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We encountered an issue where a series of git requests over ssh would sometimes fail with ssh_exchange_identification: Connection closed by remote host

There are many examples on SE/SF of structural problems (tcp-wrappers, permission on key files).

Our problem was: What is a likely cause of intermittent connection failures with this message?

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Our issue appeared to have been caused by a moderately high number of incoming requests.

As soon as the number of unauthenticated connections goes over the sshd:MaxStartUps parameter, sshd starts rejecting those connections.

The solution lies in modifying MaxStartups in sshd_config

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    It can also indicate a brute force attack, please make use of /etc/hosts.{allow,deny} files to limit connections. aboutlinux.info/2005/10/using-tcp-wrappers-to-secure-linux.html – Andrew McGlashan Nov 26 '14 at 20:41
  • @AndrewMcGlashan it depends on the definition of moderately high number in this context. I think we had a Jenkins host checking out repositories from our git server, all within our own network. This host could very well handle the bursts, so we increased that limit. – Henk Langeveld Nov 27 '14 at 14:38

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