1. A method, comprising: receiving, at a first border node between a reactive routing network and a proactive routing network that includes a plurality of border nodes, unsolicited route reply (RREP) packets from each other border node of the proactive routing network, wherein an unsolicited RREP from a particular other border node includes an address of the other border node and an indication that the other border node borders the proactive routing network and another reactive routing network; receiving, at the first border node, an inter-domain route request (RREQ) from a requestor for a destination; determining whether the destination is known to the first border node; in response to knowing the destination at the first border node, responding to the requestor; and in response to not knowing the destination at the first border node: when the first border node is ingressing the inter-domain RREQ into the proactive routing network, encapsulating the inter-domain RREQ in a multicast message and sending the encapsulated multicast message to each of the other border nodes of the proactive routing network, wherein routes to the other border nodes are known to the first border node based on the unsolicited RREP packets from the other border nodes; and when the first border node is ingressing the inter-domain RREQ into the reactive routing network, stripping the inter-domain RREQ from a multicast message sent from one of the other border nodes and sending the stripped inter-domain RREQ into the reactive routing network as a flooded request.