For the EBBR to be discovered, the EBBR must be the source of the route for the multicast source. This means that the EBBR has to generate the multicast source route and advertise it using IGP in one of the following ways:
Single area: the EBBR is directly connected to the multicast source and therefore is the source of the multicast source route.
Single area: the EBBR has a static route for the multicast source and redistributes this into IGP. Consequently, it becomes the source of the route for the multicast source.
Multiple areas: the EBBR is an ABR and re-advertises the multicast source, making the EBBR the source of that route. In this case, the IBBR must be in the same area.
Multiple areas: the EBBR is an ASBR, and the IBBR has to be in the same AS and area as the EBBR.