Yesterday the namecheap dns servers, to which some of my domains were delegated, were inaccessible for a certain period of time. At the same time there was a problem: do not connect to the server from filezilla via sftp.
The log file /var/log/auth.log was filled with the following errors:
sshd : [ip] failed - POSSIBLE BREAK-IN ATTEMPT for your hostname.site.com [ip] failed! sshd : fatal: Write failed: Connection reset by peer [preauth]
The solution was found quickly enough. It is necessary to add the parameter UseDNS no in the configuration file / etc / ssh / sshd_config .
I encountered this problem for the first time. The problem was caused just by the “fall” of the mentioned dns. As I understand it, OpenSSH could not determine the dns records for the domain that pointed to my static ip, and rejected the authorization.