A method for communication in a packet data network that includes at least first and second subnets interconnected by multiple routers and having respective first and second subnet managers. The method includes assigning respective local identifiers to ports for addressing of data link traffic within each subnet, such that the first subnet manager assigns the local identifiers in the first subnet, and the second subnet manager assigns the local identifiers in the second subnet. The routers are configured by transmitting and receiving control traffic between the subnet managers and the routers. Data packets are transmitted between network nodes in the first and second subnets via one or more of the configured routers under control of the subnet managers.