As you can see, I configured the 4 routers with OSPF. Everything works fine. Now I want to configure my router 1 only with static routing and the goal is to ping the router 6. Can you confirm that I should add all the networks (192.168.2-3-4-5-6-7.0) in my route (GW is router 2 of course)?
Try a default route on RE1 to send all traffic to RE2, something like "0.0.0.0 0.0.0.0 192.168.1.x" (insert RE2 IP address instead of 192.168.1.x) and under the OSPF config redistribute the connected routes.