The embodiments herein relate to methods, a source host device, an edge router device and a hop router device for routing data packets in a network topology. A method includes sending a request to a server for requesting an autonomous system number of an autonomous system to which a destination host belongs; receiving a response including the autonomous system number; inserting the received number between layer 2 and layer 3 of the data packet and sending the data packet towards the autonomous system hosting the IP address of the destination host. When a router belonging to the autonomous system receives the packet, the number is removed and forwarded to the destination host.