This object controls how this router advertises a default multicast route to its DVMRP neighbors on an interface: not at all, alongside its other routes, or exclusively instead of specific routes. An admin sets this to originate or only on a router meant to act as the default gateway for multicast traffic leaving a stub network, and leaves it disabled elsewhere to avoid unintended default-route advertisements. For example, setting this to only(3) on an edge router would make it advertise nothing but the default route to its DVMRP neighbors, simplifying their routing tables.