1. A method for communicating data packets between a transmitting virtual router in a transmitting computer device and a receiving virtual router in a receiving computer device, the method comprising the steps of a) establishing a security association for the secure transmission of data packets between the transmitting computer device and the receiving computer device, b) identifying the transmitting virtual router and the receiving virtual router within said security association, c) in the transmitting computer device, using the identification of the transmitting virtual router within the security association in the selection of the security association for processing a data packet coming from the transmitting virtual router, d) in the receiving computer device, selecting the security association for processing a data packet coming from the transmitting computer device on the basis of values contained within the data packet, and e) in the receiving computer device, directing the data packet processed within the security association to the receiving virtual router on the basis of the identification of the receiving virtual router within the security association.