In one embodiment, a method includes receiving a neighbor discovery message and a border routing message through an interface at a particular router. The interface communicates with a border network segment between first nodes routing with IPv6 using a first routing protocol and different second nodes routing using a different routing protocol. The messages are received from an alien router. The border routing message includes foreign routing data that indicates a route among the second nodes. If the alien router's interface on the border segment does not have a global IPv6 address, then a fictive IPv6 address is generated, which includes a global prefix of an IPv6 address for the particular router and an interface identifier associated with the alien router. The fictive IPv6 address and the foreign routing data are inserted into a domain scope external advertisement message that is sent to the first nodes.