Central banks around the world are actively researching and investigating the benefits, challenges, and design options of wholesale and retail central bank digital currencies (CBDCs). Since CBDCs are one of the most critical components of a national payment system (NPS), it is important that their interoperability with other payment systems is one of the key considerations in the design process. The ITS Technology and Innovation (ITSI) team, in collaboration with the World Banks's Finance Competitiveness and Innovation (FCI) Global Practice, has conducted technology design experiments on two specific scenarios regarding CBDC system interoperability with fast payment systems (FPS). In the first scenario, the experiment investigated the option of settling FPS obligations in a wholesale CBDC system, including the option to reserve funds to guarantee the settlement of FPS net obligations. In the second scenario, the team investigated the interoperability between users within the FPS and retail CBDC users, including the transfer of funds among both types of users, using common services such as address resolution services. This experiment illustrated how CBDC systems can interoperate with retail payment systems through an interlinking bridge that was used to route messages and application programming interface (API) calls among different systems. The programmability features of distributed ledge technology (DLT) were used to link the settlement in CBDC to the transfer of funds in the FPS. The technical applicability for this type of interoperability was demonstrated through the experiments, with the caveat that these experiments do not take into account complexities that may be involved with live systems.