thibault75, It is true that all nodes in a cluster need to be running the same version of OneFS in order to properly communicate with one another.  You'll need to update OneFS 5.5 on the third node to match the other nodes. 
Hi,  I have 3 nodes that i have reset properly from serial cable.  First one is the master, it's a OneFS 6.5 IQ12000X node. Here is the configuration :  EXT-A 192.168.XX.1 - 192.168.XX.5 INT-A 192.168.YY.1 - 192.168.YY-5  Second one is a OneFS 6.5 IQ12000X node. At wizard panel it has detected correctly the first node when typing "Join cluster"  Problem is with the 3rd one, it's a OneFS 5.5 IQ12000X node. At wizard panel it doesn't see anything. I can't join my cluster. I tried to setup a new cluster with this node  EXT-A 192.168.XX.4 - 192.168.XX.4 INT-A 192.168.YY.3 - 192.168.YY-3  It's starting correctly, and i'm able to ping other node from INT-A so connectivity is good. All node are connected threw an infiniband switch. Any advice to make my cluster visible for this node? IS it a problem between 5.5 and 6.5?   Thanks
Cannot add 3rd node to my isilon cluster