How to make an offline network of Raspberry Pis?

I'm building an installation with 6 Linux computers (Raspberry Pis) connected to a switch. Right now they are connected to my home home router, that is DHCPing them an ip and all of them are happy and can see each other both IP wise 192.168.1.x and with their respective hostnames Rpi1.local - Rpi6.local . So some of them run a web server, other get info from them using GET requests etc… This network should also run when I disconnect them from the router and reboot them. As soon as they are booted they automatically start looking for their peers on the network. How can I make sure that they wil

Question by kaosbeat on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.