Hi,
> I have insatlled a very fresh SL6.3 on a node. The problem is from SL6.3 I
> can ssh to a nother node (ubuntu) but can not ssh from ubuntuu to SL.
Could you please test with "ssh -c aes128-ctr" ?
It seems like https://bugzilla.redhat.com/show_bug.cgi?format=multiple&id=821079