Approved for public release, distribution is unlimited / In order to address the requirements of the rapidly growing Internet, network processors have emerged as the solution to the customization and performance needs of networking systems. An important component in a network is the router, which receives incoming packets and directs them to specific routes elsewhere in the system. Network processors and the associated software control the routers and switches and allow software designers to deploy new systems such as multicasting forwarder and firewalls quickly.This thesis introduces network processors and their features, focusing on the Intel IXP1200 network processor. A multicast design for the IXP1200 using microACE is proposed. This thesis presents an approach to building a multicasting forwarder using the IXP1200 network processor layer-3 forwarder microACE that carries out unicast routing. The design is based on the Intel Internet exchange architecture and its active computing element (ACE). The layer-3 unicast forwarder microACE is used as a basic starting point for the design. Some software modules, called micoblocks, are modified to create a multicast forwarder that is flexible and efficient. / Lieutenant Junior Grade, Turkish Navy