Connection closed [preauth]

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http://serverfault.com – On a Ubuntu 12.04 server, I am getting the following pair of messages in auth.log several times a minute: Jan 17 22:04:25 binx sshd[14659]: Connection closed by [preauth] Jan 17 22:04:25 binx sshd[14661]: Connection closed by [preauth] Both those IP addresses belong to separate computers ( is our firewall/router, is our backup machine), and seem to be associated with some sort of failed public key login. Is there some way to see what is causing the errors, or what user the machines are trying to connect to? (HowTos)