Which command helps protect against brute force attacks in OpenSSH?

The command that helps protect against brute force attacks in OpenSSH is fail2ban. This tool works by monitoring log files for authentication failures and other suspicious activity. When a certain threshold of failed login attempts from a particular IP address is detected, fail2ban will automatically take action, such as blocking that IP address for a specified duration. This helps to mitigate the risk of brute force attacks, where an attacker tries multiple passwords in quick succession to gain unauthorized access.

Denyhosts is similar to fail2ban in that it also focuses on preventing brute force attacks by managing hosts that have failed to authenticate. However, fail2ban is often preferred because it is more versatile and can provide security for a wider range of services beyond just SSH, including web applications and email servers.

While ipset is used for managing IP sets in firewall rules and firewalld is a dynamic firewall management tool, neither is specifically designed for monitoring and responding to brute force attacks like fail2ban and denyhosts. Hence, fail2ban stands out as the dedicated solution for this security purpose in OpenSSH environments.