How to cluster Redis service

Question

Imagine 6 servers running Redis on all of them:

192.168.10.1
192.168.10.2
192.168.10.3
192.168.10.4
192.168.10.5
192.168.10.6

They have divided into 2 site:

Site 1

192.168.10.1
192.168.10.2
192.168.10.3

Site2

192.168.10.4
192.168.10.5
192.168.10.6

There is no Sentinel behind any Redis. I just want to make a cluster like this picture: enter image description here

How to define this cluster on each server? What is the respective command for each node?

Thanks