NFShunt: A Linux firewall with OpenFlow-enabled hardware bypass

Data-intensive research computing requires the capability to transfer files over long distances at high throughput. Stateful firewalls introduce sufficient packet loss to prevent researchers from fully exploiting high bandwidth-delay network links. To work around this challenge, the Science DMZ design trades off stateful packet filtering capability for loss-free forwarding via an ordinary Ethernet switch [1]. We propose a novel extension to the Science DMZ design, which uses an SDN-based firewall. This paper introduces NFShunt, a firewall based on Linux's Netfilter combined with OpenFlow switching. Implemented as an OpenFlow 1.0 controller coupled to Netfilter's connection tracking, NFShunt allows the bypass-switching policy to be expressed as part of an iptables firewall rule-set. Our implementation is described in detail, and latency of the control-plane mechanism is reported. TCP throughput and packet loss is shown at various round-trip latencies, with comparisons to pure switching, as well as to a high-end Cisco firewall. The results support reported observations regarding firewall introduced packet-loss, and indicate that the SDN design of NFShunt is a viable approach to enhancing a traditional firewall to meet the performance needs of data-intensive researchers.