fail2ban

1. Install fail2ban

2. Edit /etc/fail2ban/jail.local

[DEFAULT]
bantime = 24h
findtime = 10m
maxretry = 5
ignoreip = a.b.c.d/24    - for your NW 

[sshd]
enabled = true
port = ssh
logpath = %(sshd_log)s
backend = %(sshd_backend)s
mode = aggressive

sudo systemctl restart fail2ban
sudo systemctl status fail2ban
sudo fail2ban-client status
sudo fail2ban-client status sshd
cat /var/log/auth.log | grep -i invalid