Hello Fabian,
thank you for your answer. If I pull the cable from node-2, ring0 than the node is isolated from 1 and 3.
Nov 17 15:58:34 proxmox-2 corosync[2951]: [MAIN ] Completed service synchronization, ready to provide service.
Nov 17 15:58:35 proxmox-2 corosync[2951]: [KNET ] rx...