I have to set up a MongoDB replication set with 3 nodes, 1 of them arbiter. Authentication has to be enabled. Node1 and Node2 are fine. On the arbiter I have a 2.6 installation and it is arbiter for another configuration. I started a new mongod on that server on a different port and tried to add it to the 3.2 replication set. It is added but it says "not reachable".
From any node I can connect to the new instance in the arbiter host so communication between servers is not a problem. I don't see anywhere in the documentation that all the nodes must be the same version.
Any ideas what am I doing wrong? I could add a 3.2 arbiter with no problem and the replica set is working perfectly, but for some reason I cannot get it to work with a 2.6 arbiter.