i have set a dhcp on a clients rb and it works fine but anytime the rb restarts a new route will be created in the route table pointing 0.0.0.0/0 to the ether1 port.
i have look at the configuration and seem not to get where the route is coming from .

please help.

The route can come from the dhcp-client configuration. There is an option add-default-gateway=yes, when route is added for the DHCP client.