A smart NIC (Network Interface Card) is provided with features to enable the smart NIC to operate as an in-line NIC between a host's NIC and a network. The smart NIC provides pass-through transmission of network flows for the host. Packets sent to and from the host pass through the smart NIC. As a pass-through point, the smart NIC is able to accelerate the performance of the pass-through network flows by analyzing packets, inserting packets, dropping packets, inserting or recognizing congestion information, and so forth. In addition, the smart NIC provides a lightweight transport protocol (LTP) module that enables it to establish connections with other smart NICs. The LTP connections allow the smart NICs to exchange data without passing network traffic through their respective hosts.