One of the bigger changes made in Knot Resolver 6 is the almost complete rewrite of its I/O (input/output) system and management of communication sessions.

To understand why this rewrite was needed, let us first take a brief look at the history of Knot Resolver’s I/O.

In the beginning, the Resolver’s I/O was really quite simple. As it only supported DNS over plain UDP and TCP (nowadays collectively called Do53 after the standardized DNS port), there used to be only two quite distinct code paths for communication – one for UDP and one for TCP.