System and method for supporting a partitioned switch forwarding table in a high performance computing environment. Described methods and systems can support partitioned switch forwarding tables (e.g., partitioned LFTs) by setting up hardware registers that divide the LFT into at least two partitions, a first partition that supports legacy forwarding (e.g., standard LID based forwarding without the need to use portions of the GRH), and a second partition to support the GRH based forwarding that is described above. In such a manner, switches and other hardware within a core fabric can behave as legacy nodes/switches having standard LFTs, while also being able to support the extended addressing supplied through the use of portions of the GRH.