Given the rapid evolution of attack methods and toolkits, software-based solutions to secure the network infrastructure have become overburdened. The performance gap between the execution speed of security software and the amount of data to be processed is ever widening. A common solution to close this performance gap is through hardware implementation of security functions. Possessing the flexibility of software and high parallelism of hardware, reconfigurable hardware devices, such as Field Programmable Gate Arrays (FPGAs), have become increasingly popular for this purpose. FPGAs support the performance demands of security operations as well as enable architectural and algorithm innovations in the future. This paper presents a survey of the state-of-art in FPGA-based implementations that have been used in the network infrastructure security area, categorizing currently existing diverse implementations. Combining brief descriptions with intensive case-studies, we hope this survey will inspire more active research in this area.