Защита SSH-сервера - 3 попытки за один день

3 дня действия Ubuntu Server 14:)

grep sshd.*Did /var/log/auth.log | tail -50

Feb 14 09:41:35 mantykora sshd[3797]: Did not receive identification string from 88.249.106.23
Feb 14 10:17:18 mantykora sshd[4027]: Did not receive identification string from 94.102.48.193
Feb 15 01:41:04 mantykora sshd[17267]: Did not receive identification string from 79.71.81.207
Feb 15 02:31:55 mantykora sshd[17321]: Did not receive identification string from 113.108.21.16
Feb 15 09:07:58 mantykora sshd[19183]: Did not receive identification string from 58.49.91.194
Feb 15 15:54:03 mantykora sshd[3128]: Did not receive identification string from 62.210.24.250
Feb 15 19:12:11 mantykora sshd[3723]: Did not receive identification string from 117.253.221.81
Feb 16 10:08:41 mantykora sshd[4953]: Did not receive identification string from 122.241.63.225
Feb 17 02:01:40 mantykora sshd[5839]: Did not receive identification string from 198.251.79.208

Я пытаюсь защитить с помощью sudo ufw limit OpenSSH 3 попытки в один день, но я не знаю, как это сделать. Как это сделать?