Certain embodiments described herein are generally directed to methods and apparatus for providing a security parameter index (SPI) value for use in establishing a security association between a source tunnel endpoint and a destination tunnel endpoint. In some embodiments, utilization of the SPI bit space is optimized to allow the scaling of key policies within a network. In some embodiment, using an SPI derivation formula, a server in the network is able to generate SPI values whose bit spaces are optimized to allow key policies to scale out.