But you may be using Unix-y software to manage the interfaces and do offload programming:

* https://en.wikipedia.org/wiki/Vector_Packet_Processing

* https://www.youtube.com/watch?v=ptm9h-Lf0gg ("VPP: A 1Tbps+ router with a single IPv4 address")

* https://en.wikipedia.org/wiki/Cumulus_Networks