Limago: An FPGA-Based Open-Source 100 GbE TCP/IP Stack

The realization that the network is becoming an important bottleneck in computing clusters and in the cloud has led in the past years to an increase scrutiny of how networking functionality is deployed. From TCP Offload Engines (TOEs) to Software Defined Networking (SDN), including Smart NICs and In-Network Data Processing, a wide range of approaches are currently being explored to increase the efficiency of networks and tailor its functionality to the actual needs of the application at hand. To address the need for an open and customizable networking stack, in this paper we introduce Limago, an FPGA-based open-source implementation of a TCP/IP stack operating at 100 Gbit/s. To our knowledge, Limago provides the first complete description of an FPGA-based TCP/IP stack at these speeds, thereby illustrating the bottlenecks that must be addressed, proposing several innovative designs to reach the necessary throughput, and showing how to incorporate advanced protocol features into the design. As an example, Limago supports the TCP Window Scale option, addressing the Long Fat Pipe issue. Limago not only enables 100 Gbit/s Ethernet links in an open source package, but also paves the way to programmable and fully customizable NICs based on FPGAs.