A datagram network is operated by placing a group address in the source address field of the datagram. Nodes within the datagram network forward the datagram in dependence on the contents of the source address field. This provides many of the scalability advantages offered by Multiprotocol Label Switched (MPLS) networks without introducing the overheads caused by connection set-up in MPLS networks. The method can also easily provide different quality of service levels to different types of packets and is especially useful in providing Virtual Private Networks across a shared internetwork such as the public Internet.