Re: services dhcp-local-server vs service dhcp and vlan

yes you are right,

for testing: I changed the maximum-lease-time 5second and then I unlplugged/wait/plugged again and the IP changed !

or manually I can do this "clear dhcp server binding" , it also works 

So both of the above solutions are working but  my point is , if you change configuration from this 

host maclaptop {                 
            hardware-address AA:BB:XX:XX:XX:XX;
            ip-address 192.168.3.20;    
        }      

to 

host maclaptop {                 
            hardware-address AA:BB:XX:XX:XX:XX;
            ip-address 192.168.3.30;    
        }      

 then

commit

the Juniper I guess should clear the row of this IP automatically or probabily this is a normal behavior .