On Demand Routing, do not mistake this for DDR (Dial on Demand). Cisco on how to configure this on 12.4.

ODR is a feature that provides IP routing for stub sites, with minimum overhead. The overhead of a general, dynamic routing protocol is avoided without incurring the configuration and management overhead of static routing.

Prefix based, as such supports VLSM

router odr – enables ODR on the hub router. On the stub router, no IP routing protocol must be configured. From the standpoint of ODR, a router is automatically considered to be a stub when no IP routing protocols are configured.

ODR uses CDP to carry minimal routing information between the hub and stub routers. The stub routers send IP prefixes to the hub router. The hub router provides default route information to the stub routers, thereby eliminating the need to configure a default route on each stub router.

• no cdp run – global configuration disables the propagation of ODR stub routing information entirely.
• no cdp enable – interface configuration disables the propagation of ODR information on a particular interface.

Use a distribute-list in on the hub to filter incoming advertisements.

Use the CDP timers to influence ODR route advertisements, ODR aging timers are used for dropping old routes.

Further notes:

For interfaces that specify dialer mappings, CDP packets will make use of dialer map configuration statements that pertain to the IP protocol. Because CDP packets are always broadcast packets, these dialer map statements must handle broadcast packets, typically through use of the dialer map broadcast keyword. The dialer string interface configuration command may also be used.

On DDR interfaces, certain kinds of packets can be classified as interesting. These interesting packets can cause a DDR connection to be made or cause the idle timer of a DDR interface to be reset. For the purposes of DDR classification, CDP packets are considered uninteresting. This classification occurs even while CDP is making use of dialer map statements for IP, where IP packets are classified as interesting.