover
sending Select for 192.168.3.208...
lease of 192.168.3.208 obtained, lease time 4294967295
deleting routers
route: SIOCDELRT: No such process
adding dns 192.168.1.1


it seems to work to get an valid ip address from the dhcp server.....but 
if I unplug my cable the script isn?t called...and if I plug in my cabel 
again the script isn?t called too ?

Thank you for your help