replica set with multiple primary nodes

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http://serverfault.com – I am trying to configure a replica set with three nodes: node A, B and C. I execute the rs.add()'s from node A and after that rs.status() shows that the three nodes are PRIMARY. Moreover node B and C have 0 pingMs. If I execute rs.status() from node B or C the only node listed is the self (As PRIMARY). I tried adding an arbiter but it didn't work (it behaved as the nodes B and C). I think this can be a networking problem but I can't figure it out. (HowTos)