ODR – On-Demand Routing was nothing that i had heard of before i hit it in the workbook. The idea is kind of clever, but limited. The idea is to use CDP to advertise a default route in a topology with hub and stub spoke routers. Where a default route and only a default route will ever be needed. The implementation is simple, one single command on the hub routers lets the router advertise a default route to connected routers via CDP.
To make ODR work you need to enable CDP, obviously. And also make sure no other routing protocol is running there. Also kind of makes sense. And ofcourse the one command to enable the ODR function – “router odr”