US Patent 7630392 Multi-homing using controlled route leakage at a backup service provider

A technique for implementing route aggregation in a computer network containing a multi-homed customer site connected to primary and second networks, which in turn are both connected to a common “backbone” network. According to the technique, the primary network allocates a block of network addresses for the customer site, and the customer site notifies the secondary network of its allocated addresses. The secondary network first determines whether the primary network has already advertised an aggregated route which incorporates the customer site's route. If so, the secondary network “suppresses” (i.e., does not advertise) the customer site's route. The secondary network only “unsuppresses” the customer site's route if it detects that the primary network has lost connectivity to the customer site and/or the backbone network.