What is the high performance networking API?

Question

C++ / C#

Hello everyone, I would like to ask those who are involved in network applications: do you use any api with high performance for client-server applications, and what could you advise me?
Thank you for attention.

Answer 1

zeromq, nanomsg

Answer 2

In terms of API? There is a UPD protocol for which there are services with such an API.
If there is a task and conditions, perhaps I will prompt more precisely.