Certain embodiments described herein are generally directed to allocating security parameter index (“SPI”) values to a plurality of endpoints in a network. The SPI values may be derived using an SPI derivation formula and a plurality of parameters. In some embodiments, the SPI values may be derived by an endpoint and in other embodiments by a server. Using the SPI derivation formula and the plurality of parameters enables endpoints and servers to instantaneously derive SPI values without the need for servers to store them.