Denyhosts is another utility similar to fail2ban. It parses log files to identify potential attacks against SSH services. A clear advantage that Denyhosts has over fail2ban is the synchronisation mechanism since version 2.0[1]. Denyhosts permits communication with a central server to exchange information about denied hosts by other Denyhosts daemons. However unlike fail2ban, it does not modify any firewall (iptables) rules, instead it relies on tcpwrapper and the hosts.deny file to block ssh access. Fail2ban also offers the advantage of monitoring other services and logs, whereas Denyhosts is specific to SSH. There are other utilities which use tcpwrapper such which can handle additional services[2].
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