To exploit the high data rates offered by the physical media, efficient protocol processing in every network node is a must. Network Interface Units (NIU) have a significant role in this regard. Balanced protocol partitioning and processing in a host machine and an NIU, is a key to achieve faster protocol processing in a network node. This paper discusses various issues related to partitioning a protocol stack between a host machine and an NIU. We describe the experiments carried out to understand the partitioning or the OS! protocol layers between a host machine and an NIU. OSINET, a networking software developed at IIT Madras, is used in the experiments that were designed specifically for this purpose. The implementation details of the work along with performance measurements are presented. © 1992 IEEE.